CN117729990A

CN117729990A - Board with fibre reinforced dense layer

Info

Publication number: CN117729990A
Application number: CN202280051643.1A
Authority: CN
Inventors: A·维兰斯卡; M·K·亨普希尔; Y·桑; N·S·琼斯; K·O·弗雷泽; J·克劳斯; T·H·刘
Original assignee: Knauf Gips KG
Current assignee: Knauf Gips KG
Priority date: 2021-07-09
Filing date: 2022-07-08
Publication date: 2024-03-19

Abstract

A composite gypsum board is disclosed that includes a set gypsum core disposed between a front side (e.g., manila) cover sheet and a back side (e.g., news) cover sheet. The set gypsum core is formed from a core slurry comprising stucco, water, and optionally additives such as foaming agents, migrating starches, accelerators, retarders, dispersants, and the like. A densified layer formed from a densified layer slurry comprising stucco, water, fibers (e.g., paper fibers), and optionally strength enhancing starch is disposed between the core and the facestock. The densified layer slurry includes a higher concentration of fibers and optionally strength-enhancing starch than the core slurry, but the concentration of one or more other additives (e.g., accelerators, retarders, dispersants, or combinations thereof) in the densified slurry is lower or the same as the core slurry. A method of manufacturing a board using a board mixer is also disclosed. In embodiments, the paper fibers are added to water to form a suspension. The suspension is introduced into the dense slurry in a non-layered state. An apparatus, such as an extractor and additive injection system, which may be part of the cementitious slurry mixing and dispensing assembly is also disclosed.

Description

Board with fibre reinforced dense layer

Cross Reference to Related Applications

This application claims priority from U.S. patent application Ser. No. 17/855,732, filed on even 30 th 6 of 2022, which in turn claims the benefits of U.S. provisional patent application Ser. No. 63/220,245, filed on even 9 th 7 of 2021, and U.S. provisional patent application Ser. No. 63/295,016, filed on even 30 th 12 of 2021, all of which are incorporated by reference.

Background

Set gypsum is a well known and commonly used material for many products, including panels and other products for construction and reconstruction. One such panel, commonly referred to as a gypsum board, is in the form of a set gypsum core sandwiched between two cover sheets (e.g., paper facer sheets) and is commonly used in the dry wall construction of the interior walls and ceilings of buildings. One or more dense layers, commonly referred to as "skim coats," may be included on either side of the core, typically at the paper-core interface.

Gypsum (calcium sulfate dihydrate) is naturally occurring and can be mined in rock form. It may also be in synthetic form (known in the art as "syngyp") as a byproduct of industrial processes such as flue gas desulfurization. From either source (natural or synthetic), gypsum can be calcined at high temperatures to form stucco (i.e., calcined gypsum primarily in the form of calcium sulfate hemihydrate) and then rehydrated to form set gypsum of the desired shape (e.g., as board). During board manufacture, stucco, water, and other ingredients are typically mixed, as the term is used in the art, in a wallboard slurry mixer. The slurry is formed and discharged from the mixer onto a moving conveyor carrying a cover sheet (typically upstream of the mixer) to which one of the skim coats, if any, has been applied. The slurry is spread over the paper (optionally including a skim coating on the paper). Another cover sheet, with or without skim coating, is applied to the slurry with the aid of, for example, a forming plate or the like, to form a sandwich structure of desired thickness. The mixture is cast and hardened to form set (i.e., rehydrated) gypsum by reacting the calcined gypsum with water to form a matrix of crystalline hydrated gypsum (i.e., calcium sulfate dihydrate). It is the desired hydration of calcined gypsum that enables the formation of an interlocking matrix of set gypsum crystals, thereby imparting structural strength to the gypsum in the product. The calcined gypsum reacts with the water in the wallboard preform and sets as the conveyor moves the wallboard preform down the production line. The wallboard preform is cut into sections at points along the line where the preform has sufficiently solidified. Heat is typically used (e.g., in a kiln) to drive off the remaining free (i.e., unreacted) water to produce a dry product.

It is extremely important to reduce the density of the board as long as sufficient strength is maintained. To reduce weight, the mass may be removed from the volume of the board and replaced with, for example, voids, such as air voids created by foam and water voids created by evaporation of water beyond that required for stucco to rehydrate to gypsum. Perlite and other lightweight fillers can also be used as an alternative or supplement to air and water voids. The lighter weight panels are easier to handle, transport and install, thereby achieving the desired efficiency in the installation of the panels. While lighter weight boards are desired, they should not be at the expense of the strength of the boards desired by the consumer. Maintaining adequate strength and integrity in the plate is a challenge when the mass is removed from the plate.

Existing apparatus and methods for addressing some of the operational problems associated with gypsum wallboard production are disclosed in commonly assigned U.S. Pat. nos. 5,683,635;5,643,510;6,494,609;6,874,930;7,007,914; and 7,296,919, which are incorporated by reference. There is a continuing need in the art to provide additional solutions to improve the yield of cementitious panels.

It should be appreciated that this background description is created to aid the reader and should not be taken as an indication of any indicated problem itself as understood in the art. While in some aspects and embodiments the described principles may alleviate problems inherent in other systems, it should be understood that the scope of the protected innovation is defined by the appended claims and is not defined by the ability of any disclosed feature to solve any specific problem described herein.

Disclosure of Invention

As described herein, the present disclosure provides gypsum boards, methods of making gypsum boards, and various apparatuses. The gypsum board may be in the form of wallboard. As used herein, the term wall panel is not limited to panels used on walls, but may also include panels for ceilings, partitions, and the like. The board includes a set gypsum core disposed between a first cover sheet and a second cover sheet (typically a front sheet and a back sheet, respectively). The front face of the plate is generally outwardly facing and visible when in suspension use, while the back face is inwardly facing towards a support structure such as a stud. A fiber reinforced dense layer is disposed between the core and the positive cover sheet.

The dense layer slurry is formulated differently than the core layer slurry. The densified layer slurry includes a higher concentration of fibers and optionally strength-enhancing starch (e.g., pregelatinized or uncooked non-migrating starch) than the core layer, but the densified layer slurry has the same or lower concentration of other additives (e.g., one or more of accelerators, retarders, polyphosphates, dispersants, foaming agents, migrating starch, etc.) than the core slurry. In some embodiments, the core slurry has significantly fewer or no fibers and optionally the strength enhancing starch.

In embodiments, one plate mixer equipped with a stirrer may be used to prepare the plates, as understood in the art. Stucco, water, and optional additives may be inserted into the body of the board mixer to form a base slurry. The plate mixer comprises a main discharge conduit for the slurry forming the plate core and an auxiliary discharge conduit for the slurry forming the dense layer. The fibers and optionally strength enhancing starch are inserted into the auxiliary discharge conduit and mixed with the base slurry exiting the body of the mixer to form a dense layer slurry. By including fibers in this manner, it has been found unnecessary to include fibers in the base slurry or core slurry. In some embodiments, the polyphosphate may optionally be inserted into the secondary discharge conduit and into the dense layer slurry.

The foaming agent may be inserted into the core slurry in any suitable manner. For example, in embodiments, the foaming agent is preferably included in the primary exhaust conduit such that the core is formed to have a smaller density than the densified layer, as such foam would then be minimized in the densified layer. These components may be included in the base slurry and/or the core slurry, respectively, by inserting the other components into the plate mixer body and/or into the main discharge conduit. Such ingredients include, for example, accelerators, retarders, polyphosphates, dispersants, migrating starches, and the like. In this way, the specific component will be introduced into the core slurry in the same amount as the dense layer slurry, wherein the component is only inserted into the plate mixer body. The specific component will be introduced into the core slurry in a larger amount than the dense layer slurry in which it is introduced into the main discharge conduit (instead of the auxiliary discharge conduit).

In some embodiments, the paper fibers are included in a densified layer slurry. The paper fibers may be delivered in water as a pulp suspension. In embodiments, when the paper fibers are delivered to the slurry for forming the densified layer, the flow of the paper fiber suspension is in a non-laminar (e.g., turbulent) state sufficient to form a fiber-reinforced densified slurry and avoid agglomeration and formation of substantial amounts of flocs. In this regard, it is desirable that 10% or less of the fibers be in the form of such floes so that the fiber suspension can be properly mixed into the dense layer slurry to allow for enhanced strength enhancement.

Boards comprising fiber reinforced dense layers are particularly useful at ultra-light board densities, e.g., 35pcf or less, such as 31pcf or less, in maintaining strength according to ASTM 473-10 method B, e.g., at least 72lb.

Accordingly, in one aspect, the present disclosure provides a gypsum board comprising a set gypsum core disposed between a first cover sheet and a second cover sheet. The gypsum core is formed from a core slurry that includes stucco, water, a foaming agent, and one or more additives such as dispersants, migration starches, accelerators, retarders, and/or other ingredients. A densified layer is disposed between the core and the first cover sheet. The densified layer is formed from a densified layer slurry that includes stucco, water, fibers in any suitable amount (such as at least 0.8% by weight of the stucco), and optionally strength enhancing starch. The densified layer slurry preferably includes a higher concentration of fibers (and optionally strength-enhancing starch) than the core slurry, and the core slurry preferably includes at least one of a promoter, a retarder, a dispersant, and migrating starch at the same or higher concentration than the densified layer slurry. In some embodiments, the densified layer has a dry density of at least 40pcf and a dry thickness of 0.05 inches or less. The panel may have any desired density, such as a density of 35pcf or less, and a nail pull resistance of at least 72lb according to ASTM 473-10 method B. In some embodiments, the densified layer slurry consists of stucco, water, fiber, and optionally strength enhancing starch and polyphosphate.

In another aspect, the present disclosure provides a method of making a gypsum board. The method includes obtaining a first cover sheet and a second cover sheet. A densified layer in bonded relation is applied to the first coversheet. The densified layer is formed from a slurry comprising stucco, water, fibers in any suitable amount (e.g., at least 0.8 weight percent of the stucco), and optionally strength enhancing starch. In some embodiments, the densified layer has a dry density of at least 40 pcf. A core layer in bonded relation is applied to the dense layer. The core layer has a density of 35pcf or less, and has a first surface and a second surface. The densified layer slurry preferably includes a higher concentration of fibers (and optionally strength enhancing starch) than the core slurry, and the core slurry preferably includes at least one of a promoter, a retarder, a dispersant, and migrating starch at the same or higher concentration than the densified layer slurry. The second cover sheet is disposed in bonded relation to the second core surface. The panel has a nail pull resistance of at least 72lb according to ASTM 473-10 method B.

In another aspect, a method of making a panel is provided. The method includes providing a plate mixer including a main body and respective primary and secondary discharge conduits. Stucco and water are inserted into the body of the mixer to form a base slurry. A majority of the base slurry is discharged from the main body into the main discharge conduit to form a core slurry. A small portion of the base slurry is discharged from the main body into the auxiliary discharge conduit to form a dense layer slurry. A suspension comprising water and paper fibres is prepared. The suspension is inserted into the dense layer slurry in the auxiliary discharge conduit while the suspension is in a non-layered state sufficient to avoid 10% or more by weight of the fibers being present in the form of floes. A first cover sheet and a second cover sheet are provided. The densified layer slurry is deposited onto the first cover sheet, typically as it moves along a conveyor. The core slurry is deposited on the dense layer slurry. The second cover sheet is applied over the core slurry.

In another aspect, the present disclosure relates to embodiments of an additive injection system for preparing cementitious products. In embodiments, the additive injection system may be part of a cementitious slurry mixing and dispensing assembly and is used to inject additive into an auxiliary slurry discharge conduit that carries an auxiliary stream of cementitious slurry produced in the assembly such that the auxiliary slurry stream is different from the main slurry stream discharged from the main slurry discharge conduit.

In another aspect, the present disclosure is directed to embodiments of a mixer extractor. In one embodiment, a mixer extractor includes an additive injection assembly having a body and a port member. The body defines a slurry channel and a port channel. The port channel has a port opening in fluid communication with the slurry channel. The port member defines an additive channel. The port member is adapted to be removably mounted to the body such that the additive channel is in fluid communication with the slurry channel via the port opening of the port channel.

In another aspect of the present disclosure, embodiments of a slurry mixing and dispensing assembly are described. In one embodiment, a slurry mixing and dispensing assembly includes a mixer, a primary discharge conduit, and a secondary discharge conduit. The mixer includes a housing and a stirrer disposed within the housing. The housing has a first outlet and a second outlet. The agitator is configured to agitate the water and cementitious material to form an aqueous cementitious slurry. The primary discharge conduit is in fluid communication with the first outlet and the secondary discharge conduit is in fluid communication with the second outlet. The auxiliary discharge conduit includes an additive injection system having a body and a port member configured to introduce at least one additive into an auxiliary slurry stream discharged from the mixer via the auxiliary slurry discharge conduit.

In another aspect of the disclosure, embodiments of a method of making a cementitious product are described. In one embodiment of the method of making cementitious products, water and cementitious material are stirred in a mixer to form an aqueous cementitious slurry. A main flow of cementitious slurry is discharged from the mixer from the first outlet into a main discharge conduit. An auxiliary flow of cementitious slurry is discharged from the mixer from the second outlet into an auxiliary discharge conduit. At least one additive is introduced into the auxiliary stream via an additive injection system associated with the auxiliary exhaust conduit.

In another aspect of the disclosure, embodiments of a system for manufacturing gypsum board are described. The system includes a mixer including a housing and a stirrer disposed within the housing. The housing has a first outlet and a second outlet. The agitator is configured to agitate the water and cementitious material to form an aqueous cementitious slurry. The system also includes a primary exhaust conduit, a secondary exhaust conduit, and an additive injection system. The primary discharge conduit is in fluid communication with the first outlet. The auxiliary discharge conduit is in fluid communication with the second outlet. The additive injection system has an injection body and a port member. The injection body defines a slurry channel and a port channel. The slurry channel includes a portion of the auxiliary discharge conduit such that the slurry channel is in fluid communication with the second outlet of the mixer. The port channel is in fluid communication with the slurry channel. The port member defines an additive channel. The port member is removably connected to the injection body such that the additive channel is in fluid communication with the port channel.

Further and alternative aspects and features of the disclosed principles will be understood from the following detailed description and drawings. As will be appreciated, the additive injection systems, extractors, slurry mixing and dispensing assemblies, and techniques for manufacturing cementitious products disclosed herein are capable of implementation and use in other and different embodiments, and of modification in various respects. Accordingly, it is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the scope of the claims as appended.

Drawings

Fig. 1 is a perspective view of an embodiment of a mixer extractor assembly constructed in accordance with the principles of the present disclosure.

Fig. 2 is an end elevation view of the mixer extractor assembly of fig. 1 having an additive injection system in cross-section along a plane transverse to a longitudinal axis of the mixer extractor assembly.

Fig. 3 is an end elevation view of the additive injection body of the additive injection system of fig. 2, showing the additive injection body partially in cross section for illustrative purposes.

Fig. 4 is a cross-sectional view of the additive injection body of fig. 3 taken along line IV-IV in fig. 3.

Fig. 5 is a perspective view of another embodiment of an additive injection system constructed in accordance with the principles of the present disclosure from a first end thereof.

Fig. 6 is a perspective view of the additive injection system of fig. 5 from a second end thereof.

Fig. 7 is a longitudinal cross-sectional view of the additive injection system of fig. 5.

Fig. 8 is a perspective view of another embodiment of an additive injection body constructed in accordance with the principles of the present disclosure.

Fig. 9 is a side elevational view of the additive injection body of fig. 8.

Fig. 10 is a perspective view of an additive injection block of the additive injection body of fig. 8.

Fig. 11 is a perspective view of an inlet portion of the additive injection body of fig. 8.

Fig. 12 is a perspective view of an outlet portion of the additive injection body of fig. 8.

Fig. 13 is a schematic plan view of an embodiment of a cementitious slurry mixing and dispensing assembly including an embodiment of a mixer extractor assembly constructed in accordance with the principles of the present disclosure, each incorporated into a pair of auxiliary discharge ducts.

Fig. 14 is a schematic elevation view of an embodiment of the wet end of a gypsum wallboard production line, including an embodiment of a mixer extractor assembly constructed in accordance with the principles of the present disclosure, each incorporated into a pair of auxiliary discharge ducts.

Fig. 15A shows an injection port having an inner diameter of 1 "as described in example 4.

Fig. 15B shows an injection port having an inner diameter of 0.504 "as described in example 4.

Fig. 15C shows an injection port having an inner diameter of 0.374 "as described in example 4.

Fig. 15D shows an injection port having an inner diameter of 0.227 "as described in example 4.

Fig. 16 is a plot of pulp density (Y-axis) versus port size (X-axis) measured in an experiment involving the insertion of paper fibers into a densified layer pulp using injection ports of different inside diameter sizes as described in example 4.

Fig. 17 is a graph of flow rate (Y-axis on left) versus average flow (Y-axis on right) measured in an experiment involving the insertion of paper fibers into a densified layer slurry using an injection port of 0.375 "inside diameter size as described in example 4.

Fig. 18 is a graph of the friction head loss (Y-axis) versus the overall flow rate (X-axis) measured in an experiment involving a slurry suspension moving through a hose at various flows as described in example 6.

It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated schematically and in partial views. In certain instances, details that are not necessary for an understanding of the present disclosure or that render other details difficult to perceive may have been omitted. It is to be understood that the present disclosure is not limited to the particular embodiments shown herein.

Detailed Description

Introduction to the invention

Embodiments of the present disclosure provide gypsum boards, methods of making gypsum boards, and apparatus such as mixer extractors and slurry mixing and dispensing assemblies. The gypsum board includes a board core comprising set gypsum sandwiched between front and back cover sheets. The set gypsum core is formed from a core slurry comprising stucco, water, and optional ingredients as desired, including, for example, foaming agents, accelerators (e.g., heat resistant accelerators), retarders, dispersants, migrating starches, polyphosphates, and the like. A densified layer is disposed between the core and the positive cover sheet. According to embodiments of the present disclosure, a densified layer is formed from a densified layer slurry comprising water, stucco, and a strength enhancing amount of fibers. The dense layer typically has a density that is significantly greater and a significantly smaller thickness than the density and thickness of the board core.

Surprisingly and unexpectedly, it has been found that including fibers in the thin dense layer provides significant strength benefits as a reinforcing agent and allows the gypsum board to be lightweight (e.g., having a density of 35pcf or less), with good mechanical strength (e.g., nail pull resistance of at least 72lb. According to ASTM 473-10 method B). For example, in some embodiments, the plate has a nail pull resistance of at least 77lb, such as 77 lb.to 105lb, 77 lb.to 98lb, etc., according to ASTM 473-10 method B. However, it should be understood that the features of the present disclosure may be used in heavier plates having densities greater than 35pcf, if desired. Optionally, if desired, strength enhancing starches and/or polyphosphates may be included with the fibers in the slurry to form a dense layer.

The inclusion of fibers in the densified layer also surprisingly and unexpectedly allows for the use of a smaller amount of strength-enhancing additives in the slurry used to form the board core. For example, fiber and strength-enhancing starches (e.g., pregelatinized or uncooked non-migrating starches) may be included in the core in a lesser relative amount than in a board having a dense layer without fiber. In some embodiments, the core may be substantially free of fiber and strength enhancing starch. Surprisingly and unexpectedly, these benefits can be achieved even though the densified layer contributes a much smaller portion of the total sheet weight and thickness than the greater contribution of the core.

Optionally, in some embodiments, the sheet may be prepared to include a second densified layer disposed between the core and the back cover sheet. The second densified layer may be formed from the same or different slurry as used to make the densified layer between the core and the positive cover sheet. In this regard, it should be appreciated that the strength of the panel may generally be distributed to enhance the strength of the front face of the panel.

In some embodiments, the dense layer slurry has a higher concentration of certain ingredients than the core slurry. Surprisingly and unexpectedly, embodiments of the board can be made wherein the densified layer slurry has a higher concentration of paper fibers and optionally strength enhancing starch as compared to the core slurry. Other additives, such as accelerators (e.g., heat resistant accelerators), retarders, foam, dispersants, and other ingredients, are present in the core slurry at a concentration less than or equal to the concentration of these additives in the dense slurry layer. As discussed herein, the components added to the base slurry are considered to be introduced into the dense slurry and the core slurry by the same weight, as long as additional amounts of those components are not added to the main discharge conduit and the auxiliary discharge conduit, respectively, regardless of any fluctuations in concentration due to differences between the other components. In this way, in embodiments, the core slurry may include the same or higher concentrations of additives other than paper fibers, and optionally strength enhancing starch and/or polyphosphate.

Surprisingly and unexpectedly, in contrast to a two-plate mixer system, where the core slurry is mixed in one mixer and the dense layer slurry is mixed in an auxiliary mixer, a single plate mixer (e.g., a pin or non-pin mixer) can be used to manufacture the plates. In this regard, the mixer includes a mixer, a primary discharge conduit for discharging the core slurry as known in the art, and a secondary discharge conduit, which in some embodiments is generally located upstream of the primary discharge conduit. In embodiments, fibers that are typically added to water to form a suspension may be inserted (e.g., injected) using an auxiliary discharge conduit instead of a main discharge conduit, such that the fibers are not included in or minimally present in the core slurry. Optionally, if desired, a secondary discharge conduit may also be used to introduce the strength-enhancing starch (e.g., by adding to the fiber suspension, or alternatively, separately through a different injection port). A predetermined component, such as foam, may be inserted (e.g., injected) into the main discharge conduit to adjust the formulation of the core slurry as desired. In some embodiments, the fibers are paper fibers that are preferably added to the secondary discharge conduit and thus to the densified layer slurry, while the paper fibers are not added to the mixer body or the primary discharge conduit (although fibers other than paper may be added to the mixer body or the primary discharge conduit if desired).

By inserting additives in the main and auxiliary exhaust ducts, respectively, boards having different concentrations can be prepared, as described herein. If desired, some of the wet or dry ingredients may be inserted directly into the body of the plate mixer so that these ingredients will be found in both the dense slurry and the core slurry. In embodiments, for convenience, an auxiliary discharge conduit may be provided upstream of the main discharge conduit so that the densified layer slurry may be applied to a cover sheet that is moving on a conveyor. The cover sheet may typically be a positive cover sheet, as the sheet is typically formed upside down at the wet end of the production line. The primary discharge conduit may be arranged such that the core slurry is deposited on the dense slurry on the moving cover sheet with the dense slurry applied. In embodiments, the core slurry is typically deposited downstream of the mixer.

The auxiliary discharge conduit may be in any suitable form. In some embodiments, fibers (e.g., paper fibers) may be added to water to form a pulp suspension. The paper fiber suspension may be injected into the auxiliary discharge conduit using, for example, a single port, but multiple ports (such as via a ring) may be used if desired. Surprisingly and unexpectedly, the inventors have found that in embodiments, when a paper fiber suspension is added to a slurry to form a dense layer, the paper fiber suspension should be in a substantially non-laminar (e.g., turbulent) state. In this way, the suspension avoids agglomerations and considerable amounts of floes which would hinder proper mixing of the fibers in the dense layer slurry, which would result in fibers not being distributed in the dense layer slurry in a uniform manner and thus in a reduced strength enhancement of the resulting board. Thus, as described herein, the use of a single plate mixer embodiment for forming the densified slurry and the core slurry, respectively, surprisingly and unexpectedly improves and enhances the use of paper fibers, thereby enhancing the strength of the densified layer, and thus the strength of the plate. The use of a single plate mixer also improves efficiency by reducing energy use and downtime due to the use of additional mechanical equipment.

The slurry suspension may be prepared and delivered in any suitable manner. For example, the slurry suspension may be stored in a holding tank equipped with a stirrer and then pumped through a hose to an auxiliary discharge conduit. In an embodiment, the fiber suspension is inserted into the slurry to form the dense layer when the flow rate is higher than a turbulent start-up speed of the slurry suspension comprising a predetermined amount of fibers. The turbulence onset speed is the flow rate of the pulp suspension when it enters a turbulent state. In this regard, the slurry suspension is in a turbulent state when the slurry suspension flows at a velocity greater than the turbulence onset velocity. As described herein, the turbulence onset speed of the slurry suspension is determined by the rheometer tip friction loss test or shear rate ramp test.

The present disclosure also provides various embodiments of additive injection systems that can be used to manufacture products, including cementitious products, such as, for example, gypsum wallboard. For example, embodiments of additive injection systems constructed in accordance with the principles of the present disclosure may be used in manufacturing processes to effectively introduce one or more additives into an auxiliary cementitious slurry stream discharged from a mixer into an auxiliary conduit.

The present disclosure also provides various embodiments of cementitious slurry mixing and dispensing assemblies that can be used to manufacture different types of cementitious products, as will be appreciated by those skilled in the art. Embodiments of cementitious slurry mixing and dispensing assemblies constructed in accordance with the principles of the present disclosure may include an additive injection system adapted to inject one or more additives into an auxiliary cementitious slurry stream that is discharged from a mixer into an auxiliary conduit via at least one injection port member. In embodiments, a variety of different injection port members may be provided, each including a different channel (e.g., having a different port orifice size) to easily change the flow state of the additive flow therethrough, such as, for example, changing the injection pressure to achieve a desired flow state. In embodiments, cementitious slurry mixing and dispensing assemblies constructed in accordance with the principles of the present disclosure may be used to manufacture cementitious panels such as, for example, gypsum wallboard, acoustical panels, or portland cement panels.

Embodiments of cementitious slurry mixing and dispensing assemblies constructed in accordance with the principles of the present disclosure can be used to mix constituent materials to form a cementitious slurry (e.g., an aqueous calcined gypsum slurry) and deposit the cementitious slurry onto an advancing web (e.g., paper or mat) moving on a conveyor during a continuous board (e.g., gypsum wallboard) manufacturing process. In one embodiment, a slurry mixing and dispensing assembly includes a mixer, a main discharge conduit, and an auxiliary discharge conduit having an additive injection system constructed in accordance with the principles of the present disclosure.

The mixer includes a housing and a stirrer disposed within the housing. The housing has a first outlet and a second outlet. The agitator is configured to agitate the water and cementitious material to form an aqueous cementitious slurry. The primary discharge conduit is in fluid communication with the first outlet and the secondary discharge conduit is in fluid communication with the second outlet. The auxiliary discharge conduit includes an additive injection system having a body and a port member configured to introduce at least one additive into an auxiliary slurry stream discharged from the mixer via the auxiliary slurry discharge conduit.

In embodiments, the additive injection system may be used to produce a fiber-reinforced densified layer that may be disposed between a core and a positive cover sheet. In accordance with embodiments of the present disclosure, a densified layer is formed from an auxiliary slurry stream comprising water, stucco, and fibers having an amount of at least 0.8 weight percent stucco. In embodiments, the fibers are introduced into the slurry stream in the auxiliary exhaust conduit via an additive injection system to create the densified layer in situ in the auxiliary exhaust conduit.

Board board

According to an embodiment of the present disclosure, a gypsum board includes a board core including set gypsum sandwiched between a front cover sheet and a back cover sheet, wherein a densified layer is disposed between the board core and the front cover sheet. The board core slurry and the dense layer slurry are formulated differently.

The core slurry and the dense layer slurry include water and stucco (or other cementitious materials as mentioned herein), respectively. Stucco is sometimes referred to as calcined gypsum, and may be in the form of alpha calcium sulfate hemihydrate, beta calcium sulfate hemihydrate, and/or calcium sulfate anhydrite. The calcined gypsum may be fibrous in some embodiments, non-fibrous in other embodiments, or a combination thereof in other embodiments. In embodiments, the calcined gypsum can include at least 50% calcium sulfate beta hemihydrate. In other embodiments, the calcined gypsum can include at least 86% calcium sulfate beta hemihydrate. While the use of stucco and calcium sulfate dihydrate ("gypsum," "set gypsum," or "hydrated gypsum") is illustrated herein, it is understood that other cementitious materials may be used in addition to or as an alternative to stucco. Non-limiting examples of other cementitious materials include portland cement, oxalis cement, slag cement, fly ash cement, and calcium aluminum cement.

The reinforcing fibers in the densified layer slurry may be any suitable composition for reinforcing the strength of the panel. The fibers may be hydrophobic or hydrophilic, trimmed or untrimmed. The fibers may have any suitable length, for example, a length of 0.1mm to 25 mm. The fibers may also have any suitable diameter, such as 1 micron to 30 microns. For example, the fibers may be in the form of cellulosic fibers (e.g., paper, wood, cotton, and/or rayon fibers, etc.), carbon fibers, mineral fibers, glass fibers, polymer fibers, or any combination thereof.

In some embodiments, the fibers are paper fibers. Any suitable paper source may be used for the paper fibers. For example, the paper fibers may be derived from manila, news, or recycled waste paper, such as Old Corrugated Containers (OCC). The paper fibers may have any suitable average length, such as a length of 0.1mm to 3mm, such as 0.5mm to 3mm meters, or 1mm to 3mm. The paper fibers may also have any suitable diameter, such as at least 1 micron, at least 10 microns, at least 20 microns, etc. (e.g., 1 micron to 40 microns, 10 microns to 30 microns, 15 microns to 40 microns, 15 microns to 30 microns, 20 microns to 40 microns, 20 microns to 30 microns, etc.). In some embodiments, the paper fibers are dry chopped, having any suitable length, for example, having an average length of 0.5mm to 4mm, such as 2mm to 3mm.

In some embodiments, the fibers are natural pulp fibers, such as wood pulp fibers. For example, wood pulp fibers can include softwood pulp fibers and hardwood pulp fibers; straw fibers; plant and grass pulp fibers such as hemp pulp fibers, jute pulp fibers, kenaf pulp fibers and bamboo pulp fibers; cotton pulp fibers or any combination thereof, such as wood pulp fibers for use in papermaking. The wood fibers may also have any suitable diameter, such as at least 1 micron, at least 10 microns, at least 20 microns, etc. (e.g., 1 micron to 40 microns, 10 microns to 30 microns, 15 microns to 40 microns, 15 microns to 30 microns, 20 microns to 40 microns, 20 microns to 30 microns, etc.).

In some embodiments, the fibers may comprise glass fibers. For example, the fibers may include chopped glass fibers and/or continuous glass fibers. The glass fibers may have any suitable dimensions, for example, having an average diameter of 1 micron to 30 microns and a length of 1mm to 25 mm. In the case of carbon fibers, they are known in the art and are typically polymers (and sometimes also referred to as graphite fibers). The carbon fibers may have any suitable dimensions, such as, for example, a diameter of 1 micron to 30 microns and a length of 100 microns to 25 mm. Carbon fibers generally consist primarily of carbon atoms.

In some embodiments, the fibers comprise polymer fibers of any suitable composition. For example, the polymer fibers may include one or more of polyester, polyethylene, polypropylene, nylon, polyacetate, polyacrylic acid, polystyrene, polyvinyl acetate, rayon, and/or polyvinyl chloride, as well as any copolymers thereof and combinations thereof, such as synthetic polymer fibers comprising polyester, polyethylene, polypropylene, or any combination thereof. In some embodiments, the fibers comprise mineral fibers. The mineral fibers may be in any suitable form. For example, the mineral fibers may be spun or drawn mineral rock material. The mineral fibers may have any suitable dimensions, such as, for example, a diameter of 1 micron to 30 microns and a length of 1mm to 25 mm.

The fibers may be included in the densified layer slurry in any suitable amount. For example, the fibers may be included in an amount of at least 0.8% by weight of stucco (e.g., 0.8% to 8%, 0.8% to 5%, 0.8% to 4%, 0.8% to 3%, 0.8% to 2%, 11% to 5%, 1% to 4%, 1% to 2%, etc.).

Strength-enhancing starch refers to starch that increases the strength of the board (e.g., relative to nail pull strength) compared to the same board that does not include starch in the densified layer. Starches for strength enhancement are discussed in, for example, U.S. Pat. nos. 9,540,810, 9,828,441, 10,399,899, and 10,919,808. Any suitable strength enhancing starch may be used, including hydroxyalkylated starches, such as hydroxyethylated or hydroxypropylated starches, or combinations thereof; pregelatinized starch; or uncooked non-migrating starch.

As described in us patent 10,399,899 and 9,828,441, any suitable pregelatinized starch can be included in the dense layer slurry, including the method of its preparation and the desired viscosity ranges described therein. The pregelatinized starch, if included, can exhibit any suitable viscosity. In some embodiments, the pregelatinized starch is a medium viscosity starch as measured according to the VMA method known in the art and as set forth in U.S. patent 10,399,899, which is hereby incorporated by reference. In other embodiments, the pregelatinized starch has a greater viscosity, such as greater than 700 centipoise (e.g., 773 centipoise) according to the VMA test.

In some embodiments, the starch comprises uncooked starch having (i) a hot water viscosity of 20BU to 300BU according to the hot water viscometry (HWVA method), and/or (ii) a medium peak viscosity of 120BU to 1000BU, when the viscosity is measured by placing the starch into a slurry with water at a starch concentration of 15% solids, and using a Viscograph-E instrument set at 75rpm and 700cmg, as described in us patent 10,919,808, when the starch is heated from 25 ℃ to 95 ℃ at a rate of 3 ℃/min, the slurry is held at 95 ℃ for 10 minutes, and the starch is cooled to 50 ℃ at a rate of-3 ℃/min. As described herein, combinations of different strength enhancing starches may also be used in the dense layer slurry if desired.

For example, in some embodiments, the strength-enhancing starch comprises uncooked medium hydrolyzed acid modified starch (e.g., uncooked acid modified corn starch having a hot water viscosity of 180 BU); and/or a pregelatinized starch of medium viscosity and medium molecular weight (e.g., pregelatinized corn flour starch having a cold water viscosity of 90 centipoise).

The strength enhancing starches are different from migrating starches such as LC-211, commercially available from Archer-Daniels-Midland, chicago, illinois. Migrating starches typically have a smaller chain length (e.g., due to acid or enzyme modification) and migrate to the core-cover sheet interface for further bond enhancement. For example, in some embodiments, the core or base slurry includes migrating starch having a molecular weight of 6,000 daltons or less.

The optional strength enhancing starch, if included, may be included in the densified layer slurry in any suitable amount. For example, in some embodiments, the densified layer slurry includes strength enhancing starch in an amount of at least 0.5% by weight of stucco (e.g., 0.5% to 5% by weight of stucco, such as 0.5% to 3% by weight of stucco, 1% to 5% by weight, 1% to 3% by weight, 2% to 5% by weight, 2% to 4% by weight, 2% to 3% by weight, etc.). In some embodiments, the core slurry is substantially free of strength enhancing starches, e.g., having 2% by weight or less of stucco, such as 1% by weight or less of stucco.

As regards the base slurry and/or the core slurry, foaming agents and other additives may be included. The foaming agent may be added by being added in the main discharge conduit. In some embodiments, the blowing agent comprises a major part by weight of an labile component and a minor part by weight of a stabilizing component (e.g., a combination of labile and stable/labile blends). The weight ratio of the labile component to the stabilizing component is effective to form an air void distribution within the set gypsum core. See, for example, U.S. Pat. nos. 5,643,510;6,342,284; and 6,632,550. It has been found that suitable void distribution and wall thickness can be effective in enhancing strength, especially in lower density boards (e.g., 35pcf or less). See, for example, U.S. patent nos. 9,802,866 and 9,840,066. The evaporated water voids, typically having voids of 5 μm or less in diameter, also constitute the total void distribution together with the above-mentioned air (foam) voids.

Polyphosphates may optionally be included in the base slurry and/or the core slurry, for example, to enhance sag resistance of the board. Trimetaphosphate compounds can be used including, for example, sodium trimetaphosphate, potassium trimetaphosphate, lithium trimetaphosphate, and ammonium trimetaphosphate. If included, the polyphosphate may be included in the core slurry in the same or greater amounts as the dense layer slurry. Alternatively, if desired, the polyphosphate may be included in the dense layer slurry in a greater amount than the core slurry (e.g., via addition through an auxiliary discharge conduit).

Regarding polyphosphates, such as sodium trimetaphosphate, the core slurry and/or base slurry may be included in any suitable amount, such as, for example, 0.01 to 0.5 weight percent stucco, 0.01 to 0.4 weight percent stucco, 0.05 to 0.3 weight percent stucco, 0.1 to 0.5 weight percent, 0.1 to 0.4 weight percent, 0.1 to 0.3 weight percent, 0.1 to 0.2 weight percent, 0.15 to 0.5 weight percent, 0.2 to 0.4 weight percent, 0.3 to 0.5 weight percent, and the like.

Further, in some embodiments, the base and/or core slurry may optionally include at least one dispersant to enhance flowability. Like the other ingredients, the dispersant may be included in dry form with the other dry ingredients and/or in liquid form with the other liquid ingredients in the core slurry. Examples of the dispersant include naphthalene sulfonates such as polynaphthalenesulfonic acid and salts (polynaphthalenesulfonic acid) and derivatives thereof, which are condensation products of naphthalene sulfonic acid and formaldehyde; and polycarboxylate dispersants such as polycarboxylic ethers, e.g., PCE211, PCE111, 1641F, or PCE 2641 type dispersants, e.g., mellux 2641F dispersants, mellux 2651F dispersants, mellux 1641F dispersants, mellux 2500L dispersants (BASF), and COATEX Ethacryl M available from Coatex, inc; and/or lignosulfonate or sulfonated lignin.

The base and/or core slurry may include an accelerator and/or retarder. Accelerators (e.g., wet gypsum accelerators, heat resistance accelerators, climate stabilization accelerators) and retarder agents are well known and may be included in the core slurry if desired. See, for example, U.S. Pat. nos. 3,573,947 and 6,409,825. In some embodiments including accelerators and/or retarders, the accelerators and/or retarders may each be present in the base and/or core slurry in an amount on a solid basis, such as from 0 wt.% to 10 wt.% (e.g., from 0.1% to 10%) of stucco, such as, for example, from 0 wt.% to 5 wt.% (e.g., from 0.1% to 5%) of stucco.

Other additives may be included (by addition to the base slurry and/or the core slurry) at concentrations equal to or greater than the concentration in the dense layer slurry. Such additives include structural additives including mineral wool, perlite, clay, calcium carbonate, and chemical additives including fillers, sugars, reinforcing agents (such as phosphonates, borates, and the like), binders (such as latex), colorants, fungicides, biocides, hydrophobing agents (such as silicone-based materials including, for example, silanes, siloxanes, or silicone matrices), and the like. For example, in us patent 7,244,304;7,364,015;7,803,226;7,892,472;6,342,284;6,632,550;6,800,131;5,643,510;5,714,001; and 6,774,146; and U.S. patent application publication 2002/0045074 describes embodiments using some of these and other additives. Other examples of such additives include fire resistant and/or water resistant products, which may also optionally be included in the base and/or core slurry, including for example silicones (water resistant); heat dissipating additives such as Aluminum Trihydrate (ATH), magnesium hydroxide, and the like; and/or high expansion particles (e.g., expandable to 300% or more of the original volume when heated at 1560°f for about 1 hour). See, for example, U.S. patent 8,323,785 for a description of these and other ingredients. In some embodiments, highly expanded vermiculite is included, although other refractory materials may be included.

The weight ratio of water to calcined gypsum may be any suitable ratio, although as will be appreciated by those of ordinary skill in the art, a smaller ratio may be more effective because less excess water will remain after the hydration process of stucco is completed during manufacture, thereby saving energy. In some embodiments, cementitious slurries may be prepared by combining water and calcined gypsum in a suitable weight ratio of water to stucco for board production, the weight ratio of water to stucco depending on the product, such as in the range between 0.6 and 1.2, for example 0.8. In embodiments, for any given board, the densified layer slurry may have a greater water/stucco ratio than the core slurry. For example, the core slurry formulation may be made with any suitable water/stucco ratio, such as 0.6 to 1.2, 0.6 to 1.1, 0.6 to 1, 0.6 to 0.9, 0.6 to 0.85, 0.6 to 0.8, 0.6 to 7.5, 0.6 to 0.7, 0.6 to 0.65, and the like. The densified layer slurry formulation may be made with any suitable water/stucco ratio, such as 0.8 to 1.5, 0.8 to 1.4, 0.8 to 1.3, 0.8 to 1.2, 0.8 to 1.1, 0.8 to 1.0, 0.8 to 0.95, 0.8 to 0.9, 0.8 to 0.85, and the like.

Surprisingly and unexpectedly, the use of fibers in the densified layer according to embodiments of the present disclosure allows for the reduction or elimination of the use of fibers in the board core, even though the densified layer contributes significantly less to the board weight and thickness than the core as described herein. For example, in some embodiments, the core slurry is substantially free of glass fibers; cellulosic fibers such as paper fibers, cotton, rayon, or wood fibers; and/or polymer fibers (e.g., having 0.5% or less, 0.3% or less, or 0.1% or less of glass fibers, cellulose fibers, pulp fibers, and/or polymer fibers by weight of stucco).

With respect to the cover sheet, it can be formed of any suitable material and basis weight. For example, some embodiments of the present disclosure allow good panel strength even with lower basis weight cover sheets, such as, for example, less than 45lb/MSF (e.g., 33lb/MSF to 45 lb/MSF) even for lower weight panels (e.g., having a density of 35pcf or less). However, in some embodiments, a heavier basis weight may be used, if desired, for example, to further enhance nail pull resistance or to enhance the process, for example, to promote the desired "feel" characteristics of the end user. In some embodiments, to enhance strength (e.g., nail pull strength), particularly for low density boards, one or both of the cover sheets may be formed of paper and have a basis weight of, for example, at least 45lb/MSF (e.g., 45lb/MSF to 65lb/MSF, 45lb/MSF to 60lb/MSF, 45lb/MSF to 55lb/MSF, 50lb/MSF to 65lb/MSF, 50lb/MSF to 60 lb/MSF). If desired, in some embodiments, one cover sheet (e.g., the "positive" paper side when installed) may have the aforementioned greater basis weight, e.g., to enhance nail pull resistance and handling, while the other cover sheet (e.g., the "back" sheet when installed) may have a slightly lower basis weight (e.g., a basis weight of less than 45lb/MSF, e.g., 33lb/MSF to 45lb/MSF (e.g., 33lb/MSF to 40 lb/MSF), if desired.

Method for manufacturing the plate

The plate may be prepared in any suitable manner. In embodiments, a primary mixer comprising a stirrer is used at the wet end of the production line, as is understood in the art. The stirrer may be in the form of pins, discs, impellers, propellers, rotors rotating inside a stationary housing, etc. The main mixer can be used to prepare base slurries for preparing core and dense slurries, respectively. Stucco, water, and optionally a basic additive package are inserted into the main mixer. The mixer includes a main discharge conduit and an auxiliary discharge conduit. The slurry is discharged from a main discharge conduit into which a core additive, such as foam (see, e.g., U.S. Pat. No. 5,683,635), is inserted to form a core slurry. The slurry is also discharged from the secondary discharge conduit, wherein fibers (e.g., paper, glass, or polymer fibers) and optionally strength enhancing starch and/or polyphosphate are inserted into the base slurry to form a dense layer slurry.

The relative amounts of base stock discharged through the primary and secondary discharge conduits, respectively, may be selected to form a core layer and a dense layer of desired dimensions. In embodiments, a majority (i.e., greater than 50%) of the base slurry is discharged through the primary discharge conduit because the core layer generally has a greater thickness than the dense layer. In some embodiments, at least 60% of the base slurry is discharged through the main discharge conduit (e.g., at least 70%, at least 80%, at least 90%, at least 95%, such as 50% to 99%, 50% to 95%, 50% to 90%, 60% to 99%, 60% to 95%, 60% to 90%, 60% to 85%, 60% to 80%, 70% to 99%, 70% to 95%, 70% to 90%, 70% to 85%, 70% to 80%, 80% to 99%, 80% to 95%, or 80% to 90%).

In an embodiment, the fibers inserted into the auxiliary discharge conduit are paper fibers. The paper fibers are placed in an aqueous suspension prior to being added to the auxiliary discharge conduit. The suspension may have any suitable amount of paper fibers, such as 1% to 7% fibers, 1% to 6% fibers, 1% to 5% fibers, 1% to 4% fibers, 1% to 3% fibers, 2% to 7% fibers, 2% to 6% fibers, 2% to 5% fibers, 2% to 4% fibers, 3% to 7% fibers, 3% to 6% fibers, 3% to 5% fibers, or 3% to 4% fibers, etc.). The pulp suspension is subjected to a non-laminar (e.g. turbulent) flow prior to insertion into the auxiliary discharge conduit.

In some embodiments, the paper fibers are typically delivered in water. The fibers form a pulp suspension in water. When the paper fiber suspension is inserted into the slurry to form a dense layer, it is desirably in a non-laminar (e.g., turbulent) state. In this regard, the pulp suspension is delivered in a sufficiently turbulent manner to avoid agglomeration of the paper fibers and formation of appreciable amounts of flocs (e.g., at least 3mm in length). The flocs typically have a fiber length of greater than 3mm, such as 3mm to 8mm, or 3mm to 5mm. In this regard, it is desirable that 10% or less of the fibers be in the form of such floes so that the fiber suspension can be properly mixed into the dense layer slurry to allow for enhanced strength enhancement. In embodiments, 7% or less of the fibers form flocs, such as 5% or less, 3% or less, or 1% (e.g., 1% to 10%, 1% to 7%, 1% to 5%, 1% to 3%, 3% to 10%, 3% to 7%, 3% to 5%, 5% to 10%, 5% to 8%, or 7% to 10%, etc.) or less.

The paper fiber suspension may be prepared and inserted into the slurry in any suitable manner to form a densified layer. For illustration, in embodiments, paper fiber and water may be added and mixed in a tank that includes a stirrer to mix and maintain the contents therein as a suspension. The suspension is delivered to the auxiliary discharge conduit via a passage such as a pipe, tube, hose, conduit, etc., which terms are used interchangeably, etc., wherein the constricted inner diameter promotes the formation of the desired non-laminar (e.g., turbulent) state. The size of the inner diameter will vary depending on the particular conditions, including fiber size and the amount of fibers in the suspension. In some embodiments, the inner diameter of the hose is less than 0.625 inches (such as less than 0.5 inches or less than 0.375 inches, for example, 0.125 to 0.625 inches, 0.125 to 0.5 inches, 0.125 to 0.375 inches, 0.125 to 0.225 inches, 0.225 to 0.375 inches, 0.25 to 0.625 inches, 0.25 to 0.5 inches, 0.25 to 0.375 inches, 0.375 to 0.625 inches, or 0.375 to 0.5 inches). The suspension desirably remains non-laminar, such as in a turbulent state, upon entering the auxiliary discharge conduit prior to being added to the slurry to form a dense layer.

Paper fibers have a large aspect ratio (measured as a ratio of length to diameter), for example 40:1 to 100:1, and result in significant contact between the fibers in the pulp suspension. Such contact may tend to result in the formation of undesirable flocs. Surprisingly and unexpectedly, the inventors have found that by delivering a suspension of fibers in a non-lamellar (e.g., turbulent) state to avoid the formation of these floes, the fibers can be properly mixed and effectively and uniformly added to the slurry to form a dense layer. In this way, surprisingly and unexpectedly, the inventors have found that plug flow can be avoided by breaking up the flocs by shear stress from non-laminar (e.g. turbulent) flows. In this regard, plug flow is undesirable and can occur when pulp fibers interact with one another to form flocs and undesirably flow as a rigid body. Otherwise uneven pulp suspension (i.e., fiber concentrated flocculated phase and aqueous phase) will result.

It is believed that the increased shear forces from turbulence will disperse individual fibers in the water. Thus, in embodiments, the slurry suspension is in turbulence such that the slurry fibers can be delivered uniformly and individual fibers can be dispersed in the dense layer gypsum slurry, rather than undesirably having flocs.

In some embodiments, the desired turbulent state is formed when the paper fiber suspension is subjected to a flow velocity greater than the turbulent initiation velocity of the paper fiber suspension. The turbulence onset speed may be determined from a rheology test or a head friction test. Rheology tests are described in venturi, c. "Modeling Pulp Fiber Suspension Rheology," TAPPI Journal, pages 20 to 26 (2008). The toe rub test is described in venturi, c. "Flow Dynamics of Pulp Fiber Suspensions," TAPPI Journal, volume 6, phase 7, pages 17 to 23 (2007).

The fibers may be included in the water in any suitable amount to form a suspension. By way of illustration and not limitation, in one embodiment, the paper fibers are added to water in an amount to form a pulp suspension comprising 3% paper fibers. The slurry suspension was kept in a holding tank equipped with a stirrer and then pumped through a hose. In embodiments, the slurry suspension is added to the slurry at a flow rate that is higher than the turbulent initiation rate of the particular slurry suspension to form the dense layer. According to the tube head friction loss test as described herein, a turbulence onset speed of 3% slurry suspension was found to be 3m/s. The diameter of the hose is chosen to ensure that the slurry flow is above 3m/s and is thus in a turbulent state. For this design, a hose with an inside diameter of 0.375 inch produced a flow rate of 3.2m/s at a flow rate of 40.5 lb/min, leaving the slurry in a turbulent state. Using this procedure, turbulence can be achieved for a given amount of fibers in the pulp suspension.

As an alternative test, reynolds number (R _e ) Can be used to identify laminar flow and turbulence. Reynolds number (R) _e ) The value of (2) can be expressed as R _e ρvd/μ, where ρ is the density of the fluid, V is the fluid velocity, D is the hydraulic diameter of the channel (such as pipe, tube, hose, conduit, etc.), and μ is the fluid viscosity. The viscosity was measured using a rheometer with a shear rate ramp. The viscosity is defined by the speed of the slurry in the hose. If the Reynolds number reaches 2300, the flow is considered laminar. Thus, in some embodiments, the desired non-laminar flow may be represented as having a reynolds number greater than 2300. If the Reynolds number is greater than 3500, the flow is considered turbulent, with a faster and irregular flow path maximizing inertial forces in the system. In some embodiments, turbulence may be expressed as having a reynolds number greater than 3500. In embodiments, the tube head friction test is preferred as a technique for determining laminar versus turbulent flow. It should be noted that it is not necessary to use reynolds numbers to determine flow type nor is it necessary to use more than one of the alternative methods to determine laminar versus turbulent flow.

While both the dense layer slurry and the core slurry contain the components included in the base slurry, the addition to the primary and secondary discharge conduits, respectively, allows the formulation of the respective dense and core slurries to be individually tailored. In this regard, the dense layer slurry includes a greater amount of fibers (e.g., paper fibers) and optionally strength enhancing starch than the core slurry.

In embodiments, the core slurry includes additives (e.g., accelerators, retarders, polyphosphates, dispersants, migrating starches, etc.) in an amount greater than or about equal to the weight of the dense layer slurry. In this regard, some or all of these components may optionally be added directly to the core slurry via the primary discharge conduit, in which case the concentration of such additives in the core slurry will be greater than in the dense layer slurry. One or more of these additives may be inserted into the main mixer and will thus be present in the base slurry. Addition in this manner will result in similar concentrations in the dense and core layers. Surprisingly and unexpectedly, by selectively targeting specific ingredients into the dense and core slurries in this manner, boards can be prepared with low board weights and densities while maintaining good board strength (e.g., via nail pull resistance) in an efficient manner.

A first mobile covering sheet is provided (e.g., on a mobile conveyor). The plates are typically formed upside down at the wet end of the apparatus so that the first moving coversheet is typically the positive coversheet, although this is not mandatory. The dense layer slurry is deposited on the moving coversheet. The core slurry is deposited on the dense layer. A second moving coversheet (e.g., backing paper) is applied over the core slurry layer to form a sandwich structure of panel precursors. In embodiments, the dense layer slurry is deposited on the moving cover sheet upstream of the mixer, while the core slurry is deposited on the cover sheet carrying the dense layer downstream of the mixer. In some embodiments, the secondary discharge conduit is provided on the mixer upstream of the primary discharge conduit to conveniently accommodate such placement of the deposited layer relative to the location of the mixer.

If desired, it will be appreciated that two separate mixers equipped with agitators may be used to prepare the board, with one mixer dedicated to preparing the core slurry and the other mixer dedicated to preparing the core slurry. In this way, each of the dense layer slurry and the core slurry may be formulated separately (without the need for a base slurry) and discharged from each mixer and then applied to form a panel as described herein.

After the sandwich of panel precursors is formed at the wet end of the production line, the panel precursors solidify as they travel, for example, by a conveyor, to other stations including knives, where the panel precursors are cut into sections. The board may then be turned over and dried in a kiln to form the final board product and processed to final dimensions, for example, at the dry end of the production line, as will be appreciated by those of ordinary skill in the art.

Apparatus and method for controlling the operation of a device

Turning now to the drawings, an embodiment of an additive injection system 20 constructed in accordance with the principles of the present disclosure is shown in fig. 1 and 2. The additive injection system 20 is suitable for use with embodiments of slurry mixing and dispensing assemblies that follow the principles of the present disclosure. In embodiments, the additive injection system 20 may be configured to introduce at least one additive into the secondary flow of cementitious slurry dispensed from the mixer into the secondary discharge conduit 21 such that the secondary flow of cementitious slurry is different from the core flow of cementitious slurry dispensed from the primary discharge conduit.

Referring to fig. 1, in the illustrated embodiment, the additive injection system 20 includes a mixer extractor configured to extract and deliver auxiliary slurry from the mixer. Additive injection system 20 includes an extractor 30, an auxiliary conduit section 32, an injection body 34, and a plurality of injection port members 40 attached to injection body 34.

The extractor 30 may be any suitable extractor configured to facilitate discharge of the secondary slurry stream from the mixer. In embodiments, the extractor 30 may be a commercially available extractor that is compatible for use with a mixer intended for use, as will be appreciated by those skilled in the art.

A conduit section 32 extends between the extractor 30 and the injection body 34. The conduit section 32 may comprise a portion of an auxiliary discharge conduit. In an embodiment, a similar conduit section is installed downstream of the injection body 34 and is of sufficient length to deliver the auxiliary slurry to a suitable discharge point along the production line.

In embodiments, the catheter 32 is made of any suitable resiliently flexible material, such as a suitable resiliencyThe bulk material (e.g.,tubes, etc.), and has sufficient strength and flexibility to enable a reduction in size (e.g., to about half of the original diameter) when subjected to radial compression pressure. In embodiments, any catheter having elastic properties may be used. Preferably, the conduit 32 has a cross-sectional diameter in the range of between 1 inch and 4 inches and has a cross-sectional diameter of about ¹ / ₄ -wall thickness in inches. However, in other embodiments, other cross-sectional diameters and wall thicknesses may be used to suit the intended application. Exemplary factors that may affect the particular thickness and configuration of conduit 32 employed include the thickness of the wallboard being produced, the amount of slurry required, the distance between the mixer and the discharge point of the auxiliary slurry, and the specific characteristics of the slurry formulation, including setting rate, water/stucco ratio, fiber usage, and any other desired percentages of additives.

In embodiments, the injection body 34 may include a portion of an auxiliary discharge conduit in fluid communication with a mixer adapted to generate the main core flow and at least one auxiliary flow of cementitious slurry. The injection body 34 may be made of any suitable material, such as a suitable metal or any other suitable material, that may be used to deliver cementitious slurry therethrough during the manufacture of a cementitious product using any suitable technique. In embodiments, the injection body 34 may be made of a suitable metal, such as aluminum, stainless steel, brass, and the like. In embodiments, at least a portion of the injection body 34 may be plated with a suitable material (e.g., chromium) to increase its durability.

Referring to fig. 1 and 2, the injection port member 40 may be removably mounted to the injection body 34 via suitable threaded fasteners. The injection body 34 is compatible with different types of injection port members having similar footprints and external mounting structures, but having different internal passages for delivering additives therethrough. The injection port member 40 and injection body 34 shown in fig. 2 include an embodiment of an additive injection system 20 constructed in accordance with the principles of the present disclosure. In embodiments, a suitable number of injection port members 40 may be associated with the injection body 34. Different types of injection port members may be used interchangeably with the injection body 34 to inject one or more additives (such as, for example, aqueous fibers) into the cementitious slurry stream passing through the injection body 34 under different flow conditions. In use, a set of injection port members includes at least one type of injection port member that is different from the other injection port members in the set, the injection port members in the set being removably mountable to the injection body 34 at a given time.

Referring to fig. 3 and 4, in an embodiment, the injection body 34 defines a slurry channel 43 and at least one port channel 44 in fluid communication with the slurry channel 43. In an embodiment, the injection body 34 defines at least two port channels 44 in fluid communication with the slurry channel 43.

Referring to fig. 3, in the illustrated embodiment, the injection body 34 defines three port channels 44 in fluid communication with the slurry channel 43. In embodiments, the additive injection system 301 may include at least two different types of injection port members, each corresponding to the number of port channels 44 in the injection body 34. The injection body 34 defines a plurality of tap fastener holes 45 configured to threadably receive fasteners therein for mounting a suitable injection port member to the injection body 34 such that the injection port member is associated with one of the port channels 44.

Referring to fig. 4, in an embodiment, the slurry channel 43 of the injection body 34 is adapted to receive and convey a cementitious slurry stream to a downstream portion of the manufacturing system. The illustrated injection body 34 includes a portion of the auxiliary discharge conduit and includes a slurry inlet end 47 defining a slurry inlet opening 48 and a slurry discharge end 49 defining a slurry discharge opening 50. The slurry channel 43 is in fluid communication with a slurry inlet opening 48 and a slurry discharge opening 50. In embodiments, the slurry inlet end 47 and the slurry discharge end 49 may be adapted to be secured to an upstream portion and a downstream portion, respectively, of the cementitious mixing and dispensing assembly.

The illustrated slurry inlet end 47 and slurry discharge end 49 of the injection body 34 each have outer barbed surfaces 52, 53 configured to facilitate a friction fit between the outer barbed surfaces 52, 53 and the inner surface of an appropriately sized auxiliary discharge conduit. An adjustable hose clip may be fitted to the outer surface of the discharge conduit, placed in overlapping relationship with the portion of the injection body 34 disposed within the slurry conduit, and tightened to further facilitate the retaining engagement of the discharge conduit with the injection body 34.

In embodiments, the slurry inlet end 47 of the injection body 34 may be adapted to be placed in fluid communication with a slurry mixer and to receive an auxiliary flow of slurry therefrom. One or more additives, such as, for example, aqueous fibers, may be injected into the secondary slurry stream inside the slurry channel 43 via one or more injection port members removably mounted to the injection body 34 to form a dense slurry. The dense slurry may exit the slurry discharge end 49 from the injection body 34. In embodiments, the slurry discharge end 49 of the injection body 34 may be arranged with a delivery conduit of the auxiliary discharge conduit adapted to deliver the dense slurry to a discharge point for application to one of the cover sheets. In the illustrated embodiment, the slurry discharge opening 50 is larger than the slurry inlet opening 48 to allow for the introduction of additives via the injection port member.

Referring to fig. 3, each of the illustrated port channels 44 has a similar configuration. Thus, it should be understood that the description of one port channel 44 applies equally to each of the other port channels 44. Each port channel 44 has a port opening 55 in fluid communication with the slurry channel 43. Each port channel 44 is arranged in a relationship substantially perpendicular to the direction of flow of slurry through the slurry channel 43. In other embodiments, at least one port channel 44 may have a different orientation relative to slurry channel 43 along at least one plane relative to the direction of slurry flow through slurry channel 43.

The port channels 44 are shown substantially evenly spaced from each other about the circumference of the slurry channel 43 such that they are about 120 degrees from each other. In other embodiments, the injection body 34 may define different relative spacing between the port channels 44.

Referring to fig. 2, each of the illustrated injection port members 40 is of similar construction. Thus, it should be understood that the description of one injection port member 40 applies equally to each of the other injection port members 40. In embodiments, the injection port member 40 is suitable for use in embodiments of the additive injection system 20 that follow the principles of the present disclosure. The injection port member 40 may be adapted to receive at least one additive flow, such as aqueous fibers from a fiber supply conduit in fluid communication with a supply of aqueous fibers, such as, for example, from an aqueous fiber tank, and inject the additive into cementitious slurry passing through slurry channels 43 of a compatible injection body 34 of the additive injection system 20 to which the injection port member 40 is removably mounted.

Each injection port member 40 may be made of any suitable material, such as a suitable metal or any other suitable material, that may be used to deliver the additive therethrough using any suitable technique under pressure suitable for injecting the additive into the cementitious slurry during the manufacture of the cementitious product. In embodiments, the injection port member 40 may be made of a suitable metal, such as aluminum, stainless steel, brass, and the like. In embodiments, at least a portion of the injection port member 40 may be plated with a suitable material (e.g., chromium) to increase its durability.

Referring to fig. 2, each injection port member 40 includes a port insert body 70 extending along a longitudinal axis LA between an additive supply end 71 and a mounting end 72. The port insert body 70 is generally in the form of a hollow cylinder such that the injection port member 40 defines an additive channel 74 therethrough. The additive supply end 71 defines an additive inlet opening 76 and the mounting end 72 defines an additive outlet opening 77 (see also fig. 4). The additive channel 74 extends between and is in fluid communication with an additive inlet opening 76 and an additive outlet opening 77.

The injection port member 40 is adapted to be removably mounted to the mating injection body 34 such that the additive channel 74 is in fluid communication with the slurry channel 43 of the injection body 34 and with the slurry channel 43 through the port channel 44 defined in the injection body 34. The injection port member 40 is adapted to receive the additive flow into the additive inlet opening 76 and inject the additive flow into the cementitious slurry flow through the slurry channel 43 of the injection body 34 to which the injection port member 40 is removably mounted by discharging the additive flow out of the additive outlet opening 77.

The supply end 71 is adapted to remain engaged with a suitable additive supply conduit. The illustrated supply end 71 includes an external threaded surface 78 adapted to sealingly engage a mating internal threaded surface of a suitable coupler of an additive supply conduit.

In other embodiments, the supply end 71 may include another suitable mounting structure for maintaining a coupling with the additive supply conduit. For example, in other embodiments, the supply end 71 may include an outer barb surface that may facilitate a friction fit between the outer barb surface and an inner surface of a suitably sized supply conduit. The adjustable hose clip may be fitted to the outer surface of the additive supply conduit, placed in partially overlapping relation with the supply end 71 disposed within the additive supply conduit, and tightened to further facilitate the retaining engagement of the additive supply conduit with the supply end 71 of the injection port member 40.

In embodiments, the mounting end 72 of the injection port member 40 may include structure adapted to removably mount the injection port member 40 to the mating injection body 34. In embodiments, when the injection port member 40 is removably mounted to the port channel 44 of the injection body 34, at least a portion of the mounting end 72 of the injection port member 40 may be disposed in the port channel of the injection body, for example as shown in fig. 2.

The illustrated injection port member 40 includes a mounting flange 80 extending radially outwardly from the port insert body 70. The mounting flange 80 defines a pair of mounting holes 81 that are each configured to receive a fastener therethrough. In embodiments, the mounting flange 80 may define only one mounting hole 81 or more than two mounting holes 81. Each mounting hole 81 of the mounting flange 80 may be adapted to align with a mating mounting hole 45 defined in the compatible injection body 34 such that one or more fasteners may be used to removably mount the injection port member 40 to the compatible injection body 34.

Referring to fig. 2, each injection port member 40 is configured to be removably mounted to the injection body 34 such that the mounting end 72 of the injection port member 40 is disposed within the port channel 44 defined in the injection body 34. The mounting end 72 of the illustrated injection port member 40 includes a distal portion 84 having a reduced outer diameter. An elastomeric o-ring 85 may be fitted around the distal portion 84 for sealing engagement with the port channel 44 of the injection body 34.

In embodiments, the injection port member may be secured using other techniques. For example, in an embodiment, the mounting end 72 of the injection port member 40 may include a threaded surface adapted to retentively engage a mating threaded surface of the injection body 34, which may be associated with the port channel 44. In embodiments, the mating threaded surface of the injection body 34 may be an internal threaded surface in each port channel 44 of the injection body 34.

To facilitate compatibility of different types of injection port members with the same additive supply conduit and the same mating injection body 34, the additive channel 74 may include a tapered inlet portion 87 and a main portion 88. The tapered inlet portion 87 may include the inlet opening 76. The inlet portion 87 may provide a variable transition region in which the additive flow moves from a supply conduit having a particular cross-sectional area to a main portion 88 of the additive channel 74 that includes an orifice having an orifice size that is different than the size of the supply conduit. In embodiments, the inlet portion 87 may be configured to facilitate the transition of the additive flow from the supply conduit to the injection port member 40 to help facilitate injection of the additive into the auxiliary flow.

The inlet portion 87 is shown as being frustoconical in longitudinal cross-section. In other embodiments, the inlet portion 87 may have a different shape adapted to transition the additive flow from a supply conduit having a supply outlet opening of a particular cross-sectional area to the main portion 88 of the additive channel 74. Additive inlet opening 76 is shown having a size greater than the orifice size of outlet opening 77. The illustrated main portion 88 has a cross-sectional dimension corresponding to the orifice dimension of the outlet opening 77. The illustrated main portion 88 has a substantially uniform cross-sectional area along its length on the longitudinal axis LA.

In embodiments, the geometry of the slurry channel 43 within the injection body 34 is not compromised or disturbed when different types of injection port members are mounted to the injection body 34. In an embodiment, when the injection port member is fully installed to the injection body 34, the injection port member does not protrude into the slurry channel 43 such that the flow of cementitious slurry through the slurry channel 43 is not disturbed by the structural features of the injection port member.

In an embodiment, the injection port member 40 may be adapted to include flush mounting features in which the mounting end 72 is substantially flush with the internal geometry of the slurry channel 43 of the compatible injection body 34. In the illustrated embodiment, the mounting end 72 of the injection port member 40 has a distal face with a concave portion having a radius of curvature that matches the radius of curvature of the slurry channel 43 to define a substantially flush interface therebetween.

In embodiments, different types of injection port members may have different shapes of additive channels 74. In embodiments, the additive channel 74 may have a configuration suitable for promoting fluid flow characteristics. In an embodiment, each of the different types of injection port members is adapted to be removably mounted to any one of the port channels 44 of the injection body 34.

Each type of injection port member is adapted to be removably mounted to the injection body 34 such that the respective additive channel 74 is in fluid communication with the slurry channel 43 via the port channel 44 associated with the injection port member. In the illustrated embodiment, each port channel 44 is configured to receive therein a mounting end 72 of any of at least two types of injection port members.

In an embodiment, each type of injection port member is adapted to be removably mounted to the injection body 34 in the same manner as the first type of injection port member 40 such that its respective additive channel is in fluid communication with the slurry channel 43 via its associated port channel 44. In an embodiment of an additive injection system according to the principles of the present disclosure, a first type of injection port member and a second type of injection port member, similar in construction, may be provided, including mounting structures, but with different orifice sizes and/or additive channel characteristics. Each type of injection port member is removably mounted to the same compatible injection body 34 such that the corresponding additive channel is in fluid communication with the slurry channel 43 of the injection body 34 via the port channel 44. The particular injection port member 40 mounted to the injection body 34 may be removed and replaced with other types of injection port members to alter the flow of additive into the slurry channel 43 that mates with the injection body 34, such as altering the injection pressure of the cementitious slurry flow through the slurry channel 43 of the injection body 34.

In embodiments, an additive injection system according to the principles of the present disclosure may include more than two types of injection port members, each having an additive channel with a different shape and/or size configured to create at least one variable flow characteristic by using different types of injection port members. In embodiments, an additive injection system according to the principles of the present disclosure may include a set of different types of injection port members having additive channels with different orifice sizes of variable inner diameters within a predetermined range, such as, for example, a set of different types of injection port members having variable orifice sizes between 1/4 inch and one inch inner diameters. In embodiments, the size of the set of different types of injection port members may be progressively larger within the range of orifice sizes, such as a set of different types of injection port members having an inner diameter that progressively increases in size from 1/4 inch to one inch in increments of 1/16 inch (i.e., 1/4 inch, 5/16 inch, 3/8 inch, 7/16 inch, 1/2 inch, 9/16 inch, 5/8 inch, 11/16 inch, 3/4 inch, 13/16 inch, 7/8 inch, 15/16 inch, and 1 inch). In other embodiments, different increments and/or ranges of aperture sizes (including sets of metrics) may be used.

Referring to fig. 5-7, another embodiment of an additive injection system 120 constructed in accordance with the principles of the present disclosure is shown. The additive injection system 120 is suitable for use with embodiments of slurry mixing and dispensing assemblies that follow the principles of the present disclosure. In embodiments, the additive injection system 120 may be configured to introduce at least one additive into the secondary flow of cementitious slurry dispensed from the mixer into the secondary discharge conduit such that the secondary flow of cementitious slurry is different from the core flow mixer of cementitious slurry dispensed from the main discharge conduit of the mixer.

Referring to fig. 5 and 6, in the illustrated embodiment, the additive injection system 120 includes an injection body 134, an injection port member 140 removably attached to the injection body 134, and a valve 142 mounted to the body 134. Referring to fig. 7, in an embodiment, the injection body 134 may include a portion of an auxiliary discharge conduit in fluid communication with a mixer adapted to generate a main core flow and at least one auxiliary flow of cementitious slurry. The injection body 134 defines a slurry channel 143, a port channel 144 in fluid communication with the slurry channel 143, and a valve channel 146 in communication with the port channel 144.

The slurry channel 143 of the injection body 134 is adapted to receive the cementitious slurry stream and deliver it to a downstream portion of the manufacturing system. The illustrated injection body 134 includes a portion of the auxiliary discharge conduit and includes a slurry inlet end 147 defining a slurry inlet opening 148 and a slurry discharge end 149 defining a slurry discharge opening 150. The slurry channel 143 is in fluid communication with a slurry inlet opening 148 and a slurry discharge opening 150. In embodiments, the slurry inlet end 147 and the slurry discharge end 149 may be adapted to be secured to an upstream portion and a downstream portion, respectively, of the cementitious mixing and dispensing assembly.

The port channel 144 is configured to be associated with one of a plurality of different types of injection port members 140 for receiving the additive flow in the slurry channel 143 via the injection port member 140 mounted to the body 134. The port channel 144 may include an internally threaded surface 190 for threadably mating with an externally threaded surface 191 of the injection port member 140. The port channels 144 are disposed at a nominal 45 degree port angle to the discharge axis DA defined by the slurry channels 143. In embodiments, the port angle may be in a range between 15 degrees and 75 degrees. The injection port member 140 is adapted to be removably mounted to the mating injection body 34 such that the additive channel 174 is in fluid communication with the slurry channel 143 of the injection body 134 and with the slurry channel 43 through a port channel 144 defined in the injection body 134.

The valve passage 146 is configured to receive the valve 142 therein. In an embodiment, the valve 142 is configured to selectively close the port opening 155 of the port channel 144. In an embodiment, when no additive is injected through injection port member 140 mounted to body 134, valve 142 may be controlled to close port opening 155 of port channel 144.

In embodiments, any suitable valve 142 may be used to close the port opening 155. In the illustrated embodiment, the valve 142 comprises a pneumatic valve that may be arranged with a suitable air source controlled to reciprocate the piston 192 between an open position (as shown in fig. 7) in which additive flow may be injected into the slurry channel 143 via the injection port member 140 and a closed position in which the port opening is closed by the piston 192. As will be appreciated by those skilled in the art, the additive injection system 120 may be otherwise similar to the additive injection system 20 of fig. 1.

Referring to fig. 8-12, another embodiment of an injection body 434 is shown that is suitable for use in an additive injection system constructed in accordance with the principles of the present disclosure. The injection body 434 is suitable for use with embodiments of slurry mixing and dispensing assemblies that follow the principles of the present disclosure. In embodiments, the injection body 434 may be configured to introduce at least one additive into the secondary flow of cementitious slurry dispensed from the mixer into the secondary discharge conduit such that the secondary flow of cementitious slurry is different from the core flow of cementitious slurry dispensed from the main discharge conduit of the mixer.

Referring to fig. 8 and 9, in an embodiment, the injection body 434 may include a portion of an auxiliary discharge conduit in fluid communication with a mixer adapted to generate a main core flow and at least one auxiliary flow of cementitious slurry. In the illustrated embodiment, the injection body 434 includes an injection port member 440, a slurry inlet member 447, a slurry discharge member 449, and an injection block 451. The injection port member 440 is removably attached to the injection block 451 via a threaded connection. The slurry inlet member 447 and slurry discharge member 449 are detachably connected to opposite ends of the injection block 451 via threaded fasteners 454.

Referring to fig. 9, the components of the injection body 434 are hollow such that they define internal channels that cooperate together to define a slurry channel 443 and a port channel 444. The slurry inlet member 447 and the slurry discharge member 449 are in abutting relationship with one another and define a slurry channel 443 that extends through a longitudinal through-hole 455 (see also fig. 10) defined in the injection block 451. The injection block 451 defines a port channel 444 that is in fluid communication with a slurry channel 443 via a cross bore opening 458 defined in a slurry discharge member 449 (see also fig. 12). In embodiments, the injection block 451 may define more than one port channel 444, each of which is in fluid communication with the slurry channel 443.

Referring to fig. 9, in an embodiment, the slurry channel 443 of the injection body 434 is adapted to receive and convey a cementitious slurry stream to a downstream portion of the manufacturing system. The illustrated injection body 434 includes a portion of the auxiliary discharge conduit and includes a slurry inlet member 447 defining a slurry inlet opening 448 and a slurry discharge member 449 defining a slurry discharge outlet opening 450. The slurry channel 443 is in fluid communication with the slurry inlet opening 448 and the slurry outlet opening 450. In embodiments, the slurry inlet member 447 and the slurry discharge member 449 may be adapted to be secured to an upstream portion and a downstream portion, respectively, of the cementitious mixing and dispensing assembly.

In embodiments, the slurry inlet member 447 of the injection body 434 may be adapted to be placed in fluid communication with a slurry mixer and to receive an auxiliary flow of slurry therefrom. One or more additives, such as, for example, aqueous fibers, may be injected into the secondary slurry stream inside the slurry channel 443 via one of a selected set of injection port members 440 that are removably mounted to the injection block 451 such that it is in fluid communication with the port channel 444. The dense slurry may be discharged from the injection body 434 out of the slurry discharge outlet opening 450 of the slurry discharge member 449. In an embodiment, the slurry discharge member 449 of the infusion body 434 may be arranged with a delivery conduit of the auxiliary discharge conduit adapted to deliver the dense slurry to a discharge point for application to one of the cover sheets. In the illustrated embodiment, the cross-sectional area of the slurry discharge outlet opening 450 is greater than the cross-sectional area of the slurry inlet opening 448 to allow for the introduction of additives via the injection port member.

The injection port member 440 is adapted to be removably mounted to the injection block 451 such that the additive channel is in fluid communication with the slurry channel 443 of the injection body 434 through a port channel 444 defined in the injection block 451 and in fluid communication with the slurry channel 443. In an embodiment, the port channel 444 is configured to be associated with one of a plurality of different types of injection port members 440 for receiving the additive flow in the slurry channel 443 via the injection port member 440 mounted to the injection block 451. In embodiments, a set of at least two different types of injection port members may be provided. For example, in embodiments, at least one injection port member may have a through passage with an inner diameter that is different from another injection port member. In other embodiments, at least one injection port member may include in its through passage a restriction not found in at least one other injection port member of the set of injection port members. Each such injection port member may be threadably mounted to injection block 451 in series via mating threaded surfaces such that the through channel of each injection port member is in fluid communication with port channel 444.

The port channels 444 are disposed at a nominal 90 degree port angle θ from the discharge axis DA defined by the slurry channels 443. In embodiments, the port angle θ may be in a range between 45 degrees and 135 degrees. In embodiments, the port angle θ may be in a range between 60 degrees and 120 degrees. In embodiments, the port angle θ may be in a range between 75 degrees and 105 degrees. In an embodiment, the additive flow delivered to the injection block 451 is turbulent. Turbulence is maintained as the additive flow passes through the port channel 444 into the slurry channel 443 where it mixes with the base slurry from the mixer and passes through the slurry channel 443.

Referring to fig. 9 and 10, in the illustrated embodiment, injection block 451 defines one port channel 444 in fluid communication with longitudinal throughbore 455. Referring to fig. 10, the injection block 451 defines a plurality of tap fastener holes 445 configured to threadably receive one of the fasteners 454 therein for mounting the slurry inlet member 447 and the slurry discharge member 449 to a respective one of the ends of the injection block 451. The port channel 444 includes an internally threaded surface 490 configured to threadedly mate with an external surface of the injection port member such that the injection port member is fluidly associated with the port channel to deliver fluid therethrough to the slurry channel.

Referring to fig. 11, a perspective view of the slurry inlet member 447 of the additive injection body 434 of fig. 10 is shown. Referring to fig. 12, a perspective view of the slurry discharging member 449 of the additive injection body 434 of fig. 10 is shown. The illustrated slurry inlet member 447 and slurry discharge member 449 of the injection body 434 each have an outer barbed surface 452, 453 configured to facilitate a friction fit between the outer barbed surfaces 452, 453 and the inner surface of an appropriately sized auxiliary discharge conduit. An adjustable hose clip may be fitted to the outer surface of the discharge conduit, placed in overlapping relation with portions of the corresponding members 447, 449 disposed within the slurry conduit, and tightened to further facilitate the retaining engagement of the discharge conduit with the injection body 434.

Referring to fig. 11 and 12, each of the slurry inlet member 447 and slurry discharge member 449 includes mounting flanges 461, 462 for securing the respective members 447, 449 to the injection block 451 with fasteners 454. Elastomeric o-rings 463, 464 may be fitted around the outer surface of each of slurry inlet member 447 and slurry discharge member 449 for sealing engagement with longitudinal throughbore 455 of injection block 451.

Referring to fig. 9, elastomeric o-rings 463, 464 are provided upstream and downstream of the port channel 444, respectively, to effectively seal against leakage of additive flow from the injection block 451. The slurry inlet member 447 includes a distal downstream portion 465 that includes an expanded internal cross-sectional area relative to its upstream portion 466. The slurry discharge member 449 has an internal cross-sectional area substantially the same as the expanded cross-sectional area of the distal downstream portion 465 of the slurry inlet member 447.

In embodiments, the expansion zone created by the slurry inlet member 447 and the terminal downstream portion 465 of the slurry discharge member 449 may help mitigate process problems that may occur as a result of introducing an additive flow into the slurry passing through the slurry channel 443 via the port channel 444.

In embodiments, the additive injection block 434 may be otherwise similar to the additive injection block 34 of fig. 1, as will be appreciated by those skilled in the art. In embodiments, the additive injection block 434 may be otherwise similar to the additive injection block 134 of fig. 5, as will be appreciated by those skilled in the art.

In embodiments, additive injection systems constructed in accordance with the principles of the present disclosure may be associated with auxiliary discharge conduits of conventional gypsum slurry mixers (e.g., pin mixers) as known in the art. An additive injection system constructed in accordance with the principles of the present disclosure may be advantageously configured as a retrofit in existing wallboard manufacturing systems. The additive injection system may be used with components of a conventional exhaust conduit.

In embodiments, an auxiliary slurry dispensing apparatus constructed in accordance with the principles of the present disclosure may be placed in fluid communication with a slurry mixer to produce a cementitious slurry. In one embodiment, a slurry mixing and dispensing assembly includes a mixer, a primary slurry dispensing device, and a secondary slurry dispensing device.

In an embodiment, a mixing apparatus for mixing and dispensing slurry includes a mixer having a mixer motor and a housing configured to receive and mix the slurry. The housing defines a chamber for containing the slurry and may have a generally cylindrical shape. The housing may have an upper wall, a lower wall, and an annular peripheral wall. Calcined gypsum and water, as well as other materials or additives commonly used in slurries to prepare gypsum products, can be mixed in a mixing apparatus. A first outlet, also known as a mixer outlet, a discharge gate or a trough, may be provided in the peripheral wall for discharging a substantial portion of the cementitious slurry into the primary slurry distribution apparatus. A second mixer outlet may be provided in the peripheral wall for discharging a small portion of the cementitious slurry into the auxiliary slurry dispensing apparatus. The secondary dispensing apparatus may include a cylindrical flexible elastomeric tube or conduit having an inlet in slurry receiving communication with the second mixer outlet and an additive injection system constructed in accordance with the principles of the present disclosure.

Referring to fig. 13, an embodiment of a cementitious slurry mixing and dispensing assembly 210 constructed in accordance with the principles of the present disclosure is shown. The cementitious slurry mixing and dispensing assembly 210 includes a slurry mixer 220 in fluid communication with a main discharge conduit 225 and a pair of auxiliary discharge conduits 227, 228.

The slurry mixer 220 is adapted to agitate the water and cementitious material to form an aqueous cementitious slurry. The slurry mixer 220 is in fluid communication with a main discharge conduit 225 and a pair of auxiliary discharge conduits 227, 228. As known in the art, both water and cementitious material may be supplied to the mixer 220 via one or more inlets. In embodiments, any other suitable slurry additive may be supplied to mixer 220, as is known in the art of manufacturing cementitious products. As will be appreciated by those skilled in the art, any suitable mixer (e.g., pin mixer) may be used.

The mixer 220 includes a housing and a stirrer disposed within the housing. The housing has a main outlet and a pair of auxiliary outlets. The agitator is configured to agitate the water and cementitious material to form an aqueous cementitious slurry.

The main discharge conduit 225 is configured to deliver a main stream of cementitious slurry downstream from the mixer to another manufacturing station (e.g., on a moving web of cover sheet material in an embodiment for producing gypsum wallboard). The main discharge conduit 225 is in fluid communication with the mixer 220. In embodiments, the main exhaust conduit 225 may include any suitable exhaust conduit components, as will be appreciated by those skilled in the art. The illustrated main discharge conduit 225 includes a delivery conduit 230, a foam injection system 235, a flow modification element 240, and a slurry dispenser 245.

Delivery conduit 230 defines a slurry channel. Conduit 230 is connected to mixer 220 such that the slurry channel is in fluid communication with the main outlet. In embodiments, delivery catheter 230 may be made of any suitable material and may have different shapes. In some embodiments, delivery catheter 230 may comprise a flexible catheter.

In an embodiment, the flow modifying element 240 is part of the main discharge conduit 225 and is adapted to regulate the flow of cementitious slurry from the mixer 220 through the main discharge conduit 225. The flow modifying element 240 is disposed downstream of the foam injection system 235 relative to the flow direction of the cementitious slurry stream from the mixer 220 through the main discharge conduit 225. In embodiments, one or more flow modifying elements 240 may be associated with the main discharge conduit 225 and adapted to control the main flow of slurry discharged from the slurry mixer 220. The flow modifying element 240 may be used to control the operating characteristics of the main flow of aqueous cementitious slurry. In the illustrated embodiment of fig. 13 and 14, the flow modifying element 240 is associated with the primary discharge conduit 225. Examples of suitable flow modifying elements include volume restrictors, pressure reducers, pinch valves, tanks, etc., including, for example, U.S. Pat. nos. 6,494,609;6,874,930;7,007,914; and those described in 7,296,919.

In embodiments, slurry dispenser 245 may be any suitable end portion of a conventional discharge conduit, such as a length of conduit in the form of a flexible hose or a component commonly referred to as a "boot. In embodiments, the protective cover may be in the form of a multi-leg drain protective cover.

In other embodiments, the slurry dispenser 245 may be similar to U.S. patent application 2012/0168527;2012/0170403;2013/0098268;2013/0099027;2013/0099418;2013/0100759;2013/0216717; 2013/023380; and 2013/0308411. In some of such embodiments, the main discharge conduit 225 may include suitable components for splitting the main flow of cementitious slurry into two flows that are recombined in the slurry distributor 245.

In an embodiment, the foam injection system 235 may be arranged with at least one of a mixer 220 and a delivery conduit 230. The foam injection system 235 may include a foam source (e.g., such as a foam generating system configured as known in the art) and a foam supply conduit.

In embodiments, any suitable foam source and blowing agent may be used. Preferably, the aqueous foam is produced in a continuous manner, wherein a mixture stream of foaming agent and water is directed to the foam generator, and the resulting aqueous foam stream exits the generator and is directed to and mixed with the cementitious slurry. Some examples of suitable blowing agents are described, for example, in U.S. Pat. nos. 5,683,635 and 5,643,510.

The aqueous foam supply conduit may be in fluid communication with at least one of the slurry mixer 220 and the discharge conduit 230. The aqueous foam from the source may be added to the constituent materials through the foam supply conduit at any suitable location downstream of the mixer and/or the mixer itself to form the foamed cementitious slurry that is provided to the slurry dispenser 240. In the illustrated embodiment, the foam supply conduit is disposed downstream of the slurry mixer and is associated with the discharge conduit 230. In the illustrated embodiment, the aqueous foam supply conduit has a manifold-type arrangement for supplying foam to a plurality of foam injection ports defined within an injection ring or block associated with the delivery conduit, for example, as described in U.S. patent 6,874,930.

In other embodiments, one or more foam supply conduits may be provided in fluid communication with the mixer 220. In other embodiments, the aqueous foam supply conduit may be in fluid communication with the slurry mixer alone. As will be appreciated by those skilled in the art, the means for introducing the aqueous foam into the cementitious slurry in the cementitious slurry mixing and dispensing assembly, including its relative position in the assembly, may be varied and/or optimized for providing a uniform suspension of the aqueous foam in the cementitious slurry to produce a board suitable for its intended purpose.

As will be appreciated by those of ordinary skill in the art, one or both of the webs of cover sheet material may be pretreated with a very thin, relatively dense gypsum slurry layer (relative to the gypsum slurry comprising the core) and/or hard edges (if desired), which is commonly referred to in the art as a skim coat. To this end, the first auxiliary discharge conduit 227 is adapted to deposit a dense aqueous calcined gypsum slurry stream (i.e., a "positive skim coat/hard edge stream") that is relatively denser than the main stream of aqueous calcined gypsum slurry discharged from the main discharge conduit 225. The first auxiliary discharge conduit 227 may deposit a positive skim coating/hard edge stream on the moving web of cover sheet material upstream of a skim coating roller 250 adapted to apply a skim coating to the moving web of cover sheet material and define a hard edge of the moving web perimeter by virtue of the width of the roller being less than the width of the moving web, as is known in the art. The hard edge may be formed from the same dense slurry that forms the thin dense layer by directing portions of the dense slurry around the ends of the rolls used to apply the dense layer to the web.

The first auxiliary drain conduit 227 may include an additive injection system 20 that is similar in construction and function to the additive injection system shown and described herein in connection with fig. 1. The additive supply 252 may be in fluid communication with the additive injection system 20 of the first auxiliary drain conduit 227 to inject at least one additive into the positive skim coating/hard edge stream. In an embodiment, the additive supply 252 includes fibers.

The second auxiliary discharge conduit 228 is adapted to deposit a dense aqueous calcined gypsum slurry stream (i.e., a "back skim coating stream") that is relatively denser than the main stream of aqueous calcined gypsum slurry discharged from the main discharge conduit 225. The second auxiliary discharge conduit 228 may deposit a back skim coating layer flow on the second moving web of cover sheet material upstream of the skim coating roller 255, which is adapted to apply a skim coating to the second moving web of cover sheet material, as is known in the art (see also fig. 14).

The second auxiliary exhaust conduit 228 may include an additive injection system 20 that is similar in construction and function to the additive injection system shown and described herein in connection with fig. 1. The additive supply 257 may be in fluid communication with the additive injection system 20 of the second auxiliary exhaust conduit 228 to inject at least one additive into the back skim coating layer stream. In an embodiment, additive supply 257 comprises fibers.

In other embodiments, one or both of the auxiliary exhaust conduits may include another embodiment of an additive injection system constructed in accordance with the principles of the present disclosure. In other embodiments, a separate auxiliary discharge conduit having an additive injection system constructed in accordance with the principles of the present disclosure may be connected to the mixer to deliver one or more separate edge streams to the moving web of cover sheet material. In other embodiments, the additive injection system may be omitted from one of the first auxiliary exhaust conduit 227 and the second auxiliary exhaust conduit 228. In other embodiments, the second auxiliary exhaust conduit 228 (and its associated additive injection system) may be omitted.

Referring to fig. 14, an exemplary embodiment of a wet end 350 of a gypsum wallboard production line is shown. The illustrated wet end 350 includes a cementitious slurry mixing and dispensing assembly 210, a hard edge/positive skim coating roller 250 disposed upstream of a slurry distributor 245 of a main discharge conduit 225 and supported on a forming table 354 such that a first moving web 356 of cover sheet material is disposed therebetween, a post skim coating roller 255 disposed on a support member 360 such that a second moving web 362 of cover sheet material is disposed therebetween, and a forming station 364 adapted to form a preform to a desired thickness. The skim coat rolls 250, 255, forming table 354, support member 360, and forming station 364 may all comprise conventional equipment suitable for the intended purpose as known in the art. The wet end 350 may be equipped with other conventional equipment as known in the art.

The water and calcined gypsum may be mixed in mixer 220 to form an aqueous calcined gypsum slurry. In some embodiments, the water and calcined gypsum may be added to the mixer continuously at a water/calcined gypsum ratio of 0.5 to 1.3, and in other embodiments 0.75 or less.

The gypsum board product is typically formed "face down" such that the advancing web 356 acts as a "positive" cover sheet for the finished board. A positive skim coat/hard edge stream 366 (denser aqueous calcined gypsum slurry layer relative to the aqueous calcined gypsum slurry main and core streams) can be applied to the first moving web 356 upstream of the hard edge/positive skim coat roll 250 relative to the machine direction 368 to apply a skim coat to the first web 356 and define the hard edge of the board.

The foam injection system 235 may be used to inject aqueous foam into the calcined gypsum slurry produced by the mixer 220. A main stream 321 of aqueous calcined gypsum slurry is discharged from the mixer 220 into a main discharge conduit 225. Aqueous foam is injected into the main stream 321 of aqueous calcined gypsum slurry via foam injection system 235 to form a stream 323 of foamed calcined gypsum slurry. The main stream 323 of foamed calcined gypsum slurry can be acted upon by one or more flow modifying elements 240 and discharged from the slurry distributor 245 of the main discharge conduit 225 on a first moving web 356.

The positive skim coat/hard edge stream 366 may be deposited from the mixer 220 at a point upstream relative to the direction of movement of the first moving web 356 in the machine direction 368, wherein the foam calcined gypsum slurry stream 323 is discharged from the main discharge conduit 225 on the first moving web 356. A back skim coat flow 384 (relative to the denser aqueous calcined gypsum slurry layer in the main stream of foamed calcined gypsum slurry) can be applied to the second moving web 362. The back skim coating layer 384 may be deposited from the mixer 220 at a point upstream relative to the direction of movement of the second moving web 362 of the back skim coating roll 255. The second moving web 362 of cover sheet material may be placed over the foam slurry discharged from the main discharge conduit 225 on the advancing first web 356 to form a sandwich panel preform that is fed to a forming station 364 to form the preform to a desired thickness. In embodiments, fibers, starches, aqueous foam, or other additives 390 may be added to the slurry including the forward skim coating and/or the reverse skim coating via additive injection systems 20 associated with the first auxiliary discharge conduit 227 and the second auxiliary discharge conduit 228, respectively.

The main flow 323 of cementitious slurry has a first volumetric flow rate, the positive skim coat/hard edge flow has a second volumetric flow rate, and the back skim coat flow 384 has a third volumetric flow rate. In an embodiment, the first volumetric flow rate is greater than the second volumetric flow rate, and the first volumetric flow rate is greater than the second volumetric flow rate. In an embodiment, the second volumetric flow rate is greater than the third volumetric flow rate.

The wet end 350 may be used in conjunction with known equipment as a production line. For example, the plate manufacturing techniques described in, for example, U.S. patent 7,364,676 and U.S. patent application publication 2010/0247937 may be used with wet end 350.

Board size, density and strength

Depending on, for example, the type of product and the market, the board may be made in different sizes. The plate may have any suitable width (e.g., 48 inches to 54 inches), length (e.g., 96 inches to 192 inches), and thickness (e.g., 1/4 inches, 3/8 inches, 1/2 inches, 5/8 inches, 3/4 inches, 1 inch, etc.). The size of the different markets may vary somewhat, as is well known in the art.

The dense layer according to embodiments may also have any suitable dimensions. In general, the contribution of the dense layer in the total plate weight and thickness is much smaller, as it can be relatively thin. Once the panel is fabricated, microscopy can be performed at various locations along the entire width of the panel to determine the dense layer thickness. Any form of microscope may be used, such as an optical or Scanning Electron Microscope (SEM), to determine, for example, the thickness of the various layers in the plate sample.

For optical microscopy, a dense layer of the plate sample was observed even at lower magnification. Any suitable dye, including food dyes, may be added to the plate sample if desired to aid in the depiction of the layers of the plate. If desired, a fluorescent dye may optionally be used, but is not required. In the case of SEM, no dye is typically required, as the density differences between layers are evident at the resolution of SEM. To determine the thickness of the layer, image analysis software (e.g., imageJ) or other suitable method may be used to identify the distance between the two points. The layer thickness is the distance between the start of the layer/end of the paper and the end of the layer/start of the core. Measurements can be made at a plurality of locations on the board. Unless indicated otherwise, the thickness was measured using a microscopic test as the plate dried.

Other tests may be used during the manufacturing process to determine the thickness, density and hardness of the core and dense layers. During manufacture, the thickness of the dense layer is measured using a thickness gauge (e.g., a wet film thickness gauge comb, commercially available from TCP Global, san Diego, california) that is periodically used at various locations along the dense layer. The thickness was measured by recording the amount of gauge immersed in the dense layer slurry when inserted and removed at a 90 ° angle.

During the manufacturing process, the density of both the dense layer and the core can be monitored by measuring the wet density as follows. The slurry was poured into a cup of known volume and the weight recorded. Periodically, samples of both the dense layer slurry and the core layer slurry were poured into a mold (cube or tray) and both wet and dry densities were estimated by measuring both weight and size before and after drying.

The plate thickness may vary depending on the type of application of the product (e.g., 1/2 inch conventional plate or 5/8 inch refractory plate, i.e., 0.625 inch). For example, in some embodiments, for a nominal 1/2 inch thick plate, the dense layer may have a dry thickness of 0.02 inch to 0.05 inch, e.g., 0.02 inch to 0.04 inch, or 0.025 inch to 0.035 inch. For other thickness plates, the thickness of the dense layer can be adjusted to be consistent with the exemplary thicknesses mentioned for 1 inch plates, and those adjustments can be readily calculated by one of ordinary skill in the art and are contemplated herein.

In some embodiments, the densified layer comprises 2% to 15%, e.g., 2% to 10%,2% to 8%,2% to 5%,5% to 15%,5% to 10%,5% to 8%,8% to 15%,10% to 15%, etc., of the total thickness of the sheet. If included, the second dense gypsum can be provided, for example, in any of these dimensions, if desired.

The plate weight is a function of thickness. Because the board is typically made in different thicknesses, board density is used herein as a measure of board weight. The advantages of using a fiber reinforced dense layer according to embodiments of the present disclosure can be seen across various board densities, for example 40pcf or less, such as 10pcf to 40pcf, 12pcf to 40pcf, 16pcf to 35pcf, 20pcf to 40pcf, 24pcf to 37pcf, and the like. However, preferred embodiments of the present disclosure have particular utility at lower densities, where the enhanced strength provided by the fiber-reinforced dense layer advantageously enables production of lower weight panels with good strength. For example, in some embodiments, the board density may be, for example, 12pcf to 35pcf, 12pcf to 30pcf, 12pcf to 27pcf, 16pcf to 30pcf, 16pcf to 27pcf, 16pcf to 24pcf, 18pcf to 30pcf, 18pcf to 27pcf, 20pcf to 30pcf, 20pcf to 27pcf, 24pcf to 35pcf, 27pcf to 34pcf, 27pcf to 30pcf, 30pcf to 34pcf, and the like.

The dense layer has a density that is much greater than the density of the board core. For example, the dense layer may have a density of 40pcf to 70pcf, for example 45pcf to 65pcf, or 50pcf to 60 pcf. As described herein, the use of a dense layer with fibers allows for the use of smaller board cores and thus, overall, lighter weight and lower density boards.

The core may have any suitable density, but lower densities may be used, such as 35pcf or less, such as 31pcf or less, or 27pcf or less. For example, the core may have a density of 15pcf to 35pcf, such as 20pcf to 31pcf, 20pcf to 24pcf, or 24pcf to 27pcf, or the like.

In some embodiments, the density difference between the densified layer and the core is desirably significant, e.g., at least 10pcf, at least 15pcf, at least 20pcf, at least 25pcf, or at least 30pcf, such as 10pcf to 50pcf, about 10pcf to 40pcf, 10pcf to 30pcf, 10pcf to 20pcf, 15pcf to 50pcf, 15pcf to 40pcf, 15pcf to 30pcf, 20pcf to 50pcf, 20pcf to 40pcf, from 20pcf to 30pcf, 25pcf to 50pcf, 25pcf to 40pcf, 20pcf to 30pcf, 25pcf to 35pcf, and the like. The density ratio of the dense layer to the core may be any suitable ratio. For example, in some embodiments, the density ratio of the dense layer to the core may be 1.25:1 to 5:1, such as 1.25:1 to 4:1, 1.25:1 to 3:1, 1.25:1 to 2:1, 1.5:1 to 5:1, 1.5:1 to 4:1, 1.5:1 to 3:1, 2:1 to 5:1, 2:1 to 4:1,2:1 to 3:1, 3:1 to 5:1, or 3:1 to 4:1, etc.).

The panels prepared with the fiber-reinforced dense layers as described herein exhibit good strength. For example, in some embodiments, a panel according to the present disclosure meets the test protocol according to ASTM standard C473-10 method B. In this regard, in some embodiments, when the plate is cast at 1/2 inch thickness, the plate has a nail pull resistance of at least 65lb (e.g., at least 68lb., at least 70lb., at least 72lb., at least 75lb., at least 77lb., in each case having any suitable upper limit, such as 110lb. Or greater, etc.) as determined according to ASTM C473-10 method B. . With respect to flexural strength, in some embodiments, when cast into a 1/2 inch thick plate, the plate has a flexural strength in the machine direction (e.g., at least 38lb., at least 40lb., etc., in each case having any suitable upper limit, such as 80lb. Or greater, etc.) of at least 36lb., and/or in the cross-machine direction as determined according to ASTM standard C473 of at least 107lb. (e.g., at least 110lb., at least 112lb., etc., in each case having any suitable upper limit, such as 140lb. Or greater, etc.). These criteria may be met even for lower density boards (e.g., 35pcf or less) as described herein, due at least in part to the fiber reinforced dense layer according to embodiments of the present disclosure.

Aspects of

The disclosure is further illustrated by the following exemplary aspects. However, the present disclosure is not limited to the following aspects.

(1) A gypsum board, the gypsum board comprising: a set gypsum core disposed between a first cover sheet and a second cover sheet, the gypsum core formed from a core slurry comprising stucco, water, a foaming agent, and at least one of the following ingredients: accelerators, retarders, dispersants and migrating starches; a densified layer disposed between the core and the first cover sheet, the densified layer formed from a densified layer slurry comprising stucco, water, and fibers (e.g., paper fibers) having an amount of at least 0.8% by weight of the stucco, the densified layer having a density of at least 40 pcf; the densified layer slurry preferably includes a higher concentration of the fibers (e.g., paper fibers) than the core slurry, and the core slurry preferably includes the same or higher concentration of the at least one of the accelerator, retarder, dispersant, and migrating starch than the densified layer slurry; and the plate has a density of 35pcf or less and a nail pull resistance of at least 72lb according to ASTM 473-10 method B.

(2) The gypsum board of claim 1, wherein the fibers comprise cellulosic fibers, carbon fibers, mineral fibers, glass fibers, polymer fibers, or any combination thereof.

(3) The gypsum board of claim 1 or 2, wherein the fibers in the dense layer slurry comprise paper fibers and the core slurry further comprises second fibers that do not comprise paper fibers, such as cellulose fibers, carbon fibers, mineral fibers, glass fibers, polymer fibers, or any combination thereof, and preferably, if any, are in an amount greater than or equal to the amount in the dense layer slurry.

(4) A gypsum board according to any one of claims 1 to 3, wherein the fibers are wet pulp paper fibers having an average length of 0.5mm to 4.0mm, such as 2mm to 3 mm.

(5) The gypsum board of any one of claims 1-4, wherein the fibers are dry crushed paper fibers having an average length of from 0.5mm to 4 mm.

(6) The gypsum board of any one of claims 1-5, wherein the fibers comprise chopped glass fibers.

(7) The gypsum board of any one of claims 1-6, wherein the fibers comprise glass fibers having an average diameter of 3 microns to 20 microns.

(8) The gypsum board of any one of claims 1-7, wherein the fibers comprise polymeric fibers comprising one or more of polyester, polyethylene, polypropylene, nylon, polyacetate, polyacrylic, polystyrene, polyvinyl acetate, rayon, polyvinyl chloride, copolymers thereof, and combinations thereof, such as synthetic polymeric fibers comprising polyester, polyethylene, polypropylene, or combinations thereof.

(9) The gypsum board of any one of claims 1-8, wherein the fibers comprise natural pulp fibers such as: wood pulp fibers, including softwood pulp fibers and hardwood pulp fibers; straw fibers; plant and grass pulp fibers such as hemp pulp fibers, jute pulp fibers, kenaf pulp fibers and bamboo pulp fibers; cotton pulp fiber; or any combination thereof, such as wood pulp fibers for use in papermaking.

(10) The gypsum board of any one of claims 1-9, wherein the densified layer has a thickness of 0.02 inches to 0.05 inches (e.g., 0.02 inches to 0.04 inches, or 0.025 inches to 0.035 inches).

(11) The gypsum board of any one of claims 1-10, wherein the core slurry is substantially free of glass fibers, paper fibers, and polymer fibers, such as 0.5% by weight or less, 0.3% by weight or less, or 0.1% by weight or less of the stucco.

(12) The gypsum board of any one of claims 1 to 11, wherein the core has a density of 35pcf or less, such as 31pcf or less, or 27pcf or less.

(13) The gypsum board of any one of claims 1 to 12, wherein the densified layer has a density of 40pcf to 70pcf, such as 45pcf to 65pcf, or 50pcf to 60pcf, and the core has a density of 15pcf to 35pcf, such as 20pcf to 31pcf, or 24pcf to 27 pcf.

(14) The gypsum board of any one of claims 1-13, wherein the densified layer slurry comprises a polyphosphate, such as sodium trimetaphosphate, for example, in an amount from 0.01% to 0.5% by weight of the stucco.

(15) The gypsum board of any one of claims 1-14, wherein the densified layer slurry consists of stucco, water, fibers, such as paper fibers, and optionally strength enhancing starches and/or polyphosphates.

(16) The gypsum board of any one of claims 1-15, wherein the densified layer slurry comprises a strength enhancing starch, e.g., in an amount of from 0.5% to 5% by weight of the stucco, such as from 2% to 3% by weight of the stucco.

(17) The gypsum board of claim 16, wherein the core slurry is substantially free of strength enhancing starch, such as less than 2% by weight of the stucco, such as less than 1% by weight of the stucco.

(18) The gypsum board of any one of claims 1-17, wherein the board has a nail pull resistance of at least 77lb, such as 77 lb.to 105lb, 77 lb.to 98 lb.etc., according to ASTM 473-10 method B.

(19) The gypsum board of any one of claims 1-18, further comprising a second densified layer disposed between the core and the second cover sheet, the second densified layer formed from a second densified layer slurry that is the same as or different from the densified layer slurry.

(20) A method of making gypsum board, the method comprising: obtaining a first cover sheet and a second cover sheet; applying a densified layer to the first coversheet in adhering relationship, the densified layer being formed from a slurry comprising stucco, water, and fibers (e.g., paper fibers), the fibers being in an amount of at least 0.8% by weight of the stucco, the densified layer having a dry density of at least 40 pcf; applying a first surface of a core in bonded relation to the densified layer, the core having a density of 35pcf or less; and applying the second cover sheet in adhering relation to a second surface of the core; the densified layer slurry preferably includes a higher concentration of the fibers than the core slurry, and the core slurry preferably includes the same or higher concentration of at least one of the accelerator, retarder, dispersant, and migrating starch as the densified layer slurry, and the board has a nail pull resistance of at least 72lb according to ASTM 473-10 method B.

(21) The method of claim 20, further comprising disposing a second densified layer between the core and the second cover sheet, the second densified layer formed from a second densified layer slurry that is the same as or different from the densified layer slurry.

(22) The method of claim 20 or 21, wherein the fibers comprise cellulosic fibers, carbon fibers, mineral fibers, glass fibers, polymer fibers, or any combination thereof.

(23) The method of any one of claims 20 to 22, wherein the core slurry further comprises second fibers that do not comprise paper fibers, such as cellulose fibers, carbon fibers, mineral fibers, glass fibers, polymer fibers, or any combination thereof, and preferably in an amount greater than or equal to the amount in the densified layer slurry, if any.

(24) The method of any one of claims 20 to 23, wherein the fibers comprise wet pulp paper fibers having an average length of 0.5mm to 4.0mm, such as 2mm to 3 mm.

(25) The method of any one of claims 20 to 24, wherein the paper fibers are dry chopped fibers having an average length of 0.5mm to 4 mm.

(26) The method of any one of claims 20 to 25, wherein the fibers comprise chopped glass fibers.

(27) The method of any one of claims 20 to 26, wherein the fibers comprise glass fibers having an average diameter of 3 microns to 20 microns.

(28) The method of any one of claims 20 to 27, wherein the fibers comprise polymer fibers comprising one or more of polyester, polyethylene, polypropylene, nylon, polyacetate, polyacrylic, polystyrene, polyvinyl acetate, rayon, polyvinyl chloride, copolymers thereof, and combinations thereof, such as synthetic polymer fibers comprising polyester, polyethylene, polypropylene, or combinations thereof.

(29) The method of any one of claims 20 to 28, wherein the fibers comprise natural pulp fibers such as: wood pulp fibers, including softwood pulp fibers and hardwood pulp fibers; straw fibers; plant and grass pulp fibers such as hemp pulp fibers, jute pulp fibers, kenaf pulp fibers and bamboo pulp fibers; cotton pulp fibers or any combination thereof, such as wood pulp fibers for use in papermaking.

(30) The method of any one of claims 20 to 29, wherein the dense layer has a dry thickness of 0.02 to 0.05 inches, such as 0.02 to 0.04 inches, or 0.025 to 0.035 inches.

(31) The method of any of claims 20-30, wherein the core slurry is substantially free of glass fibers, paper fibers, and polymer fibers, such as 0.5 wt.% or less, 0.3 wt.% or less, or 0.1 wt.% or less of the stucco.

(32) The method of any one of claims 20 to 31, wherein the core has a dry density of 35pcf or less, such as 31pcf or less, or 27pcf or less.

(33) The method of any one of claims 20 to 32, wherein the densified layer has a dry density of 40pcf to 70pcf, such as 45pcf to 65pcf, or 50pcf to 60pcf, and the core has a dry density of 15pcf to 35pcf, such as 20pcf to 31pcf, or 24pcf to 27 pcf.

(34) The method of any one of claims 20-33, wherein the densified layer slurry comprises a polyphosphate, such as sodium trimetaphosphate, for example, in an amount of from 0.01% to 0.5% by weight of the stucco.

(35) The method of any one of claims 20 to 34, wherein the core slurry is substantially free of polyphosphates, such as sodium trimetaphosphate, such as in an amount less than 0.01%, such as 0.005% or less, or 0.001% or less by weight of stucco.

(36) The method of any one of claims 20 to 35, wherein the densified layer slurry includes strength enhancing starch, for example, in an amount of from 0.5% to 5% by weight of the stucco, such as from 2% to 3% by weight of the stucco.

(37) The method of claim 36, wherein the core is substantially free of strength enhancing starch, such as less than 2 weight percent of the stucco, such as less than 1 weight percent of the stucco.

(38) The method of any one of claims 20 to 37, wherein the board has a nail pull resistance of at least 77lb, such as 77 lb.to 105lb, 77 lb.to 98lb, etc., according to ASTM 473-10 method B, and the board has a density of 35pcf or less, 31pcf or less, or 27pcf or less, such as 15pcf to 35pcf, 20pcf to 35pcf, 24pcf to 35pcf, 15pcf to 31pcf, 20pcf to 31pcf, 24pcf to 31pcf, 15pcf to 27pcf, 20pcf to 27pcf, 15pcf to 24pcf, etc.

(39) A method of making a panel, the method comprising: providing a plate mixer comprising a main body and respective main and auxiliary discharge ducts; inserting stucco and water into the body of the mixer to form a base slurry; discharging a majority of the base slurry from the main body into the main discharge conduit to form a core slurry; discharging a small portion of the base slurry from the main body into the auxiliary discharge conduit to form a dense layer slurry; preparing a suspension comprising water and paper fibers; inserting the suspension into the dense layer slurry in the auxiliary discharge conduit while the suspension is in a non-layered state sufficient to avoid more than 10 wt% of fibers forming floes having an average length of 3mm or more; providing a first cover sheet and a second cover sheet; depositing the fiber-reinforced dense layer slurry on the first cover sheet; depositing the core slurry on the fiber-reinforced dense layer slurry; and applying the second cover sheet over the core slurry.

(40) The method of claim 39, wherein a second densified layer slurry is disposed between the core slurry and the second cover sheet, wherein the second densified layer slurry can be the same as or different from the fiber reinforced densified layer slurry.

(41) The method of claim 39 or 40, wherein the non-laminar state is turbulent.

(42) The method of any one of claims 39 to 41, wherein the suspension is added to the dense layer slurry with a flow rate greater than a turbulence onset speed of the suspension as determined according to a head friction test.

(43) The method of any one of claims 39 to 42, wherein prior to inserting the suspension into the dense layer slurry, the suspension is passed through a channel having an inner diameter sufficient to subject the suspension to turbulent flow.

(44) The method of claim 43, wherein the passageway has an inner diameter of 0.125 inches to 0.625 inches.

(45) The method of claim 44, wherein the passageway has an inner diameter of 0.2 inches to 0.5 inches.

(46) The method of claim 45, wherein the channel has an inner diameter of 0.2 inches to 0.375 inches.

(47) The method of any one of claims 39 to 46, wherein the suspension when added to the dense layer slurry has a reynolds number of at least 2300.

(48) The method of claim 47, wherein the suspension when added to the dense layer slurry has a reynolds number of at least 3500.

(49) The method of any one of claims 39 to 48, wherein the suspension comprises 1% to 4% of the fibers.

(50) The method of any one of claims 39 to 49, the suspension further comprising strength-enhancing starch.

(51) The method of any one of claims 39 to 50, the suspension further comprising a polyphosphate.

(52) The method of any one of claims 39 to 51, wherein the auxiliary exhaust conduit is located upstream of the main exhaust conduit.

(53) The method of any one of claims 39 to 52, wherein the dense layer slurry is deposited upstream of the mixer.

(54) The method of any one of claims 39 to 53, wherein the core slurry is deposited downstream of the mixer.

(55) The method of any one of claims 39 to 54, wherein at least one of the following ingredients is injected into a main mixer body or the main discharge conduit but not into an auxiliary mixer: accelerators, retarders, dispersants, migrating starches and polyphosphates.

(56) The method of claim 55, wherein the densified layer slurry preferably has a higher concentration of the fibers and optionally the strength enhancing starch than the core slurry, and the core slurry preferably has the same or higher concentration of at least one of the accelerator, retarder, dispersant, migrating starch than the fiber-enhanced densified layer slurry.

(57) The method of claim 56, wherein the core slurry preferably has the same or higher concentration of at least three additives other than paper fibers as compared to the fiber-reinforced dense slurry.

(58) The method of claim 56 or 57 wherein the core slurry preferably has the same or higher concentration of at least four additives other than paper fibers as compared to the fiber-reinforced dense slurry.

(59) A system for manufacturing gypsum board, the system comprising: a mixer comprising a housing having a first outlet and a second outlet and a mixer disposed within the housing, the mixer configured to mix water and cementitious material to form an aqueous cementitious slurry; a primary discharge conduit in fluid communication with the first outlet; a secondary discharge conduit in fluid communication with the second outlet; and an additive injection system having an injection body defining a slurry channel including a portion of the auxiliary discharge conduit such that the slurry channel is in fluid communication with the second outlet of the mixer and a port member in fluid communication with the slurry channel, the port member defining an additive channel, the port member being removably connected to the injection body such that the additive channel is in fluid communication with the port channel.

(60) The system of claim 59, wherein the injection port member comprises a port insert body extending along a longitudinal axis between an additive supply end defining an additive inlet opening and a mounting end defining an additive outlet opening, the additive channel extending between and in fluid communication with the additive inlet opening and the additive outlet opening.

(61) The system of claim 60, wherein the mounting end of the injection port member is detachably mounted to the injection body, the system further comprising: an additive supply conduit connected to the additive supply end of the injection port member such that the additive supply conduit is in fluid communication with the additive channel.

(62) The system of any one of claims 59-61, wherein the additive channel has a tapered inlet portion and a main portion, the tapered inlet portion including the additive inlet opening, the inlet portion having a variable transition to the main portion of the additive channel, the main portion having an orifice with an orifice size that is smaller than the additive inlet opening.

(63) The system of claim 62, wherein the inlet portion is frustoconical in longitudinal cross-section and the main portion has a cross-sectional dimension corresponding to the orifice dimension of the outlet opening.

(64) The system of any one of claims 59-63, wherein the port member comprises a first port member, the system further comprising: a second port member defining an additive channel different from the additive channel of the first port member, the second port member being removably connected to the injection body in place of the first port member such that the additive channel of the second port member is in fluid communication with the port channel.

(65) The system of claim 64, wherein the additive channel of the first port member has a first orifice size and the additive channel of the second port member has a second orifice size, the first orifice size being larger than the second orifice size.

(66) The system of claim 64 or claim 65, wherein the port channel of the injection body comprises a first port channel, the injection body defines a second port channel in spaced relation to the first port channel, the second port channel is in fluid communication with the slurry channel, and the port member comprises a first port member, the system further comprising: a second port member defining a second additive channel, the second port member being removably connected to the injection body such that the second additive channel is in fluid communication with the second port channel.

(67) The system of any one of claims 59 to 66, wherein the injection body includes a slurry inlet end defining a slurry inlet opening and a slurry discharge end defining a slurry discharge opening, and the slurry channel is in fluid communication with the slurry inlet opening and the slurry discharge opening.

(68) The system of claim 67, wherein the auxiliary discharge conduit comprises an upstream portion and a downstream portion, the slurry inlet opening of the injection body being in fluid communication with the upstream portion of the auxiliary discharge conduit, and the slurry discharge opening of the injection body being in fluid communication with the downstream portion of the auxiliary discharge conduit.

(69) The system of claim 67 or claim 68, wherein said slurry inlet end and said slurry discharge end of said injection body each have an outer barbed surface.

(70) The system of any one of claims 67 to 69, wherein the slurry discharge opening is larger than the slurry inlet opening.

(71) The system of any one of claims 59-70, wherein the injection body defines a valve channel in communication with the port channel, and the port channel includes a port opening, the system further comprising: a valve mounted to the injection body such that at least a portion of the valve is disposed in the valve passage of the injection body, the valve being adapted to selectively close the port opening.

(72) The system of claim 71, wherein the valve comprises a pneumatic valve comprising a reciprocally movable piston adapted to be arranged with an air supply and to selectively reciprocally move the piston between an open position in which a port opening is at least partially unobstructed to allow additive flow through the port channel to move into the slurry channel and a closed position in which the port opening is closed by the piston.

(73) The system of any one of claims 59 to 72, wherein the injection body comprises a slurry inlet member, a slurry discharge member, and an injection block, the slurry inlet member and the slurry discharge member being detachably connected to opposite ends of the injection block.

(74) A gypsum board, or a method of making a gypsum board, as described herein.

(75) A system for manufacturing gypsum board substantially as shown and described.

(76) An additive injection system substantially as shown and described.

(77) A method of manufacturing gypsum board substantially as shown and described.

(78) A plasterboard substantially as shown and described.

It should be noted that the foregoing aspects are illustrative and not limiting. Other exemplary combinations will be apparent from the entire description herein. Those of ordinary skill in the art will also appreciate that various embodiments can be variously combined with other embodiments provided herein.

The following examples further illustrate the disclosure but, of course, should not be construed as in any way limiting its scope.

Example 1

This example demonstrates the exemplary benefit of including fibers in a gypsum composition according to the principles of embodiments of the present disclosure. Inclusion of fibers in the gypsum composition can increase nail pull resistance when compared to a gypsum composition that does not contain fibers.

Specifically, paper fibers are included in the gypsum slurry as a reinforcing additive. The paper fibers are introduced into the slurry in the form of wet pulp or dry chopped fibers. Typically, paper fibers may be added to a mixture of wet additives, or as a dry material mixed with stucco, as is understood in the art and in manufacturing. To record the benefits of including fibers in the gypsum composition, 10 disks (1A-1I) were prepared having a diameter of 4 inches and a thickness of 7/16 inch (0.44 inch). The tray was prepared from a slurry comprising stucco in an amount of 100% and further comprising a heat resistant accelerator (1.0%), highly hydrolyzed acid modified migrating starch in the form of LC-211 (commercially available from Archer-Daniels-Midland, chicago, illinois) having a cold water solubility of 10% and a hot water viscosity of less than 10BU (1%), uncooked acid modified corn starch having a hot water viscosity of 180BU (as an example of an uncooked medium hydrolyzed acid modified starch) (1%), retarder (0.06%) and dispersant (0.3%), all amounts by weight of stucco. The type 1A-1G slurry forming trays contained Sodium Trimetaphosphate (STMP) (0.1%), while the type 1I slurry forming trays did not contain STMP.

Uncooked acid modified corn starch (as an example of uncooked hydrolyzed acid modified starch) with a hot water viscosity of 180BU is provided to enhance the strength (e.g., nail pull strength or core hardness) of the board, while acid modified migrating starch (e.g., LC-211) is provided not to enhance strength but to improve the bond between gypsum and materials such as the center.

Discs were prepared by using a Waring Blender (Waring Blender), commercially available from Conair LLC, stamford, connecticut, the set discs were heated at 350°f for 30 minutes, and then dried overnight at 110°f. As shown in table 1, each type of tray was made into samples prepared with dried shredded or pulp paper fibers and/or without STMP at 35pcf and/or 50 pcf. Nail pull resistance was measured for each sample according to ASTM 473-10 method B. Table 1 sets forth the nail pull resistance ("NP") for each sample.

TABLE 1

As shown in table 1, an increase in the paper fiber (wet pulp or dry crushed paper) content in the gypsum increases the NP strength of the gypsum board. The density of gypsum has a significant impact on the NP strength increase. Table 1 shows the NP percent increase (158% increase in 1% paper fiber addition) for the 50pcf samples versus the NP percent increase (104% increase) for the 35pcf samples. According to the present disclosure, since the density of the densified layer of the wallboard may be 50PCF or a density in the range of about 50PCF, adding paper fibers to the densified layer is expected to significantly increase the NP strength of the wallboard. As shown in comparative discs 1G and 1I, the discs have similar NP intensities with and without STMP present, respectively.

Example 2

This example demonstrates the benefit of a board prepared with a densified layer formed from a slurry comprising paper fibers in nail pull strength.

Specifically, five panels (2A-2E) were made in the laboratory with a gypsum core having a density of 29pcf sandwiched between front and back cover sheets. A dense gypsum layer having a density of 50pcf was deposited between the facer paper and the gypsum core. The back side does not include any dense layer. The same type (i.e., manila) paper is used on both sides.

The gypsum core and the gypsum compact layer are formed from separate slurries in view of the density differences. Paper fibers are included in the slurry used to form the densified layer in an amount of 1 or 2 weight percent of stucco. The densified gypsum layer has a thickness of 0.025 inches or 0.035 inches. The gypsum core was made without paper fibers and included other additives in the form of stucco, heat resistant accelerator (1%), sodium trimetaphosphate (0.2%), dispersant (0.5%) and retarder (0.027%), with amounts based on the weight of stucco.

Optional additives in the form of modified starch (2% by weight of stucco) and polyphosphate (0.2% by weight of stucco) are also included in the slurry for forming a densified layer. The modified starch is in the form of uncooked medium hydrolyzed acid modified starch, and specifically uncooked acid modified corn starch having a hot water viscosity of 180 BU. However, other strength enhancing starches may be used alternatively or in addition to uncooked starches of the type described above, including medium viscosity and medium molecular weight pregelatinized starches, and/or highly hydrolyzed acid modified migrating starches. For example, the medium viscosity and medium molecular weight pregelatinized starch can be in the form of pregelatinized corn flour starch having a cold water viscosity of 90 centipoise. The highly hydrolyzed acid modified mobile starch may be in the form of highly hydrolyzed acid modified mobile starch having a cold water solubility of 10%. Polyphosphate in the form of sodium trimetaphosphate, another optional ingredient, is further used in the dense layer to enhance dimensional stability.

Table 2A illustrates the properties of the dense layer.

TABLE 2A

Table 2B illustrates the nail pull of a 2A-2E laboratory plate according to ASTM 473-10 method B. "nail pull delta" refers to the difference in nail pull strength between the front and back sides (indicating the increase in nail pull strength due to the inclusion of paper fibers in the densified layer).

TABLE 2B

As can be seen from the results, a larger nail pull was imparted due to the inclusion of paper fibers in the densified layer. For example, the nail pull between the front side, which includes a 0.025 inch thick densified layer with 1% paper fiber, and the back side, which has the same core but no densified layer, was increased by 19.6lb.

In addition, a comparison was made between a plate having a dense layer without fibers and a plate having a dense layer with fibers. Boards 2F and 2G were prepared according to the same method as for preparing boards 2A and 2B except that board 2G was used for comparison purposes because it did not include paper fibers in its densified layer.

TABLE 2C

As shown in table 2C, wallboard samples having a densified layer without paper fiber reinforcement had 80.1lb nail pulls, while wallboard samples including 1% paper fiber in the densified layer had 87.6lb nail pulls. Thus, the densified layer comprising 1% paper fibers significantly increases the nail pull strength, specifically 7.5lb.

Example 3

This example demonstrates the results of the equipment production of boards formed from a densified layer formed from stucco slurry including cellulosic fibers. In particular, equipment trials recorded the benefits of using pulp in combination with uncooked acid modified corn starch (as an example of uncooked medium hydrolyzed acid modified starch) having a hot water viscosity of 180BU and its impact on nail pull resistance ("NP"). As indicated in example 1, inclusion of fibers in the gypsum composition can increase NP when compared to a gypsum composition that does not contain fibers.

In particular, the board is prepared on a gypsum board production line. These panels are prepared to include a core sandwiched between front and back cover sheets formed of paper. A dense layer ("skim coat") is applied between the core and the positive cover sheet. The densified layer was prepared from a densified layer slurry comprising stucco, water, paper fibers in a slurry suspension (hereinafter sometimes simply referred to as "slurry") and uncooked acid-modified corn starch having a hot water viscosity of 180 BU.

According to the formulation set forth in table 3, the core and dense layer were each formed from a slurry. The boards were prepared using a single motherboard mixer (as opposed to a dual mixer system). The wet and dry components of the core slurry are added to the body of the plate mixer. The foaming agent is injected into the discharge conduit of the mixer to allow the core to include air voids and thus have a lower density. The dense slurry is released from the mixer upstream of the discharge conduit through an extractor device such that the dense slurry includes a minimal amount of foaming agent or is free of foaming agent. Uncooked acid modified corn starch with a paper fiber and hot water viscosity of 180BU was injected into the extractor to make the board core free of these additives.

The plate is formed upside down. The dense slurry was applied to a paper tape used as the positive cover sheet. The board core slurry exits the discharge conduit and is applied to the positive cover sheet carrying the dense slurry. A back cover sheet is applied over the core slurry to form a sandwich of panels. The plate was allowed to set and cut, dried and processed to form a plate having dimensions of 1/2 inch thick, 48 inches wide and 96 inches long.

Table 3 describes the corresponding compositions of the core slurry and the dense layer slurry. The dense layer slurry has a water/stucco ratio of between 1.05 and 1.1 and the core slurry has a water/stucco ratio of between 0.83 and 0.88.

TABLE 3 Table 3

As shown in table 3, the amounts of additives were the same in the densified layer slurry and the core slurry except for the paper fiber and the uncooked acid-modified corn starch having a hot water viscosity of 180BU, which were greater in the densified layer slurry according to embodiments of the present disclosure. The extracted densified layer slurry was enhanced with paper fiber and uncooked acid modified corn starch having a hot water viscosity of 180 BU.

To record the benefits of using pulp in combination with uncooked acid modified corn starch having a hot water viscosity of 180BU on NP strength, three board types (3A-3C) were produced for equipment testing. A control panel type (3A) containing neither pulp nor uncooked acid modified corn starch with a hot water viscosity of 180BU was used as a control. A second board type (3B) was produced comprising a slurry, but without further addition of uncooked acid-modified corn starch having a hot water viscosity of 180 BU. A third board type (3C) was produced comprising paper fiber and uncooked acid modified corn starch having a hot water viscosity of 180BU, as described below.

Paper fibers are derived from the production of waste paper. The desired test pulp consistency target is calculated by dividing the weight of the collected paper fibers by the desired pulp consistency target percentage. The results indicate how many pounds of water are needed to achieve the desired slurry percentage. To achieve a concentration of, for example, 2.7%, an initial weight of 23 lbs. of paper fiber, 852 lbs. of water would be required.

For the purposes of the equipment test as described in this example, the test pulp consistency is nominally 3% dry fiber. To prepare the slurry, water was first collected in a holding tank capable of holding approximately 300 gallons using a fixed volume 200 gallon tote. The paper fibers are added to the tank and thoroughly mixed to achieve the target consistency. Once the target consistency is reached, uncooked acid-modified corn starch with a hot water viscosity of 180BU is added to produce a slurry that forms a third board type.

Once the batch procedure is completed, each slurry is pumped into the process skid. The skid includes a stirred tank and a progressive cavity tank screw for pumping a pumped mixture into a dense bed injection member.

After production is complete, the panel type is subjected to NP strength testing according to ASTM 473-10 method B. Table 4 sets forth NP intensities for various plate types.

TABLE 4 Table 4

As shown in table 4, "difference from the previous condition" means NP with respect to the plate type directly above. In addition to using uncooked acid modified corn starch with a hot water viscosity of 180BU, the use of pulp had a significant impact on the increase in NP strength as shown in board type 3B. In addition, uncooked acid modified corn starch with a hot water viscosity of 180BU was added to the slurry to further increase the NP intensity of board type 3C to 90.35, while the NP intensity produced by the control was 84.84.

Thus, this example shows that adding a combination of syrup and uncooked acid-modified corn starch with a hot water viscosity of 180BU, in accordance with the present disclosure, increases NP strength.

Example 4

This example demonstrates the insertion of paper fibers into a densified layer slurry using injection ports of different inside diameter dimensions, particularly with respect to the flow characteristics of the paper fibers in water.

Experiments were performed using the formulations of the dense layer slurries set forth in table 3. In particular, experiments were performed using injection ports having different inner diameters ("IDs", hereinafter) in order to record the effect on pulp flow consistency and density. For experimental purposes, four different injection port inner diameters were studied: 1"ID, 0.5" ID, 0.375"ID, and 0.25" ID.

To test the different injection ports, drop tests were performed using a slurry skid and 40 gallons of 3% slurry formulation. Drop tests refer to a method of checking flow accuracy over a period of time and are performed by the following steps. To achieve a measurable flow, the pump was turned on and the discharge hose was left free to pump for 15 seconds. After 15 seconds have passed, the drain hose is placed in a 5 gallon bucket. After 30 seconds, the drain hose was removed and the bucket was then weighed. To measure the flow (pounds per minute), the weight of the barrel and its contents is subtracted from the weight of the barrel itself and multiplied by 2. This process was repeated three times to achieve the average flow and standard deviation. This process is repeated for each of the nozzles identified above.

The slurry slide rail is a progressive cavity metering pump. Specifically, the progressive cavity metering pump includes a 150 gallon tank with a level sensor, a flow meter to measure the discharge flow of the metering pump, and an air diaphragm pump to refill the 150 gallon tank. For the purposes of these experiments, pump SP was set at 21.8 pounds per minute. The final effect on pulp density (as measured in lb/cut) is recorded in fig. 16. The effect of ID on flow rates (ft/min and m/s) is recorded in Table 5 below. Three individual droplets per injection port inside diameter size were recorded.

TABLE 5

As shown in table 5, the use of a smaller injection port inside diameter has a significant impact on flow rate. The reduction of the inner diameter results in a larger flow rate, which is advantageous because it reduces the amount of pulp "floe" and the deviation of the mass flow. Fig. 16 is a box plot of density versus port size. As shown in fig. 16, the pulp density decreases with decreasing port size. This indicates a more consistent flow.

To record the effects of turbulence and laminar flow on flow accuracy and the likelihood of clogging, further experiments were performed using four different injection port IDs as described above, with the results shown in tables 6A and 6B. Using the drop test described above, 4E and 4F injection ports were studied using laminar flow (e.g., flow rates less than 3.0 m/s) and 4G and 4H injection ports were studied using turbulent flow (e.g., flow rates greater than 3.0 m/s).

TABLE 6A

TABLE 6B

As shown in tables 6A and 6B above, the density then varies with each injection port size, corresponding to a corresponding overall drop in slurry density. In addition, tables 6A and 6B show flow accuracy and flow rate. These results indicate which injection port size is required to achieve consistent and accurate flow and exceed turbulent flow velocities.

Further experiments were recorded in tables 7A and 7B using an injection port ID of 0.375 "using the methods of 6A and 6B. The injection port size was tested to record the correlation between flow and flow rate. The 4I and 4J injection ports were investigated using laminar flow, while the 4K-4N injection ports were investigated using turbulent flow.

TABLE 7A

TABLE 7B

As shown in tables 7A and 7B above, when an injection port of 0.375"id is used, the flow rate increases as the average flow increases, which is advantageous because the minimum flow can be achieved while maintaining turbulence.

Example 5

The experiments were performed using a pulp suspension comprising pulp with a consistency of 2.7% according to the rheology test as described in venturi, c. "Modeling Pulp Fiber Suspension Rheology," TAPPI Journal, pages 20 to 26 (2008)).

To measure the relationship between shear stress and shear rate of the slurry suspension, a Discovery mixer rheometer 20 (as used herein, "DHR 20", commercially available from TA Instruments, new cast le, delaware) was used, which had a blade geometry at room temperature (about 75°f). DHR 20 is used to vary the shear rate, which refers to the rotational speed of the blade, and the shear stress is measured from 0.001s ^-1 To 3500s ^-1 Is measured with a shear rate ramp of (c). Room temperature was chosen to simulate the temperature used in the production line for the slurry suspension.

The rheology profile (i.e., the shear stress versus shear rate curve) recorded by DHR 20 for a 2.7% pulp suspension indicates a turbulent flow initiation speed of 2.3m/s. The initial velocity of the turbulence is 2.3m/s, indicating that the slurry suspension is homogeneous when it is transported at a velocity higher than 2.3m/s, which is advantageous because the fibers can be homogeneously added to the gypsum slurry of the dense layer.

Example 6

The experiments were performed using a pulp suspension comprising pulp with a consistency of 3% according to the pulp head friction test as described in venturi, c. "Flow Dynamics of Pulp Fiber Suspensions," TAPPI Journal, volume 6, phase 7, pages 17 to 23 (2007).

To record the effect of flow rate on friction loss, the slurry suspension was pumped through ball valves at different rates into 10 foot hoses or 40 foot hoses with pipe diameters of 3/8 or 1/2 inch. The flow rates used were 1.21, 3.14, 3.37, 4.84, 5.65, 6.10, 7.75 and 8.3 gallons/minute, which were varied by adjusting the ball valve. The flow range is chosen to cover the desired turbulence onset speed.

As a result, especially the change in speed is measured by a drop test. The friction head loss was calculated by comparing the change in velocity between 10 foot and 40 foot hoses, the results of which are recorded in fig. 18. As shown in FIG. 18, the turbulence start speed was about 3m/s. When the pulp suspension is pumped at above 3m/s, the pulp suspension is in a turbulent state, which is advantageous because the pulp suspension is transported in a homogeneous state.

Example 7

This example shows that boards prepared from dense layer slurries with or without Sodium Trimetaphosphate (STMP) have similar nail pull ("NP") strength values.

Laboratory plates were produced according to the core and dense layer slurry formulations as set forth in table 8. A control plate with a densified layer sample was prepared that was formed from a slurry containing 0.1% STMP but no paper fibers. A second plate having a dense layer prepared from a slurry containing 1% paper fibers and 0.1% STMP was prepared, while a third plate having a dense layer prepared from a slurry containing 1% paper fibers but no STMP was prepared.

TABLE 8

The slurry was prepared using a waring blender commercially available from Conair LLC of stamford, ct. The corresponding densified layer slurry was poured on top of a 0.025 inch thick manila facestock cover sheet. The core slurry is then poured on top of the dense layer slurry. A newsprint cover was added on top of the core slurry. The set samples were then heated to 440°f for 9 minutes, followed by another 21 minutes at 280°f. The heated samples were then dried overnight at 110°f.

Table 9 shows the nail pull resistance ("NP") for each sample. The NP resistance of each sample was measured according to ASTM 473-10 method B.

TABLE 9

As shown in table 9, the NP value for the control plate was 70.9lb, 7lb to 9lb lower than the sample with the fiber reinforced dense layer. The NP values of the plaques with the dense layer comprising STMP were not significantly different from the plaques with the dense layer without STMP. Thus, the results indicate that the densified layer reinforced with paper fibers, with or without STMP, increased nail pull strength.

All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

The use of the terms "a" and "an" and "the" and "at least one" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The term "at least one" (e.g., "at least one of a and B") as used after a listing of one or more items is to be construed to mean one item (a or B) selected from the listed items or any combination of two or more of the listed items (a and B), unless otherwise indicated herein or clearly contradicted by context. Stucco and water are the basic ingredients in the slurry and are therefore not considered additives. When comparing the amounts between the core slurry and the dense layer slurry, it is understood that this is in relation to the relative comparison, i.e. the concentration. To the extent that certain portions of the specification may refer to the main and auxiliary discharge conduits as a whole of the plate mixer, while other portions may refer to them as separate parts, it should be understood that any such differences in the specification do not imply or imply a different arrangement unless otherwise indicated. The terms "comprising," "having," "including," and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to,") unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Unless indicated otherwise, all amounts are by weight rather than by volume. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

1. A gypsum board, the gypsum board comprising:

a set gypsum core disposed between a first cover sheet and a second cover sheet, the gypsum core formed from a core slurry comprising stucco, water, a foaming agent, and at least one of the following ingredients: accelerators, retarders, dispersants and migrating starches;

A densified layer disposed between the core and the first cover sheet, the densified layer formed from a densified layer slurry comprising stucco, water, and first fibers comprising paper fibers in an amount of at least 0.8% by weight of the stucco, the densified layer having a density of at least 40 pcf;

the densified layer slurry preferably includes a higher concentration of the paper fibers than the core slurry, and the core slurry preferably includes the same or higher concentration of the at least one of the accelerator, retarder, dispersant, and migrating starch than the densified layer slurry; and is also provided with

The panel has a density of 35pcf or less and a nail pull resistance of at least 72lb according to ASTM 473-10 method B.

2. The gypsum board of claim 1, wherein the fibers comprise cellulosic fibers, carbon fibers, mineral fibers, glass fibers, polymer fibers, or any combination thereof.

3. The gypsum board of claim 1 or 2, wherein the core slurry further comprises a second fiber that does not comprise paper fibers, such as cellulose fibers, carbon fibers, mineral fibers, glass fibers, polymer fibers, or any combination thereof, and preferably in an amount greater than or equal to the amount in the densified layer slurry, if any.

4. A gypsum board according to any one of claims 1 to 3, wherein the paper fibres are wet pulp fibres having an average length of 0.5mm to 4.0mm, such as 2mm to 3 mm.

5. The gypsum board of any one of claims 1-4, wherein the paper fibers are dry chopped fibers having an average length of from 0.5mm to 4 mm.

6. The gypsum board of any one of claims 1-5, wherein the fibers further comprise chopped glass fibers.

7. The gypsum board of any one of claims 1-6, wherein the fibers comprise glass fibers having an average diameter of 3 microns to 20 microns.

8. The gypsum board of any one of claims 1-7, wherein the fibers comprise polymeric fibers comprising one or more of polyester, polyethylene, polypropylene, nylon, polyacetate, polyacrylic, polystyrene, polyvinyl acetate, rayon, polyvinyl chloride, copolymers thereof, and combinations thereof, such as synthetic polymeric fibers comprising polyester, polyethylene, polypropylene, or combinations thereof.

9. The gypsum board of any one of claims 1-8, wherein the fibers comprise natural pulp fibers such as: wood pulp fibers, including softwood pulp fibers and hardwood pulp fibers; straw fibers; plant and grass pulp fibers such as hemp pulp fibers, jute pulp fibers, kenaf pulp fibers and bamboo pulp fibers; cotton pulp fiber; or any combination thereof, such as wood pulp fibers for use in papermaking.

10. The gypsum board of any one of claims 1-9, wherein the densified layer has a dry thickness of from 0.02 inches to 0.05 inches, such as from 0.02 inches to 0.04 inches, or from 0.025 inches to 0.035 inches.

11. The gypsum board of any one of claims 1-10, wherein the core slurry is substantially free of glass fibers, paper fibers, and polymer fibers, such as 0.5 weight percent of the stucco

Or less, 0.3 wt% or less, or 0.1 wt% or less.

12. The gypsum board of any one of claims 1 to 11, wherein the core has a dry density of 35pcf or less, such as 31pcf or less, or 27pcf or less.

13. The gypsum board of any one of claims 1 to 12, wherein the densified layer has a dry density of 40pcf to 70pcf, such as 45pcf to 65pcf, or 50pcf to 60pcf, and the core has a density of 15pcf to 35pcf, such as 20pcf to 31pcf, or 24pcf to 27 pcf.

14. The gypsum board of any one of claims 1-13, wherein the densified layer slurry comprises a polyphosphate, such as sodium trimetaphosphate, for example, in an amount from 0.01% to 0.5% by weight of the stucco.

15. The gypsum board of any one of claims 1-14, wherein the densified layer slurry consists of stucco, water, fiber, and optionally strength enhancing starch and/or polyphosphate.

16. The gypsum board of any one of claims 1-15, wherein the densified layer slurry comprises a strength enhancing starch, e.g., in an amount of from 0.5% to 5% by weight of the stucco, such as from 2% to 3% by weight of the stucco.

17. The gypsum board of claim 16, wherein the core slurry is substantially free of strength enhancing starch, such as less than 2% by weight of the stucco, such as less than 1% by weight of the stucco.

18. The gypsum board of any one of claims 1-17, wherein the board has a nail pull resistance of at least 77lb, such as 77 lb.to 105lb, 77 lb.to 98 lb.etc., according to ASTM 473-10 method B.

19. The gypsum board of any one of claims 1-18, further comprising a second densified layer disposed between the core and the second cover sheet, the second densified layer formed from a second densified layer slurry that is the same as or different from the densified layer slurry.

20. A method of making gypsum board, the method comprising:

obtaining a first cover sheet and a second cover sheet;

applying a densified layer to the first coversheet in bonding relationship, the densified layer formed from a slurry comprising stucco, water, and first fibers, the first fibers comprising paper fibers in an amount of at least 0.8% by weight of the stucco, the densified layer having a dry density of at least 40 pcf;

Applying a first surface of a core in bonded relation to the densified layer, the core having a density of 35pcf or less; and

applying the second cover sheet in adhering relation to a second surface of the core;

the densified layer slurry preferably includes a higher concentration of the first fibers than the core slurry, and the core slurry preferably includes the same or higher concentration of the at least one of the accelerator, retarder, dispersant, and migrating starch as the densified layer slurry, and the board has a nail pull resistance of at least 72lb according to ASTM 473-10 method B.

21. The method of claim 20, further comprising disposing a second densified layer between the core and the second cover sheet, the second densified layer formed from a second densified layer slurry that is the same as or different from the densified layer slurry.

22. The method of claim 20 or 21, wherein the first fibers further comprise cellulosic fibers, carbon fibers, mineral fibers, glass fibers, polymer fibers, or any combination thereof.

23. The method of any one of claims 20 to 22, wherein the core slurry further comprises a second fiber, such as cellulose fibers, carbon fibers, mineral fibers, glass fibers, polymer fibers, or any combination thereof, that does not comprise paper fibers, and preferably, if any, in an amount greater than or equal to the amount in the densified layer slurry.

24. The method of any one of claims 20 to 23, wherein the paper fibers comprise wet pulp fibers having an average length of 0.5mm to 4.0mm, such as 2mm to 3 mm.

25. The method of any one of claims 20 to 24, wherein the paper fibers are dry chopped having an average length of 0.5mm to 4 mm.

26. The method of any one of claims 20 to 25, wherein the fibers comprise chopped glass fibers.

27. The method of any one of claims 20 to 26, wherein the fibers comprise glass fibers having an average diameter of 3 microns to 20 microns.

28. The method of any one of claims 20 to 27, wherein the fibers comprise polymer fibers comprising one or more of polyester, polyethylene, polypropylene, nylon, polyacetate, polyacrylic, polystyrene, polyvinyl acetate, rayon, polyvinyl chloride, copolymers thereof, and combinations thereof, such as synthetic polymer fibers comprising polyester, polyethylene, polypropylene, or combinations thereof.

29. The method of any one of claims 20 to 28, wherein the fibers comprise natural pulp fibers such as: wood pulp fibers, including softwood pulp fibers and hardwood pulp fibers; straw fibers; plant and grass pulp fibers such as hemp pulp fibers, jute pulp fibers, kenaf pulp fibers and bamboo pulp fibers; cotton pulp fibers or any combination thereof, such as wood pulp fibers for use in papermaking.

30. The method of any one of claims 20 to 29, wherein the dense layer has a dry thickness of 0.02 to 0.05 inches, such as 0.02 to 0.04 inches, or 0.025 to 0.035 inches.

31. The method of any of claims 20-30, wherein the core slurry is substantially free of glass fibers, paper fibers, and polymer fibers, such as 0.5 wt.% or less, 0.3 wt.% or less, or 0.1 wt.% or less of the stucco.

32. The method of any one of claims 20 to 31, wherein the core has a dry density of 35pcf or less, such as 31pcf or less, or 27pcf or less.

33. The method of any one of claims 20 to 32, wherein the densified layer has a dry density of 40pcf to 70pcf, such as 45pcf to 65pcf, or 50pcf to 60pcf, and the core has a density of 15pcf to 35pcf, such as 20pcf to 31pcf, or 24pcf to 27 pcf.

34. The method of any one of claims 20-33, wherein the densified layer slurry comprises a polyphosphate, such as sodium trimetaphosphate, for example, in an amount of from 0.01% to 0.5% by weight of the stucco.

35. The method of any one of claims 20 to 34, wherein the core slurry is substantially free of polyphosphates, such as sodium trimetaphosphate, for example in an amount less than 0.01%, such as 0.005% or less, or 0.001% or less by weight of stucco.

36. The method of any one of claims 20 to 35, wherein the densified layer slurry includes strength enhancing starch, for example, in an amount of from 0.5% to 5% by weight of the stucco, such as from 2% to 3% by weight of the stucco.

37. The method of claim 36, wherein the core is substantially free of strength enhancing starch, such as less than 2 weight percent of the stucco, such as less than 1 weight percent of the stucco.

38. The method of any one of claims 20 to 37, wherein the board has a nail pull resistance of at least 77lb, such as 77 lb.to 105lb, 77 lb.to 98lb, etc., according to ASTM 473-10 method B, and the board has a density of 35pcf or less, 31pcf or less, or 27pcf or less, such as 15pcf to 35pcf, 20pcf to 35pcf, 24pcf to 35pcf, 15pcf to 31pcf, 20pcf to 31pcf, 24pcf to 31pcf, 15pcf to 27pcf, 20pcf to 27pcf, 15pcf to 24pcf, etc.

39. A method of making a panel, the method comprising:

providing a plate mixer comprising a main body and respective main and auxiliary discharge ducts;

inserting stucco and water into the body of the mixer to form a base slurry;

Discharging a majority of the base slurry from the main body into the main discharge conduit to form a core slurry;

discharging a small portion of the base slurry from the main body into the auxiliary discharge conduit to form a dense layer slurry;

preparing a suspension comprising water and paper fibers;

inserting the suspension into the dense layer slurry in the auxiliary discharge conduit while the suspension is in a non-layered state to form a fiber reinforced dense slurry;

providing a first cover sheet and a second cover sheet;

depositing the fiber-reinforced dense layer slurry on the first cover sheet;

depositing the core slurry on the fiber-reinforced dense layer slurry; and is also provided with

The second cover sheet is applied over the core slurry.

40. The method of claim 39, wherein a second densified layer slurry is disposed between the core slurry and the second cover sheet, wherein the second densified layer slurry can be the same as or different from the fiber reinforced densified layer slurry.

41. The method of claim 39 or 40, wherein the non-laminar state is turbulent.

42. The method of any one of claims 39 to 41, wherein the suspension is added to the dense layer slurry with a flow rate greater than a turbulence onset speed of the suspension as determined according to a head friction test.

43. The method of any one of claims 39 to 42, wherein prior to inserting the suspension into the dense layer slurry, the suspension is passed through a channel having an inner diameter sufficient to subject the suspension to turbulent flow.

44. The method of claim 43, wherein the passageway has an inner diameter of 0.125 inches to 0.625 inches.

45. The method of claim 44, wherein the passageway has an inner diameter of 0.2 inches to 0.5 inches.

46. The method of claim 45, wherein the channel has an inner diameter of 0.2 inches to 0.375 inches.

47. The method of any one of claims 39 to 46, wherein the suspension when added to the dense layer slurry has a reynolds number of at least 2300.

48. The method of claim 47, wherein the suspension when added to the dense layer slurry has a reynolds number of at least 3500.

49. The method of any one of claims 39 to 48, wherein the suspension comprises 1% to 4% of the fibers.

50. The method of any one of claims 39 to 49, the suspension further comprising strength-enhancing starch.

51. The method of any one of claims 39 to 50, the suspension further comprising a polyphosphate.

52. The method of any one of claims 39 to 51, wherein the auxiliary exhaust conduit is located upstream of the main exhaust conduit.

53. The method of any one of claims 39 to 52, wherein the dense layer slurry is deposited upstream of the mixer.

54. The method of any one of claims 39 to 53, wherein the core slurry is deposited downstream of the mixer.

55. The method of any one of claims 39 to 54, wherein at least one of the following ingredients is injected into a main mixer body or the main discharge conduit but not into an auxiliary mixer: accelerators, retarders, dispersants, migrating starches and polyphosphates.

56. The method of claim 55, wherein the densified layer slurry preferably has a higher concentration of the fibers and optionally the strength enhancing starch than the core slurry, and the core slurry preferably has the same or higher concentration of at least one of the accelerator, retarder, dispersant, migrating starch than the fiber-reinforced densified layer slurry.

57. The method of claim 56, wherein the core slurry preferably has the same or higher concentration of at least three additives other than paper fibers as compared to the fiber-reinforced dense slurry.

58. The method of claim 56 or 57 wherein the core slurry preferably has the same or higher concentration of at least four additives other than paper fibers as compared to the fiber-reinforced dense slurry.

59. A system for manufacturing gypsum board, the system comprising:

a mixer comprising a housing having a first outlet and a second outlet and a mixer disposed within the housing, the mixer configured to mix water and cementitious material to form an aqueous cementitious slurry;

a primary discharge conduit in fluid communication with the first outlet;

a secondary discharge conduit in fluid communication with the second outlet; and

an additive injection system having an injection body defining a slurry channel including a portion of the auxiliary discharge conduit such that the slurry channel is in fluid communication with the second outlet of the mixer and a port member in fluid communication with the slurry channel, the port member defining an additive channel, the port member being removably connected to the injection body such that the additive channel is in fluid communication with the port channel.

60. The system of claim 59, wherein the injection port member comprises a port insert body extending along a longitudinal axis between an additive supply end defining an additive inlet opening and a mounting end defining an additive outlet opening, the additive channel extending between and in fluid communication with the additive inlet opening and the additive outlet opening.

61. The system of claim 60, wherein the mounting end of the injection port member is detachably mounted to the injection body, the system further comprising:

an additive supply conduit connected to the additive supply end of the injection port member such that the additive supply conduit is in fluid communication with the additive channel.

62. The system of any one of claims 59-61, wherein the additive channel has a tapered inlet portion and a main portion, the tapered inlet portion including the additive inlet opening, the inlet portion having a variable transition to the main portion of the additive channel, the main portion having an orifice with an orifice size that is smaller than the additive inlet opening.

63. The system of claim 62, wherein the inlet portion is frustoconical in longitudinal cross-section and the main portion has a cross-sectional dimension corresponding to the orifice dimension of the outlet opening.

64. The system of any one of claims 59-63, wherein the port member comprises

A first port member, the system further comprising:

a second port member defining an additive channel different from the additive channel of the first port member, the second port member being removably connected to the injection body in place of the first port member such that the additive channel of the second port member is in fluid communication with the port channel.

65. The system of claim 64, wherein the additive channel of the first port member has a first orifice size and the additive channel of the second port member has a second orifice size, the first orifice size being larger than the second orifice size.

66. The system of claim 64 or claim 65, wherein the port channel of the injection body comprises a first port channel, the injection body defines a second port channel in spaced relation to the first port channel, the second port channel is in fluid communication with the slurry channel, and the port member comprises a first port member, the system further comprising:

A second port member defining a second additive channel, the second port member being removably connected to the injection body such that the second additive channel is in fluid communication with the second port channel.

67. The system of any one of claims 59 to 66, wherein the injection body includes a slurry inlet end defining a slurry inlet opening and a slurry discharge end defining a slurry discharge opening, and the slurry channel is in fluid communication with the slurry inlet opening and the slurry discharge opening.

68. The system of claim 67, wherein the auxiliary discharge conduit comprises an upstream portion and a downstream portion, the slurry inlet opening of the injection body being in fluid communication with the upstream portion of the auxiliary discharge conduit, and the slurry discharge opening of the injection body being in fluid communication with the downstream portion of the auxiliary discharge conduit.

69. The system of claim 67 or claim 68, wherein said slurry inlet end and said slurry discharge end of said injection body each have an outer barbed surface.

70. The system of any one of claims 67 to 69, wherein the slurry discharge opening is larger than the slurry inlet opening.

71. The system of any one of claims 59-70, wherein the injection body defines a valve channel in communication with the port channel, and the port channel includes a port opening, the system further comprising:

a valve mounted to the injection body such that at least a portion of the valve is disposed in the valve passage of the injection body, the valve being adapted to selectively close the port opening.

72. The system of claim 71, wherein the valve comprises a pneumatic valve comprising a reciprocally movable piston adapted to be arranged with an air supply and to selectively reciprocally move the piston between an open position in which a port opening is at least partially unobstructed to allow additive flow through the port channel to move into the slurry channel and a closed position in which the port opening is closed by the piston.

73. The system of any one of claims 59 to 72, wherein the injection body comprises a slurry inlet member, a slurry discharge member, and an injection block, the slurry inlet member and the slurry discharge member being detachably connected to opposite ends of the injection block.