MXPA01006795A - Method of producing moulded pulp articles with a high content of dry matter - Google Patents

Abstract

Method of manufacturing articles from an aqueous fibre suspension, by deposition of fibres on a suction mould (2), comprising the steps of:applying suction to the suction mould, supplying a fibre suspension to the mould by immersing the suction mould in a vat (5) containing the fibre suspension, raising the suction mould from the fibre suspension, flowing ambient air by said suction through an article formed by a layer of fibre material deposed on the suction mould, characterised by the steps of:providing a substantially hermetically sealed space over the article or articles on the suction mould, supplying a de-watering fluid to the sealed space, and flowing substantially exclusively the de-watering fluid through the article or articles.

Description

METHOD FOR THE PRODUCTION OF MOLDEATED PAPERWORK PASTE, WITH A HIGH CONTENT OF DRY MATTER TECHNICAL FIELD The present invention relates to a method for producing molded articles of pulp with a high content of dry matter when leaving the suction wheel according to the preamble of claim 1, and to an apparatus for carrying out the method according to the preamble. of claims 12 and 29. In this context, the term "pulp" is to be understood as applying to a fiber containing pulp mass, which may also contain or constitute scrap paper.

BACKGROUND OF THE INVENTION US-3,654,076 discloses a continuous mass production method of articles of pulp material using a molding machine with a rotating mold carrier, on the periphery from which the suction molds are placed side by side. The molded articles of pulp are formed by immersing the suction molds in a vat of the pulp suspended material while suction is applied, in order to form a pulp body in the form of the desired article, by deposition of fiber. The suction mold is then removed from the vat of the suspended pulp material, and the suction is generally continued to compact the deposited fibers while removing the residual liquid therefrom. The wet molded articles are removed from the suction mold, partly by blowing air through a suction mold, and partially by sucking the articles onto a corresponding transfer rotor. From the transfer rotor, the articles are placed on the support and transport means, adapted to transport the articles to a drying oven, for a drying process. The molded articles have, when they leave the suction mold, a relatively low dry matter content, which is typically about 25% by weight. A dry matter content of approximately at least 90% by weight has to be achieved by drying the articles in a drying oven. The low initial dry matter content of the articles when they leave the suction mold results in a high amount of energy used to dry the articles in the oven. In addition, articles with their low dry matter content are difficult to handle due to their stability in shape, for example these need to be handled carefully. U.S. Patent No. 4,448,640 discloses a method of continuous mass production of articles from stock material using a molding machine with a rotary mold carrier according to the principles described above, which is provided with a stationary bell that roughly encapsulates a part of the rotating mold carrier. This arrangement allows a mixture of hot air or moist hot air and ambient air to flow through the articles on the suction molds.

DESCRIPTION OF THE INVENTION In the above background, the aim of the present invention is to provide a method of the type initially referred to, with which it is possible to produce articles with a high content of dry matter when they leave the suction mold. The advantages of a high content of dry matter are a better stability of form that results in easier handling of the articles in the subsequent production steps, such as, for example, the post-pressing and a reduction in the energy needed to dry the articles. This objective is achieved with the method as defined in claim 1. By distributing a dewatering fluid into a substantially hermetically sealed space on the article, it is possible to flow the dewatering fluid through the article, which does not mix with the ambient air and in this way a substantially improved dewatering effect is achieved which leads to a higher dry matter content of the molded articles of pulp. The present invention also relates to an apparatus for carrying out the aforementioned method as defined in claims 12 and 29. By providing a bell over the suction molds or the mold carrier in combination with sealing packages between the molds and the bell or bells, a space above the item can be efficiently sealed from the ambient air. By distributing a dewatering fluid into the space encapsulated on the surface of the mold, only the dewatering fluid is flowed by suction through the molded articles of pulp onto the mold, without the ambient air being mixed in the fluid of the mold. Dehydration A further object of the invention is to provide a method of the type initially referred to, in which steam is used as a dehydration fluid.

BRIEF DESCRIPTION OF THE DRAWINGS In the subsequent detailed portion of the description, the invention will be explained in more detail with reference to the drawings, in which: Figure 1 shows diagrammatically one embodiment of a pulp molding machine, a conveyor system and a drying oven Figure 2 shows a detailed view of the rotating mold carrier and the bell, and Figure 3 shows a view of the rotary mold carrier and the side bell in view of Figure 2. Figure 4 shows diagrammatically a second embodiment of the invention.

Figure 5 shows diagrammatically a third embodiment of the invention. Figure 6 shows diagrammatically a fourth embodiment of the invention. Figure 7 shows diagrammatically a fifth embodiment of the invention. Figure 8 shows diagrammatically a sixth embodiment of the invention.

DESCRIPTION OF THE PREFERRED MODALITY Figure 1 diagrammatically shows a suction molding station for molding articles from pulp material. The station comprises a rotating mold carrier 1, on the outside of which are placed several suction molds 2 permeable to the liquid, adapted to be connected with a source of sub-atmospheric pressure and a source of super-atmospheric pressure. The mold carrier 1 is with a portion of its circumferential surface submerged in a tub 5 of pulp containing a suspension of fiber stock. This pulp can be made from a raw material containing fiber, including scrap paper or waste paperboard. During immersion in the pulp mass, a layer of fiber material is deposited by suction on the surfaces of the suction mold 2. Subsequently, when the molds 2 are removed from the fiber suspension in the pulp vat 5, the suction is continued to compact the deposited fibers while the residual liquid is extracted from them. After removing the mold from the pulp tub 5, the mold will follow the rotary path of the rotary mold carrier 1 and with this it will pass under a bell 3 which is in sealing interaction with the packages 4 placed on the mold carrier 1 rotating, which seals the mold surface from the ambient air. A dewatering fluid is introduced into the sealed space between the bell 3 and the suction mold 2, while the source of the sub-atmospheric pressure is connected to the mold 2. The dewatering fluid is thus made to flow through the freshly molded article, on the surface of the mold. The article is thereby dehydrated, and the dry matter content of the article is increased. After removing the mold 2 from the tub 5 of pulp and before supplying the dewatering fluid, water is sprayed onto the articles in order to remove the residual pulp.

The articles are typically three-dimensional molded pulp packages as trays for fruits and eggs. These items have a wall of relatively thin fiber material. The hood 3 can cover a substantial section of the rotating mold carrier 1 in order to provide sufficient time for the dewatering fluid to flow through the molded articles. After passing under the bell 3, the molds 2 are further rotated to engage a transfer rotor 6 which is placed with its axis parallel to the axis of the rotating mold carrier 1, and to the periphery of the latter . From the suction mold 2 on the rotating mold carrier 1, the fiber layer that has been deposited by suction is blown by supplying air under pressure to the latter coming from the source of super-atmospheric pressure. At the same time, the wet article is being sucked onto the transfer molds 14 on the transfer rotor 6. From the transfer rotor 6, the moist article is blown and drawn towards a transfer tray 7, on which the article is transported through a drying oven 8. From the drying oven 8, the substantially or completely dry article is placed on a surface of transportation (not shown), from which it is transported upward and passing a number of post-treatment stations (not shown) to complete its processing. Figure 2 shows a detailed view on the side of the hood 3 covering a sector of the carrier 1 of the rotating mold. The hood 3 coverage begins just above the point where the molds leave the pulp tub and extend approximately one quarter of the circumference of the rotary mold carrier 1 and terminate before the transfer rotor 6. The bell 3 comprises a curved wall extending over the width of the rotating mold carrier. The curved wall of the hood 3 follows an arc with its center of rotation falling together with the axis of the rotating mold carrier 1 (Figure 3). At least two side walls 3a, 3b extend substantially perpendicularly from the curved wall along the sides of the rotating mold carrier 1 towards the axis of the latter. The side walls of the hood are provided with gaskets 4a, preferably in the form of a labyrinth seal that interacts sealingly with the side walls of the rotating mold carrier, or vice versa. The curved wall of the bell is in sealing contact in the packages 4 placed on the rotary mold carrier 1 before and after each suction mold or suction mold group. The packages 4 extend in a direction substantially parallel to the axis of the rotating mold carrier. The rotating mold carrier 1 is thus divided by the packages 4 into groups of one or groups of various molds 2. When it passes under the bell 3, an encapsulated space is formed on each of the molds 2 or group of molds between two packages 4. A source of dehydration fluid 9 is connected to the bell 3 by a duct 10 which conducts the dewatering fluid under the curved surface of the bell. The dehydration fluid is supplied at a higher pressure than that of the sub-atmospheric pressure source. A valve 11 is placed in a duct 10 distributing the dewatering fluid to the bell, so that the distribution of the dewatering fluid can be controlled. The distribution duct 10 can be divided into several ducts each comprising a valve 11, so that a controlled distribution to different parts of the hood 3 is possible according to the suction molds 2 passing under the hood. The inlet openings in the bell 3 for the inlet of the dehydration fluid are preferably concentrated towards the side of the bell 3 where the suction molds 2 enter. The pressure of the dehydration fluid distributed to the bell can be varied and is in the range of 0.1 to 12 bars; preferably from 0.5 to 2 bars. When a suction mold 2 or a group of suction molds is under the hood 3 and forms the sealed chamber, the valve 11 opens and the dewatering fluid enters the space encapsulated on the mold or molds, after which it is sucked through the molded article of pulp on the mold 2, whereby the latter is dehydrated. After passing the bell 3, the molds 2 are additionally rotated to the position where the articles are blown from the suction molds 2 and sucked onto the transfer rotor 6. After a part of a revolution of the transfer rotor, the articles they are blown from it on a conveyor 7 which transports the articles to a drying oven for a drying process. In the drying oven, the articles reach their final dry weight content of at least 90 weight percent.

The dry weight content of the articles when they are blown from the suction mold, depends on the type of dehydration agent that is used. The dehydration fluid can be distributed in the form of a vapor. According to a preferred embodiment of the present invention, the dehydrating agent is steam. Steam with a temperature of up to 300 ° C has a better drying effect than hot air. This effect is, however, minimized when the ambient air is mixed together with the steam. The steam preferably has a temperature in the range between 100 and 150 ° C. Other dehydration fluids such as hot and / or compressed air, or other gases suitable for dehydration are used in another embodiment of the invention. The valves in the conduit leading the dehydration fluid to the hood are preferably of the electromagnetic type to allow control from a logic control unit. The logic control unit can be integral with a logic control unit that directs the entire production process. The logic control unit can be programmed to choose the quantity of dehydration fluid, as well as its pressure and distribution time. In particular, such a choice can be made automatically under consideration of other process parameters such as production speed. The use of valves can be avoided if a constant flow is desired. Before supplying the dewatering agent, the water can be sprayed onto the articles as they leave the pulp tub in order to remove any residual pulp on the sites where the deposition of the pulp is not desired. By adjusting the size of the sector of the rotating mold carrier that is enclosed by the bell, the time available for the dewatering fluid to pass through the articles can be adjusted according to the circumstances. In a mass production molding machine, the rotational speed of the rotary mold carrier is relatively high. Typically, there are only a few seconds available to pass the dewatering fluid through the freshly molded article. Therefore, the present invention offers a greater advantage in improving this part of the molding process.

If necessary, the opening and closing of electric valves 11 is controlled by a PLC 12. The PLC can also be used to control other process parameters. The second embodiment of the invention as shown in Figure 4, comprises a number of movable bells 23 coupled to a movable bell carrier 21, which rotates synchronously with the rotary mold carrier 1. The movable bells 23 are coupled with the suction molds 2 on the rotary mold carrier 1 in order to form a hermetically sealed space on the articles in the suction molds 2. The movable bells 23 are provided with gaskets (not shown) which come into sealing abutment with the suction mold 2 or the rotating mold carrier 1, in order to provide a hermetic seal. The advantage of this embodiment is that there is the abutment or stop joint of stationary seal between the bell 23 and the suction mold 2. The third embodiment of the invention as shown in Figure 5, is in principle substantially equal to the embodiment according to figure 4, but instead of a rotating bell carrier, a conveyor belt 25 is used to move the movable bells 23, when coupling them to the conveyor belt 25. The conveyor belt 25 runs along a curved path which forms an arc of a circle with its center on the axis of the rotating mold carrier 1. The fourth embodiment of the invention as shown in Figure 6, comprises a stationary bell in the form of a curved plate 28 extending along an arc of a circle with its center on the axis of the rotating mold carrier 1 . Each of the suction molds 2 is surrounded by sealing plates 30, 33 that extend radially. The plates 30 extending parallel to the direction of rotational movement of the rotating mold carrier 1 have a circumferential edge cooperating with the curved plate 28 to form a hermetic seal, for example by the use of a labyrinth seal. The sealing plates 33 extending transversely to the rotational movement of the carrier of the rotating mold 1 enter in connection with the sealing stop with the curved plate 28. The fifth embodiment of the invention as shown in figure 7, comprises a moving band curved 35 instead of a curved plate 28. In this way, the sealing plates 30 with the curved edge can come into stationary contact with the band 35, forming a sealing butt joint. The band 25 may be provided with sealing plates 36 which extend transversely to the direction of movement of the band 35 and spaced such that each of the suction molds 2 is surrounded by the sealing plates. This embodiment can instead comprise (not shown in Figure 7) stationary sealing plates 33 accommodated on the rotating mold carrier 1 in order to surround the suction molds with the sealing plates. In this way, all the sealing is by means of stationary stop joining. The band 35 runs synchronously with the rotary mold carrier 1 allowing stationary stop joining between the sealing plates 33 and the band 35. The sixth embodiment according to the invention as shown in Figure 8, comprises a foldable bell 26 associated with a suction mold 2 and accommodated on the rotating mold carrier 1. After the suction mold 2 has undergone immersion inside the pulp tub 5, the collapsible hood is pulled over the suction mold 2 to hermetically seal it from the ambient air. The dewatering fluid is provided through a conduit (not shown) which is integrated in the rotating mold carrier 1. When the dewatering fluid has passed into the article, the folding hood 26 collapses in order to discover the suction mold 2, so that it is ready to be submerged again in the tub 5. The folding hood cooperates with the radially extending sealing plates, with a curved edge 30. According to yet another embodiment (not shown), the mold carrier is an operation carrier in steps that moves the mold carrier downwardly. for submerging the mold or suction molds on the mold carrier in the pulp vat, and moving upwards to retract the mold or molds from the pulp vat. In this embodiment, the bell extends on one side of the mold carrier, to define the sealed space. Various modifications are possible within the scope of the invention as defined in the claims, such as blowing the dehydration fluid through the article by applying an overpressure in the sealed space on the article.

LIST OF PARTS 1 Rotary mold carrier 2 Suction mold 3 Bell 4 Packaging 4a Packaging 5 Tub of pulp 6 Transfer rotor 7 Conveyor 8 Drying oven 9 Fluid source ze dehydration Conduit 11 Valve 12 PLC 13 Sub-atmospheric pressure source 14- Transfer mold 21 Rotating bell carrier 23 Movable bell 25 Conveyor belt 26 Folding hood 28 Curved plate 30 Sealing plate with curved edge 33 Sealing plate 35 Band 36 Sealing plates

Claims (30)

1. Method for manufacturing articles from an aqueous fiber suspension, by depositing the fibers on a suction mold, comprising the steps of: the suction application of the suction mold; the supply of a fiber suspension to the mold by immersing the suction mold in a tub comprising the fiber suspension; lifting the suction mold from the fiber suspension; the flow of ambient air by said suction through an article formed by a layer of fiber material deposited on the suction mold; characterized by the steps of: providing a space substantially hermetically sealed on the article or articles on the suction mold; the supply of a hydration fluid to the sealed space and the flow substantially exclusively of the dewatering fluid through the article or articles.

2. Method according to claim 1, characterized in that the suction mold is placed on a rotary mold carrier.

3. Method according to claim 1 or 2, characterized in that the dehydration fluid is made to flow through the article suction when it is placed on the suction mold, and / or by applying pressure to the space on the article .

4. Method according to any of claims 1 - 3, characterized by the provision of a movable hood on each suction mold that moves together with such a simple suction mold, over a certain distance from the rotational movement of the suction mold, with the order to define the sealed space on the article or articles.

5. Method according to claim 4, characterized in that the movable bells are coupled to a rotating bell carrier that moves synchronously with the rotating mold carrier, or to a conveyor or chain.

6. Method according to any of claims 1 - 3, characterized by the step of providing a stationary bell placed on a sector of the carrier of the rotating mold, to seal with this one or more suction molds of the environmental area and thus define the Encapsulated space on the article or articles.

7. Method according to any of claims 1-6, characterized in that the dehydration fluid is steam, saturated steam or superheated steam.

8. Method according to claim 7, characterized in that the temperature of the vapor is up to 300 ° C, preferably in the range between 100 and 150 ° C.

9. Method according to any of claims 1 - 8, characterized in that the pressure of the dehydration fluid is supplied with an overpressure in the range of 0.1 to 12 bar, preferably 0.5 to 2 bar.

10. Method according to any of claims 1-9, characterized in that the dehydration fluid is hot and / or compressed air.

11. Method according to any of claims 1-10, characterized in that the dehydration fluid is applied for a period of 0.1 to 10 seconds, preferably 0.1 to 1.0 seconds.

12. Apparatus for carrying out the method according to claim 1, comprising: a rotating mold carrier, provided with at least one suction mold on the periphery of the rotating mold carrier; a tub comprising an aqueous fiber suspension in which the rotating mold carrier is partially submerged; a sub-atmospheric pressure source connectable to at least one suction mold, characterized in that it comprises the means for covering one or more molds in a sector of the rotating mold carrier to thereby define a space encapsulated on the mold or molds, which is substantially hermetically sealed from ambient air, and further comprising a means for providing a dewatering fluid to the encapsulated space.

13. Apparatus according to claim 12, characterized by at least two transfer packets extending radially with respect to the rotary mold carrier and circumferentially spaced with one or more suction molds therebetween.

14. Apparatus according to claim 12 or 13, characterized in that it comprises a stationary bell having an arc-shaped wall with which the gaskets come into sealing contact to define a sealed space to which the dewatering fluid can be supplied.

15. Apparatus according to claim 14, characterized in that the two side walls extend substantially perpendicularly from the curved wall of the bell towards the rotating mold carrier.

16. Apparatus according to claim 15, characterized in that it comprises packages preferably of the labyrinth type, provided on each side wall of the bell and cooperating with a peripheral element of the rotating mold carrier.

17. Apparatus according to claim 12 or 13, characterized in that it comprises a movable hood on each suction mold, which moves together with such simple suction mold on a certain sector of the rotational movement of the suction mold, in order to define the Sealed space on the article or articles.

18. Apparatus according to claim 17, characterized in that the movable bell is coupled to a rotating bell carrier that moves synchronously with the rotary mold carrier.

19. Apparatus according to claim 17, characterized in that the movable bells are coupled to a chain or conveyor belt that moves synchronously with the rotating mold chamber.

20. Apparatus according to claim 12 or 13, characterized in that it comprises a stationary bell placed on a sector of the rotating mold carrier, to seal this one or more suction molds of the ambient air and thus define the space encapsulated on the article or articles, whereby the packages are preferably provided between the stationary or movable bell and the rotating mold carrier.

21. Apparatus according to any of claims 12-20, characterized in that the dewatering fluid is supplied to at least one dehydration inlet opening in the stationary or movable bell.

22. Apparatus according to claim 21, characterized in that the various inlet dehydration openings are distributed on the stationary or movable bell.

23. Apparatus according to claim 22, characterized in that the dehydration inlet openings are concentrated at the end of the stationary or movable bell where the suction molds enter.

24. Apparatus according to any of claims 14-16, characterized in that the stationary bell is formed by a curved plate that extends along an arc of a circle, with its axis center of the rotating mold carrier.

25. Apparatus according to any of claims 16 - 23, characterized in that the movable bell is formed by a band that moves along a curved path that extends along an arc of a circle with its center on the axis of the rotating mold carrier, wherein the band is possibly provided with transversely extending sealing plates, which seal before and after a suction mold.

26. Apparatus according to any of claims 12 - 25, characterized in that the rotating mold carrier is equipped with a number of sealing plates having a circular edge cooperating with the curved plate or the band to create a sealed space.

27. Apparatus according to claim 12 26, characterized in that the suction molds are surrounded by radially extending packages or sealing plates cooperating with the curved plate or the band, to define a sealed space.

28. Apparatus according to any of claims 12 - 27, characterized in that it comprises one or more electrically controlled valves, which regulates the distribution of the dehydration fluid.

29. Apparatus for carrying out the method according to claim 1, comprising: a step of operating up and down the mold carrier provided with at least one suction mold; a tub containing an aqueous fiber suspension in which the mold carrier up and down is periodically submerged; a sub-atmospheric pressure source connectable to at least one suction mold, characterized in that it comprises: means for covering the mold carrier upwardly-downward to thereby define an encapsulated space on the mold or molds that is sealed of the ambient air, and further comprising a means for providing a dewatering fluid to the sealed area.

30. Apparatus according to claim 29, characterized in that the upstream and downward movement mold carrier comprises gaskets for coupling the bell in a sealing stop connection.