WO2023229996A1 - Formule de plâtre à modeler à porosité accrue - Google Patents

Formule de plâtre à modeler à porosité accrue Download PDF

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Publication number
WO2023229996A1
WO2023229996A1 PCT/US2023/023107 US2023023107W WO2023229996A1 WO 2023229996 A1 WO2023229996 A1 WO 2023229996A1 US 2023023107 W US2023023107 W US 2023023107W WO 2023229996 A1 WO2023229996 A1 WO 2023229996A1
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WO
WIPO (PCT)
Prior art keywords
pottery
pottery plaster
stucco
plaster
composition
Prior art date
Application number
PCT/US2023/023107
Other languages
English (en)
Inventor
Guy L. Rosenthal
Christian Huch
Jeffrey F. Grussing
Pamela L. HARGROVE
Original Assignee
United States Gypsum Company
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US18/074,664 external-priority patent/US20230382793A1/en
Application filed by United States Gypsum Company filed Critical United States Gypsum Company
Publication of WO2023229996A1 publication Critical patent/WO2023229996A1/fr

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/14—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing calcium sulfate cements
    • C04B28/145—Calcium sulfate hemi-hydrate with a specific crystal form
    • C04B28/147—Calcium sulfate hemi-hydrate with a specific crystal form beta-hemihydrate
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/00939—Uses not provided for elsewhere in C04B2111/00 for the fabrication of moulds or cores
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/00956—Uses not provided for elsewhere in C04B2111/00 for making sculptures or artistic casts

Definitions

  • This disclosure relates to pottery plaster formulations, pottery plaster molds with increased porosity and improved water absorption, methods for making pottery plaster molds, and methods for slip casting various products in the molds.
  • Pottery plaster is commonly used for making molds which are used for casting ceramic articles in various industries, including aircraft, automotive, sanitaryware, construction, tableware and many others where a shaped ceramic product may be needed. Pottery plaster molds are particularly suitable for producing ceramic products, including dishes, pots, toilets, and bathroom sinks among many others.
  • pottery plaster is formulated as a dry mixture in which calcined gypsum is the main component.
  • Various additives may be optionally included in the mixture as well.
  • Various pottery plaster formulations are known in the art, including those described in U.S. patents 2,391,855, 4,443,261 and 6,398,864, all these patents are incorporated by reference herein.
  • a pottery plaster mold has to be sufficiently porous such that the mold would remove water from a casting ceramic product.
  • the gypsum mold has to be strong enough to withstand handling and in order to be reusable.
  • pottery plaster has to meet certain requirements for strength and also for porosity because a pottery plaster mold must be durable and reusable for many cycles, and at the same time, moisture and air should pass freely though the mold for efficient drying of a casting ceramic product and also in order to easily remove the ceramic product from the mold after the casting is completed.
  • beta stucco for strength
  • beta stucco for porosity
  • Batch-produced beta stucco tends to hydrate producing thin, needle-like gypsum crystals in a porous network that fits with the porosity requirements for pottery plaster applications.
  • beta stucco produced by continuous calcining in a kettle tends to hydrate by producing blocky or plate-like crystals. These blocky and plate-like crystals inhibit porosity, preventing water and air from being removed through a mold. It was conventionally believed in the field that using continuously produced stucco in pottery plaster formulations should be avoided or minimized because the stucco may produce pottery plaster formulations with unacceptably low porosity.
  • This disclosure provides pottery plaster formulations having improved moisture absorption properties.
  • this disclosure provides a pottery plaster composition, wherein the pottery plaster composition is a dry mixture comprising: alpha-calcined stucco, continuously- calcined-in-a-kettle (CCK) stucco, Rochelle salt, and at least one of the following: potassium sulfate and/or one or more phosphate compounds.
  • the pottery plaster composition may comprise 5 to 40 wt% of alpha stucco, 60 to 94 wt% of CCK stucco, 0.02 to 0.2 wt% of Rochelle salt and 0.05 toO .5 wt% of one or more of the following: potassium sulfate and/or the phosphate compound.
  • the pottery plaster compositions may comprise the phosphate compound, and more preferably, the phosphate compound may include a trimetaphosphate salt and/or a tetrametaphosphate salt.
  • Some pottery plaster compositions according to this disclosure may further comprise at least one set-retarding agent.
  • Some pottery plaster compositions according to this disclosure may consist essentially of: 15 to 30 wt% of alpha-calcined stucco, 70 to 84 wt% of CCK stucco, 0.02 to 0.1 wt% of Rochelle Salt, and 0.05 to 0.3 wt% of potassium sulfate.
  • a pottery plaster composition according to this disclosure may have a shelf-life of at least 6 months.
  • a pottery plaster composition according to this disclosure may have a water absorption capacity of at least 25 wt% when calculated as an increase in pottery plaster weight measured in the full immersion test at 60 minutes.
  • this disclosure provides a pottery plaster slurry comprising the pottery plaster composition according to this disclosure and water, wherein the pottery plaster slurry has a water-to-stucco (WSR) ratio by weight in the range from about 0.5 to about 0.9.
  • Some pottery plaster slurries may comprise a set-retarding agent which can be preferably used in an amount from about 0.1 wt% to about 5 wt%, based on a weight of the pottery plaster composition.
  • this disclosure provides a method for making a pottery plaster mold, the method comprising: i) mixing a pottery plaster slurry comprising the pottery plaster composition according to this disclosure and water into a mixture; ii) pouring the mixture into a form; and iii) removing the pottery plaster mold from the form after the mixture hardened.
  • Some embodiments of the method include those in which the mixture has a water- to-stucco (WSR) ratio by weight in the range from about 0.5 to about 0.9.
  • WSR water- to-stucco
  • the method may further comprise adding to the mixture in step i) one or more set-retarding agents.
  • this disclosure provides a method for slip casting a ceramic article, the method comprising: i) preparing a clay slip; ii) pouring the clay slip into a pottery plaster mold, wherein the pottery plaster mold contains alpha stucco, CCK stucco, Rochelle salt and one or more of the following: potassium sulfate and/or a phosphate compound; iv) casting a ceramic article in the pottery plaster mold; and v) removing the ceramic article from the pottery plaster mold.
  • the casting of the method may include removing water from the casting ceramic article under negative pressure applied to the pottery plaster mold.
  • the method may further comprise drying the pottery plaster mold after step v).
  • the method may comprise repeating steps i) to v) at least once.
  • this disclosure provides a pottery plaster formulation, wherein the pottery plaster formulation is a dry mixture comprising, consisting essentially of, or consisting of alpha stucco, continuously-calcined-in-kettle stucco and a combination of crystal growth modifiers, wherein the combination of crystal growth modifiers comprises, consists essentially of, or consists of Rochelle Salt and at least one of the following: potassium sulfate and/or one or more phosphate compounds.
  • Rochelle Salt may be used interchangeably with potassium sodium tartrate tetrahydrate (KNaC-iH-iCTNI-bO).
  • calcined gypsum may be used interchangeably with calcium sulfate hemihydrate, stucco, calcium sulfate semi-hydrate, calcium sulfate half-hydrate or plaster of Paris.
  • gypsum includes naturally mined gypsum (ore), landplaster as well as synthetic gypsum.
  • gypsum may be used interchangeably with the term “calcium sulfate dihydrate.”
  • synthetic gypsum can be also referred to as “chemical gypsum.”
  • formulation may be used interchangeably with the term “composition.”
  • a composition (formulation) or mixture may be referred to as “dry” composition or mixture.
  • dry means that no water was added to the composition or mixture. Nevertheless, a dry composition or dry mixture may have some moisture content.
  • dry pottery plaster mixture may have a moisture content of about 1 wt% or less, about 0.05 wt% or less, or about 0 wt%.
  • the term “about” means a range of plus/minus 5% of the stated value.
  • “about 100” means 100 ⁇ 5 and “about 200” means 200 ⁇ 10.
  • wt% means percentage by weight.
  • “calcination” means a process by which gypsum (CaSO4 2H 2 O) is dehydrated into calcined gypsum (CaSC 1/2H 2 O). The process includes heating gypsum to evaporate crystalline water. Calcined gypsum can be produced in different crystalline forms such as alpha calcium sulfate hemihydrate and beta calcium sulfate hemihydrate.
  • U.S. Pat. No. 3,410,655 to Ruter et al. incorporated herein by reference in its entirety, teaches producing alpha calcium sulfate hemihydrate.
  • Ruter et al. states the alpha- hemihydrate forms non-needle like crystals, as opposed to the beta calcium sulfate hemihydrate which forms needle-like crystals.
  • Ruter et al. also states the usual plaster of Paris (calcium sulfate hemihydrate) is the beta calcium sulfate hemihydrate. However, depending on the manner of preparation, the plaster of Paris still contains more or less anhydrous calcium sulfate, and/or alpha calcium sulfate hemihydrate.
  • plasters with definite alpha-hemihydrate content exhibit higher strengths.
  • Ruter et al. teaches to make alpha calcium sulfate hemihydrate in the form of non-needle-like crystals by elutriating the dihydrate with water to remove organic impurities and fine and slimy crystal portions, forming an aqueous suspension of the dihydrate at a pH about 1.5-6, and subsequently heating the suspension under closely controlled conditions.
  • alpha-hemihydrate is prepared by heating the dihydrate under controlled vapor pressure conditions in the presence of steam or in an aqueous solution.
  • U.S. Pat. No. 4,234,345 to Fassle discloses fast-setting alpha calcium sulfate hemihydrate made from calcium sulfate dihydrate by hydrothermally recrystallizing calcium sulfate dihydrate to form a mixture containing 95%-99% by weight alpha calcium sulfate hemihydrate and 5 to 1% calcium sulfate dihydrate. The dihydrate in this mixture is then converted to beta calcium sulfate hemihydrate by calcining, except for a remainder of up to 0.5 percent of dihydrate, which remains in the mixture.
  • U.S. Pat. No. 7,588,634 to Lynn discloses a method for producing a blend of alpha- and beta-stucco including a slurry calcination step to produce alpha calcium sulfate hemihydrate followed by a fluidized bed calcination step to produce beta calcium sulfate hemihydrate.
  • beta stucco Methods for producing beta stucco are known in the art and include a batch process and continuous calcining in a kettle.
  • CCK stucco beta stucco produced by continuously calcining in a kettle
  • CCK stucco is not suitable for pottery plaster formulations because CCK stucco tends to hydrate by producing blocky or plate-like crystals and these crystals inhibit porosity and do not allow movement of water and air through a gypsum mold.
  • CCK stucco is referred to stucco produced by continuous calcining of gypsum in a kettle.
  • the kettle contains a fluidized bed.
  • continuous calcining in a kettle is conducted at a temperature in the range from about 250°F to about 600°F. More preferably, continuous calcining in a kettle can be conducted at a temperature in the range from 275°F to 356°F (135-180°C). It is not necessary to increase pressure in the kettle. Instead, the process can be conducted at atmospheric pressure.
  • gypsum can be continuously fed into the kettle from a conveyor terminating with an outlet to the kettle.
  • CCK stucco can be continuously drawn out from the kettle without stopping operation of the kettle.
  • Kettles and methods for producing CCK stucco are known in the art, including as described in U.S. Pat. Nos. 3,307,915, 3,236,509, 4,113,836, 4,183,908, 4,201,595, 4,117,070 and 4,153,373, all incorporated herein by reference in their entirety.
  • a suitable dry pottery plaster formulation can be made with CCK stucco if the formulation includes a combination of crystal growth modifiers, wherein the combination of crystal growth modifiers comprises, consists essentially of, or consists of Rochelle Salt and at least one of the following: potassium sulfate and/or one or more phosphate compounds.
  • the combination of crystal growth modifiers comprises, consists essentially of, or consists of Rochelle Salt and at least one of the following: potassium sulfate and/or one or more phosphate compounds.
  • this pottery plaster formulation can be stored in bags as dry mixture without adverse aging effects for a period of time, such as for example, 6 months or 12 months.
  • the formulation sets into a gypsum mold with increased porosity, the porosity being comparable to formulations made with batch-made stucco.
  • a pottery plaster formulation may be a dry mixture comprising alpha-stucco, CCK stucco, Rochelle Salt, and one or more from potassium sulfate and/or a phosphate compound.
  • the pottery plaster formulations (compositions) according to this disclosure may have a water absorption capacity of at least 10 wt%, more preferably at least 25 wt%, and most preferably 30 wt%, calculated as an increase in pottery plaster weight measured in the full immersion test at 60 minutes.
  • a pottery plaster formulation according to this disclosure may be a dry mixture which contains from about 60 wt% to about 94 wt% of CCK stucco and about 40 wt% to about 5 wt% of alpha stucco.
  • the pottery plaster formulation may contain from about 70 wt% to about 85 wt% of CCK stucco and about 30 wt% to about 15 wt% of alpha stucco.
  • the pottery plaster formulations according to this disclosure contain Rochelle Salt in an amount from about 1 pound to about 4 pounds of Rochelle Salt per 2,000 pounds of the pottery plaster formulation.
  • the pottery plaster formulations according to this disclosure may comprise from about 0.02 wt% to about 0.2 wt% of Rochelle Salt, and more preferably from about 0.02 wt% to about 0.1 wt% of Rochelle Salt.
  • the pottery plaster formulations may contain potassium sulfate and/or one or more phosphate compounds. It has been discovered that it is not necessary to use both types of compounds: potassium sulfate and a phosphate compound. Instead, potassium sulfate or the phosphate compound may be used in combination with Rochelle Salt. If present, potassium sulfate or the phosphate compound may be preferably used in an amount from about 2 to about 6 pounds of potassium sulfate or the phosphate compound per 2,000 pounds of the pottery plaster formulation.
  • the pottery plaster formulations according to this disclosure may comprise from about 0.05 wt% to about 0.5 wt% of potassium sulfate or the phosphate compound, and more preferably from about 0.05 wt% to about 0.3 wt% of potassium sulfate or the phosphate compound.
  • Suitable phosphate compounds for the pottery plaster formulations according to this disclosure include, but are not limited to, trimetaphosphate salts and tetrametaphosphate salts.
  • Particularly preferred phosphate compounds include sodium trimetaphosphate (“STMP”), potassium trimetaphosphate, ammonium trimetaphosphate, sodium hexametaphosphate, tetrapotassium tripolyphosphate, ammonium polyphosphate, aluminum trimetaphosphate or any combination thereof.
  • a particularly preferred phosphate compound is sodium trimetaphosphate (“STMP”).
  • STMP sodium trimetaphosphate
  • the pottery plaster formulations according to this disclosure may comprise from about 0.05 wt% to about 0.5 wt% of the phosphate compound, and more preferably from about 0.05 wt% to about 0.3 wt% of the phosphate compound.
  • the phosphate compound may be replaced with potassium sulfate in some embodiments.
  • Table 1 provides some preferred pottery plaster formulations according to this disclosure:
  • the pottery plaster dry mixtures according to this disclosure may have a shelf life of at least 6 months, and more preferably of at least 12 months.
  • the pottery plaster formulations according to this disclosure have a commercially advantageous anti-aging property.
  • the pottery plaster formulations according to this disclosure may further comprise other additives, including additives which are typically used for controlling the setting reaction in a gypsum slurry.
  • additives may include, but are not limited to, additives that slow down the setting reaction of stucco after it is mixed with water. These additives may be referred in this disclosure as set-retarding additives.
  • Suitable set-retarding additives include, but are not limited to sodium citrate, SodateTM (comprising plaster of Paris, sodium citrate and crystalline silica, available from USG, Illinois, USA), SUMA retarder which is a proteinaceous retarder produced from animal hair and/or hooves, cream of tartar (potassium bitartrate) and/or any combination thereof.
  • the set-retarding additive may be added to the dry mixture pottery plaster formulation is small amounts, e.g., from about 0.01 wt% to about 0.5 wt% of the dry mixture, or the set-retarding additive may be added directly to a slurry when the pottery plaster formulation is mixed with water for making a mold.
  • this disclosure relates to pottery plaster slurries comprising one or more of the pottery plaster formulations according to this disclosure, water and optionally one or more additional additives for controlling the setting reaction of the pottery plaster slurry.
  • These slurries include those with water-to-stucco ratio (“WSR”) by weight in the range from about 0.5 to about 0.9, and more preferably from about 0.5 to about 0.8.
  • WSR water-to-stucco ratio
  • the setting time of the pottery plaster slurry may be delayed up to several hours by using a small amount, e.g., 0.1 wt% to 5 wt%, of a suitable set-retarding additive such as for example, sodium citrate, SodateTM, SUMA retarder, cream of tartar and/or any combination thereof.
  • a suitable set-retarding additive such as for example, sodium citrate, SodateTM, SUMA retarder, cream of tartar and/or any combination thereof.
  • the porosity of set pottery plaster can be measured by one of the two methods.
  • the pottery plaster formulations according to this disclosure include those which have a weight increase of at least 10%, preferably 25% and most preferably at least 30% in the “full immersion” test at 60 minutes.
  • technical advantages of the pottery plaster mold according to this disclosure include increased water absorption, preferably by at least 10 percent in comparison to molds prepared without the combination of crystal growth modifiers, and a better purge rate with which water is removed from a casting ceramic article. This results in decreasing the residency time for a casting ceramic article in the mold, making production more efficient.
  • the pottery plaster formulations according to this disclosure may be used for producing working molds for slip casting various ceramic items, including tableware (pots, plates, mugs, vases, etc.) and sanitaryware (toilets, sinks).
  • This disclosure also provides methods for makings pottery plaster molds.
  • the methods comprise mixing one or more of the pottery plaster formulations according to this disclosure with water into a pottery plaster slurry, preferably with a water-to-stucco ratio by weight in the range from about 0.5 to about 0.9, and more preferably from about 0.5 to about 0.8.
  • the methods may include adding one or more of set-retarding additives and/or other additives conventionally used with pottery plaster slurries.
  • the pottery plaster slurry is then poured over a form and allowed to hydrate until the setting reaction is complete, the mold has hardened and can be removed from the form.
  • this disclosure relates to methods for making a ceramic article by slip casting.
  • a mold made from the pottery plaster slurry according to this disclosure is used.
  • a clay slurry, which is referred to as a clay slip, comprising at least clay, silica and water may be prepared according to any standard formulation used in clay slips for making ceramic pottery and other ceramic wares.
  • the clay slip is then poured into the pottery plaster mold according to this disclosure. Water from the forming ceramic article is absorbed through the pottery plaster mold.
  • the forming process may be accelerated by applying negative (less then atmospheric) pressure to the mold and/or applying a positive (above atmospheric) pressure to the forming ceramic article. This process is known as pressure casting.
  • the pottery plaster molds according to this disclosure are suitable for pressure casting.
  • the pottery plaster molds according to this disclosure have an increased water absorption and accordingly, they absorb water from a clay slip and reduce the time required for greenware to form, leading to the greenware ceramic article being ready for removal from the mold sooner.
  • the article can be further processed, including drying in an oven, painting, glazing and/or by applying any other techniques conventionally used for producing ceramic articles.
  • the freed-up mold can be reused for making another article. However, before the mold can be used for casting another article, the mold must be dried. In order to purge water from the mold, it can be treated with heat and/or pressure to drive off the absorbed water.
  • the molds according to this disclosure are durable enough to be used for at least 50 and preferably at least 80 cycles of casting. These molds are strong enough for drying by applying heat and/or pressure.
  • Pottery plaster formulations according to this disclosure were prepared by dry mixing components shown in Columns “Trial #2” and “Trial #3” of Table 2.
  • a pottery plaster formulation was prepared with batch beta-molding plaster as shown in Column “Control” of Table 2.
  • a pottery plaster formulation was also prepared with CCK stucco, but without the combination of crystal growth modifiers, as shown in Column “Trial #1.”
  • the pottery plaster formulations according to this disclosure have an increased water absorption in comparison to the trial #1 formulation prepared with CKC stucco, but without a combination of Rochelle salt and Potassium Sulfate and without a combination of Rochelle salt and the phosphate compound. Furthermore, it was observed that the water absorption in the pottery plaster formulations according to this disclosure (trial #2 and trial #3) was comparable with a control pottery plaster formulation made with batch-calcined stucco.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Inorganic Chemistry (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Mold Materials And Core Materials (AREA)

Abstract

Dans un aspect, l'invention concerne une formulation de plâtre à modeler ayant une absorption d'eau accrue, comprenant de l'alpha stucco, du stuc calciné en continu, et une combinaison de sel de Rochelle et d'un ou plusieurs des éléments suivants : le sulfate de potassium et/ou un composé de phosphate. Selon un autre aspect, l'invention concerne des moules de plâtre à modeler ayant une absorption d'eau accrue et des procédés de fabrication et d'utilisation des moules de plâtre à modeler pour le coulage en barbotine d'articles en céramique.
PCT/US2023/023107 2022-05-27 2023-05-22 Formule de plâtre à modeler à porosité accrue WO2023229996A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US202263346557P 2022-05-27 2022-05-27
US63/346,557 2022-05-27
US18/074,664 2022-12-05
US18/074,664 US20230382793A1 (en) 2022-05-27 2022-12-05 Plaster formula with increased porosity

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WO2023229996A1 true WO2023229996A1 (fr) 2023-11-30

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AU2013240076A1 (en) * 2012-03-30 2014-11-06 United States Gypsum Company A method of modifying beta stucco using diethylene-triamine-pentaacetic acid
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Publication number Priority date Publication date Assignee Title
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US2907667A (en) 1956-03-30 1959-10-06 United States Gypsum Co Process of calcining gypsum
US3236509A (en) 1961-11-13 1966-02-22 British Plaster Board Holdings Process and apparatus for continuous calcining of powdered gypsum rock
US3307915A (en) 1964-01-22 1967-03-07 Georgia Pacific Corp Apparatus for continuous calcination of gypsum
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