HK1117820A - Methods of and systems for adding a high viscosity gypsum additive to a post-mixer aqueous dispersion of calcined gypsum - Google Patents

Abstract

Provided are methods and systems for introducing a wet gypsum accelerator or other high viscosity production additive to an aqueous dispersion of calcined gypsum in a discharge apparatus downstream of a stucco mixer in which the dispersion was prepared. These methods and systems are useful in the production of various gypsum products such as board including wallboard and ceiling tiles.

Description

Method and system for adding high viscosity gypsum additives to a post-mixing aqueous dispersion of calcined gypsum

Technical Field

Background

Set gypsum (calcium sulfate dihydrate) is a conventional material commonly included in a variety of products, such as gypsum board used in the construction of typical drywall of interior walls and ceilings of buildings. Typically, gypsum-containing boards are prepared by forming a mixture of calcined gypsum (that is, calcium sulfate hemihydrate and/or calcium sulfate anhydrite) and water, as well as other components, if desired. The mixture is typically cast into a predetermined shape on a conveyor belt surface or in a pan. As it travels along the conveyor belt, the calcined gypsum reacts with the water to form a matrix of crystalline hydrated gypsum or calcium sulfate dihydrate. The desired hydration of the calcined gypsum is a hydration that is capable of forming an interlocking matrix of set gypsum crystals, thereby imparting strength to the gypsum structure in the gypsum-containing product. Mild heating can be used to drive off unreacted water to obtain a dry product. Gypsum mixers and methods of making gypsum products are described, for example, in U.S. patent nos. 1,767,791; 2,253,059 No; 2,346,999 No; 4,183,908 No; U.S. Pat. No. 5,683,635; U.S. Pat. No. 5,714,032; and U.S. Pat. No. 6,494,609.

Accelerator materials are commonly used in the production of gypsum products to enhance hydration efficiency and control set time. Accelerators are described, for example, in U.S. Pat. nos. 3,573,947; 3,947,285 No; 4,054,461 No; and U.S. Pat. No. 6,409,825. Some accelerators include finely ground dry calcium sulfate dihydrate, commonly referred to as "gypsum seeds". The gypsum seeds enhance the nucleation of set gypsum crystals, thereby increasing their crystallization rate. Typically, the accelerator is added in the same mixer chamber as used to combine the water with the calcined gypsum. Although adding an accelerator to the mixer has the advantage of well and uniformly mixing the accelerator with the water and calcined gypsum mixture, the accelerator can also cause the gypsum to begin to set prematurely. Premature setting can lead to clogging of the mixer, can lead to damage to the mixer, limits efficiency, and requires more frequent mixer cleaning. Mixer cleaning requires shutting down the board production line, which severely compromises productivity. Although additives, including retarders, have been used in mixers to overcome premature setting, such additions create additional costs and considerations.

Thus, new materials and methods are needed to aid in the setting of gypsum.

Disclosure of Invention

In accordance with one aspect of the present invention, a method is provided for introducing a Wet Gypsum Accelerator (WGA) into a post-mixing aqueous dispersion of calcined gypsum. An aqueous dispersion of calcined gypsum is formed in a mixer chamber of a stucco mixer and discharged to a discharge apparatus. WGA is introduced into the aqueous dispersion in the discharge apparatus.

According to another aspect of the invention, a method is provided for introducing a high viscosity production additive into a post-mixing aqueous dispersion of calcined gypsum. An aqueous dispersion of calcined gypsum is formed in a mixer chamber and discharged to a discharge apparatus. The high viscosity production additive is introduced into the aqueous dispersion in the discharge apparatus. The viscosity ratio of the high viscosity production additive to the aqueous dispersion is between about 10: 1 to about 2: 1.

As one aspect of the invention, a system for introducing a wet gypsum accelerator into a post-mixing aqueous dispersion of calcined gypsum is provided. The system includes at least one WGA source; a conveying device; a mixer for forming an aqueous dispersion of calcined gypsum; discharge means operatively associated with the outlet of the mixer-source, the conveying means and said discharge means are operatively associated with each other.

For example, the invention has particular utility in the manufacture of gypsum board (e.g. wall or ceiling panels). In the example, after the high viscosity production additive (e.g., WGA) is added to the aqueous dispersion of calcined gypsum, the dispersion is deposited on a moving cover sheet. In the case of wallboard, a second cover sheet is applied to the deposited contents before drying. In some embodiments, such as some ceilings, the second cover plate is not used.

The methods, systems, and elements thereof, of the present invention are further described in the figures and detailed description that provide representative embodiments.

Drawings

Fig. 1 shows a schematic plan view of a system for adding a high viscosity gypsum additive to a post-mixing aqueous dispersion of calcined gypsum.

Fig. 2 shows a partial schematic cross-sectional view of the system shown in fig. 1 including an injection ring with injection ports.

Figure 3 shows a variation of the schematic cross-sectional view of figure 2 incorporating a tee fitting.

Fig. 4 shows a schematic plan view of a variation of the system shown in fig. 1.

FIG. 5 shows a partial perspective view of the mixer and discharge apparatus.

FIG. 6 shows a perspective view of a first portion of a mixer discharge apparatus system.

FIG. 7 shows a perspective view of a second portion of the mixer discharge apparatus system.

Fig. 8 shows a schematic plan view of the system depicted in fig. 6 and 7.

Fig. 9 shows a schematic plan view of a variation of the system depicted in fig. 8.

Fig. 10 shows a schematic plan view of a variation of the system depicted in fig. 9.

While the invention is susceptible to various modifications and alternative constructions, certain illustrative embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific embodiments disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention as defined by the appended claims.

Detailed Description

The present invention is premised, at least in part, on the following surprising findings: high viscosity production additives, such as wet gypsum accelerators, can be added to the relatively low viscosity aqueous dispersion calcined gypsum in the discharge apparatus downstream of the stucco mixer and still achieve sufficient mixing to obtain a gypsum product with an acceptable set time. Advantageously, the discharge apparatus of the present invention does not require a separate power source to mix the high viscosity production additive with the aqueous dispersion of calcined gypsum as it flows from the stucco mixer to the discharge apparatus.

In accordance with one aspect of the present invention, a system 12 for adding a high viscosity production additive to a post-mixing aqueous dispersion of calcined gypsum is provided. The system 12 includes a high viscosity production additive source 15, which in some embodiments may contain a Wet Gypsum Accelerator (WGA). Although only a single source 15 is shown for illustrative purposes, multiple sources may be provided. The system 12 further includes a delivery device 18; it may comprise a pump, and in some embodiments is a positive displacement pump (positive displacement pump). Suitable pumps for use in the system of the present invention are described in more detail in relation to the process of the present invention. The system 12 further includes a mixer 21 for producing the aqueous dispersion of calcined gypsum. The mixer 21 has an interior or mixing chamber 24 provided with at least one outlet 27. Extending from the mixer outlet 27 is a discharge apparatus 30 through which the aqueous gypsum slurry can flow and ultimately exit at outlet 31. In some embodiments, the outlet comprises a cannula. The casing is suitable for use in a discharge apparatus for depositing a large portion of slurry, rather than a densified layer slurry. In other embodiments, the outlet is provided as a conduit (e.g., a hose). The conduit or hose outlet is suitable for a densified layer discharge apparatus.

The source 15, delivery device 18 and discharge apparatus 30 are operatively connected to flow WGA and/or other production additives. In some embodiments, the connectivity is provided by a transmission line 33, so the transmission line may have several segments, e.g., 36, 39, according to the embodiments. The transfer line 33 may have a pressure gauge 42 for measuring the pressure of the production additive in the transfer line. The transfer line 33 is connected to the injection ring 45. The injection ring 45 comprises at least one injection port 48 through which the transfer line 33 can be fed. A more detailed description of the injection ring and related elements is shown in fig. 2 and 3. Although the inject ring is described in connection with both the present system and method, other inject members may be used in addition to or in place of the inject ring. For example, in some embodiments, a needle on the delivery line may be used for delivery to the ejection device. In some embodiments, a connecting tube is provided in the discharge apparatus to allow delivery to the apparatus.

The system 12 may further incorporate one or more additional discharge devices (e.g., 130 and 230). The additional discharge apparatus (e.g., 130 and 230) may be operatively associated with each element in a manner similar to that described for discharge apparatus 30. The delivery devices 118, 218, mixer outlets 127, 227, discharge apparatus outlets 131, 231, delivery lines 133 (including 136 and 139 in some embodiments), 233 (including 236 and 239 in some embodiments), pressure gauges 142, 242, injection rings 145, 245, injection ports 148, 248 are operatively coupled in a manner similar to those described for the discharge apparatus 30 and associated components. Although fig. 1 shows the system 12 having three discharge apparatuses 30, 130, and 230, and related elements, the system 12 may have as few as 1 discharge apparatus 30, with no expected upper limit on the number of additional apparatuses.

Fig. 2 shows an embodiment in which the delivery line 33 comprises a breast-like member, manifold, or other device having a branching volume 51 that divides the delivery line 33 into a plurality of branches 53, 57, and 60. The 3 branches are shown for illustrative purposes only. The injection ring 45 of fig. 2 is shown with multiple injection ports 48, 48', and 48 ", but again the number of injection rings 45 is shown for illustrative purposes only. Branches 53, 57 and 60 feed injection ports 48, 48' and 48 ", respectively. In some embodiments, additional implant rings (e.g., 145, 245 as depicted in fig. 1) may be present and incorporate the features described above.

Fig. 3 shows a variation of the embodiment shown in fig. 2, which incorporates a tee 63 to mix the production additive from source 15 with one or more additional production additives of no particular viscosity prior to injection into the discharge apparatus 30. The tee 63 includes a junction 66 where a first additive 69 and a second additive 72 meet. Although fig. 3 shows a tee 63 for only one injection port 48, this representation is for illustrative purposes only. Any number of injection ports may have a tee 63 associated therewith.

Fig. 4 shows a system 112, which is a variation of that shown in fig. 5. Again, the system 112 includes a production additive source 15 from which high viscosity production additives (e.g., WGA) are fed to respective discharge apparatuses 30, 130, and 230. Unlike system 12, system 112 uses a single delivery device 18 (e.g., a pump), and a breast-like member, manifold, or other device having a branching capacity 75 that divides delivery line 33 into several branches (e.g., 78, 81, and 84) that are separate from one another at 87. The branches (e.g., 78, 81, and 84) may include valves or similar devices 79, 82, and 85 to control flow to the branches, and the valves may also or alternatively be associated with the branching device 75. Each branch is finally directed to an injection ring 45, 145 and 245 on the respective exhaust device 30, 130 and 230. In some embodiments, the delivery device 18 that facilitates delivery of the additive from the source 15 to the discharge apparatus 30 and the second delivery device 118 that utilizes the udder, manifold or other device having a branching capacity 75 to facilitate delivery of the additive from the source 15 to both the second and third discharge apparatuses 130, 230 utilizing at least 2 branches 81, 84 without the third delivery device 218. The number of branches and other elements is shown for illustrative purposes only and other numbers are possible as well. In still other embodiments, each discharge apparatus has its own source.

Fig. 5 shows a discharge apparatus 430, which is one embodiment of discharge apparatus 30, 130, 230, etc. The discharge apparatus 430 also exhibits a number of different elements and features that may be generally included in and/or operatively associated with the discharge apparatus. The discharge apparatus includes a gate 425 with a gate opening 426, a series of hose sections 432, 434, and 438, a cage valve 440, and two injection rings 45, 445 with injection ports 48, 448, and an outlet 431. The gate 425 serves as a connector to connect the conduit of the discharge apparatus to the mixer 21 at the mixer outlet 27. The gate 425 is shown with an optional injection port 548. The injection ports 48, 448 and 548 are examples of possible locations for WGA, foam or other production additive inlets. The rings 45, 445 and gate 425 may be configured with several injection ports (e.g., as shown in fig. 2 and 3). In some embodiments, the hose sections 434 separating the rings 45, 445 are about 15 to about 16 inches long. The transfer line 33 or other transfer lines may be connected at any injection port. The position of the cage valve 440 may vary along the length of the discharge conduit 430 and may control the flow therein. Cage valves and/or other valve types may also be used. The evacuation apparatus and system of the present invention may incorporate elements or subsystems as described in commonly owned U.S. patent No. 6,494,609.

Additional systems of the present invention will be described herein in terms of the following examples. Although the hose system is discussed in connection with the examples, it is not limited to use as set forth in those examples.

The present methods may utilize one or more of the systems, subsystems, and elements described herein, e.g., as described with respect to the figures. However, the method may use other suitable systems, subsystems, and elements. While the methods have been described with respect to various systems, subsystems, and elements, the description is provided to assist the reader in understanding the invention and is not intended to limit the invention, as set forth in the appended claims. The process described herein is described in terms of adding WGA to an aqueous dispersion of calcined gypsum, but is for illustrative purposes only. Other additives having high viscosities similar to WGA or other suitable viscosities described herein may also be used. Also, one or more additional accelerators may be used. Examples of such accelerators include caustic potash, Heat Resistant Accelerators (HRA), Climate Stable Accelerators (CSA), and any accelerator known in the gypsum industry. In those embodiments in which one or more additional accelerators are used, the additional accelerators may be added in the calcined gypsum aqueous dispersion mixer or external to the mixer (i.e., in the discharge apparatus). In some embodiments, caustic potash in granular and/or powder form is used as an additional accelerator.

Wet Gypsum Accelerator (WGA) and/or other high viscosity additives (e.g., starch solutions) may be used in accordance with the present methods. The high viscosity additive may include one or more additional additives that may themselves have a low viscosity, provided that when combined with the high viscosity additive, the high viscosity of the high viscosity additive is maintained. WGA and other high viscosity additives of the invention typically have a viscosity between about 3000 to about 5000 centipoise. In some embodiments, the range should be between about 2000 to about 10000 centipoise. In some embodiments, the range should be between about 2500 to about 9500 centipoises. In some embodiments, the range should be between about 3000 to about 9000 centipoises. In some embodiments, the range should be between about 3500 to about 8500 centipoises. In some embodiments, the range should be between about 4000 to about 8000 centipoise. In some embodiments, the range should be between about 4500 to about 7500 centipoises. In some embodiments, the range should be between about 5000 to about 7000 centipoise. In some embodiments, the range should be between about 5500 to about 6500 centipoise. In some embodiments, the range should be between about 2500 to about 5500 centipoise. In some embodiments, the range should be between about 2750 to about 5250 centipoise. In some embodiments, the range should be between about 3250 to about 4750 centipoise. In some embodiments, the range should be between about 3500 to about 4500 centipoise. In some embodiments, the range is from about 3750 to about 4250 centipoise. In some embodiments, the viscosity of the wet gypsum accelerator is about 1000 centipoise or more and about 5000 centipoise or less. In some embodiments, the viscosity of the wet gypsum accelerator is from about 2000 centipoise to about 4000 centipoise. The viscosity measurements described herein are reflectance measurements made at ambient temperature. A representative WGA for use in the invention is described in U.S. Pat. No. 6,409,825 AND concurrently filed AND commonly owned application "WET GYPSUM ACCELERATOR AND METHOD, COMPOSITION, ANDPRODUCT RELATED THERETO" (attorney docket No. 234912) U.S. patent application __________. The viscosity of the high viscosity additive used may be limited by the constraints of the system used, for example, whether the pump used is effective enough to deliver the additive to the discharge apparatus. One skilled in the gypsum industry, based on the teachings of the present invention and the knowledge available in the art, should be able to determine the appropriate type of WGA for a given gypsum application.

One aspect of the invention provides a method of introducing a Wet Gypsum Accelerator (WGA) into a post-mixing aqueous dispersion of calcined gypsum, wherein the method comprises forming an aqueous dispersion of calcined gypsum in a mixer chamber; conveying the aqueous dispersion to a discharge apparatus; and introducing the WGA into the aqueous dispersion in the discharge apparatus. In some embodiments, the WGA comprises calcium sulfate dihydrate, water, and at least one phosphorus additive selected from the group consisting of: (a) an organic phosphonic compound; (b) a phosphate-containing compound; and (c) mixtures of (a) and (b). In some embodiments, the ground product of the WGA comprises calcium sulfate dihydrate and has a median particle size of 5 μ ι η or less. The milled product is the result of wet milling to produce WGA. This process is discussed in commonly owned U.S. Pat. No. 6,409,825 AND concurrently filed AND commonly owned application WET GYPSUMACCELERATOR AND METHOD, COMPACTION, AND PRODUCT RELATGTHERETO (attorney docket No. 234912) U.S. patent application _________. In some embodiments, the ground product of the WGA has a median particle size of about 0.5 μ ι η to about 2 μ ι η. In some embodiments, the ground product of the WGA has a median particle size of about 1 μ ι η to about 1.7 μ ι η. In some embodiments, the ground product of the WGA has a median particle size of about 1 μ ι η to about 1.5 μ ι η.

In some embodiments, the phosphorus additive is present in an amount of about 0.1% to about 10% by weight of the accelerator. In some embodiments, the ground product of the WGA is substantially amorphous. In some embodiments, the phosphorus additive is a mixture of at least one organophosphonic acid compound and at least one phosphate-containing compound, wherein the organophosphonic acid compound is present in an amount of about 0.05% to about 9.95% by weight of the accelerator, and wherein the phosphate-containing compound is present in an amount of about 0.05% to about 9.95% by weight of the accelerator.

In some embodiments, the WGA comprises an organic phosphonic compound selected from the group consisting of: aminotris (methylene-phosphonic acid), 1-hydroxyethylidene-1, 1-diphosphonic acid, diethylenetriamine penta (methylene phosphonic acid), hexamethylenediamine tetra (methylene phosphonic acid), pentasodium, trisodium, tetrasodium, sodium, ammonium, potassium, calcium, or magnesium salts of any of the foregoing acids, and combinations thereof.

In some embodiments, the WGA comprises a phosphate-containing compound selected from the group consisting of orthophosphates, polyphosphates, and combinations thereof. In some embodiments, the WGA comprises a phosphate-containing compound selected from the group consisting of: tetrapotassium pyrophosphate, sodium acid pyrophosphate, sodium tripolyphosphate, tetrasodium pyrophosphate, sodium potassium tripolyphosphate, sodium hexametaphosphate salt having from 6 to about 27 phosphate units, ammonium polyphosphate, sodium trimetaphosphate, and combinations thereof.

It will be appreciated by those skilled in the art that the invention can be embodied in various forms without departing from the scope of the invention. For example, in some embodiments, the WGA comprises a mixture of aminotris (methylenephosphonic acid) pentasodium salt at about 0.5% by weight of calcium gypsum dihydrate and sodium trimetaphosphate at about 0.5% by weight of calcium gypsum dihydrate. The solids content of the WGA may vary depending on the particular application. Likewise, the viscosity of the WGA may vary depending on the particular application. Thus, as will be appreciated by those skilled in the art, if the viscosity or solids content of the WGA is undesirably high for the intended application, the WGA may be diluted with water prior to use. By way of illustration and not limitation, in some embodiments, the WGA includes a solids content comprising calcium sulfate dihydrate in an amount of at least about 20% by weight of the accelerator. In some embodiments, the accelerator comprises a solid portion of calcium sulfate dihydrate is present in an amount of 35% to about 45% of the accelerator, and water is present in an amount of about 55% to about 65% by weight of the accelerator. Those skilled in the art will also appreciate the versatility of the WGA of the invention. For example, in some embodiments, when a WGA of the invention is added to a mixture comprising calcined gypsum and water for forming an interlocking matrix of set gypsum, the WGA allows for a time to 50% hydrate the calcined gypsum of about 6 minutes or less. In some embodiments, the WGA allows for a time to 50% hydration of the calcined gypsum of about 5 minutes or less when added to a mixture comprising calcined gypsum and water for forming an interlocking matrix of set gypsum. The desired set time depends on various factors including the solids content of the WGA, the viscosity of the WGA, and the particle size of the WGA solids. Other factors that may affect set time when the WGA is used to manufacture gypsum board include line speed, line length, gypsum characteristics, and the like, as will be appreciated by those skilled in the art.

The WGA and/or other high viscosity additive is introduced into an aqueous dispersion of relatively low viscosity calcined gypsum contained with the discharge apparatus 30. In some embodiments, the aqueous dispersion has a viscosity of between about 700 to about 1200 centipoise. In some embodiments, the dispersion has a viscosity of between about 100 to 1750 centipoise. In some embodiments, the dispersion has a viscosity of between about 200 to 1650 centipoise. In some embodiments, the dispersion has a viscosity between about 300 to 1550 centipoise. In some embodiments, the dispersion has a viscosity of between about 400 to 1500 centipoise. In some embodiments, the dispersion has a viscosity of between about 450 to 1450 centipoises. In some embodiments, the dispersion has a viscosity of between about 500 to 1400 centipoise. In some embodiments, the dispersion has a viscosity between about 550 to 1350 centipoise. In some embodiments, the dispersion has a viscosity of between about 600 to 1300 centipoise. In some embodiments, the dispersion has a viscosity of between about 650 to 1250 centipoise. In some embodiments, the dispersion has a viscosity of between about 750 to 1150 centipoise. In some embodiments, the dispersion has a viscosity of between about 800 to 1000 centipoise. In some embodiments, the dispersion has a viscosity of between about 850 to 950 centipoises.

In some embodiments, the dispersion has a viscosity of between about 875 to 925 centipoise. According to the invention, WGA and/or other high viscosity production additives to be introduced into the aqueous dispersion of calcined gypsum in the discharge apparatus may also be expressed in terms of a ratio. For example, the viscosity of the WGA may be about 4 times that of the aqueous dispersion. In some embodiments, the viscosity of the WGA may be about 3 times that of the aqueous dispersion. Suitable ratios include 10: 1, 9: 1, 8: 1, 7: 1, 6: 1, 5:1, 4.5: 1, 4.25: 1, 4.1, 3.75: 1, and 3.5: 1, 3.25: 1, 3: 1, 2.75: 1, 2.5: 1, 2.25: 1, 2: 1, and ratios intermediate to the ratios.

The inventive method includes delivering a high viscosity production additive (e.g., WGA) from a source 15 to a discharge apparatus 30 where the additive is introduced into an aqueous dispersion of calcined gypsum discharged from a gypsum mixer (e.g., a paddle mixer, a multipass mixer, a non-paddle mixer, or other mixer useful for obtaining an aqueous dispersion of gypsum), where the aqueous dispersion has been mixed. Although gravity conveyance is contemplated, the WGA is typically moved from the source 15 to the discharge apparatus 30 with the aid of one or more conveyance devices (e.g., 18, 118, 218). In some embodiments, the delivery device is a pump. In some embodiments, the pump is a positive displacement pump, but other pump types (e.g., centrifugal pumps) may be used in addition or alternatively. Examples of suitable positive displacement pumps include propulsor chamber pumps, gear pumps, and peristaltic pumps. The slurry pressure entering the discharge apparatus should be maintained at a pressure higher than the discharge apparatus contents pressure in order to minimize back pressure and allow for efficient delivery of HRA slurry. In some embodiments, the pressure in the discharge apparatus is between about 5 and about 15 p.s.i. The pressure of the WGA in the transfer line 33 between the source 15 and the discharge apparatus 30 may be measured using a pressure gauge 42. However, if the pump used is self-regulating, this gauge need not be used. In some embodiments, the gauge has a range of 0-30p.s.i.

The WGA may be discharged to the discharge apparatus 30 through an injection port 48, which may be associated with an injection ring 45. In some embodiments, the WGA splits into several branches to allow several inlets to the discharge apparatus 30. The several inlets may be obtained by providing several inlets (e.g., 48', and 48 ") in the injection ring 45. In some embodiments, the WGA is combined with one or more additional additives (e.g., foam) prior to introduction into the aqueous dispersion of the discharge apparatus 30. The combination may be implemented using a tee 63 formed by the entry of WGA or other high viscosity additive 69 and another additive 72 regardless of viscosity. In some embodiments, the WGA and one or more additional additives are combined at about 3 inches from the point of injection into the discharge apparatus. In some embodiments, the WGA is fed into a discharge apparatus downstream of a pinch valve operatively associated therewith.

Several discharge apparatuses can be constructed for a particular gypsum product. For example, if the desired product is wallboard and top and bottom densified layers are desired, second and third discharge apparatuses (i.e., densified layer extractors) 130, 230 may be provided. For certain wallboard products, as well as other board products (e.g., ceiling tiles), see commonly owned, co-pending U.S. patent application No. 10/804,359, only a single densified layer is applied. In some embodiments, WGA from source 15 is delivered to discharge apparatuses 30, 130, and 230 using separate delivery devices 18, 118, and 218. In other embodiments, there is a single conveyor 30 for conveying the WGA to all three discharge apparatuses. In still other embodiments, the conveyor 18 is used for the discharge apparatus 30 and the conveyor 118 is used for the discharge apparatuses 130 and 230. Regardless of the number of delivery devices or the presence of delivery devices, the WGA may be distributed into branch delivery lines using udder, tees, manifolds or other devices that allow branching of the delivery lines. Control of WGA flow into a particular branch may be controlled using a valve or other element having similar functionality.

WGA and/or other high density production additives are typically introduced into the post-mixing aqueous dispersion in a stream perpendicular to the flow of dispersion in the discharge apparatus. However, other WGA introduction directions are possible. The WGA is introduced into the discharge apparatus near the mixer outlet 27 rather than the discharge outlet 31 for the desired incorporation of the aqueous dispersion. In some embodiments, the introduction occurs at about 2.5 inches to 3 inches from the mixer outlet 27. In some embodiments, the introducing occurs at about 1 inch from the mixer outlet. Typically, moving the introduction of WGA downstream of the discharge apparatus will serve to delay solidification acceleration.

When the method of the present invention is used to manufacture a wallboard product having first (e.g., bottom) and second (e.g., top) densified layers, each densified layer discharge apparatus 130, 230 can include and/or be operatively associated with one or more of the following components: a hose and a ring (e.g., 145, 245). The percentage of WGA that provides proper setting depends on the amount of aqueous slurry to be applied to the densified layer of the board. For example, if 10% of the primary gypsum slurry (i.e., the aqueous dispersion from mixer 21) is to be applied to the first (e.g., bottom) densified layer, then preferably about 10% of the WGA is directed to the bottom densified layer through bottom discharge apparatus 130. If a second (e.g., top) densified layer is utilized, the proportion of WGA again preferably approximately matches the percentage of gypsum slurry to be applied to the top densified layer. The percentage of gypsum slurry from the mixer 21 is typically between about 5% to about 20%. The words top and bottom, as well as front and back and other equivalents, are relative words with respect to the direction in which the gypsum product is intended. For purposes of illustration only, bottom refers to the first paper (i.e., cover sheet) that travels under the gypsum mixer and the densified layer applied to the first paper. Top refers to the second paper, which is applied after the gypsum slurry is added to the bottom paper by the main discharge apparatus 30, and the densified layer is applied to the second paper. In some embodiments, a dispersant is added to the discharge apparatus, such as lignin, naphthalene sulfonate, or other suitable dispersant.

A benefit of the present system and method is to delay the setting of the aqueous dispersion of calcined gypsum by delaying the introduction of WGA until after the dispersion exits the stucco mixer 21. In some embodiments, the method adds less water to the stucco mixer, which results in a lower water-stucco ratio, which results in less setting in the mixer due to the lack of accelerator in the mixer interior 24. Methods and systems also contemplate the introduction of the WGA directly into the mixer 21 in addition to its introduction into the discharge apparatus.

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

Example 1: addition of WGA to the discharge apparatus

This example illustrates that WGA can be added in a discharge apparatus to obtain a desired gypsum product. The WGA used for this test was the following formulation: 0.5% pentasodium salt and 0.5% sodium trimetaphosphate, and 42% solids by weight of WGA and 58% water by weight of WGA. A test was conducted in which WGA was introduced in the main gate of the main discharge apparatus and the back densified layer discharge apparatus. For comparison, the WGA was also injected into the emergency water port inside the vane mixer. WGA successfully sets the board uniformly when it is added to the interior or "exterior" of the mixer. The amount of WGA used was not changed whether it was introduced inside or outside the mixer. In both cases, no Heat Resistant Accelerator (HRA) was added to set the panel, but HRA was used during initial start-up. The HRA used in this test was a 99.5% gypsum/0.5% sugar mixture ground to a fine particle size in dry form. The test uses typical gypsum board paper. Table 1 summarizes the test conditions and records the accelerator usage (HRA and WGA) and water usage. The units in Table 1 (if appropriate) are lbs/MSF. The stucco used for this test was 1235 lbs./MSF. WGA% solids 42%.

Table 1: test parameters [ all units are expressed as LBS./MSF ]

Time of day	Condition	HRA	Main slurry layer WGA	Densified layer WGA	Dispersing agent	Mixing machine water	Foam water	WGA water	Total water
										14:32	Start-Up after one day of parking WGA addition to the Mixer exterior	10.0	35.0	3.5	5.0	764.0	96.0	22.3	882.3
14:53	Reduction of HRA, increase of WGA	3.0	40.0	4.0	5.0	736.0	123.0	25.5	884.5
										15:01	Reduction of HRA, increase of WGA	1.5	45.0	4.5	5.0	738.0	123.0	28.7	889.7
15:06	Reduction of HRA, increase of WGA	1.5	55.0	5.5	5.0	736.0	123.0	35.1	894.1
										15:11	Full exhaustion of HRA	-	55.0	5.5	5.0	736.0	123.0	35.1	894.1
15:17	Reduction of water	-	55.0	5.5	5.0	721.0	123.0	35.1	879.1
										15:25	Reduction of water	-	55.0	5.5	5.0	710.0	125.0	35.1	870.1
15:40	Reduction of WGA	-	50.0	5.0	5.0	708.0	125.0	31.9	864.9
										15:45	Reduced dispersants, including WGA	-	55.0	5.0	3.5	706.0	125.0	34.8	865.8
										16:10	Foam reducing water	-	55.0	5.0	3.0	708.0	105.0	34.8	847.8
										16:16	Transfer WGA to the Mixer	-	60.0	-	3.0	707.0	105.0	34.8	846.8
	Followed by a short stop due to bottom sheet break test
18:12	HRA only, Normal production	21.0	-	-	4.0	762.0	101.0	-	863.0

This experiment used a system 612 schematically depicted in fig. 6, 7 and 8. Below the system is a first paper 614 to which an aqueous dispersion of calcined gypsum is applied. After the gypsum is applied to paper 614, a second paper is applied to form the wallboard. A densified layer is applied only to the bottom paper. In other embodiments, the densified layer may be applied to only the top sheet, or to both the top and bottom sheets. System 612 includes a mixer 621 having an interior 624 and outlets 627, 727. The gates 625, 825 of the discharge devices 630, 730 are operatively connected to the outlets 627, 727. Operatively associated with the mixer 621 are therefore a main slurry discharge 630 and a thickened layer discharge 730. Each discharge apparatus 630, 730 is supplied by a separate WGA source 15, 615, respectively. Separate delivery lines 633 (including sections 636 and 639), 733 (including 736 and 739) and pumps 18, 618 are used to deliver WGA to the devices 630, 730. The mixer 621 included an emergency water port 622 through which WGA was delivered during certain periods of the test. The mixer 621 and discharge apparatus 630 are operatively connected to the WGA source 15 by branch transfer lines 638, 639, respectively. Control valves 23, 623 are provided on the branch delivery lines 638, 639, respectively, to control the delivery of WGA to the mixer 621 and the discharge apparatus 630.

The main mixer gate 625 is operatively associated with the first flange 671 and the second flange 673 mounted against it is operatively associated with the first hose section 634 of the discharge apparatus 630. Moyno, where WGA is supplied from source 15 and used as a positive displacement pump^TMThe pump assists in the delivery. WGA was injected into a flange 673 with 3 3/8 "ID ports 648, 648', and 648" with an Inner Diameter (ID) of 1 plus 3/4 ". The ports of the flange 673 are fed by 3 branches 653, 657 and 660, which are provided in 3 pieces 1/2 "in a manner similar to that shown for the ring 45 in fig. 2A hose branched from the breast member 51. Although no pressure gauge 642 was used during this test, such a gauge could be placed on one of the branches (e.g., 53) immediately prior to injection into flange 673. In some embodiments, a 0-30p.s.i. scale is used. Arrow 654 indicates that the branch from the breast member is ultimately joined to flange 673. In other embodiments, the assembled 671, 673 flange may be replaced with a similar injection ring.

The foam ring 745 includes ports 748, 748', 748 ", and 748 * which supply foam from a foam source using foam delivery lines, one of which is provided with a pressure gauge 742. The delivery lines feeding the ports are 753, 757, 760, and 761, respectively. The foam ring is supplied with foam and water using a configuration similar to that shown in figure 2 for ring 45. Although in other embodiments the foam ring 745 was in a position in which the second flange 673 was located, for the test the foam ring 745 was moved a further 13 "inches forward along the discharge apparatus 630, using a 2" ID Tygon^TMA hose 634 connects the two together. Foam ring 745 is a 1 and 3/4 "ID to 2" ID expanding foam ring. Thus, about 9 feet long 2 and 1/4 "ID Tygon^TMThe hose 638 leads to a single long cannula 631. The densified layer discharge apparatus 730 terminates at 731. Line 790 carries sodium trimetaphosphate.

Seepex was used for the back surface densified layer discharge apparatus 730^TMA pump 618 (which is a push chamber pump) draws WGA from a separate tank 615 and injects it into a gate 825. Hose 639 is sized for entry into gate 825 at the port, and a pressure gauge 842 (e.g., 0-30p.s.i.) is positioned adjacent port 826 to measure WGA pressure in port 826. The WGA usage of the densified layer was designed to be about 10% of the WGA usage of the majority of the slurry. The WGA is injected into the 1/4 "line, which in other embodiments may be the point where foam and water are added to the extractor. A 1 "ID foam injection ring 845 was installed approximately 10" inches downstream from the point where WGA was injected into the discharge apparatus 730. The injection ring 845 includes an injection port 848 to supply foam and water to the delivery line 834.

This test uses WGA with an efficiency of 60lbs/MSF, where MSF stands for thousand square feet, although other WGA efficiencies can be used (e.g., 42lbs/MSF for the 1/2' product). This relative inefficiency was addressed by using a manufacturing procedure that evaluates viscosity versus milling time in a horizontal media mill (available from Premier). The manufacturing process includes using the specified viscosity as an indication of when to stop grinding-as opposed to grinder loading or constant grinding time. Viscosity can be measured by using any commercially available viscometer (e.g., one manufactured by Brookfield). A study of the relationship between WGA efficiency AND its viscosity is discussed in U.S. Pat. No. 6,409,825, AND concurrently filed AND commonly owned application "WET GYPSUM ACCELERATOR AND METHOD, COMPOSITION, AND PRODUCT RELATED THERETO" (attorney docket number 234912) U.S. patent application ________.

WGA efficiency is determined using the same procedure as one determines HRA efficiency, which includes assessing hydration rates using standard stucco and the WGA or HRA of interest. A Climate Stabilizing Accelerator (CSA) may also be used as a benchmark. The hydration rate of the sample was compared to the hydration rate using the same standard stucco and standard accelerator. If the WGA or HRA is more effective in accelerating hydration than a standard accelerator, it will give an efficiency of greater than 100. Since the hydration process is an exothermic reaction, the rate of hydration is typically determined by measuring the temperature profile over time in a fully insulated environment. At the end of the exothermic reaction or complete hydration, the material should reach a constant temperature. Basically, how quickly the stucco/water slurry can reach a constant temperature provides for how quickly the hydration rate. WGA, HRA or other accelerators have been used to shorten the time to reach a constant temperature. HRA is described in further detail in U.S. patent application __________, commonly owned and co-owned by the same applicant as "METHOD OF AND SYSTEMS FOR PREPARING A HEAT RESISTANT ACCELERANT SLURRYAND ADDING THE ACCELERANT SLURRY TO A POST-MIXER AQUEOUSISOPSISION OF CALCINED GYPSUM" (attorney reference 234911).

This test was conducted on 1/2 "product at 180 feet/minute. Tests with WGA introduced outside the mixer were performed for 1-3/4 hours, with tests also being performed for shorter or longer durations. The introduction of WGA inside the mixer was performed for approximately 10 minutes before the small lumps caused paper breaks, which forced the board line to shut down. The lumps may be caused by a change from outside the mixer configuration to inside the mixer configuration (a change that causes the ports of the densified layer discharge apparatus to become clogged).

The hardening rate was about 21 seconds for the back side densified layer and 30 seconds for most slurries. Hardness test measurements using a USG durometer tester immediately before cutting were 67 to 70. When the off-line inspection plate cuts the sample, the hardness of the entire plate is extremely uniform. The boards produced during the test did not exhibit any paper-thickening layer adhesion problems. Nail pull values are characteristic of plates made from HRA.

The on-line hydration temperature rise measurement system (TRS) during WGA testing was as follows: at 15:17, the time to 50% hydration of the densified layer was 4.1 minutes and 52.8% hydration at the cut. At 15:27, the time to 50% hydration for most slurries was 3.6 minutes and 58.6% hydration at the cut. The time to 50% hydration of the densified layer was 3.9 minutes at 15:38 and 54.1% hydration at the cut. At 15:51, the time to 50% hydration for most slurries was 3.8 minutes and 57.4% hydration at the cut.

Example 2

Another experiment similar to that described in example 1 was performed except that a single WGA source 15 was used to supply both discharge apparatuses 630, 730 and WGA was not supplied to the mixer 24. For this experiment, a system 712 as shown in fig. 9 was used, which is a modified form of the system 612. System 712 includes a single source 15 and lacks a WGA transfer line to the blender. System 712 is advantageous because only a single source need be used.

Example 3

Yet another experiment similar to that set forth in example 2 was conducted, but utilizing another refining system 812. Unlike systems 612 and 712, the system 812 shown in fig. 10 includes a single injection ring 945 on the main discharge apparatus 630. The injection ring 945 is operatively associated with at least one tee 63 assembled in a manner similar to that shown in figure 3 for the injection ring 45. The densified layer discharge apparatus removes ring 845 and injects foam and WGA at gate 1045 using tee 63 assembled in a manner similar to that shown in fig. 3 for injection ring 45.

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 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. Unless otherwise stated; the words "including," "having," and "containing" are to be construed as open-ended words (i.e., meaning "including, but not limited to"). 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. The methods set forth 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. Various modifications to those preferred embodiments will become apparent to those skilled 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 (46)

1. A method of introducing a Wet Gypsum Accelerator (WGA) into a post-mixing aqueous dispersion of calcined gypsum, the method comprising:

forming an aqueous dispersion of calcined gypsum in a mixer chamber;

discharging the aqueous dispersion into a discharge apparatus;

introducing the WGA into the aqueous dispersion in the discharge apparatus.

2. The method of claim 1 wherein the WGA comprises:

a ground product comprising calcium sulfate dihydrate;

water; and

at least one additive selected from the group consisting of:

(a) an organic phosphonic compound;

(b) a phosphate-containing compound; and

(c) a mixture of (a) and (b).

3. The method of claim 2, wherein the milled product has a median particle size of about 5 μ ι η or less.

4. The method of claim 2, wherein the milled product has a median particle size of about 0.5 μ ι η to about 2 μ ι η.

5. The method of claim 2, wherein the milled product has a median particle size of about 1 micron to about 1.7 μ ι η.

6. The method of claim 2, wherein the milled product has a median particle size of about 1 micron to about 1.5 μ ι η.

7. The method of claim 2, wherein the additive is present in an amount of about 0.1% to about 10% by weight of the accelerator.

8. The method of claim 2, wherein the milled product is a substantially amorphous product.

9. The method of claim 2 wherein the additive is a mixture of at least one organophosphonic acid compound and at least one phosphate-containing compound, wherein the organophosphonic acid compound is present in an amount of from about 0.05% to about 9.95% by weight of the accelerator, and wherein the phosphate-containing compound is present in an amount of from about 0.05% to about 9.95% by weight of the accelerator.

10. The method of claim 2, wherein the organic phosphonic compound is selected from the group consisting of: aminotris (methylene-phosphonic acid), 1-hydroxyethylidene-1, 1-diphosphonic acid, diethylenetriamine penta (methylene phosphonic acid), hexamethylenediamine tetra (methylene phosphonic acid), pentasodium, trisodium, tetrasodium, sodium, ammonium, potassium, calcium, or magnesium salts of any of the foregoing acids, and combinations thereof.

11. The method of claim 2, wherein the phosphate-containing compound is selected from the group consisting of orthophosphates, polyphosphates, and combinations thereof.

12. The method of claim 2, wherein the phosphate-containing compound is selected from the group consisting of: tetrapotassium pyrophosphate, sodium acid pyrophosphate, sodium tripolyphosphate, tetrasodium pyrophosphate, sodium potassium tripolyphosphate, sodium hexametaphosphate salt having from 6 to about 27 phosphate units, ammonium polyphosphate, sodium trimetaphosphate, and combinations thereof.

13. The method of claim 2, wherein the additive is a mixture of about 0.5% pentasodium salt of aminotris (methylenephosphonic acid) by weight of the calcium gypsum dihydrate and about 0.5% sodium trimetaphosphate by weight of the calcium gypsum dihydrate.

14. The method of claim 2, wherein the calcium sulfate dihydrate is present in an amount of at least about 20% by weight of the accelerator.

15. The method of claim 2, wherein water is present in an amount of about 55% to about 65% by weight of the accelerator.

16. The method of claim 2, wherein the viscosity of the wet gypsum accelerator is from about 1000 centipoise to about 5000 centipoise.

17. The method of claim 2, wherein the viscosity of the wet gypsum accelerator is from about 2000 centipoise to about 4000 centipoise.

18. The method of claim 1 wherein the WGA has a viscosity between about 3000 to about 5000 centipoise, and wherein the aqueous dispersion has a viscosity between about 700 to about 1200 centipoise.

19. The method of claim 1 wherein the ratio of WGA viscosity to aqueous dispersion viscosity is between about 10: 1 to about 2: 1.

20. The method of claim 1 wherein the ratio of WGA viscosity to aqueous dispersion viscosity is between about 4: 1 to about 3: 1.

21. The method of claim 1 wherein the WGA is introduced substantially perpendicular to the discharge apparatus.

22. The method of claim 2, wherein the accelerator has a time to 50% hydration of calcined gypsum of about 6 minutes or less when added to a mixture comprising calcined gypsum and water for forming an interlocking matrix of set gypsum.

23. The method of claim 11, wherein the accelerator is allowed to have a time to 50% hydration of calcined gypsum of about 5 minutes or less when added to a mixture comprising calcined gypsum and water for forming an interlocking matrix of set gypsum.

24. The method of claim 1, further comprising:

discharging the contents of the discharge device onto a moving cover.

25. The method of claim 24, further comprising:

applying a second cover plate to the discharged contents.

26. The method of claim 25, further comprising:

the cover plate and deposited contents were dried.

27. A method of introducing a production additive to an aqueous dispersion of post-mixing calcined gypsum, the method comprising:

forming an aqueous dispersion of calcined gypsum in a mixer chamber;

discharging the aqueous dispersion to a discharge apparatus;

introducing the production additive into the aqueous dispersion in the discharge apparatus;

wherein the viscosity ratio of the production additive to the aqueous dispersion is between about 10: 1 to about 2: 1.

28. The method of claim 27, wherein the viscosity ratio of the production additive to the aqueous dispersion is between about 4: 1 to about 2: 1.

29. The method of claim 27, wherein the production additive comprises an accelerator.

30. The method of claim 29, wherein the accelerator comprises a Wet Gypsum Accelerator (WGA).

31. The method of claim 27, wherein the production additive further comprises a foam.

32. The method of claim 27, wherein the production additive comprises a starch solution.

33. A system for introducing a wet gypsum accelerator into a post-mixing aqueous dispersion of calcined gypsum, the system comprising:

a source of WGA;

a conveying device;

an aqueous dispersion mixer of calcined gypsum;

a discharge device operatively associated with the outlet of the mixer;

the source, delivery device and the discharge apparatus are operatively connected to one another.

34. The system of claim 33, wherein the delivery device comprises a pump.

35. The system of claim 34, wherein the pump comprises a positive displacement pump.

36. The system of claim 33, further comprising a pressure gauge operatively coupled to a delivery line, wherein the delivery line is operatively coupled to the discharge apparatus.

37. The system of claim 33, further comprising a second discharge device operatively coupled to the mixer.

38. The system of claim 37, further comprising a pressure gauge operatively coupled to a transfer line, wherein the transfer line is operatively coupled to the second discharge apparatus.

39. The system of claim 33, further comprising a second delivery device operatively associated with said mixing tank and said second discharge apparatus.

40. The system of claim 39, wherein the delivery device comprises a pump.

41. The system of claim 40, wherein the pump comprises a positive displacement pump.

42. The system of claim 33 further comprising a subsystem comprising at least one member selected from the group consisting of a breast member, a manifold, a tee, a valve and a hose, said subsystem operatively associated with said evacuation apparatus, a source and a delivery device to deliver WGA to a plurality of evacuation apparatuses.

43. The system of claim 33, wherein the exhaust apparatus comprises a ring having a plurality of inlets, the port operatively associated with the source.

44. The system of claim 33, wherein the system comprises a delivery line operatively coupled to the discharge apparatus and a source, wherein the delivery line is operatively coupled to the discharge apparatus via a needle inserted into the discharge apparatus.

45. The system of claim 43 wherein the system comprises a delivery line and an udder or manifold, wherein the delivery device, delivery line, udder or manifold and ring are operatively linked to deliver the WGA to a plurality of inlets.

46. The system of claim 33 comprising a tee operatively connected to the discharge apparatus to allow the WGA and foam solution to mix before entering the discharge apparatus.