Abstract:
A process and system for manufacturing gypsum wallboard that aerates and cools a portion of the stucco used in the manufacturing process. This conditioning of the stucco reduces the amount of water needed to manufacture the gypsum wallboard which in turn reduces the amount of energy and cost needed to manufacture the wallboard.

Description:
RELATED APPLICATIONS 
       [0001]    This U.S. Utility patent application claims priority to U.S. Provisional Patent Application 61/030,161, which was filed on Feb. 20, 2008. 
     
    
     BACKGROUND OF INVENTION  
       [0002]    The subject invention relates generally to methods and apparatuses for calcining gypsum, and in particular to methods and apparatuses for continuously calcining natural gypsum, synthetic gypsum, or combinations of natural and synthetic gypsum. Calcined gypsum, more commonly known as stucco, is useful as a major ingredient of gypsum wallboard and plaster-based products. Stucco has the valuable property of being chemically reactive with water and will “set” rather quickly when the two are mixed together. It is this quick setting time that makes stucco ideal to work with in the mass production of wallboard. 
         [0003]    Typically, wallboard consists essentially of a gypsum core sandwiched between two sheets of paper and is used as a cost-effective replacement of conventional plaster walls. To be commercially profitable, wallboard is typically manufactured by continuous high speed processes. Typically, gypsum (calcium sulfate dihydrate) predominately makes up the wallboard. Manufacturers mine (or receive synthetic gypsum) and transport gypsum to a board mill in order to dry it, grind it and calcine it to yield stucco (the “milling process”). Drying refers to the removal of the free water from the gypsum (water not bonded to calcium sulfate) and calcination refers to the conversion of calcium sulfate dihydrate to calcium sulfate. The reaction for the creation of stucco is characterized by the following equation: 
         [0000]      CaSO 4 .2H 2 O+heat→CaSO 4 .½H 2 O+1½H 2 O 
         [0000]    This equation shows that calcium sulfate dihydrate plus heat yields calcium sulfate hemihydrate (stucco) plus water vapor. This process is normally conducted in a flash calcination impact mill, of which there are several types known in the art. Such an impact mill simultaneously dries, grinds, and calcines the gypsum to produce stucco. 
         [0004]    As mentioned above, calcined gypsum (stucco) has the valuable property of being chemically reactive with water, and will “set” rather quickly when the two are mixed together. This setting reaction reverses the above-described stucco chemical reaction performed during the calcination step. The reaction proceeds according to the following equation: 
         [0000]      CaSO 4 .½H 2 O+1½H 2 O→CaSO 4 .2H 2 O+heat 
         [0000]    In this reaction, the calcium sulfate hemihydrate is rehydrated to its dihydrate state over a fairly short period of time. The actual time required for this setting reaction generally depends upon the type of calciner employed, reagents added, and the type of gypsum rock that is used. 
         [0005]    In manufacturing wallboard, a “stucco slurry” is formed by mixing together dry and wet ingredients in a pin mixer. The dry ingredients can include, but are not limited to, any combination of calcium sulfate hemihydrate (stucco), fiberglass, accelerator(s), and in some cases natural polymer (i.e., starch) The wet ingredients can be made up of many components, including but not limited to, a mixture of water, paper, pulp and potash. The stucco slurry is then discharged from the mixer through a tube which spreads the slurry on a moving, continuous bottom facing material (e.g., cover paper), which is slightly wider than the desired board width. A moving, continuous top facing material (e.g., cover paper) is placed on the slurry and the bottom facing material so that the slurry is positioned in between the top and bottom layers of the facing materials to form a “wet wallboard.” Typically, forming plates are used to form the wallboard to the desired thickness and width. The board then travels along rollers for several minutes, during which time the setting reaction occurs and the board stiffens. The boards are then cut into a desired length and then fed into a large, continuous oven/kiln for drying. The end product is a wallboard with a gypsum core. 
         [0006]    While conventional gypsum wallboard products have many advantages, it has also long been desired to reduce the cost of manufacturing gypsum wallboard. One method of reducing the cost of manufacturing gypsum wallboard has been to reduce the amount of water used in the manufacturing of the wallboard. Reduction in water reduces the amount of free water left in the wallboard after the setting reaction. A lower amount of free water left in the wallboard results in less drying energy being expended to remove the free water, which in turn saves energy costs associated with drying wallboard (i.e., the fuel cost associated with operating a kiln to dry the wallboard). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The included drawings are for illustrative purposes and serve only to provide examples of possible structures for the disclosed invention. These drawings in no way limit any changes in form and detail that may be made to the invention by one skilled in the art without departing from the spirit and scope of the invention. 
           [0008]      FIG. 1  illustrates an exemplary system for the commercial manufacture of wallboard; and 
           [0009]      FIG. 2  illustrates a close up view of region  11  of  FIG. 1 . 
       
    
    
     SUMMARY  
       [0010]    As discussed herein, the present invention relates to systems and methods for producing a stucco slurry with a portion of the stucco being conditioned. Such systems and methods involve dividing a supply of stucco into two separate portions conditioning and aerating one portion of the stucco prior to supplying it to the mixer, and then adding the conditioned portion of the stucco along with the unconditioned portion of the stucco to the mixer with at least water to produce a stucco slurry that is used to manufacture gypsum wallboard. 
         [0011]    In one embodiment, a portion of the stucco is conditioned by utilizing a blender to aerate and cool the first portion of the stucco. Such blenders can range in size and height, but an example of such a blender used can have a diameter that falls within the range of about 12 inches to about 24 inches. The blender can also be equipped with a mechanism to introduce cold air into the blender. An example of such a mechanism is equipping the bottom half of the blender with a water jacket and equipping the top half of the blender with vortex tubes and air nozzles. The supply of stucco to the blender and to the mixer can be controlled by feed control mechanisms that control the rate that a portion of the stucco to be conditioned is supplied to the blender and controls the rate of the remaining portion of the stucco is supplied to the mixer. In one example, the rate that the portion of stucco is supplied to the blender falls within the range of about 10 tons per hour to about 19 tons per hour. 
         [0012]    To divide the stucco, multiple conveyors can be used in association with a gate that directs the portion of the stucco to be conditioned to the blender and directs the portion of the stucco that is unconditioned to a separate conveyor. In the use of the blender, the portion of the stucco to be conditioned travels from the stucco source (e.g., an impact mill) to the blender and the portion of the stucco that is not conditioned travels from the stucco source to the mixer. The two portions of the stucco can either be separately supplied to the mixer or the two portions of the stucco can be mixed back together prior to adding them to the mixer. 
       DETAILED DESCRIPTION OF THE INVENTION  
       [0013]      FIG. 1  shows an exemplary wallboard manufacturing system  10  for the commercial manufacture of wallboard. As shown in  FIG. 1 , a bottom cover paper  21 A is supplied by a bottom cover paper supply source  20 A comprising two large spindles, each capable of supporting one huge roll of cover paper or like facing material used to manufacture wallboard. A top cover paper  21 B is supplied by a separate top cover paper supply source  20 B, which configuration is substantially similar to the configuration  20 A for the bottom cover paper. While “cover paper” is used throughout this disclosure to discuss the facing materials used to create the wallboard, it is appreciated that any suitable facing material, including but not limited to fiberglass, can be used to create the wallboard. 
         [0014]    As the bottom cover paper  21 A leaves its point of origin, it travels along a conveyor, roller, belt or other like system  13  to a point where its edges are scored and upturned at substantially right angles with respect to the otherwise horizontally oriented bottom cover paper. Methods and devices for creating such upturned edges on cover paper on the fly are well known in the art, and any such methods and devices for performing this function may be utilized. A stucco slurry  12  is produced by adding the wet ingredients and dry ingredients to a mixer  50 . While any suitable mixer can be used, a pin mixer is utilized in this embodiment to form the slurry  12 . 
         [0015]      FIG. 2  shows a close up view of region  11  of the gypsum wallboard manufacturing system  10  illustrated in  FIG. 1 . As shown in  FIG. 2 , a chute  52 , commonly known as a boot, extends off of the mixer  50  and forms a pathway for the slurry  12  to exit out of the mixer  50  and onto the moving continuous sheet of bottom cover paper  21 A. While the chute is shown in a vertical arrangement, it is appreciated by one skilled in the art that the chute can be a horizontal arrangement as well. The slurry  12  exits at a given location, which is preferably after the edges on the bottom cover paper have been upturned to form a shallow trough for receiving and containing the slurry. The slurry  12  quickly settles and evens out within the moving bottom cover paper  21 A due to the liquid state of the slurry and the ongoing forward motion of the bottom cover paper. 
         [0016]    Still referring to  FIG. 2 , the stucco  6  is supplied from a stucco source  70  (e.g., an impact mill) to either conveyor  54  or blender  55 . A gate  72  can occupy a first position (see  FIG. 2 ) that blocks stucco from being placed on conveyor  54 , so that all the stucco leaving the impact mill  70  will enter blender  55 . Gate  72  can move over to a second position that blocks stucco from being placed on blender  55 , so that all stucco leaving the impact mill  70  will enter conveyor  54 . Conveyor  54  leads to a hopper, funnel or similar device  60  which feeds stucco  6   a  to the main stucco conveyor  58 . In this manner, gate  72  allows a portion of the stucco  6   b  to be diverted through a blender  55  before being added to the main stucco conveyor  58  and allows a portion of stucco  6 a to be diverted to the main stucco conveyor  58  through funnel  60 . It will be appreciated by one of ordinary skill in the art that while gate  72  is described as a slide gate that any type of diversion mechanism can be used to direct stucco to the blender  55  and conveyor  54 , including but not limited, to a rotor gate. 
         [0017]    Conveyor  54  leads to a measurement device  74   a  that measures the amount of stucco  6   a  that is provided to the main stucco conveyor  58 . Moreover, a measurement device  74   b  can be used to measure that amount of stucco  6   b  that is provided to blender  55 . The combination of stucco  6   a  and  6   b  comprises the desired amount of stucco to pin mixer  50  to create the stucco slurry. 
         [0018]    Through the use of the device  74   b,  the blender is fed at a desired rate which is largely dependent upon the size of the blender. In one embodiment, the blender is fed at a rate of anywhere from about 10 tons per hour to about 19 tons per hour. It will be appreciated by one skilled in the art that any number of feed control mechanisms could be used as devices  74   a  and  74   b,  including without limitation a bin discharger, milltronics, a rotary-plow type discharger, or a weigh belt. Once device  74   b  transfers stucco  6   b  to blender  55 , blender  55  is operated to aerate and cool the stucco  6   b  prior to stucco  6   b  being added to mixer  50 . While it will be appreciated by one of ordinary skill in the art that any sized blender could be used to condition the stucco based off a manufacturer&#39;s needs, exemplary blenders used in system  10  can range in diameter from about 12 inches to about 24 inches and can average about eight feet in length. Blender  55  can be equipped with any number of paddles  90  that are rotated by a rotary shaft  92  to circulate and condition the stucco. 
         [0019]    In this embodiment, once stucco  6   a  passes through conveyor  54 , device  74   a  and funnel  60  and stucco stream  6   b  passes through device  74   b  and blender  55 , both stucco  6   a  and  6   b  are added to the main stucco conveyor  58 . Once combined back into stucco stream  6 , the unconditioned stucco  6   a  and conditioned stucco  6   b  are added to mixer  50  by passing it through hopper  56 . While any suitable conveyors may be used to transport the stucco  6  to the mixer  50 , conveyors  54  and  58  comprise a screw conveyor in this embodiment. Other suitable conveyors include a high angle type conveyor, a chain conveyor, or a recirculation conveyor. It will be appreciated by one skilled in the art that instead of combining stucco  6   a  and  6   b  in a main stucco conveyor, stucco  6   a  and  6   b  can instead be added directly to and combined in the mixer. 
         [0020]    In other embodiments, blender  55  can be equipped with a water jacket on the bottom half of the blender and air nozzles and vortex tubes attached to the top half of the blender in order to introduce cold air to cool the blender while the stucco is being conditioned. For example, cold air can be added to the blender  55  by utilizing Vortec® cold air and vortex tubes manufactured by ITW Air Management. Vortex tubes create cold air and hot air by forcing high pressure compressed air through a generation chamber which spins the air centrifugally along the inner walls of the tube at approximately one million revolutions per minute towards the control valve. A percentage of the hot, high speed air is permitted to exit at the control valve. The remainder of the (now slower) air stream is forced to counter flow up through the center of the generation chamber finally exiting through the opposite end as extremely cold air. Such tubes are capable of generating temperatures down to 100° Fahrenheit below the inlet compressed air temperature using 100 pounds per square inch compressed air. After the vortex tubes create cold air, the cold air is introduced into the blender  55  by the air nozzles. It will be appreciated by one skilled in the art that any suitable sources of cold air can be used to introduce cold air into the blender  55  and that the use of a water jacket, vortex tubes, and air nozzles are only one example. 
         [0021]    Referring to both  FIGS. 1 and 2 , the top cover paper  21 B, at some distance after the slurry  12  has been deposited onto the bottom cover paper  21 A, is directed into place atop the wet slurry and bottom cover paper, thereby forming a “sandwich” of slurry within sheets of cover paper. The top cover paper leaves its point of origin at source  20 B and travels along a similar but separate conveyor, roller, belt or other like system  80  until it is directed into place atop the slurry and bottom cover paper. A “wet” wallboard is formed at this point, and several minutes are generally required until the wet wallboard has set sufficiently such that it can be cut and dried further. Because the manufacturing process would be considerably slowed by allowing this newly formed “wet” wallboard to sit in place while it sets for cutting, this newly formed wallboard is continually moved forward on conveyor  13  so that new wet wallboard can continue to be made while setting occurs. This conveyor  13  can be referred to as a “board line” and can extend for hundreds or thousands of feet before cutting. 
         [0022]    A cutting mechanism such as a rotary knife  30  is located at the end of the board line and is used to cut the now set wallboard into smaller and more manageable sections  31 . Although a rotary knife or blade type device is preferred, other cutting mechanisms, as would be readily understood by those skilled in the art, may also be used. This rotary knife  30  generally comprises a blade that extends across the width of passing wallboard and rotates in a direction compatible with the direction of the wallboard when activated to cut passing wallboard. The rotary knife  30  is also preferably controlled by or at least receives information from a control system  40  that is capable of measuring various parameters, assisting in the optimal placement of cover paper splices, and adjusting the timing of the knife cuts as necessary to isolate selected defects. 
         [0023]    After this initial cutting of the wallboard by the rotary knife  30 , the cut wallboard sections  31  are then placed onto a separate conveyor or roller system  14  by automated means so that they can be processed through heating kiln  15  or any other appropriate device for fully hardening and drying wallboard. Once these wallboard sections are sufficiently dried and hardened by the drying kilns or other drying device, they can then be further cut, bundled, packaged and processed in accordance with the desires of the manufacturer and the needs of consumers, through standard methods that are readily known to those skilled in the art. Such drying, bundling and packaging steps may be undertaken in any of a variety of ways. 
         [0024]    By utilizing blender  55  to aerate and cool a portion of the stucco prior to it being added to the pin mixer, a manufacturer can decrease the amount of water needed in the hydration process by about 6 to about 8 percent, increase line speeds by about 10 to 15 feet per minute and reduce kiln drying temperatures. Each of these reductions produce a cost savings to manufacturers. 
         [0025]    The following example is included to demonstrate some of the possible embodiments of the invention. Those of ordinary skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific described example which is disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. 
         [0026]    To determine the reduction of water that could be obtained by conditioning a portion of the stucco in this manner, one-half inch thick wallboards were produced utilizing the slurry formulation outlined below in Table I. 
         [0000]                                  TABLE I               Typical Formulation by Mass Percent Based on Stucco                                    Stucco   100%           Accelerator   0.08%-0.60%           Starch   .20%-.90%           Coalescing Additive   0           Potash   .02%-.15%           Pulp Paper   .09%-.15%           Pulp Water    5.0%-12.6%           Gauging Water   49%-68%           Dispersant   .19%-.75%           Retarder   .01%-.02%           Soap   0.03%-.12%            Foam Water    7.5%-18.7%                        
In this embodiment, the blender was 12 inches in diameter and 8 feet in length and was obtained from Hayes &amp; Solz Ind. MFG. Co., Inc. The blender was equipped with four atomizing nozzles with cold air tubes, a water jacket, and was fed at a rate of 10 tons per hour. The blender operated at high-speed during the trial. The trial resulted in an average reduction of the water required to form the wallboard by approximately 6 to 8%.
 
         [0027]    While the subject invention has been described in detail with reference to certain exemplary embodiments thereof, such are offered by way of a non-limiting example of the invention, as other versions are possible. For example, it will be appreciated by those skilled in the art that other means aside from utilizing a blender may be used to aerate and cool a portion of the slurry prior to adding it to a pin mixer. It is anticipated that a variety of other modifications and changes will be apparent to those having ordinary skill in the art and that such modifications and changes are intended to be encompassed within the spirit and scope of the invention as defined by the following claims.