Method for producing an embossed gypsum panel
This is a division of application Ser. No. 911,932, filed Sept. 26, 1986, now U.S. Pat. No. 4,781,558. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to building products and more particularly, to an apparatus for making decorative panels made from a hardenable gypsum slurry and a method for making said decorative panels. 
     2. Description of the Prior Art 
     Panels or tiles having an embossed surface have been available for installation in commercial and residential areas. These panels have generally been made of wood fiber, mineral wool or glass fibers in either a wet process using a fourdrinier-type machine or a molded process using a rather thick, moldable slurry. The surfaces of the panels have been embossed while the panel is in either a wet stage or after it has been dried. 
     Panels have also been made of a slurry which contains gypsum that hardens or sets during a drying cycle. Generally, gypsum panels have not been embossed to produce a decorative surface. Gypsum panels usually comprise a core of set gypsum covered on both sides by paper sheets and thus, the gypsum is not available for embossing. The surface of the panels are usually embossed, or have holes of fissures therein for enhanced acoustical qualities. The holes or fissures can be put into the surfaces while the product is wet or dry. 
     SUMMARY OF THE INVENTION 
     The present invention concerns an embossed gypsum panel and the process for making said panel. The panel may be a relatively low density (8 to 25 pounds per cubic foot) gypsum-based panel. However, the actual density of the panel may vary depending upon the amount of low density aggregate used. The embossing is done by an embossing drum which is locatable with respect to the location of the desired degree of &#34;set&#34; of the gypsum composition. 
     It is an object of the present invention to provide a novel process for producing an embossed gypsum panel. 
     It is a further object of the invention to provide a novel process for producing an embossed gypsum panel in an economical manner. 
    
    
     Other objects and features of the invention will become apparent to those skilled in the art when the present description is considered in the light of the accompanying drawing in which like numerals indicate like elements and in which: 
     FIG. 1 is a schematic layout of the essential apparatus of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With refernce to FIG. 1, there is therein shown a gypsum panel manufacturing apparatus comprising a conveyor belt or other panel moving device 10 mounted for movement on conveyor drums 12. An optional roll 14 carries a roll of backing material; such as, paper, foil or glass fiber 16. The paper, foil or glass fiber forms a sheet of predetermined width which moves over a guide roll or drum 18 and is moved along the upper surface of conveyor 10. Roll 14 may be slipped over a mandrel 20 which acts as a central axis for roll 14. 
     A mixer 22 is positioned over conveyor belt 10 to deposit a slurry of gypsum on sheet 16. If desired, side deckles (not shown) can be located along each side of conveyor 10 to confine the gypsum slurry in forming a continuous layer on sheet 16. 
     Mixer 22 may be a ball mixer, a pin mixer, a combination of both, or may be of any other suitable type. Mixer 22 is shown schematically as depositing a single relatively wide stream of slurry designated as 30. In actual practice, a common expedient is to deposit several separate streams across the conveyor 10, the plastic streams merging by lateral gravitational flow before reaching leveling roll 24. 
     A leveling roll 24 mounted on a mandrel 26 forms a means to control the thickness of the gypsum slurry after it is deposited on sheet 16 from mixer 22. Leveling roll 24 is mounted near mixer 22 so that the slurry is leveled before any setting of the slurry occurs. The outer surface of roll 24 may be coated with Teflon or other release type material to prevent sticking of the gypsum to roll 24. 
     In order to provide a decorative surface on the upper face of the board, a drum or roll 34 having an embossing surface 36 is mounted downstream of level roll 24. Drum 34 is mounted for rotation on a mandrel or axle 38. Mandrel 38 is mounted on a support structure 40. Support structure 40 comprises a pair of braces 44 and 46 which are supported on a moveable vehicle 48. Vehicle 48 has wheels 50 and 52 which permit drum 34 to be moved longitudinally of conveyor belt 10 toward or away from mixer 22. Mandrel 38 is located above said gypsum slurry a distance such that the embossing pattern of the drum 34 engages a portion of the surface of the gypsum slurry. 
     The side of mandrel 38 opposite the side shown is supported on a similar moveable vehicle by a similar support structure (not shown). 
     The final cutting and drying operations of the process are carried out by the cutter 56 and dryer 58 which are shown in schematic form. 
     The cutting and drying apparatus described and the operation of that apparatus are entirely conventional and therefore details of the specific mounting and drive means have been omitted. 
     The slurry 30 is made by adding a generated foam and/or low density aggregate such as perlite to a gypsum-based composition. Other binders, such as starch, are added to improve the strength of the final produce and wax is added to improve water resistance. Fibers, such as glass fiber, can be added to improve strength and handleability. 
     A typical formula is as follows: 
     
         ______________________________________                                    
                Range %   Preferred %                                     
Ingredient      by Weight by Weight                                       
______________________________________                                    
Calcined gypsum 25-60     40                                              
Expanded perlite                                                          
                10-40     26                                              
Clay             8-36     24                                              
Guar gum        1/2-3     1                                               
Glass fiber     1/8-2     1/2                                             
Accelerator     1/8-2     1/2                                             
Starch           5-10     8                                               
______________________________________                                    
 
    
     The clay may be K-T Ball clay. The starch may be thick boiling corn starch. The accelerator may be finely ground rehydrated gypsum CaSO 4  2H 2  O. All ingredients are combined in an aqueous slurry at a concentration which is easily pourable (15 to 50% solids) and the slurry is deposited between moving deckles onto a moving conveyor, where it is spread out by the use of a leveling roll 24 (both the roll and the conveyor are preferably surfaced with Teflon or such so as to minimize sticking to the roll or conveyor surfaces). The slurry might also be deposited onto a sheet of paper or aluminum foil of glass fiber mat or such (instead of being put directly onto the conveyor surface) which would impart strength of other properties to the panel. 
     As with gypsum board manufacture, the time required to reach a desired degree of &#34;set&#34; of the composition is advanced by the addition of one of several accelerator additives which cause the slurry to &#34;set&#34; more rapidly to the optimum point where the surface is semi-hard but still soft enough to be shaped or penetrated with embossing or texturing rolls or tools, and then to retain that embossing or texturing through subsequent hardening so that the final surface retains all the patterning that was done to it. 
     The optimum &#34;set&#34; point in this process is critical because the degree of hardness of the slurry when it is subjected to patterning will greatly affect the definition of the retained pattern. If the slurry is too soft, it will &#34;flow back&#34; and lose details; if too hard, the surface will tear instead of becoming formed. At the optimum degree of set, the surface of the slurry will retain prefectly even the finest details of the pattern. 
     The above-mentioned optimum degree of &#34;set&#34; of the slurry is difficult to predict or maintain since even small subtle changes in raw materials or processing conditions will affect the speed of &#34;set&#34;. 
     To overcome the problem of unpredictable &#34;set&#34; and the difficulty of patterning the surface of the panel at the optimum degree of &#34;set,&#34; the surfacing or embossing device used is mounted (on wheels or a worm drive or a chain device) in such a way so that it can be moved up or down the length of the forming conveyor, so that the optimum condition of &#34;set&#34; can be found and followed if it changes because of reasons discussed earlier. Thus, if &#34;set&#34; conditions change and the surface is too wet, the device is moved downstream or away from the mixer until the optimum &#34;set&#34; is found. Likewise, if the surface is too dry, the device is moved upstream, or toward the mixer. 
     The degree of &#34;set&#34; could be monitored by an operator who would visually observe the patterning and manually move the patterning device upstream or down, as required, or this characteristic could be measured continuously by means of a thin rod 60 being pushed into the edge of the panel and withdrawn continuously by means of a plunger 62. The amount of pressure required to penetrate the panel would indicate the resistance of the mix to penetration and, therefore, the degree of &#34;set&#34;, and the device would then move itself to where the degree of &#34;set&#34; was optimum by means of an automatic device 64 equipped with a &#34;mini-computer.&#34; 
     Alternative devices for determining the degree of &#34;set&#34; may include a wheel or other device to continuously monitor the degree of &#34;set.&#34; 
     Once the panel was embossed at the determined location of the optimum degree of &#34;set&#34;, it would be processed as are most other gypsum products in that, after it had set completely, it would be cut into pieces and then dried in a conventional manner. After drying, the pieces would be cut and/or machined to the shapes and sizes required and, finally, painted. 
     Various modifications of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof.