Abstract:
Methods of manufacturing screen elements for use with vibratory separators are disclosed. The screen elements include a curved structural frame with perforations therein, the perforations designed to maximize both open area and process liquid throughput. At least one layer of screen cloth is attached to the curved structural frame by means of fluidized powdered epoxy resin.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Non-Provisional Patent Application, filed under 35 U.S.C. §111(a), claims the benefit under 35 U.S.C. §119(e)(1) of U.S. Provisional Patent Application No. 60/839,141, filed under 35 U.S.C. §111(b) on Aug. 16, 2006, and which is hereby incorporated by reference in its entirety and U.S. non-Provisional application Ser. No. 11/893,480, filed Aug. 16, 2007, now abandoned. This Non-Provisional Patent Application is related to U.S. application Ser. No. 10/922,342, entitled “Screen assemblies utilizing screen elements retained in perforated troughs,” and filed on Aug. 20, 2004 now abandoned, and to U.S. Provisional Patent Application No. 60/838,565, entitled “Screen assemblies utilizing screen elements retained in perforated supports,” and filed on Aug. 18, 2006. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not applicable. 
     INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON COMPACT DISC 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to methods of manufacturing an apparatus with which material is separated or assorted according to size or dimensions of components by presentation to a series of openings or passages through which the components having dimensions below those of the openings or passages pass while those having dimensions greater than those of the passages or openings do not pass through. More specifically, the present invention relates to methods of manufacturing screen assemblies used in vibratory separators. 
     2. Description of Related Art 
     Vibratory screen separators with replaceable screen assemblies have long been known, and include a base, a resiliently mounted housing, a vibratory drive connected to the housing, and screen assemblies positioned on the housing. The screen assemblies are periodically replaced when process conditions dictate or when the performance of the screening media degrades due to abrasion, failure, or blinding. The screening media can be flat or pleated, single or multi-layered, laminated or un-laminated. Screen assemblies include screening media bonded to components structural in nature that are used to fasten or tension the screening media to a vibratory separator so that the motion of the separator is imparted to the screening media. 
     Flexible rectangular screen assemblies constructed by using structural components that form a “J” or similar shape on two sides of screen are known as hookstrip style screens. Hookstrip style screens are fastened to vibratory separators by pulling the screen assembly taut over a crowned deck. The “crown” or “radius” in the deck is necessary because the geometry of the crown keeps the flexible screen in contact with the vibrating deck without approaching tension levels that would damage the screening media. 
     Screen assemblies constructed by bonding screening media to rectangular structural frames that minimize the flexibility of the screen assembly are known as panel style screens. The structural frame may or may not have internal supporting cross members. Panel style screens are fastened to vibratory separators by clamping one or more surfaces of the structural frame to a mating surface (or deck) of the vibratory separator. The decks of vibratory separators that accept panel screens are noticeably less crowned than the decks of vibratory separators that accept hookstrip style screens, but the decks are usually slightly crowned to prevent panel style screens from flexing or chattering when the vibratory separator is in motion. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is directed to novel methods of manufacturing screen elements for vibratory separators, especially in mass production environment. Such screen assemblies include a structural frame that is mounted in a vibratory separator into which a plurality of lightweight and flexible screen elements are inserted into multiple rows of perforated screen supports. The perforated screen supports are bonded to each other and to the structural frame. The perforated screen supports are aligned parallel to the direction in which solids are conveyed by the vibratory motion. The perforated screen supports are assembled to the structural frame so that unscreened material cannot substantially bypass the screening media. The cross sectional geometry of the perforated screen support and of the formed screen elements can be rectangular, triangular, half-circular, half-ellipsoid, catenary, hyperbola, or other similar geometric shape. The screen elements include one or more layers of screening media that may be bonded to each other and may be preformed to conform to the geometry of the perforated screen support. 
     The present invention provides methods of manufacturing screen elements that substantially increase the available area for screening compared to the available area of the prior art when a screen assembly creates a flat or crowned screening surface on a vibratory separator. Furthermore, the ease of replacing small, (typically three inches wide and 24 inches long) and lightweight (typically less than one pound) individual screen elements in the present invention saves time and material by eliminating the periodic replacement of large, heavy, and cumbersome screen assemblies in conventional vibratory separators. Typically, these conventional screen assemblies weigh anywhere from 20 to 50 pounds and are approximately two to three feet long and up to four feet wide. In addition, when the present invention is used to replace hookstrip style screens with crowned screening surfaces, the effective screening area is increased by channeling the flow of unscreened material and preventing the pooling of liquid on either side of a crown deck. The crowned screen deck causes the processed material to flow away from the center of the screen (the crown) towards the sides, causing a large area of the screen surface to be under-utilized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a further understanding of the nature, objects, and advantages of the present invention, reference should be had to the following detailed description, read in conjunction with the following drawings, wherein like reference numerals denote like elements. 
         FIG. 1  shows a screen element frame created by perforating a sheet of thin metal plate—preferably flat—to achieve a preferred pattern. 
         FIG. 2  shows a screen element forming or molding press according to the present invention. 
         FIG. 3  shows a formed screen element frame—a screen element frame of  FIG. 1  formed to a predetermined diameter by the molding press of  FIG. 2 . 
         FIG. 4  shows the screen element forming or molding press at different stages of operation, acting upon a screen element frame to produce a formed screen element frame. 
         FIG. 5  shows a fluidized bed into which formed (curved) screen element frames are dipped after being heated. 
         FIG. 6  shows a finished screen element. 
         FIG. 7  shows a cooling rack. 
         FIG. 8  shows a screen element laminating press. 
         FIG. 9  shows the removal of a round heating element from a laminated screen element. 
         FIG. 10  shows a support frame assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Before the subject invention is further described, it is to be understood that the invention is not limited to the particular embodiments of the invention described below, as variations of the particular embodiments may be made and still fall within the scope of the appended claims. It is also to be understood that the terminology employed is for the purpose of describing particular embodiments, and is not intended to be limiting. Instead, the scope of the present invention will be established by the appended claims. 
     In this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural reference unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. 
     Example 1 
     Screen Element Frame Manufacturing Steps 
     The invention features, in one aspect, a screen element frame ( 80 ) created by perforating a sheet of thin metal plate, preferably flat, to achieve a preferred pattern ( FIG. 1 ). The perforation pattern is designed to maximize open area, to provide adequate heat capacity for powder coating requirements (discussed below), and to give proper support for the precut screen cloth layers ( 92 ). 
     Using a special molding press ( 31 ), the screen element frame ( 80 ) is then curved to a predetermined diameter, thus forming a curved screen element frame ( 85 ) ( FIGS. 2 ,  3 , &amp;  4 ). This process maximizes the overall screen area and at the same time permits use of the entire available shaker (not shown) width for any shakers of the prior art. The molding press ( 31 ) is designed to produce an exact amount of curvature to the curved screen element frame ( 85 ) with a unique feature in the frame forming press cradle ( 40 ) design utilizing the two cradle side extensions ( 45 ,  55 ) that are forced towards each other by horizontal side supports ( 50 ,  60 ), respectively, to increase the roundness of the semi-circular cradle bottom ( 90 ) when the frame forming press cradle ( 40 ) is pushed down against the support beam ( 70 ), as shown in  FIG. 4 . The semi-circular cradle bottom ( 90 ) of the frame forming press cradle ( 40 ) will wrap around the forming element ( 10 ) as the horizontal side supports ( 50 ,  60 ) force up the side extensions thus extending the proper curvature all the way to the edges of the curved screen element frame ( 85 ) being formed. This is important in order for the finished screen element ( 86 ) be seated properly into the support frame ( 98 ), shown in  FIG. 10 , to provide sealing ( 99 ) between the finished screen element ( 86 ) and the support frame ( 98 ) to minimize potential process liquid bypass (not shown). 
     The exact forming method is described in Example 5, “Description of the frame forming press,” below. 
     Example 2 
     Curved Element Frame Coating 
     The curved screen element frame ( 85 ), shown in  FIG. 3 , is then cleaned to be free of contaminants such as oil, dirt, etc. by dipping it into a hot caustic bath. This is important for the epoxy ( 25 ) to properly adhere to the surface, as discussed below. 
     The curved screen element frame ( 85 ) is then heated in an oven (not shown) of any type for metal heating of the prior art. Normal temperature range for epoxy coating of metal components is 400 to 500° F., however, higher temperatures (up to 600+° F.) may be required due to the small volume of metal in the curved screen element frame ( 85 ), to compensate for rapid heat loss depending of the time it takes to move the curved screen element frame ( 85 ) from the oven to the fluidized bed ( 14 ), shown in  FIG. 5 . Generally, the curved screen element frame ( 85 ) is heated to a temperature which lies between the sintering point and the decomposition point of the coating composition (the epoxy), and below the deteriorating point of the curved element frame. 
     The hot curved screen element frame ( 85 ) is then dipped into a fluidized bed ( 14 ) containing special epoxy ( 25 ), specially designed to have low heat cure temperature and a suitable thixotropic index to prevent molten epoxy ( 25 ) from spreading, during the laminating process, into areas of screen cloth ( 92 ) covering the perforations in the curved screen element frame ( 85 ). The curved screen element frame ( 85 ) is kept in the fluidized epoxy ( 25 ) for three to five seconds. Depending on the desired epoxy coat thickness, a longer or shorter time—such as one to seven seconds—may be needed. The coated frame ( 88 ) is then placed on a cooling rack ( 16 ) to cool ( FIG. 7 ). It is important to understand that the epoxy ( 25 ) on the curved screen element frame ( 85 ) has not been cured i.e. the molecules have not fully cross linked. This state of cure is called a B-stage cure. The purpose of this type of cure is to allow the epoxy coating to be re-melted in order to laminate the precut screen cloth layers ( 92 ) into it. To cure the epoxy requires that it be maintained at an elevated temperature for a sufficient time to cure the coating, as will be described below. 
     Example 3 
     Coated Frame Lamination 
     The heat lamination press cradle ( 42 ) of  FIG. 8  is substantially the same as the frame forming press cradle ( 40 ) of  FIG. 4 , with the exception of having a slightly larger cradle bottom ( 91 ) diameter to allow the coated frame ( 88 ) and the precut screen cloth layers ( 92 ) to properly fit into it. A round heating element ( 73 ) is attached to pneumatic cylinders ( 22 ). The round heating element ( 73 ) is located directly above and is aligned parallel to the heat lamination press cradle ( 42 ). The round heating element ( 73 ) has a tubular internal heating element ( 66 ) mounted substantially in the center of round heating element ( 73 ). 
     The coated frame ( 88 ) is placed into the special heat lamination press cradle ( 42 ), as shown at  FIG. 8 . Precut screen cloth layers ( 92 ) (1 to 3 separate layers) are placed over the coated frame ( 88 ). The round heating element ( 73 ) is then lowered into the heat lamination press cradle ( 42 ). The temperature achieved by the round heating element ( 73 ) is sufficient to re-melt the epoxy coating of the coated frame ( 88 ). The heat lamination press cradle ( 42 ) is designed such that when the round heating element ( 73 ) is pushing down on it, the sides of the heat lamination press cradle ( 42 ) are forced against the coated frame ( 88 ), causing in turn very uniform pressure on the coated frame ( 88 ) and the precut screen cloth layers ( 92 ) against the round heating element ( 73 ). This provides uniform melting (“fluidizing”) of the epoxy ( 25 ). The uniform pressure is a result of the heat lamination press cradle ( 42 ) being pushed down against the support beam ( 70 ) and the heat lamination press cradle ( 42 ) cradle side extensions ( 46 ,  56 ) will force the cradle bottom ( 91 ) shape more towards a full circle thus forcing the coated frame ( 88 ) with the precut screen cloth layers ( 92 ) to be wrapped around the round heating element ( 73 ) very tightly. 
     The round heating element ( 73 ) is then kept down in the heat lamination press cradle ( 42 ) at sufficient temperature and for a predetermined amount of time, preferably about four to five minutes, for the epoxy ( 25 ) coating to first melt and be forced through all the precut screen cloth layers ( 92 ) and then to cure it. It will be appreciated by those skilled in the art that the temperature and time required to cure any epoxy that could be used with the present invention may depend on particular characteristics of the epoxy used, but that such temperature and time are readily ascertainable by one skilled in the art without undue experimentation. 
     The round heating element ( 73 ) is then lifted up, and the laminated screen element ( 89 ) is removed from the heat lamination press cradle ( 42 ) and allowed to cool ( FIG. 9 ). 
     Example 4 
     Laminated Screen Element Trimming 
     Once the laminated screen element ( 89 ) has been cooled, all excess screen cloth will be trimmed away along the outer edges of the laminated screen element ( 89 ) curved screen element frame ( 85 ), yielding a finished screen element ( 86 ) as shown at  FIG. 6 . The finished screen element ( 86 ) is then labeled to indicate the cut point, checked for defects and boxed for shipping. 
     Preferably, curved screen element frame ( 85 ) should be constructed of material that would allow adequate support for the precut screen cloth layers ( 92 ), such as carbon or stainless steel. 
     Also preferably, the curved screen element frame ( 85 ) should have the maximum open area possible to maximize process liquid throughput. 
     Also preferably, the curved screen element frame ( 85 ) should be made of material at allows precut screen cloth layers ( 92 ) to attach to it by fluidized epoxy ( 25 ), such as carbon or stainless steel. 
     Also preferably, the curved screen element frame ( 85 ) should be light weight, inexpensive and suitable for mass production. 
     Also preferably, the finished screen element ( 89 ) should retain its designed shape to facilitate installation into a support frame ( 98 ). 
     Also preferably, the element ( 89 ) should withstand the process environment long enough to yield lower overall operating cost. 
     Example 5 
     Description of the Frame Forming Press 
       FIG. 4  shows the principle of operation of the screen element frame forming press ( 21 ). The forming element ( 10 ) is mounted on a plurality of air or hydraulic cylinders ( 20 ). The hydraulic cylinders ( 20 ) are mounted on a support structure ( 30 ). The frame forming press cradle ( 40 ) is placed under the forming element ( 10 ) between two horizontal side supports ( 50 ,  60 ). The frame forming press cradle ( 40 ) is shaped in a special way, preferably with a semi-circular cradle bottom ( 90 ) and cradle side extensions ( 45 ,  55 ) extending outward in approximately 45 degree angle ( FIGS. 2 &amp; 4 ). Approximately 1 inch under the bottom of the frame forming press cradle ( 40 ) is a horizontal support beam ( 70 ), as shown by  FIG. 4 . The flat screen element frame ( 80 ) is placed approximately horizontally between the cradle side extensions ( 45 ,  55 ) in  FIG. 4 . The forming element ( 10 ) is then lowered onto the flat screen element frame ( 80 ) and then allowed to push the screen element frame ( 80 ) down into the frame forming press cradle ( 40 ). When the forming element ( 10 ) hits the bottom of the frame forming press cradle ( 40 ), the cradle with the screen element frame ( 80 ) in it is then pushed further down until the bottom of the frame forming press cradle ( 40 ) comes in contact with the support beam ( 70 ) underneath, preventing any more downward movement ( FIG. 4 ). While the frame forming press cradle ( 40 ) is pushed down, the outward pointing cradle side extensions ( 45 ,  55 ) will slide between the horizontal side supports ( 50 ,  60 ), respectively, forcing the curvature of the semi-circular cradle bottom ( 90 ) of the frame forming press cradle ( 40 ) to be more than a half circle thereby forcing the long sides of the screen element frame ( 80 ) to conform to the shape of the forming element ( 10 ). The forming element ( 10 ) is then lifted up from the frame forming press cradle ( 40 ) and the frame forming press cradle ( 40 ) will move upwards opening up to a half circle shape again. The curved screen element frame ( 85 ) is then removed from the frame forming press cradle ( 40 ) and the forming process is complete for curved screen element frame ( 85 ). 
     Example 6 
     Description and Operation of the Fluidized Bed 
     Fluidized powdered epoxy resins are applied by dipping heated metal parts into an aerated powder bed. The powdered resin coats the hot metal part, and melts. The result is a smooth, continuous plastic film encapsulating the metal part. It should be noted, however, that although a metal part may be coated with epoxy, the epoxy may or may not be cured. If the epoxy is not yet cured, certain advantages may be gained by re-melting the epoxy coat and then curing it, as described herein. 
     The fluidized bed ( 14 ) of  FIG. 5  includes a tank ( 15 ) which is divided into separate upper ( 24 ) and lower ( 35 ) compartments by a porous membrane ( 47 ). Fluidizable powdered epoxy resin ( 25 ) is placed into the upper compartment ( 24 ) via the open top of the tank ( 15 ). Compressed air is introduced into the lower compartment ( 35 ) via an air inlet ( 37 ). When the lower compartment ( 35 ) is pressurized, the porous membrane ( 47 ) allows a uniform air flow (arrows,  FIG. 5 ) through its microscopic openings into the upper compartment ( 24 ). The rising air surrounds and suspends the finely divided powdered epoxy ( 25 ) particles, causing the powdered epoxy ( 25 ) to float, or “fluidize” and form a dense-phase fluidized bed, and the powder-air mixture resembles a boiling liquid. 
     Example 7 
     Description of the Screen Element Laminating Press 
       FIG. 8  shows the operation of the screen element laminating press. The press itself is constructed like the screen element frame forming press ( 21 ) with the exception of having a round heating element ( 73 ) attached to the pneumatic cylinders ( 22 ). Inside the round heating element ( 73 ) is a tubular internal heating element ( 66 ). The round heating element ( 73 ) is heated to approximately 430° F. The required temperature for melting and curing the epoxy ( 25 ) on the coated frame ( 88 ) depends on the time the heater is kept against the frame. The lower the temperature, the longer time is required to cure the epoxy. Desired temperature range is preferably between 350-500° F. When the round hearing element ( 73 ) is heated to 430° F., it takes about five minutes to cure the epoxy. The combination of proper time and temperature is required to produce a finished product without over bleeding of epoxy on the screen cloth and with the precut screen cloth layers ( 92 ) taut and free of wrinkles. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Listing of Components 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 10 
                 forming element 
               
               
                   
                 14 
                 fluidized bed 
               
               
                   
                 15 
                 tank 
               
               
                   
                 16 
                 cooling rack 
               
               
                   
                 20 
                 hydraulic cylinders 
               
               
                   
                 21 
                 screen element frame forming press 
               
               
                   
                 22 
                 pneumatic cylinders 
               
               
                   
                 24 
                 upper compartment 
               
               
                   
                 25 
                 epoxy 
               
               
                   
                 30 
                 support structure 
               
               
                   
                 31 
                 molding press 
               
               
                   
                 35 
                 lower compartment 
               
               
                   
                 37 
                 air inlet 
               
               
                   
                 40 
                 frame forming press cradle 
               
               
                   
                 42 
                 heat lamination press cradle 
               
               
                   
                 45 
                 cradle side extension 
               
               
                   
                 46 
                 cradle side extension 
               
               
                   
                 47 
                 porous membrane 
               
               
                   
                 50 
                 horizontal side support 
               
               
                   
                 55 
                 cradle side extension 
               
               
                   
                 56 
                 cradle side extension 
               
               
                   
                 60 
                 horizontal side support 
               
               
                   
                 66 
                 tubular internal heating element 
               
               
                   
                 70 
                 support beam 
               
               
                   
                 73 
                 round heating element 
               
               
                   
                 80 
                 screen element frame 
               
               
                   
                 85 
                 curved screen element frame 
               
               
                   
                 86 
                 finished screen element 
               
               
                   
                 88 
                 coated frame 
               
               
                   
                 89 
                 laminated screen element 
               
               
                   
                 90 
                 semi-circular cradle bottom 
               
               
                   
                 91 
                 cradle bottom 
               
               
                   
                 92 
                 precut screen cloth layers 
               
               
                   
                 98 
                 support frame 
               
               
                   
                 99 
                 sealing 
               
               
                   
                   
               
             
          
         
       
     
     All references cited in this specification are herein incorporated by reference as though each reference was specifically and individually indicated to be incorporated by reference. The citation of any reference is for its disclosure prior to the filing date and should not be construed as an admission that the present invention is not entitled to antedate such reference by virtue of prior invention. 
     It will be understood that each of the elements described above, or two or more together may also find a useful application in other types of methods differing from the type described above. Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention set forth in the appended claims. The foregoing embodiments are presented by way of example only; the scope of the present invention is to be limited only by the following claims.