[0001]    This is a divisional of U.S. patent application Ser. No. 09/432,921, filed Nov. 2, 1999, allowed, the disclosure of which is incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The field of the present invention is tensioned screens having utility for vibratory separation.  
           [0003]    Vibratory separators have long been used for separation of materials, both wet and dry. Such separators have been classically divided into rectangular screen separators and circular screen separators. An example of a rectangular screen separator is illustrated in U.S. Pat. No. 4,582,597, the disclosure of which is incorporated herein by reference. A circular separator is illustrated in U.S. Pat. No. 4,613,432, the disclosure of which is incorporated herein by reference. Each type of separator has its own advantages well known in the industry.  
           [0004]    Vibratory separators may also be distinguished by the multiple ways that they provide tensioned screen cloth. One system is to employ untensioned screens using hook strips in association with tensioning mechanisms on the screening system. One such system is illustrated in U.S. Pat. No. 5,221,008. Alternatively, pretensioned screen panels including tensioned screen cloth affixed to rigid frames provide the tensioning mechanism. In such circumstances, tensioning mechanisms on the vibratory separators are avoided. The manufacture of such screens is disclosed in U.S. Pat. No. 4,968,366, the disclosure of which is incorporated herein by reference.  
           [0005]    Hook strip screens which are tensioned on the screening device require a crown on the screen bed. Such a crown has proven to be disadvantageous with regard to the distribution of material on the screen. Such devices also require multiple fasteners along the sides of the screen deck which are time consuming to operate and are susceptible to errors in assembly.  
           [0006]    Pretensioned screens have been incorporated into vibratory housings in circular screens by including screen frames with outwardly extending mounting flanges that are sandwiched between succeeding wall portions. Reference is made to U.S. Pat. No. 4,810,372, incorporated herein by reference, illustrating such flanges and their placement in the housing. Pretensioned screens which are rectangular have not employed outwardly extending mounting flanges. They have used clamps operating directly on the frame itself. One clamp system employs a pneumatic seal in association with channels to locate and retain such frames. Reference is made to U.S. Pat. Nos. 4,582,597 and 5,226,546, the disclosures of which are incorporated herein by reference.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention is directed to screens capable of being mounted to vibratory screening equipment. The screens have a screen frame forming a rigid geometric shape with a screening element affixed thereto. The frame includes an inwardly extending mounting flange designed to allow retention of the screen from below. The flange is facing toward and at a distance from the screening element.  
           [0008]    Accordingly, it is an object of the present invention to provide an improved screen for a screening system. Other and further objects and advantages will appear hereinafter. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a perspective view of a vibratory screen separator.  
         [0010]    [0010]FIG. 2 is a perspective view of a detail of the vibratory screen separator.  
         [0011]    [0011]FIG. 3 is a plan view of a screen.  
         [0012]    [0012]FIG. 4 is a cross-sectional edge view of the screen.  
         [0013]    [0013]FIG. 5 is a cross-sectional side view of a screen frame and retaining system.  
         [0014]    [0014]FIG. 6 is a cross-sectional side view of a screen frame and retaining system.  
         [0015]    [0015]FIG. 7 is a perspective view of a retaining clip.  
         [0016]    [0016]FIG. 8 is an end view of the retaining clip. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    A vibratory screen system, generally designated  10 , is illustrated in FIG. 1. The system includes a base  12 , a resiliently mounted housing  14  mounted by spring elements  16  and vibration generators  18 . The vibration generators  18  are rigidly fixed to the resiliently mounted housing  14 . An inlet  20  is provided above the resiliently mounted housing  14  to distribute materials for screening.  
         [0018]    The device illustrated as the vibratory screen system  10  is configured as a shaker, or shale shaker, used in the oil well drilling industry. Spent drilling mud returning from the hole is processed by such a shaker to separate sand and chips recovered from the well from the valuable drilling mud. The mud, once screened, is recycled to the hole.  
         [0019]    The screens  22  employed with this system are conventionally constructed rectangular pretensioned screens with the exception of the mounting flange extending inwardly, away from the periphery of the screen frame forming a mounting surface. The screen frame  24  is a right quadrilateral which could be square or rectangular as desired. The frame  24  includes a progressively formed hollow steel tube which is butt welded. The tube has a cross section which is roughly rectangular with the exception of a mounting flange  26  extending inwardly, away from the periphery. The portion of the sheet forming the frame  24  extends continuously across the bottom of the frame to form the lower surface of the mounting flange  26 . The sheet is then bent back upon itself to form the upper surface of the mounting flange  26  and then is bent up and away from the bottom surface to further define the rectangular cross section of the frame. Alternatively, the frame  24  may be of solid, usually polymeric, material with internal reinforcing as needed. At least two, opposed sides of the screen frame  24  include the inwardly extending mounting flanges  26 . All four sides of the frame  24  may include the flange  26  as seen in FIG. 3.  
         [0020]    Screen cloth  28 , forming a screening element, is tensioned across the screen frames  24 , bonded thereto and trimmed in a well known manner. The screens of the preferred embodiment are shown to include four support members  30  which are preferably aligned with the intended flow of material over the screen. These support members  30  extend to flush with the top surface of the screen frame  24  to support the screen cloth  28 . The screen cloth  28  may be bonded to these support members  30 . A support rod  32  extends from one side of the frame  24  to the other in a perpendicular direction to the support members  30 . The rod  32  contributes additional strength to the assembly.  
         [0021]    Returning to the resiliently mounted housing  14 , a mounting frame  34  includes side rails  36  bordered by upstanding walls  38 . Two side rails  36  with adjacent upstanding walls  38  define a planar support surface  40  on the side rails  36  within a cavity defined by the upstanding walls  38 . The walls  38  are spaced to closely accommodate the width of a screen frame  24 . Frame cross members  42  extend between the side rails  36 . These frame cross members  42  further define the support surface  40  by being spaced to also accommodate the screen frame  24  such that the support surface  40  will receive the underside of the screen frame in juxtaposition. Intermediate cross members  44  also extend between the side rails  36 . The intermediate cross members  44  are positioned below the support surface. The mounting frame  34  further includes support cavities  46 . The support cavities  46  face inwardly from the side rails  36  below the support surface  40 .  
         [0022]    A retaining system including clips controlled by actuators retains the screens on the resiliently mounted housing. Two clips  48  per side per screen are contemplated in the preferred embodiment. The clips  48  are positioned at least along the side rails  36  to engage with the mounting flanges  26  of the screens  22 . The clips  48  are curved or bent metal plates with pins  50  welded thereto. The configuration may be considered as having an upper lever  52  and a lower lever  54 . The upper lever  52  further includes a hook portion  56 . The lower lever  54  includes a post  55  extending outwardly from the corner of the clip. Posts at either end may also be used where appropriate, such as to create a universal part. The pins  50  extend laterally from a position between the upper lever  52  and the lower lever  54 .  
         [0023]    The upper lever  52 , lower lever  54  and hook portion  56  are roughly defined by bends in the metal plate of the clip  48 . However, location of the various components can obviate the need for such bends and the device may take on other bends or constitute a simple flat plate. The exact lever configuration depends on the pivot location relative to the mounting flange  26  of an associated screen  22  and also depends on the location of the actuator discussed below. Generally, the upper lever  52  is considered above the pivot pins  50  while the lower lever  54  is below the pivot pins  50 . The upper lever  52  at its distal end, the hook portion  56 , includes round corners so that the screen frame  24  of a screen  22  slid along the side rails  36  will not hang up on one of the clips  48 . The round corners  58  will act as a cam to move the clips  48  from interference with the ends of the frames  24 .  
         [0024]    The pins engage sockets provided for pivotal mounting. Sockets are defined within the frame cross members  42 . The intermediate cross members  44  support brackets  59  which extend upwardly. These brackets also include sockets to either side to receive the pins of adjacent clips  48 . The brackets  59  are preferably removable. Depending on the fit, the ability to remove the brackets  59  may be used to allow assembly with the pins  50  welded to the plates of the clips  48 .  
         [0025]    The clips  48  are aligned so that they are substantially parallel to the adjacent portions of the mounting frame  34  to capture a screen frame  24  between each clip  48  and the upstanding wall  38  while the screen is positioned on the side rails  36 . The clips  48  engage the inwardly extending mounting flanges  26 . This engagement may be forced such that the support frames are pushed outwardly to further tension the screen cloth  28  when the screen  22  is fully mounted to the resiliently mounted housing  14 . Two clips  48  are associated with each side rail  36  of the mounting frame  34  to retain a given screen  22 .  
         [0026]    The actuators  60  are illustrated to be located within the support cavities  46 . Elastomeric retainers  62  retain the actuators  60  in position. The actuators  60  are pneumatic and each includes a thick base  64  to interlock with an elastomeric retainer  62 . An actuator contact  66  is connected to the base  64  by means of a flexible diaphragm  68 . The diaphragm  68  cooperates with the base  64  to define an inflatable body. The diaphragm  68  is relaxed in a retracted position but can be inflated to an extended position with the actuator contact forced outwardly against the lower lever  54  of the clip  48 . The actuators  60  may be a continuous tube or separately closed pneumatic devices associated with each clip  48 .  
         [0027]    A return device  70  is illustrated in FIG. 6. The support brackets  59  on the mounting frames  34  each carry a resilient element in the form of a compression spring  74  which engages the lower lever  54  on each of the adjacent clips  48  to either side of each bracket  59  on the intermediate cross members  44 . The spring  74  is in resilient deformation against the lower levers to insure that the clips  48  will take the retracted position when released for easy replacement and removal of the screens  22 . The posts  55  located at least at one end of each of the lower levers  54  of the adjacent clips  48  extend to and fit within the spring  74 . The adjacent clips  48  have the posts  55  at least at adjacent ends so that they will come together at the spring  74 . Each spring  74  and the adjacent posts  55  interlock to retain the clips  48  from moving laterally. In doing so, the spring  74  may keep the clips  48  in position with the pivot pins  50  retained in the sockets in the frame cross member  42  and the support bracket  59 .  
         [0028]    Accordingly, an improved screen mounting system in a vibratory screen separator is disclosed. While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art that many more modifications are possible without departing from the inventive concepts herein. The invention, therefore is not to be restricted except in the spirit of the appended claims.
A screen system employs a resiliently mounted housing, a vibration generator mounted to the housing, a mounting frame fixed to the resiliently mounted housing and a support surface. This system receives a screen including a screen frame and pre-tensioned screen cloth. The frame includes an inwardly extending mounting flange accessible from below the screen when placed in the housing. Clips pivotally mounted relative to the mounting frame include a first rounded lever extending upwardly to selectively engage the inwardly extending mounting flange. Second levers extend downwardly to cooperate with actuators. The actuators include inflatable bodies with contacts which, upon inflation, force the clips to engage the inwardly extending mounting flanges. This engagement retains the screen on a resiliently mounted housing and is able to further tension the screen in place.