Abstract:
A screen panel for use in a vibrating screen device. The screen panel has a plurality of in-flow slots and cross-flow slots arranged in a regular pattern to provide enhanced open area for a given slot size.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a continuation application of U.S. patent application Ser. No. 12/597,089, filed Oct. 22, 2009, which is a national stage application of International Application Number PCT/AU2008/000698, filed May 19, 2008, which claims priority to AU 2007902745 filed May 23, 2007, their entire disclosures of which are incorporated by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates to a panel for a vibrating screen. In particular, it relates to a resiliently deformable panel suitable for use in a vibrating screen for separating particulate matter, particularly mineral ores. 
       BACKGROUND ART 
       [0003]    The use of vibrating screens for separating mineral ores is well known. Vibrating screens are used in three related applications: 10 classification; dewatering; and media recovery. Classification is a process of separating feed material into two or more controlled size ranges. Dewatering separates water from the feed material and typically requires a much finer screen than classification. Media recovery is similar to dewatering as the screen is used to recover fluid from the feed material. 
         [0004]    Historically the vibrating screens use screen decks of woven wire mesh to filter material by size. The woven wire mesh defines a large number of openings of a fixed size that allow material below the fixed size to pass through while other material moves across the screen. 
         [0005]    The sized material is referred to as underflow and the remaining material is referred to as overflow. There is typically a small amount of oversize material in the underflow due primarily to damage in the panels. There is usually a larger amount of undersize material in the overflow due to limits in the performance of the vibrating screen. The measure of performance of the vibrating screen depends on the purpose of the screen but common measures of performance are ratios between overflow, underflow, undersize and oversize. For instance, the quantity of undersize in overflow compared to the quantity of oversize in underflow may be an important consideration in some applications. 
         [0006]    An important factor in screen performance is ‘open area’. Open area is the percentage of the screen deck that is open to allow material to pass through. The open area is related to the slot size of the screen deck which is determined by the size of material to be screened. Typically slots of width from 500 micron to 2 mm will be up to about 15 mm long; slots with width from 6 mm to 12 mm will be about 30 mm to 35 mm long; slots with width around 15 mm to 20 mm will be 45 mm to 50 mm long and for slots with width above 20 mm the length may be 100 mm to 150 mm. In other words, the same basic screen design will generally have increasing open area with increasing slot size up to a limit where wearability becomes a problem. Increased open area means decreased ligament size (the panel material between slots) which means greater chance of damage due to wear. In conventional screen designs there is a trade off between wearability and open area. 
         [0007]    Screen panels often operate below stated performance because of reduced open area due to pegging. Pegging of screen openings occurs when material becomes stuck in the openings. Attempts have been made to address this problem by making the mesh flexible so that plugged material is released during vibration of the screen. For instance, U.S. Pat. No. 4,120,785, assigned to Mitsuboshi Belting Limited, describes a screen for a vibratory screening machine comprising a mesh of rubber members. Each rope member comprises a rubber covered tensile member of wire. This solution incurs significant manufacturing cost. 
         [0008]    Another variation has been to replace the wire mesh with polyurethane panels that provide better wear characteristics than wire mesh with similar flexibility. The polyurethane panels are made with slots having a relief angle (wider on the underside than the upper side) to assist with release of pegging material. 
         [0009]    A typical polyurethane panel is shown in U.S. Pat. No. 4,661,245, assigned to Fioris Pty Ltd of Australia. Each panel has a grid of square openings in a moulded polyurethane block. The panels can conversely be thought of as a grid of polyurethane ribs defining the openings. When considered in this manner it can be seen that the polyurethane panel is equivalent to the woven wire mesh but with improved wear properties. However, the polyurethane panels have typically not achieved the same open area as wire mesh. 
         [0010]    The polyurethane screen panels are made by injection moulding or air casting. In either case a mould must be produced and the screen panel cast from the mould. Persons skilled in the field will appreciate that each mould is expensive to produce. Furthermore, the challenge of machining the mould limits the design to simple aperture shapes, such as the square apertures described in the Fioris patent. 
         [0011]    To further improve screen panel performance it was seen as desirable to manufacture aperture shapes other than square. Apertures formed from zigzag ribs are described in U.S. Pat. No. 4,892,767, assigned to Screenex Wire Weaving Manufacturers (Proprietary) Limited of South Africa. The Screenex patent describes a screen panel moulded from polyurethane and comprising a plurality of zigzag ribs extending between sides opposing of the panels so as to define a regular arrangement of diamond-shaped screening apertures. The ribs are resiliently deformable to facilitate unblocking of the apertures during screening operations. However, it will be appreciated from a careful consideration of the patent that the apertures are still square but merely rotated 45 degrees. 
       SUMMARY 
       [0012]    It is an object of the present invention to provide screen panels for vibratory screening machines having improved performance compared to known screen panels. 
         [0013]    It is a yet further objective to provide the public with a useful alternative to known screen panels for vibratory screening machines. 
         [0014]    Further objects will be evident from the following description. 
         [0015]    In one form, although it need not be the only or indeed the broadest form, the invention resides in a screen panel of resiliently deformable material comprising a plurality of in-flow slots and cross-flow slots forming a regular pattern. 
         [0016]    Suitably the in-flow slots and the cross-flow slots form a ‘T’ shape. In another form the in-flow slots and the cross-flow slots form a ‘cross’ pattern. 
         [0017]    In a preferred form there are multiple in-flow slots and cross-flow slots forming a compound pattern. 
         [0018]    The screen panel suitably has an open area of greater than 15%. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    To assist in understanding the invention preferred embodiments will now be described with reference to the following figures in which: 
           [0020]      FIG. 1  shows a vibrating screen machine; 
           [0021]      FIG. 2  shows a first embodiment of a screen panel having cross-flow and in-flow slots; 
           [0022]      FIG. 3  shows an enlarged section of the screen panel of  FIG. 2 ; 
           [0023]      FIG. 4  is a chart comparing screen open area; 
           [0024]      FIG. 5  shows a second embodiment of screen panel design; and 
           [0025]      FIG. 6  shows a third embodiment of screen panel design. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    In describing different embodiments of the present invention common reference numerals are used to describe like features. 
         [0027]    Referring to  FIG. 1  there is shown a conventional vibratory screening machine  10  having a frame  11  and moving screen deck  12 . A vibrator  13  vibrates the screen deck  12 . Feed material is delivered at feed point  14  and moves across the screen deck  12 . Feed material moves from the feed point  14  to the overflow  15 . Sized material falls through the screen  12  to underflow  16 . The screen deck  12  is formed from multiple screen panels which are fixed into the frame by a suitable manner. 
         [0028]    A first embodiment of a screen panel that provides cross-flow and in-flow slots is shown in  FIG. 2 . In-flow slots are slots aligned with the direction of travel of material across the panel and cross-flow slots are slots aligned across the direction of travel. The screen panel  20  consists of a two plain sides  21  and two engagement sides  22 . The engagement sides  22  have grooves  23  that engage with corresponding spigots (not shown) in the screen deck to hold the screen panels in position. In the particular embodiment of  FIG. 2 , the screen panel  20  is divided into four segments  24  by ribs  25  and each segment  24  has a repeating pattern of compound slots  30 , shown in greater detail in  FIG. 3 . 
         [0029]    The screen panel  20  is preferably moulded from polyurethane to provide appropriate flexibility and wear characteristics. Although other materials are known the inventor has found that polyurethane is most suitable. 
         [0030]    Each compound slot  30  is a combination of longitudinal (in-flow) slots  31  and transverse (cross-flow) slots  32 . While a specific slot pattern is displayed in  FIG. 3 , the invention is not limited to the precise slot pattern. However, it will be appreciated that the slot pattern provides for a larger open area for a given slot size without the wearability problems that would occur if all slots were parallel. The improved wearability is achieved because the material between the slots contains more bulk than would be achievable with parallel slots. 
         [0031]    The material between the slots is often referred to as ligament. Reduced ligament size means less tensile strength so that the ligaments tear prematurely or wear at an accelerated rate, thus significantly reducing screen life. The slot arrangement shown in  FIG. 2  maintains ligament size but increases open area. 
         [0032]    As seen in Table 1 (Sample 1 column) an open area of over 30% is achieved with a slot width of 1.25 mm. This is a significantly higher open area than in any prior art screen panel. The prior art panels listed in table 1 are: 1—Ludodeck from Ludiwici Pty Ltd; 2—PIPO TWO® from Johnson Screens®; 3—PIPO TWO Conslot from Johnson Screens®; 4—Multotec Standard from Multotec Manufacturing Pty Ltd; 5—Multotec HiFlo from Multotec Manufacturing Pty Ltd; 6—Screenex Maxiflow from Screenex Wire Weaving Manufacturers (Proprietary) Limited. The percentage open area of each screen for a given slot width is shown. The data is charted in  FIG. 4 . 
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Slot 
                 Open Area (%) 
               
             
          
           
               
                 Width 
                 Prior 
                 Prior 
                 Prior 
                 Prior 
                   
                   
                   
               
               
                 (mm) 
                 art 1 
                 art 2 
                 art 3 
                 art 4 
                 Prior art 5 
                 Prior art 6 
                 Sample 1 
               
               
                   
               
             
          
           
               
                 0.5 
                 9 
                 9 
                 13.5 
                 10.1 
                 14.5 
                 13.8 
                 18.1 
               
               
                 0.75 
                 12.1 
                 12 
                 19 
                 13 
                 15.8 
                 14.7 
                 23 
               
               
                 1.0 
                 14.3 
                 14 
                 20.8 
                 13 
                 16.9 
                 17 
                 27 
               
               
                 1.25 
                 18.6 
                 15 
                 23.5 
                 16.1 
                 20.1 
                 19 
                 30.5 
               
               
                   
               
             
          
         
       
     
         [0033]    A second embodiment of a screen panel  50  having in-flow slots  51  and cross-flow slots  52  is shown in  FIG. 5 . The second embodiment utilises a cross configuration having equal in-flow and cross-flow slots. 
         [0034]    A third embodiment  60  is shown in  FIG. 6 . The third embodiment uses slots having a ‘T’ shape. The third embodiment is similar to the first embodiment in that the in-flow slots  61  are aligned whereas the cross-flow slots  62  are staggered. The embodiment of  FIG. 6  demonstrates the versatility of the invention as it will be seen that the slots of two panels are the minor image of the other two panels. 
         [0035]    By way of comparison, table 2 shows percentage open area for the embodiments of  FIG. 5  and  FIG. 6  and of three prior art screen panel designs. The three prior art designs are a simple square, a slot design and a Screenex panel design. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Aperture 
                 Open Area (%) 
               
             
          
           
               
                 (mm) 
                 FIG. 5 
                 FIG. 6 
                 Slot 
                 Square 
                 Prior art 6 
               
               
                   
               
             
          
           
               
                 6 
                 35 
                 35 
                 30 
                 22 
                 30 
               
               
                 8 
                 38 
                 38 
                 34 
                 24 
                 34 
               
               
                 10 
                 40 
                 40 
                 35 
                 26 
                 35 
               
               
                 12 
                 40 
                 40 
                 36 
                 28 
                 36 
               
               
                   
               
             
          
         
       
     
         [0036]    Throughout the specification the aim has been to describe the invention without limiting the invention to any particular combination of alternate features.