One or more woven wire screens have been used in shaker or vibrating screen apparatus to size material passing through the woven wire screens. Known woven wire screens typically consist of a plurality of interwoven weft and warp wires forming a plurality of openings for permitting suitably sized material to pass through the screen. The openings can be square or rectangular. Alternatively, the screen can be formed as a long slot screen where the warp wires are maintained in spaced parallel relation by weft wires arranged in groups of three at spaced intervals along the length of the warp wires.
Previously known woven wire screens suffer from significant drawbacks. For example, known woven wire screens have experienced rolling of one or more wires. The problem of rolling is depicted in FIG. 1. Specifically, weft wires 2, 4, 6, 8 and 10 of woven wire cloth A have been undesirably rolled during the manufacturing process. This is problematic in that the size of the openings surrounded by one or more rolled wires is significantly different from the size of openings surrounded by non-rolled wires. This is readily evident from a comparison of opening 12 bound on opposite sides by two rolled weft wires 2 and 4 with opening 14 bound on all four sides by non-rolled wires. To properly size product or material, it is imperative to have openings in woven wire screens that conform precisely to predetermined sizes. Any variance in the size of the openings due to the manufacturing process can significantly degrade the performance of the woven wire screen. It should be noted that the amount of roll will vary further degrading the performance of the woven wire screen.
Rolling of a wire results from exceeding the yield point of the wire during assembly of the woven wire screen. Conventional thinking has been along the lines that forming woven wire screens with shallow crimps (i.e., higher knuckle forces and higher preloads) improves the longevity of the woven wire screen. However, rolling can occur especially if the configuration of the wire is modified to improve the through put of the woven wire screen. This is due at least in part to the fact that shallow crimps require less side forces to displace the corresponding wire.
Conventional woven wire screens have also been unable to achieve significant additional through put by providing additional open area. Specifically, increasing the open area of a screen has previously resulted in additional through put that is approximately equal to the increase in the open area. For example, if the open area is increased by 3% then the additional through put previously achieved would be approximately 3%. This is undesirable as the efficiency of conventional screens is limited in that the percentage of additional through put is limited to approximately the same percentage of the additional open area. Moreover, the configuration of conventional wires can cause the product to deflect upwardly even though the product is suitably sized to pass through the screen. This is particularly prevalent with screens having round wires. Further, previously known screens with wires having a cross-sectional height greater than the cross-sectional width have experienced some upward movement because the difference between the cross-sectional height and the cross-sectional width has not been great enough to eliminate or dramatically reduce upward movement of particles. This is undesirable as it can significantly reduce the efficiency of the woven wire screen.