Filtration with woven wire

A wide variety of screens and meshes are available, ranging from fine photoetched or electroformed perforated screens to the heavy duty wedge wire screens used in centrifuge and high pressure screw press construction. Simple sieves and coarse screens were used as early as the sixteenth century for processing metal ores. Modern woven wire screens are precision made cloths with aperture sizes as small as 20 pm (smaller aperture sizes are supplied by some manufacturers) for industrial separations in filtration, clarification and extraction. Plastic meshes and plastic coated metal meshes are finding an increasing number of applications in separation processes. 

Media made from metals have already been mentioned, in Section 2C, in the form of sheets and tubes made from metal fibres and powders, usually sintered together to retain their structure. By far the greatest amount of filter media made from metal, however, is in the form either of woven wire or perforated sheets, which are covered in this part of Section 2, with the conmaon features of high strength, and corrosion and abrasion resistance conveyed by the basic material of construction. The other conunon feature, of great importance to their use for filtration, is that... 

For filtration purposes, the most widely used forms of woven wire are the Dutch or hollander weaves, wherein the warp and weft are of different diameter, generally with a corresponding difference in the relative numbers of warp and weft wires. If the warp wires are thicker, the result is the plain Dutch weave the alternative is for the weft wires to be the thicker, giving the reverse plain Dutch weave . 

The use of a woven scrim, whilst not employed in every case, provides the non-woven with stability and the necessary tensile characteristics in order to withstand the stresses imposed by the predominantly pulse cleaning mechanism, whereas the batt provides the necessary filtration efficiency and also a measure of protection for the base cloth from abrasion caused by constant flexing against the cage wires. Depending on the tensile specification of the finished nonwoven, the area density of scrims is usually in the range of 50-150 gm". ... 

Obvious uniformity is found in simple form with plain-weave metal cloth of light gauge wire. As the gauge of the wire becomes heavier and the weave is changed to a twilled or Dutch-type weave, we have a more elaborate medium that is generally used for filtration. The nature of the holes is more complex and more difficult to recognize with the unaided eye. Woven fabrics become more complicated due to the flexible nature of yams, and therefore it is more difficult to try to define the size of the hole in a woven fabric. The same is tme for media with random stmcture, such as felts, paper, fibrous and porous material. 

---