Fabric constructions and properties

Three traditional weave patterns are used for filter cloths - plain, twill and satin weaves, together with a link constmction. 

The weight of multifilament cloths varies from about 100 g m to as high as lOOOg m 2 the heavier constmctions are used for more arduous duties such as vertical automatic filters. Some typical characteristics of multifilament cloths are shown in Table 2.6. 

Fabrics produced from staple spun fibres usually have a weight between about 400 and 700 g m (see Table 2.7), and find applications in conventional filter presses, vacuum leaf, pressure leaf, disc and rotary dmm filters. 

Fibre and Air permeability Weight Thickness Typical filter suitability 

Satin 7200 335 635 Belt filter, drum filter, leaf filter, filter press 

This is the most basic weave of all woven stractures that provides the framework for the tightest and most rigid of all single-layer filter fabrics (see Fig. 3.19). Because of the sinusoidal path that the yams follow, this weave is particularly suitable for flexible yams of the multifilament and short staple-fibre types. The weave is also ideally suited to applications where thread displacement, due for example to high internal pressures, may otherwise be experienced. 

Usually produced in simple 2/2 or 2/1 style, twill weaves enable more weft threads per unit length to be crammed into the fabric than the preceding design (plain weave), as shown in Fig. 3.23. As a consequence, this facilitates the production of fabrics of higher area density and hence greater bulk, features which are particularly suited 

These weaves are frequently, though not exclusively, found in belt filters, either of the vacuum, continuous multi-roll press or of the vertical automatic pressure type. Owing to the interlacing pattern of the threads, it is possible to create fabrics with a measure of a solidity and stability that are ideally suited to filters of the types identified. On the debit side, the cost of weaving such high-density fabrics tends to preclude their use in all but a limited number of niche appUcations. 

As shown in Fig. 3.26, link fabrics are produced by a novel technique in which polyester monofilaments are wound into spiral form then meshed with similar monofilaments, which are spiral wound in the opposite direction. The spirals are subsequently held together by a straight monofilament. By virtue of this form of construction, it is possible to produce endless filter belts without the need for special joining techniques such as clipper seams, which are often the weakest point in a filter belt. 

Because they are made from relatively coarse monofilaments of around 0.7 mm diameter, link constructions are generally of an open nature and are designed for the filtration of chemically flocculated sludges, these being relatively easy to separate but requiring efficient drainage. From the cross-sectional view (Fig. 3.27), it will also be 

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