Cloth Shrinkage

The critical in 5)ortance of filter cloth selection in filter press systems has been stressed in the literature [Regan, 1977], As discussed above, methods of filter cloth selection have been based on selection factors [Purchas, 1967, 1981]. These factors include textile fibre type, yam type, fabric geometry and weave pattern. Other factors include cloth shrinkage and stretching, filter cake release, cloth sur ce characteristics and cleaning. These added factors are considered below. 

Preshrinkage of brics is, therefore, widely practised in order to retain dimensional stability in service. Preshrinkage can be effected in a number of ways  

The duinkage process has to be carcfiilly controlled, in view of the large stmctural changes of to 15% dirinkage which can ensue in relaxed conditions. 

Spun le yams are reported to shrink less than conparable fiibric woven from fflament yams [Bosley, 1977]. This follows the sipping acticni of short fibres, one over the other, without major change in the overall yam dimenrion. 

---

The thermal and chanical nature of the gas stream effectively determines the type of fibre that is to be used. Table 3.1 identifies the more common types of fibres which are used in dust collection and also their basic limitations. For example, if the temperature of the gas stream is higher than can be sustained by the fibre, and the cost considerations preclude the possibility of gas cooling prior to dust collection, then alternative means of collection - perhaps by means of ceramic elements - will have to be sought. Depending on the duration of exposure, high temperatures may have several effects on the fibre, the most obvious of which are a loss in tenacity due to oxidation and less effective cleaning due to the cloth shrinkage. 

Depending on the type of filter device, additional requirements may be made of the cloth. For example, in a plate-and-frame press, the sealing properties of cloths are very important. In this case, synthetic cloths are more applicable staple cloths, followed by poly filament and monofilament cloths. In leaf filters operating under vacuum and pressure, the cloth is pulled up onto rigid frames. Since the size of a cloth changes when in contact with the suspension, it should be pretreated to minimize shrinkage. 

Ozone is being investigated for shrinkage prevention (182). Wool and blends of wool, cotton, and polyester have been finished to provide improved flame-retardant, durable-press, and shrinkage properties (183,184). Fabrics of these types are often used for uniforms or protective clothing (185). 

Figure 52-16 Use of too tightly woven, hard, reinforcing glass cloth, possibly with incorrect surface treatment. The resin in the surfacing has failed to wet it, causing delamination, then cracking due to cure shrinkage.

Fig. 12. SE images of Si02 replicas of cotton fibers/threads fixnn a cloth nafddn following calcinations (450 °Q and cold ashing n Pronounced shrinkage following calcination at high temperatures, b Hollow shape of the cotton thread after cold ashiiig.

Figure 1-31. Repeat units of some chlorofibres. temperature is low with considerable shrinkage at 70 C and have poor dyeability at moderate temperatures. These fibres are mainly used in filter cloths, flying suits (in which their property of non-flammability is an asset), curtains (owing to their resistance to degradation of light) and fishing nets (owing to their resistance to water). These fibres have regular round, dogbone or dumbell shaped cross-section and transparent, even and smooth. They are highly lustrous and silky in hand. 1.8.2 Poly (vinyl alcohol) fibres...

The shrinkage in length and width may be as much as 10% and this must be taken into consideration in determining the overfeed and the adjustment of the width. Most of the stenters make provision for overfeeds - 5% to + 40%. If the entry rollers feed the cloth at a slower speed, the cloth will be actually pulled by the... 

A typical clip chain mercerizing machine for woven cloth is shown in Fig. 9-6. In this type of mercerizing machine shrinkage is allowed in the primary stage of the... 

Figure 9-28. Shrinkage after multiple washings cotton fabric for professional clothings, 290 g/m. ...

Normally a square area is drawn on the heat-set material and measured. The marked cloth is boiled in soft water in the washing wheel for 30 min, centrifuged and air dried. The dimensions of the square are measured without ironing the dried fabric and the shrinkage is determined. A well set fabric should not show more than 1% residual shrinkage. 

Although cellulose is not thermoplastic, and rayon cannot be mechanically crimped and textured in the same way as synthetic fibers, a crimped fiber can be made by causing an imbalance in the uniformity and thickness of the skin during fiber production. Greater shrinkage of the skin in hot water, compared with shrinkage of the core, will cause the fiber to crimp. The skin effect in crimped rayon has been described by Sisson and Morehead [252]. Crimped rayon is wool like and is used alone or in blends with polyester, nylon, acetate, or wool to make carpets, upholstery, bedspreads, and clothing fabrics. 

Li X, Lu Y, Zhai L, Wang M, Li J, Wang Y. Analyzing thermal shrinkage of fire-protective clothing exposed to flash fire. Fire Tech 2015 51(1) 1-17. 

---