Monofilaments filter cloth properties

Hongxiaiig, 1991] refer to a cake moisture reduction to less than 25% as being necessary for effective cake discharge. Low moistures in variable chamber pressing of dyestuffs, metallic hydroxides and stearates followed the use of monofilament polyester cloth calendered to reduce the screen size to 30 pm [Reid, 1974], as mentioned above. Carleton and Heywood [1983] have discussed the fundamental aspects of filter cake properties and cake discharge mechanism. The effectiveness of discharge will dq>end on ... 

Saran monofilament is used in automobile seat covers and bus and restaurant upholstery. Saran has also been made into filter cloths, cordage, and industrial brushes. Its strength, aging properties, and resistance to bacterial and insect attack make it very useful for insect screens. 

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. 

In selecting cloths made from synthetic materials, one must account for the fact that staple cloths provide a good retentivity of solid particles due to the short hairs on their surface. However, cake removal is often difficult from these cloths - more than from cloths of polyfilament and, especially, monofilament fibers. The type of fiber weave and pore size determine the degree of retentivity and permeability. The objective of the process, and the properties of particles, suspension and cake should be accounted for. The cloth selected in this maimer should be confirmed or corrected by laboratory tests. Such tests can be performed on a single filter. These tests, however, provide no information on progressive pore plugging and cloth wear. However, they do provide indications of expected filtrate pureness, capacity and final cake wetness. 

The fiber cloth is the deciding ctor in the success or failure of all press operations. In view of the wide range of process variables involved in the filtration process, it is virtually in ossible to select a filter medium that will satisfy all process requirements and the usual limited time scale available for cloth selection is used to find an acceptable medium, i.e. one that will satisfy most, if not all of the requirements. In this reject, one particular requirement (e.g. filtrate clarity) may have to be relaxed, if other specifications (e.g. filtrate rate, absence of blinding) are to be maximised. Thus the more open weave Mcs will be superior in nonblinding characteristics, but may have poor particle retention. The latter will in rove in the order monofilament < muldfilament < staple fibre. Tabulated information is presented in Tables 4.2,4.3 and 4.4 below on the effect of yam properties, weave patterns, etc. on the processes of cake release, productivity, resistance to blinding, etc.. 

This division of flow has technical inq>ortance in those circumstances where the fine particles present are small enough to follow the flow into the yam. Once inade the yam, removal of these particles is effected with great difficulty. A tightfy twisted, closely woven cloth will approach the constractional and filtration characteristics of a monofilament cloth hut also will generally exhibit better mechanical properties. The effect of cloth constmction is discussed in detail below in the section dealing with mathematical models of flow in filter fabrics. 

Synthetic monofilament fabrics, because of their ductility and manory, may be flexed repeatedly without work hardening and fatigue. They may be folded or dented with less chance of damage compared with a metal cloth, and they are lighter in weight. Some appfications require the filter medium to have the physical properties of the synthetic monofilament, but with a metallized surface for static electricity dissipation. Accordingly, a metallized polyester monofilament fabric is produced coated with a 2 pm thickness of luckel. 

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