Monofilaments filter media

Rushton A. and Griffiths P.V.R., 1971. Fluid flow in monofilament filter media, Trans IChemE, 49, 49-59. 

Analytical determination of the hydraulic resistance of the medium is difficult. However, for the simplest filter medium structures, certain empirical relationships are available to estimate hydraulic resistance. The relationship of hydraulic resistance of a cloth of monofilament fiber versus fiber diameter and cloth porosity can be based on a fixed-bed model. 

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.. 

Textiles, as a woven cloth or a nonwoven fabric, are probably the most common industrial filter medium, and are made from natural (cotton, silk, wool) and synthetic fibres. Wire cloths and meshes are also widely used in industrial filtrafions, produced by weaving monofilaments of ferrous or non-ferrous metals the simpler plain weave is used for sieving and sizing operations, and the more complex weaves such as Dutch twills are used on pressure and vacuum filters. At the small scale, particularly for laboratory use, filter papers are common, made from fibrous cellulosic materials, glass fibre or synthetic polymers these papers are made using developments from conventional paper manufacturing processes. 

The properties of a fabric, especially as regards its behaviour as a filter medium, depend very much on the way in which the yams are woven together. Many properties, however, are intrinsic in the nature of the basic fibre or filament, and of the way in which it is made up into a yam. There are three basic types of yam in wide use for filter media monofilament, which is a single continuous filament of synthetic material (or silk) multifilament, which comprises a bundle of identical continuous filaments that may or may not be twisted together and staple, which... 

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. 

Flow through the clean medium will be determined by the geometric characteristics imposed on the medium by the weaver, in fitrming various patterns (plain, twill, sateen, etc.) fi om basic yams. In woven cloth, the latter are either sohd monofilaments, or are multifilamanets (which can be further subdivided into continuous or staple-fibre constmetions, depending on the type of filament used). In some cases, the sur ce of the medium may be modified to improve its ability to release the filter cake, etc. Nonwovens are paper-like, random arrays of fibres which can be obtained in many forms uniform fibres, mixed and conposhe pads, etc. These media, like wovens, can be supplied sur ce modified. 

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