Fabric filters fibres used

PTFE, known under the trade names Teflon and Fluon, is resistant to all chemicals, except molten alkalies and fluorine, and can be used at temperatures up to 250°C. It is a relatively weak material, but its mechanical strength can be improved by the addition of fillers (glass and carbon fibres). It is expensive and difficult to fabricate. PTFE is used extensively for gaskets and gland packings. As a coating, it is used to confer non-stick properties to surfaces, such as filter plates. It can also be used as a liner for vessels. 

Wang, X.Y., Gong, R.H., 2006b. Thermally bonded nonwoven filters prepared using bicomponent PP/PET fibre II. Relationships between fabric area density, air permeability and pore size distribution. J. Appl. Polym. Sci. 102 (3), 2264-2274. 

Fabric filters can cope with most industrial gas cleaning problems economically and efficiently. Filtering of hot gases before heat exchanging, catalytic oxidation in combination with bag filters, electrostatic precipitators in fabric filters with conductive filter media, dry scrubbing to bind the gaseous components, anti-static performance of filter materials, adhesive dust repellent finishes, and chemical protection of fibres are just some of the uses. 

Cellulose acetates are by far the most important organic esters. The diacetate has DS = 2.4 and is fabricated either in filament form for fibres or in powder form to melt. Diacetate filaments are obtained by dissolution in acetone, extrusion through a spin and then evaporation of the solvent. The obtained fibres are used in textiles (called simply acetate ) and in cigarette filters (tow). The triacetate (DS = 2.9) finds application in brilliant textiles easy to dye. 

As mechanical agitation is important to effect the bio-fmishing, only selected processes and machines can be used, for example tubular fabric preferably cut to open width and treated in open width washers. In the rope form the loosened fibre particles are filtered out by the fabric and cannot easily be removed. The pad-batch process, jig or package dyeing machines are not effective in bio-fmishing. 

These form a small group which have limited uses for specialized purposes. Asbestos fibre can be spun and made into fireproof fabrics or protective clothing. Fibrous glass is made in substantial and increasing quantities and it is used for insulation tape, industrial filter cloths, and for many other purposes when bonded with polystyrene or other plastic substances. 

Styrene was supplied by Monsanto Chemicals (Aust.) Ltd. and was purified by column chromatography on alumina. The cellulose used was Whatman 41 filter paper wool was plain weave fabric made from 21 y diameter Merino wool fibres polyethylene (low density) was supplied as film (0.005") from Union Carbide polypropylene was Isotactlc, doubly oriented film (0.002") ex-Shell PVC film (0.04") was commercially available GVan material. 

If impurities cannot be removed with bag filters, filter cartridges or candles are used (Fig. 7.14). The filter cartridges are inserted in individual housings or, in large-scale equipment, up to 24 cartridges are inserted side by side or one above the other and held in place with quick-release mechanisms. Resin-bonded, sintered synthetic micro fibres and metals are used as filter material. The fineness of the filter fabric (5-100 pm) determines the filtration effect. 

Filter fabrics, especially nonwoven fabrics, which are produced from short staple fibres, invariably possess surfaces with protruding fibre ends. Since such protrusions may inhibit the cake release by clinging to the dust, it is a common practice to remove them. This is achieved by singeing, a process in which the fabric is passed, at relatively high speed, over a naked gas flame, or, in another technique, over a heated copper plate. The heat of the flame causes the fibres to contract to the surface of the fabric where, in the case of thermoplastic fibres, they form small hard polymer beads (Fig. 3.8). Singeing conditions (i.e. speed and gas pressure) will normally be adjusted according to polymer type and the intensity required by either the end-use application or the individual manufacturer s preference. 

The fabric substrate used for the filter media will need to provide certain characteristics, dependent on the application. The typical properties required include abrasion resistance, stretch resistance, dimensional stability, and resistance to flex fatigue. All these performance criteria can be assessed by using suitable test methods. The fabric will also be tested for correct warp and weft sett, air permeability, thickness, density, and fabric tensile properties. All the factors will affect the performance of the filter as they are directly related. If woven fabrics are considered, the porosity will be directly related to the sett and therefore air permeability. The combinations of the fibre types, fabric constructions, and coating substrate will provide the filter manufacturer with a range of properties for use in a range of appUcations. 

Because of the wide diversity of thermal and chemical conditions that prevail in dust collectors, the correct choice of fibre type is the most fundamental of all considerations when designing or selecting the filter fabric. A selection of the more common fibre types that are used in dust collection and their properties is shown in Table 7.2. 

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