Wire cloths

Two basic forms of twilled Dutch weave are produced by combinations of warp and weft wires of different diameters. The use of heavy warp wires (Dutch twill weave) permits production of fine grades of woven wire cloths which have very smooth surfaces on both sides, but these cloths have a relatively high flow resistance. With heavy weft wires (reverse Dutch twill weave) the flow resistance is less but there is a corresponding decrease in micron retention characteristics and both sides of the cloth have rougher surfaces. 

Numerous variants of these basic weaves exist, with many being specific to particular suppliers of wire cloths - Purchas and Sutherland (2002) summarise 

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The Stedman-type column is shown in Fig. 11, 56, 25. The characteristic features are (i) the use of a fine stainless steel wire cloth formed into conical discs, and (ii) an accurately fitting Pyrex glass jacket, produced by shrinking Pyrex glass on mandrels to the required inside dimensions. Modifications incorporating a silvered vacuum jacket and an electrically-heated jacket are marketed. This column is said to possess high efficiency but is expensive. It is generally employed in conjunction with a total-condensation variable take-off still head. 

The fines are classified out of the feed and pass through the air classifier into a baghouse, from which they are fed onto sieves, containing 165 p.m—0.124 mm (105—120 mesh) stainless steel wire cloth. Oversi2e mica from the sieves returns to the mill s grinding chamber for further grinding. 

External-Cake Tubular Filters Several filter designs are available with vertical tubes supported by a filtrate-chamber tube sheet in a vertical cylindrical vessel (Fig. 18-115). The tubes may be made of wire cloth porous ceramic, carbon, plastic, or metal or closely wound wire. The tubes may have a filter cloth on the outside. Frequently a filter-aid precoat will be applied to the tubes. The prefilt slurry is fed near the bottom of the vertical vessel. The filtrate passes from the outside to the inside of the tubes and into a filtrate chamber at the top or the bottom of the vessel. The sohds form a cake on the outside ofthe tubes with the filter area actually increasing as the cake builds up, partially compensating for the increased flow resistance of the thicker cake. The filtration cycle continues until the differential pressure reaches a specified level, or until about 25 mm (1 in) of cake thickness is obtainea... 

FIG. 18-117 Section of precoated wire filter leaf. (Multi Metal Wire Cloth.)... 

Another mechanical shaker is the End-Shak, made by the Newark Wire Cloth Co. Sieves used are Newark test sieves, made to conform with the U.S. standard series. 

Screen Surfaces The selection of the proper screening surface is veiy important, and the opening, wire diameter, and open area should all be carefully considered. The four general types of screening surfaces are woven-wire cloth, silk bolting cloth, punched plate, and bar or rod screens. 

Catalogs of wire-cloth manufacturers should be consulted for further study of the different types of wire-cloth specifications. 

Sieves are often referred to by their mesh size, which is the number of wires per hnear unit. The U.S. Standard Sieve Series as described by the American Society of Testing and Materials (ASTM) document E-11-87 Standard Specification for Wire-cloth Sieves for Testing Purposes addresses sieve opening sizes from 20 [Lm (635 mesh) to 125 mm (5.00 in). Electroformed sieves with square or round apertures and tolerances of 2 [Lm, are also available. 

Woven wire cloth is available in a broad range of alloys with mesh counts as coarse as 1" in most alloys and as fine as 635 in some alloys. The following is a list of alloys normally used ... 

The carbon bed can be supported by glass wool, wire cloth, etc. Columns and fixtures can be constructed from glass, plastic, reinforced fiberglass, or metal. Borosilicate glass is commonly used. It is essential that all columns used in the pilot system have at least the same internal diameter. 

Bolting grade (wire cloth) Weaves that are uniformly woven of stainless steel to provide high strength and the largest possible pore openings. 

Market grade (wire cloth) Screens that meet general industrial specifications and have a low percentage of open area. 

Mercaptans Compounds containing sulfur which have an extremely offensive skunk-like odor. Also sometimes described as smelling like garlic or onions. Mesh count The number of threads in a linear inch of fabric/wire cloth. 

Mill grade (wire cloth) Stainless steel screens that have moderate open area and good strength. 

Surface media Captures particles on the upstream surface with efficiencies in excess of depth media, sometimes close to 100% with minimal or no off-loading. Commonly rated according to the smallest particle the media can repeatedly capture. Examples of surface media include ceramic media, microporous membranes, synthetic woven screening media and in certain cases, wire cloth. The media characteristically has a narrow pore size distribution. 

Select a 1-in. x 1-in. (center line) x 0.063-in. wire cloth -with voidage of 87.8%. 

Cotton Wool I O f Polypropylene Nylon Nomex (hl h temp. Nylon) Rayon Dynel Teflon Paper 1 Sintered Metal Woven Wire Cloth Porous Ceramics... 

Fine Series1 — Nominal Dimensions, Permissible Variations, and Limits for Woven Wire Cloth of Standard Sieves... 

ASTM Ell-01 Standard specification for wire cloth and sieves for testing purposes. ASTM Book of Standards Volume 14.02, 2001. 

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