Metallic cloths

RoUer-top cards have five to seven sets of workers and strippers to mix and card the fibers carried on the cylinder. The multiple transferring action and re-introduction of new groupings of fibers to the carding zones provides a doubling effect which enhances web uniformity. Stationary-top cards have strips of metallic clothing mounted on plates positioned concavely around the upper periphery of the cylinder. The additional carding surfaces thus estabhshed provide expanded fiber alignment with minimum fiber extraction. 

Cotton cloths are sometimes treated with metallic salts (copper sulfate) to improve their corrosion-resistant qualities. Such cloths are in the usual cotton filter cloth grades, and while they are not equivalent to metallic cloths, the treatment does materially prolong the life of the cotton fiber. When dealing with metallic cloths, the following terms are important ... 

Precipitates or salts are used when corrosive liquor must be filtered, and where there is no available medium of sufficient fineness that is corrosion-resistant and will not contaminate the cake. In these cases, precipitates or salts are used on porous supports. In the filtration of caustic liquors, ordinary salt (sodium chloride) is used as the filter medium in the form of a precoat over metallic cloth. This procedure has the advantage that the salt medium will not be detrimental to either the cake or the filtrate if inadvertently mixed with it. 

Calendering can also be used to apply a plastic surface to a substrate web such as metal, cloth, or paper. 

The amount of imbibition applied at each mill is approximately equal to the amount of water applied to the fourth mill or to the penultimate mill in a differently numbered tandem. The expressed juice is screened through perforated metal screens with l-mm diameter openings. Additional screening may be provided by stationary or vibrating metal cloths. 

Septa may be made of metal, natural, or synthetic yams. Plain, twill, and dutch weaves are available in the metal cloths. In the natural and synthetic fiber cloths, plain, twill, chain, and satin weaves in monofilament, multifilament, and staple yams have been used. 

Generally, any septum having an opening of less than 0.005 in. should be satisfactory for the medium flow rate filter aids. In metal cloths the most commonly used weave is 24 X 110 single dutch with 0.016 in. x 0.011 in. wire. A 60 x 60 twill with 0.011 in. wire and a 70 X 80 twill with 0.007 in. wire are also satisfactory. Keep in mind that mesh does not necessarily indicate the size opening it also depends upon the wire diameter. 

The weaker lasers are used in such systems as CD players and recorders and in communications and distance-measuring devices. The more-intense laser beams are used for welding and cutting of metals, cloth, skin, etc. and have even been examined as a means of inducing thermonuclear fusion reactions. 

The main types of filtering centrifuges are suspended batch machines, which are discontinuous in their operation automatic short-cycle batch machines and continuous conveyor centrifuges. In suspended centrufuges the filter media are canvas or other fabric or woven metal cloth. In automatic machines fine metal screens are used in conveyor centrifuges the filter medium is usually the slotted wall of the basket itself. 

In industrial filtration a common filter medium is canvas cloth, either duck or twill weave. Many different weights and patterns of weave are available for different services. Corrosive liquids require the use of other filter media, such as woolen cloth, metal cloth of monel or stainless steel, glass cloth, or paper. Synthetic fabrics like nylon, polypropylene, and various polyesters are also highly resistant chemically. 

Models 2400 (aortic) and 6400 (mitral) Starr-Edwards composite track valve prostheses are closed single-cage hollow metallic ball valve prostheses. The cage struts, poppets, and metallic closure supports on the inner aspect of the base ring are made of Haynes alloy No. 21 (Stellite alloy No. 21) and are easily seen radiographically. The inner aspect of the cage struts has no cloth covering and hence no metal-cloth contact. 

In some instances, precoats are used, not because of danger to filter cloth clogging, but to permit the use of a coarser filter medium such as metallic cloths. This can extend operating life or improve corrosion resistance. 

Perforated sheets and screens are used for coarse separation, as supports for filter cloths or as filter aids. Metallic cloths are characterized by the method of wire weaves as well as by the size and form of holes and by the wire thickness. Metallic cloths may be manufactured with more than 50,(XX) holes/cm and with hole sizes less than 20... 

Cellulose fiber is applied to cover metallic cloths. The fibers form a highly compressed cake with good permeability for liquids, but a smaller retention ability for solid particles than that of (hatomite or perlite. The use of cellulose is recommended only in cakes where its specific properties are required. These properties include a lack of ashes and good resistance to alkalies. The cost of cellulose is Wgher than those of diatomite and perlite. 

Pdndpal types of filteriiig centrifoges are suspended batch machines, automatic short-cycle batch machines and continuous cmiveyor centrifuges. In suspended centrifoges, the filter medium is usually canvas or a similar fabric, or woven metal cloth. Automatic machines employ fine metal screens. The filter medium in conveyor centrifoges is usually (he slotted wall of the bowl itself. 

Some widely used filter media are twill or duckweave heavy cloth, other types of woven heavy cloth, woolen cloth, glass cloth, paper, felted pads of cellulose, metal cloth, nylon cloth, Dacron cloth, and other synthetic cloths. The ragged fibers of natural materials are more effective in removing fine particles than the smooth plastic or metal fibers. Sometimes the filtrate may come through somewhat cloudy at first before the first layers of particles, which help filter the subsequent slurry, are deposited. This filtrate can be recycled for refiltration. 

The University of Massachusetts Dartmouth owns a Davis and Furber sample woolen carding machine. The machine is also known as a roller top card. The machine was reclothed by the Redman company with aggressive metallic clothing. This means the drums and rollers in the machine were given new surfaces of metallic materials not unlike a continuous saw blade wrapped around the cylinders. The purpose of reclothing the machine was to simulate the gametting/ willowing processes. 

Obvious uniformity is found in simple form with plain-weave metal cloth of light gauge wire. As the gauge of the wire becomes heavier and the weave is changed to a twilled or Dutch-type weave, we have a more elaborate medium that is generally used for filtration. The nature of the holes is more complex and more difficult to recognize with the unaided eye. Woven fabrics become more complicated due to the flexible nature of yams, and therefore it is more difficult to try to define the size of the hole in a woven fabric. The same is tme for media with random stmcture, such as felts, paper, fibrous and porous material. 

Filter fabrics are mainly woven in four common weaves plain, twill, plain reverse Dutch and satin. The first three are overlaps from wire cloth weaves but may have slightly different characteristics when put into the framework of woven non-metallic cloth. The weaves will not be detailed again here. The fourth weave is the satin weave where the shute (or warp) fibre passes over several warp (or shute) fibres, then under one in an alternating pattern. Figure 8.3 shows an over three-under one pattern for the satin weave (three shaft satin) see also Table 8.2. 

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