Dutch Twill Weaves

Table 11.2 Typical Flow Opening Sizes and Wire Diameters for Common Size Dutch Twill Weave Screens...

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. 

Weave choice should take account of both filtration and medium cleaning (see Table 2.9). Mechanical stress during operation or cleaning may require use of higher strength wire cloth, such as the Dutch twill weave. 

FIGURE 2.17 Three Dimensional Models of (a) Twilled Square, (b) Plain Dutch, and (c) Dutch Twill Weave Styles. Warp wires veer southeast (shown in red dark gray in print versions) and shute wires veer northeast (shown in gray light gray in print versions), bopp.com. 

The complex 3D pore structure can be modeled as the average of an ensemble of simple vertical capillary tubes. In reality, the Dutch Twill weave pattern creates a tortuous path and complex shaped pore. 

FIGURE 3.11 Friction Factor versus Screen Reynolds Number for Dutch Twill Weaves. 

As speculated in Chapters 4 and 5 it is believed that the shape of the actual pore structure is a secondary influence (the primary influence being the fineness of the screen) on the effective pore diameter. For example, for Dutch Twill meshes, these openings are complex 3D structures. The equilibrium L/V interface shape is complex and it depends on the size and packing of the wires. If it were possible to observe microscopically a L/V interface within a Dutch Twill weave, it might be possible to imderstand why the 450 X 2750 outperforms the 510 x 3600. Meanwhile, it is much more efficacious to look at deeper correlations between the pore diameter and geometrical properties of the mesh like the warp and shute wire diameters. Since the warp and shute diameters are a maj or factor in determining the pore shape it is likely that they have a relationship with the pore diameter. 

Characteristics Square Weave Screen Dutch Twill Weave Screen Sintered Powder Metal Fiber... 

DUTCH TWILL PLAIN OK SQUARE DUTCH WEAVE... 

There are many types of weaving patterns for woven fabrics and the four basic types are plain weave, twill weave, satin weave, and plain reverse Dutch weave (Svarovsky 1990) as shown in Figure 22.66. The filtration performances of the four types of weaves are shown in Table 22.13. 

A relatively new type of closed twill weave is available for colloidal separations. Whilst such fabrics have lower clean permeabilrties than plain or Dutch weaves, they are more easily cleaned and withstand heavy use. 

Twill weave n. A cloth weave in which the warp yarn runs alternately over two fill yarns and under one fill yarn. The twos and ones may be staggered with adjacent or r -ularly spaced warp yarns to produce a di -onal effect. In Dutch twill, wires of different sizes are used to produce a very dense screen with tortuous passages (light does not pass directly through) and an effective mesh number of 1200 or more. Twilled screens... 

There are three important types of metallic filter medium wire mesh, sintered powder, and random fiber. Wire mesh comes in a square weave or Dutch twill (woven in parallel diagonal lines). The different filter media do not perform equally with respect to their ability to hold contaminant, capture gels, etc. [11, 12]. A relative performance comparison is shown in Table 3.7. 

Wire mesh, square weave Wire mesh, Dutch twill Sintered powder Random metal fiber... 

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. 

Wire mesh square weave Wire mesh Dutch twill Sintered metal powder Random metal fibers... 

There are a number of different filter materials. Wire screens are the most common. Several t5 es of wire screens are available, such as the square mesh with plain weave and the square mesh with Dutch twill. There are also depth filtration media, such as sintered metal powder and random metal fibers. Advantages and disadvantages of different filter materials are shown in Table 1. 

The liquid is passed under centrifugal force through a filter medium or perforated plate. Filtration occurs as the liquid passes through the interstices of the solid particles that have built up on the medium surface. Depending upon the degree of separation desired, fdter media can be a filter fabric of twilled weave, dutch weave or plain weave in either stainless steel or synthetic fibre. 

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. 

There are several available weaves of woven wire. Some of these weaves lead the product to be called woven fabric. The basic types of weaves of wire cloth, which are woven for filtration purposes, are plain, twilled, plain Dutch, twilled Dutch, plain reverse Dutch, duplex (twin warp) plain Dutch, Betamesh and braided (basket of multibraid)—see Figure 8.1. 

Figure 8.1 Different types of weaves, (a) Plain square weave, (b) Plain twilled weave, (c) Plain Dutch weave, (d) Twilled Dutch weave, (e) Reverse Dutch weave, (f) Duplex (twin warp) plain Dutch weave, (g) Betamesh Dutch weave, (h) Basket (braided or multibraid) weave...

Table 3.4 lists the FTS pressure drop fitting parameters for Dutch Twill, and all other weaves, respectively. Dutch Twills yield smaller FTS pressure drops in both laminar and turbulent regimes, due to more available flow area, higher void fraction, etc. For most accurate results, a LAD designer should fit parameters to each individual screen data from Figures 3.11 and 3.12 and Table 3.4 are meant for preliminary design or where testing is imavailable. 

Table 3.5 Effective Wicking Diameters for Several Dutch Twill and Plain Dutch Weaves...

Grootenhuis (Proc. Inst. Mech. Eng. [London], A168, 837—846 [1954]) presents data which indicate that for a series of screens, the total pressure drop equals the number of screens times the pressure drop for one screen, and is not affected by the spacing between screens or their orientation with respect to one another, and presents a correlation for frictional losses across plain square-mesh screens and sintered gauzes. Armour and Cannon (AIChE J., 14,415-420 [1968]) give a correlation based on a packed bed model for plain, twill, and dutch weaves. For losses through monofilament fabrics see Pedersen (Filtr. Sep., 11, 586-589 [1975]). For screens Inclined at an angle 0, use the normal velocity component V ... 

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. 

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