Weft and warp

Fig. 8.24. Weft knit with laid-in weft and warp yarns. After Ko (1989).

Like PET, which further became more and more popular under various trade names (Dacron in USA, Rhodergon in France, Dallon in Russia and European Eastern countries), PTFE was initially used as thread, which could be woven or knitted to obtain vascular prostheses. These resulting woven devices, in which two sets of threads, respectively called weft and warp, cross each other perpendicularly, are known to easily fray near anastomoses. For knitted devices, in... 

Two methods are available By unravelling, and by chemical means. The first is the simpler and more certain method and consists in separating mechanically the threads of different types and weighing each separately. This method may be used only when the weft and warp are each composed of only one textile material, e.g., when the weft is wool alone and the warp cotton alone. 

Normally, the first step in textile conservation is the examination of the piece to determine the fibers from which it was made and the technique by which it was created. One determines the spin of the yarns, whether Z or S, and the number of wefts and warps per inch. Next, one tests for colorfastness first with distilled water, then with glycerin and water, and finally with a neutral detergent and water. If the colors run with any of these solutions, obviously the piece cannot be washed, and one tests with dry-cleaning solvents and other chemicals. 

Fabric material Scoured cotton, weft and warp ring yams Bleached cotton, weft and warp ring yams Bleached cotton, weft and warp open-end yams Polyester, weft and warp twisted mnlti-tQament Polyester, weft textured mnlti-tilament and warp intermingled mnlti-tilament... 

Five plain woven fabrics, two polyester fabrics, and three cotton fabrics were examined in a yam pullout test, as schematically shown in (Figure 1(a)). Characteristics of these fabrics are presented in (Table 2). Sample PETl is consisted of twisted multi filaments of polyester as weft and warp yams. Sample PET2 has intermingled polyester multi filaments as warp and textured polyester multi filaments as weft yams. The COTl is a scoured cotton fabric with ringspun yams as wefts and warps. The COT2 is a bleached cotton fabric with ringspun weft and warp yams, and finally COTS is a bleached cotton fabric with open-end spun wefts and warps. 

Bard PET (woven, weft knit, velour weft, and warp knit)... 

Spacer brics are three-dimensional structures that can be engineered to incorporate a wide range of attributes and hence fulfil specific pre-determined requirements. Knitted spacra fabrics can be produced on both weft and warp kiutting machines. Each of the fabric faces can be designed independently, as well as the middle layer (spacer layer), in terms of yams and structures and this will determine the unique individud properties of each fabric [1,2]. Spacer fabrics have been studied and developed for a few years now but the number of variables that can possibly be input in their constmetion gives such a wide range of possibilities that many are still to be developed and exploited commercially. 

Both weft and warp knitting machines are able to construct tubular structures. Although circular weft knitting machines can only be used in producing single tubes, flat weft knitting machines with two needle beds and double-needle bar Raschel machines are able to produce single, bifurcated and multibranched tubes. 

Spacer structures have a 3D construction consisting of two separate outer fabric layers joined together but kept apart by spacer yams or fabric layers (Liu, 2013). This kind of fabric can be manufactured by weft and warp knitting. 

Figure 6.30 Noise absorption coefficients of the combinations of weft and warp spacer fabrics.

The test bench is similar to a large protractor (cf. Fig. 21.21), which only uses, by symmetry, angles comprised within the range [0, 90 degree]. The T-shape is used to support the textile surface prototype (120 x 200 mm). This shape is manually inserted into the protractor at intervals of 5 or 10 degree. Both weft and warp directions of the textile will be tested, as illustrated in Fig. 21.22. 

Both weft and warp crimp of a fabric are important to the fabric modulus [25], in that the higher the crimp is, the lower the modulus will be. 

From what has been discussed above it can be reasoned that the fabric mass per unit area will be governed by the number of ends and picks per unit area the value of weft and warp crimp and by the mass per unit length of... 

Induced strain occurs in both weft and warp yams, though it is more pronounced in the former. As warp yams are highly packed, the swelling effect is diminished... 

In order to bypass blocked blood vessel parts, often woven, weft and warp knitted artificial vessels are used. Their diameter can be up to 30 mm wide. These pros-theses are mainly sealed using collagen or gelatin coating. An alternative is the so-called preclotting where the prosthesis is drenched in the patient s blood and implanted after the blood has clotted. 

The threads under the highest load break first. Hence, the resulting tension value reaches only about 64-75% of the theoretically possible tenacity. For woven fabrics, it is common that tenacity in the weft and warp directions is different. Often, the measured warp tension reaches only 80% of the theoretical value owing to the warp threads undulating in the fabric. In contrast, the softer weft threads often reach 100% of their theoretical values because they are clamped by the stronger warp threads. 

Mu and Meyer [51] studied the effect of orientation in cements reinforced with AR glass and PVA fabrics. They developed a model to calculate the post-crack bending capacity at different orientations, as a function of the orientation angle and the post-crack bending capacity in the weft and warp directions. The model could predict the orientation effect of the different fabrics, and it was independent of the nature of the fabric. They suggested that the influence of the fabric itself is already expressed in the bending capacity in the warf and weft directions. 

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