In the twill weave a warp yarn passes over two or more filling 

 yarns. There may be a warp twill or filling twill and a plain twill or 

 broken twill. The warp twill has more warp yarns per inch than filling 

 yarns; a filling twill has more filling yarns per inch. In a broken 

 twill the interlacing does not fall in a close regular pattern as they 

 do in the plain twill. For the most part, the yarn in twill weaves may 

 be either single or plied. 



These are the basic weaves but the variations possible are almost 

 limitless. One common variation is the oxford or basket weave which is 

 a modified plain weave. In this weave, combinations of two or more 

 yarns are woven side by side in both the warp and filling directions. 

 The yarns may be single, plied, or a combination of both. 



The strength of a fabric is dependent upon the technique used in 

 weaving the cloth and the size of the yarn. The fineness or size of a 

 yarn is often expressed in denier. The denier of a yarn is the weight 

 in grams of 9,000 meters of the yarn: the coarser the yarn, the higher 

 the denier. Use of heavier yarns or plied yarns instead of single yarns 

 can increase the strength and the stiffness of a fabric. For example, a 

 fabric may be made more stiff in the filling direction than the warp 

 direction by using four-ply yarns for the filling and two-ply yarns for 

 the warp. Thus, it is possible to construct a fabric with just about 

 any structural or mechanical characteristic desired. The actual kind of 

 substrate used does not by itself dictate the properties of the finished 

 fabric. 



Coatings 



The coating that is applied to the woven fabric substrate imparts 

 many of the physical and chemical resistive properties to the finished 

 material. 



Four common methods are used for applying the coatings to fabrics: 

 spread or knife coating, dip, calendering, and laminating [6]. 



In knife or spread coating the fabric is pulled underneath a knife 

 edge which meters the quantity and thickness of coating applied. The 

 coated fabric is then passed through a drying or curing oven. This 

 method is suitable for applying thin coatings to one side of the fabric. 

 Thicker coatings and coating on both sides of the fabric can be obtained 

 by passing the fabric through the equipment a number of times. 



In the dip method the fabric is immersed in a bath of the coating 

 compound before passing between a set of metering knives and then into 

 the drying or curing oven. This method has the advantage of coating 

 both sides of the fabric at one time, and the fibers of the fabric 

 become impregnated with the coating. This process may be repeated more 

 than once to obtain the required coating thickness. 



The calendering process involves passing the fabric between two 

 rollers where the fluid coating is forced onto the fabric. The equip- 

 ment can be designed to coat one or both sides of the fabric. The 

 method is good for applying thick coatings. 



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