Warping / Slashing

Before weaving, warp yarns are first wound on large spools, or cones, which are placed on a rack called a creel. The warp yarns are then unwound and passed through a size solution (sizing/slashing) before being wound onto a warp beam in a process known as beaming. The size solution forms a coating that protects the yarn against snagging or abrasion during weaving. 

Slashing, or applying size to the warp yarn, uses pad/dry techniques in a large range called a slasher. The slasher is made up of the following: a yarn creel with very precise tension controls; a yarn guidance system; and a sizing delivery system, which usually involves tank storage and piping to the size vessels. The yarn sheet is dipped one or more times in size solution and dried on hot cans or in an oven. A devise called a “lease” is then used to separate yarns from a solid sheet back into individual ends for weaving (EPA, 1996).

Starch, the most common primary size component, accounts for roughly two-thirds of all size chemicals used in the United States (130 million pounds per year). Starch is used primarily on natural fibers and in a blend with synthetic sizes for coating natural and synthetic yarns. Polyvinyl alcohol (PVA), the leading synthetic size, accounts for much of the remaining size consumed in the United States (70 million pounds per year). PVA is increasing in use since it can be recycled, unlike starch. PVA is used with polyester/cotton yarns and pure cotton yarns either in a pure form or in blends with natural and other synthetic sizes. Other synthetic sizes contain acrylic and acrylic copolymer components. Semisynthetic sizes, such as carboxymethyl cellulose (CMC) and modified starches, are also used. 

Oils, waxes and other additives are often used in conjunction with sizing agents to increase the softness and pliability of the yarns. About 10 to 15 percent of the weight of goods is added as size to cotton warp yarns, compared to about 3 to 5 percent for filament synthetics.

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