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مقدمات بافندگیWeaving Preparation

271Textile Technology

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Spun yarn quality characteristics that are most important for good weaving performance include short- and long-term weight uniformity, imperfections, tensile properties and hairiness.

The cost to repair a yarn failure is much less if it occurs prior to the weaving process.

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Winding

Purposes of winding process:A- Building large packages

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B- Yarn clearing

Yarn faults

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Schematic of winding process

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Tension and clearing zone of a modern automatic winding machine

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Tension device The tension device maintains a proper tension in the yarn to achieve a uniform package density. It also serves as a detector for excessively weak spots in the yarn that break under the added tension induced by the tension device.

There are three major types of tension devices:

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a) Capstan (or multiplicative) tensioner

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b) Additive tensioner

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c) Combined tensioner

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Yarn clearersThe purpose of a yarn detector is to remove thin and thick places.

Yarn detectors are usually two types: mechanical and electronic.

Air splicer

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A mechanical clearer may be as simple as two parallel blades. The distance between the plates is adjustable to allow only a predetermined yarn diameter to pass through.

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Electronic detectors are mainly two types: capacitive and photo-electric

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Stop motionThe purpose of a stop motion is to stop winding when the yarn breaks or runs out.

Winding regionMany types of package configurations can be obtained including cone, tube or cheese, dye tube or spool depending on the next stage of processing.

The basic requirement of winding is uniform tension on the yarn.

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Traversing mechanism

a) Grooved drum

a) Traversing guide

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Types of packages

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Precision WindingIn precision winding, the position of the yarn as it is laid on the package is controlled very precisely to increase the density of the package.

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Warping

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Direct Warping

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Indirect (Section) Warping

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Expanding zigzag comb

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CreelThere are various types of creels. The most commoncreel types are:

• parallel standard creel with fixed package frame(single end creel)• parallel creel with package trucks• parallel creel with swivelling package framesections (for cotton, viscose, polyester/cotton, wool colored)• parallel creel with reserve packages (magazinecreel, for synthetic filaments)• parallel creel with unrolling draw-off forpolypropylene, monofilaments

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• V-creel with reversible frames• V-creel with reversible frames and automatic knotter(for cotton, viscose, polyester/cotton)• V-creel with traveling packages

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Schematic top view of warping process (V-creel).

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SLASHING (SIZING)

The weaving process requires the warp yarn to be strong, smooth and elastic or extensible to a certain degree. To achieve these properties on the warp yarns, a protective coating of a polymeric film forming agent (size) is applied to the warp yarns prior to weaving.the size materials will be removed from the fabric during the finishing operation, which is called desizing.

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The main purposes of slashing are as follows:• to increase the strength of the yarns• to reduce the yarn hairiness that would cause problems in weaving process.• to increase the abrasion resistance of the yarnsagainst other yarns and various weavingmachine elements• to reduce fluff and fly during the weavingprocess for high speed weaving machines.

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Tension and abrasion zones in a typical loom

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Control of yarn hairiness with sizing, top: unsized; middle: improperly sized; bottom: properly sized

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The following terms are used related to sizing:

• Size concentration: the mass of oven dry solidmatter in size paste• Size take-up (size add-on): the mass of pastetaken up in the size box per unit weight ofoven dry unsized yarn• Size percentage: the mass of oven dry size per unit weight of oven dry unsized yarn

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Typical relation between size add-on andwarp breakage rate

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Sizing machine

The major parts of the slasher are the creel, size box, drying units, beaming and various control devices

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Major film forming polymersused in sizing.

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DRAWING-IN AND TYING-IN

Schematic of drawing-in

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Warp tying machine