Warp Preparation | Common Steps Involved in Warp Yarn Preparation

Common Steps Involved in Warp Preparation:
The object of warp preparation is to transfer yarn from the spinner's package to a weaver's beam that can be placed behind a loom ready for weaving. A weaver's beam usually contains several thousand ends and for a variety of reasons, it can seldom be made in one operation. It is usual to divide the warp preparation process onto four sections:

warp preparation
Fig: Warp preparation (Warping)
1. Warp Winding: The main functions of warp winding are to rewind the yarns from the spinning frame or texturing machine in a long continuous length to suit later processes. This is a process to wind the yarns into a suitable package size and shape, and also to take out imperfections such as slubs, weak places, leaves, neps and dirt, which are always present in yarn as delivered from the spinning frame. The winding machines for warp preparation can be classified as follows:

A. Drum winder: The yarn package (cheese or cone) is frictionally driven by using a driving drum or roll. Either a cam traverse or a grooved roller makes the yarn traverse motion. Due to the surface driving of the yarn package, the yarn speed is always constant, independent of the package diameter.

B. Precision winder: This is a precise-traverse winder using a yarn guide, which is controlled by means of a traverse cam or a grooved roller. The yarn package is driven positively by using a spindle. Therefore, the yarn speed is increased according to the package diameter if the spindle speed is constant. This type of winder is used for continuous filament yarns that are unsuitable for frictional winding methods like the drum winder.

2. Warping (Beaming): The purpose of warping is to arrange threads in long length, parallel to one another as preparatory to further processing. The primary operation of warp-making in which ends withdrawn from a warping creel, evenly spaced in sheet form, are wounded onto a beam (known as warper’s beam) to substantial length. There are two warping methods, i.e. direct beaming and sectional warping.

A. Direct warping/beaming: This is the winding of total number of warp ends in full width in a single operation from creeled bobbin. Direct beaming /warping is used for long runs of greige fabric and simple patterns where the amount of coloured yarn involved is less than about 15 percent of the total.

B. Sectional warping: This is a method of preparing a warp beam consisting in i) winding a warp in sections on a reel/drum and ii) beaming-off the complete warp from the reel onto a warp beam. Sectional warping is used to produce warp beam for Yarn dyed fabric.

3. Sizing/Slashing: Sizing means the operation of applying a special solution (known as size solution) to warp yarns to strengthen, smoothen and lubricate them. In machine sizing a warp is transferred from a warp beam to a loom beam. The procedure is as follows:
  • Warp in sheet form is withdrawn form a warp beam is passed through a sow-box and the squeezing rollers of a sizing machine. Application of size solution by immersion or by contact with a partially immersed roller, and penetration of the yarn by the size solution occur at this stage. The sizing agents generally used are PVA (Polyvinyl alcohol), Starch, Acrylic esters, CMC (Carboxymethyl cellulose), Wax etc.
  • The warp is dried by hot air or by contact with steam-heated cylinders en route to the loom beam.
4. Looming: Looming covers the processes involved in warp preparation after sizing upto setting them to loom. During slashing, the exact number of warp yarns required in fabric is wound onto the loom (or weaver's) beam. The warp ends are then passed through the drop wires of the warp stop motion, the heddles of the harness frames and the dents at the reed. This can be achieved by drawing -in or tying-in, the choice depending upon whether or not the new warp is different from the warp already on the loom. The processes are as follows:

Drawing-in: The process of drawing every warp end through its drop wire, heddle eye and reed dent can be performed manually or by means of automatic machines. In both case, a length of warp yarn, just enough to reach to the other side of the frame, is unwound. Leasing (i.e. selecting warp) of the warp at this stage simplifies the separation of the yarns. Then they are threaded through drop-wires, heddle eyes and reed dents. The automatic drawing machine can handle the leasing-in and drawing-in process in single operation.

Tying-in: When fabric of a particular type is being mass-produced, the new warp beams will be identical with the exhausted beams on the looms. Therefore, if every end on the new beam is tied to its corresponding end on the old beam, the drawing-in process can be omitted. Tying-in may be done by means of a small portable machine on the loom or as a separate operation away from the loom. 
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Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.

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