Yarn Preparation Process for Weaving

Weaving preparatory process:
Weaving is the most popular technique of fabric manufacturing. In case of weaving, two sets of yarn are required to produce a fabric. One is warp, which runs along the length of the fabric and the other is weft, which runs along the width of the fabric. Warp yarns are usually stronger and more compact than the weft or filling yarns. Yarns as manufactured and packaged are not actually suitable for direct use to form fabrics. It is necessary to prepare it to be handled efficiently during fabric formation. Thanks to the technique of weaving, the warp yarns are subjected to much higher stresses because of the more rigorous treatments meted out to them than the weft yarns in a weaving machine.

In order to make the warp yarns aptly prepared for that, they require extra and more elaborate preparation. The weft yarns in contrast, are subjected to far less stresses in any type of weaving system and are thus, easily prepared for the weaving process. Moreover, the feed package of weft yarn for weaving, pirn or cone, is made from the single yarn whereas, the warp beam is made from a few thousand warp ends. Therefore, the preparations of the warp and weft yarns for weaving are significantly different and the preparation of warp beam demands more precise and uniform control of tension of all the constituent warp yarns. Figure-1 indicates the process flow chart for preparation of the warp and weft yarns for weaving.

flow chart of yarn from spinning to weaving
Figure 1: Flow chart of yarn from spinning to weaving

With the advent of new methods of spinning viz. open-end, air-jet and friction spinning, the spun yarns are wound on large packages. In such cases the packages of weft yarns may not be required to be prepared further and are taken straight to the weaving process with shuttleless looms.

There are three main steps of weaving preparatory process:

  1. Winding
  2. Warping
  3. Sizing

Without these process Drawing-in and Tying-in are also done in weaving process.

Winding process:
The first stage of weaving preparatory process is winding, where the yarn, warp or weft spun in the spinning process is wound to make a suitable package for the next processing. The yarn from the spinner’s package called ring tube or bobbin, produced in the ring spinning, is transferred into a cheese, cone or spool depending on the requirement at the next stage of processing. Winding is, thus, primarily the transfer of yarn from one form of package to another but, under proper tension and in proper manner, as illustrated in Figure-2.

Yarn Winding process
Figure 2: Yarn winding process

Objects of winding:

  1. To transfer yarn from one package to another suitable package, this can be conveniently used for used for weaving process.
  2. To increase the efficiency of yarn for the next processes.
  3. Removing objectionable faults present in yarn contained in the supply package like hairiness, naps, slabs, foreign matters.
  4. To clean yarn.
  5. To increase the quality of yarn.
  6. To get a suitable package.
  7. It is used to reduce end breakage.
  8. To store the yarn.
  9. Building a package of suitable dimensions compatible with the downstream processes.

The fundamental difference between weft winding for shuttle loom and warp winding is the relative sizes of the feed and delivered packages. In case of weft winding a fairly large feed package like cheese or cone is used to produce a comparatively small delivered package like pirn, while in case of the other, the feed package, ring tube or bobbin is very much smaller than the delivered package, cheese or cone. However, if the delivered package of weft is made for shuttleless looms, then the large package like cone is used straightway.

Warping process:
After finishing the yarn winding, selected cones are transported to next process, i.e. warping. Warping is an essential weaving preparatory process in weaving mill. This is a very common say about warping, “good warping finishes fifty percent weaving.”

As indicated in Figure-1, while the preparation of weft for shuttle looms ends with pirn winding after the normal winding, preparation of warp proceeds to warping following winding. From here onwards, many warp ends are processed together to produce a warp package in the form of a beam, which in warping is the warpers’ beam. Required number of cones of warp yarns is placed on the creel and the yarns are wound side-by-side under uniform tension to produce a large parallel wound beam. Each warpers’ beam is required to contain as much yarn as possible and hence, each beam has to be prepared hard and compact (except however, those for dyeing). Although any type of yarn package can be used on the creel of the warping machine, the cone is the most suitable for high speed operation because of the reasons stated earlier.

Objectives of warping:
The major objective of warping is to prepare a warp sheet of desired length containing a desired number of yarns that are wrapped on a flanged barrel in such a manner that tension in each yarn and density of yarn mass in the cylindrical assembly are maintained within a given tolerance level throughout the wrapping of the warp beam which can be used for sizing or next process. The process of warping is dedicated to the conversion of cones into a beam of given specifications.

Sizing or slashing process:
Warp yarns are used to supply on looms where warp threads are subjected to repeatedly occurring various stresses like cyclic strain, flexing, and abrasion. These unavoidable stresses cause frequent warp breaks which consequent in the form of loom stoppages and finally, efficiency loss and fabric faults come in account. To minimize these problems, warp yarns are needed to be sized.

Warp yarn sizing is an essential process to coat warp yarns with elastic film and bind fibers of yarns and lowering fluff or hairiness so that the yarns may become so strong that they can resist the mechanical strain in weaving process, and/or maintain or improve weaving efficiency. In other words, sizing is done to provide a protective coating and to lubricate the surface of the yarn to enable it to withstand the abrasive action which occurs in the weaving process. These facts define that the sizing process is very important for a successful woven fabric manufacturing.

Final preparation of the warp beam for weaving is carried out in slashing or sizing process. Depending on the total number of warp ends required for weaving, one warp beam is prepared from a number of warpers’ beam. Although many of the faults of the warp yarns are removed mainly at winding and perhaps to some extent at warping and the qualities of the yarns are thus much improved, the yarns are not yet good enough to withstand the rigorous abrasive actions at weaving. This is taken care of at slashing or sizing, where the abrasion resistance of the yarns in addition to their strength is increased and their hairiness is reduced by applying a protective coating that is, size, on them. Slashing process consists of five main working zones as indicated in simple diagrammatic form in Figure-3.

Different zones in slashing
Figure-3: Different zones in slashing

Objectives of sizing:
The main objective of sizing is to form a uniform layer of protective coating over warp yarn and lay down protruding fibers that project out of its surface (Figure 4).

Unsized and sized yarn
Figure 4: Unsized and sized yarn

Other objectives of sizing are as follows:

  1. To increase the strength of yarn
  2. To get the required number of ends
  3. To cover the hairiness of yarn
  4. To make yarn surface smooth and pliable.
  5. To maintain flexibility in yarn

Drawing-in and Tying-in:
Drawing-in is the process of providing each end with a drop wire, a heddle in the proper harness and a dent in the reed. In short it is the process of threading each end through the drop wire, heddles and the reed.

Tying-in is merely the cutting-off of the old warp and the end-to-end tying of the yarns from the new beam to the corresponding warp yarns already in place on the loom. This operation generally occurs at the loom. When the mill is producing long runs of the same fabric, tying-in is most prevalent.

Weaving preparatory process plays major roles in achieving the desired performance at weaving. Ultimate packages of warp and weft yarns prepared at these stages are used as the feed materials for looms, where the yarns are unwound during the course of weaving. How best the yarns can be unwound from their respective packages depend on how best the packages have been prepared at the various preparatory processes. Requisite shape and size of a yarn package needed for a given type of loom can be prepared if the yarn is wound under optimum tension with as little variation as possible. Too low winding tension will result in soft packages and cause irregular withdrawal of the yarns while, too high winding tension will destroy much of the extensibility of the yarn and make the yarn vulnerable to breakage. The qualities of the feed materials for weaving have become even more stringent after the introduction of the high speed shuttleless weaving machines, which with relatively small depth of shed, demand greater uniformity in tension of all the warp yarns and smooth withdrawal of the weft yarn from its package for faultless insertion. It may therefore, be said that properly prepared warp beams and weft packages assure half the desired performance of a loom.

References:

  1. Role of Yarn Tension in Weaving by Samir Kumar Neogi
  2. Industrial Practices in Weaving Preparatory by Mukesh Kumar Singh
  3. Principles of Fabric Formation by Prabir Kumar Banerjee

You can see complete weaving process in this video:
https://www.youtube.com/watch?v=NIt9SGk55b4

You may also like:

  1. Winding and Winding Machine: Types, Features, Efficiency, Functions and Driving Methods
  2. Automation in Warping and Sizing Process

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