Yarn Preparation for Weaving

Preparatory Processes for Weaving:
The yarn manufactured in the spinning machine contains thick and thin places and objectionable faults. But for satisfactory weaving, the yarn should be free from thick and thin places and objectionable faults. Moreover, the packages from a spinning machine are small in the form of cops which usually weigh about 80g to 100g. To transport the yarn from spinning mills to weaving mills, the smaller packages have to be converted to larger packages. Moreover, the cops have to be emptied for reuse in the spinning section. All these parameters require a process called winding.

Yarn preparation for weaving, which prepare the feed materials (warp and weft) for weaving, are the most important stages between spinning and weaving. In order to achieve the desired performances of the weaving machine, yarn packages must be built with proper compactness, stability, shapes, and sizes. Figure 1 indicates the process flow chart for preparation of the warp and weft yarns for weaving.

When a fabric is to be woven on any loom, whether it is a handloom or a power loom, two sets of yarns are required. One set of yarns, called warp yarn, is used in the lengthwise direction and the other set of yarn, called weft yarn, is used in the horizontal direction. The warp yarns are put on a package called a weaver’s beam which is put at the back of the loom as shown in Figure 2. The number and length of warp yarn to be put on the weaver’s beam depend on the quality of the cloth, i.e. the number of warp yarns/cm, also called ends/cm, width of the fabric and the length of fabric to be produced from the weaver’s beam. Figure 3 shows the front of the looms as the fabric is produced.

In order to produce a weaver’s beam with a few hundred to a few thousand numbers of warp yarns and their length (m) on the beam, the spun yarns on small packages produced during the spinning process undergo the following yarn preparation processes for weaving purposes:

1. Winding
2. Warping
3. Sizing.

1. Winding:
Winding is the first process in yarn preparation for weaving. Winding is basically transforming the yarn from small package to another larger package; a cone or cheese that is more suitable for the next processes such as warping or knitting or for any other suitable use such as on shuttle-less looms. Winding is also important in removing defects in the yarn. The warp yarn has to withstand many load cycles during the weaving process, and any defect in the yarn may cause a breakage and causes fabric fault or loom stoppage. Hence, it becomes absolutely necessary to clear the yarn from its defects as much as possible. By the winding process, the yarn faults are removed to the maximum extent.

Objectives of Winding:
The main objectives of winding are

• Converting the spinning cops into larger packages weighing about 1kg to 1.5kg.
• Removing the thick and thin places, slubs and sloughs present in the yarn.
• Removing the objectionable faults.
• Giving a wax coating when the yarn is used for knitting.

2. Warping:
Warping is the second process in yarn preparation for weaving. Warping is the pro­cess of transferring many yarns from a creel of single end packages into a parallel sheet of yarn wound on a beam called a warper’s beam.

There are normally two methods of warping employing different technologies:

1. Direct warping or direct beaming (also sometimes known as beaming)
2. Indirect warping/sectional warping

Both methods can be used for spun or continuous filament yarns, depending on the circumstances and the quality of fabric to be produced.

Necessity for Warping:
To weave a cloth of say 140cm width with 30 ends per cm, a total of 4200 warp yarn is required in the beam during weaving. It is not possible to arrange 4200 supply packages or cones in the creel in order to wound the yarn on the weaver’s beam. Hence, the total number of yarns are divided into an equal number of smaller sizes. In this case, seven beams are required, each having 600 yarns. Then yarns in the seven beams are put together to get the required 4200 yarn to weave the fabric. This process is known as warping.

3. Sizing:
During weaving, due to shed formation, the warp yarn is subjected to stresses and abrasion against adjacent yarn and metal surfaces. So, it is almost impossible to weave single spun warp yarn from cotton, viscose, polyester blends, and acrylic/wool blends without the application of size (starch). Applying a coating of a polymeric film–forming agent on the warp yarn enables the yarn to withstand the stresses to which it is subjected during weaving. This is called slashing or sizing. Although sizing is a complex process which is key to successful weaving, it is also considered to be a nonvalue-added process. The following benefits are obtained due to sizing.

Benefits of Sizing:

1. The strength of the yarn is increased.
2. Yarn hairiness that would create a problem during weaving is reduced.
3. Abrasion resistance of the yarn is increased.
4. The liberation of fluff and fly during weaving is reduced.
5. Sizing keeps the slack and broken filaments together in low twist yarns.

Characteristics of Size Film:

• The size film should be flexible so that it will not affect the flexibility of the warp yarn.
• It should not be brittle.
• The size coating should not be a permanent one. Its purpose will be over once weaving is completed. Hence, size materials should be able to be removed during the desizing process.
• The size film must coat the yarn surface without excessive penetration into the yarn, because complete desizing will not be possible if the size material is penetrated deeply into the yarn.

References:

1. Fabric Manufacturing Technology: Weaving and Knitting by K. Thangamani and S. Sundaresan
2. Woven Textiles: Principles, Developments and Applications, Second Edition Edited by K. L. Gandhi
3. Role of Yarn Tension in Weaving by Samir Kumar Neogi