Weaving is the process of fabric formation in which warp and weft yarns are interlaced using a weaving machine (loom).
Warp yarns are the lengthways set of yarns in a loom whereas the weft yarns are inserted from the side of the loom, usually at right angles to the warp.
Different patterns are produced in the cloth by passing each weft yarn under or over a varying number of warp threads, forming the weave.
There are three primary motions of a loom in a weaving cycle, namely shedding, picking (weft insertion) and beating up. There are two secondary motions namely, let-off and take-up, that are used to move the material through a loom in a controlled way.
The different types of loom used for weaving wool only differ in the mechanism of shed formation, the size of the shed, the method of picking and the speed of the weaving.
Shedding involves lifting some of the warp yarns to form a tunnel through which the yarn is inserted.
There are three sorts of shedding mechanism - tappet, dobby and Jacquard. Tappets are used for simple weaves in which the number of shafts is limited. Dobby systems involve the use of a pattern chain to control the lifting of the shafts. They are the most commonly used for wool.
Jacquard systems control the lifting of each individual end to create almost unlimited patterning possibilities. Weft insertion can be by shuttle, gripper shuttle, rapier and jet.
Shuttle looms are still in common use in developing countries. The major disadvantages of shuttle looms are a low weft insertion rate (ie low productivity) and excessive noise.
Gripper shuttle looms have considerably higher production rates and are much quieter.
Rapier looms, either rigid or flexible, are much quieter than the gripper shuttle looms. Air jet looms are becoming the most popular weaving systems because of their higher speeds and relative quietness. Water jet looms are not appropriate for wool because the fibre absorb moisture.
Challenges with wool in weaving
Below are issues that are particular to warping and weaving of wool:
- Fiddle strings: These are tight ends in warping and weaving and cannot be seen until fabric is wet relaxed in scouring or dyeing. They are caused by processing yarn that is damp (from steaming or yarn dyeing) the yarn stretches and remains in its stretched state until the fabric is wet finished. Fiddle strings can appear in the weft but not unless the yarn was wound wet and stretched in winding as picks are not often subject to sufficient tension to stretch the yarn.
- Stitching: Can be solved by applying more tension to the warp in the loom, by reducing the speed by changing the sleying in the reed or by spreading the ends over more shafts. Alternatively by applying liquid wax at the beaming off stage or wax rods at the warp sheet on the loom. Sizing is the best solution but is not always available for wool.