Prior to spinning, the combed sliver undergoes a series of additional gilling operations to realign the hooked-shaped fibres into the trailing position, and to ensure complete intermixing of the wool fibres, resulting in a complete homogenous blend.
The sliver then undergoes an operation known as drawing, by passing through a roving machine. During drawing the linear weight of the sliver (grams per metre) is significantly reduced, producing what is known as a roving. The roving machine, also by means of a rubbing action, compacts the roving in order to hold the fibres together and thus minimises the chance of breakage during the subsequent spinning operation.
Although coarse yarn counts can be produced on the worsted spinning system in comparison to woollen spinning, much finer yarn counts can be, and are usually produced, both for knitting and weaving.
During worsted spinning the roving is first drafted, in the drafting zone on the spinning machine, before entering the twisting zone where a predetermined amount of twist is inserted to produce a singles (1xply) yarn.
The yarn is then wound on a winding machine which is fitted with a clearing device, detecting and removing any faults such as thick and thin places, neps and slubs.
Today most winding machines are fitted with a pneumatic splicing device in order to join or splice the ends of broken yarns, rather than tie and produce knots.
Although some yarns are sold and used in singles form, such as 1xply, the majority undergoes a twisting process where two singles yarns are twisted together to produce a two-fold, or 2xply, yarn.
After twisting, the yarn is then re-wound onto suitable packages either for knitting or for weaving. Wax is applied during the final winding of yarns destined for the knitting industry in order to reduce and even out the yarns’ frictional properties, enabling trouble-free knitting.
Longer wool fibres are used in the production of worsted-spun wool yarns for weaving to produce a yarn which is very strong to withstand the rigors of weaving, and also to produce very smooth woven fabrics. Whereas for knitting yarns, shorter fibres are produced to produce more bulky yarns - the more wool fibre ends per unit length of yarn, the more bulky the yarn will be. Too short a fibre length can lead to poor performance of the final product such as pilling in knitwear.
When producing wool yarns either for machine knitting or weaving of acceptable quality, there are many important parameters to take into consideration. These include:
- yarn count (Nm) and yarn count variation
- twist levels (turns per metre) and variation; in the case of a two-fold yarn the ratio in percentage terms between the twist levels in the single yarn and the folding twist is very important. This factor is known as the twist balance.
- yarn frictional properties
- yarn strength and elongation
- irregularity (U %)
- number of faults: thick and thin places and neps.