In terms of yarn count (Nm), coarser counts are generally produced on the woollen system in comparison to worsted spinning.
In woollen spinning there are two types of spinning methods used; these include ring spinning which is similar to what’s used to produce worsted yarns, and mule spinning which is unique to the woollen spinning industry.
Generally, blends of coarse micron wool, such as 29 micron Shetland, are ring spun, whilst finer blends (21 micron and finer Lambswool blends) tend to be spun on a mule.
During ring spinning the woollen roving continuously enters the drafting zone on the spinning machine. It is slightly drafted in the region of 20% to 30%, before entering the twisting zone where a predetermined amount of twist is inserted to produce a singles (1xply) yarn.
Mule spinning is somewhat different whereby the yarn is formed by a number of intermittent actions, rather than been formed continually.
Firstly, the rovings are drawn out about 1.5 meters by means of a moveable carriage, and then twisted slightly to increase their strength. Tension is then applied and the rovings are further drawn or drafted by some 20% to 30%. The desired amount of twist is then inserted, before the carriage moves back to its original position whilst winding the singles yarns onto bobbins. The sequence is then repeated until the bobbins of yarn reach their maximum or optimum size.
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. Because woollen yarns contain a lot of oil in contrast to worsted-spun yarns, due to the relatively high amounts of processing lubricants applied to the wool prior to carding, it’s not normally necessary to apply wax.
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.