TANGLING WITH WOOL – WOOLLEN OR WORSTED? Source: WRONZ Developments 2000

Many people think that all yarns made of wool are woollen yarns, but this is not the case. Three alternative systems are used for processing wool into yarn: the woollen, semi-worsted and worsted systems. Each route is distinctly different, in terms of the machinery used, the types of wools that can be economically processed, and they produce yarns that are quite different in their properties.

Irrespective of the processing route chosen, there are some features common to all three routes (see the flow diagram). The basic requirement of yarn manufacture is to take wool in the scoured form (where the fibres tend to be clumped together), separate out the individual fibres, and reassemble them into a twisted arrangement called a yarn. The steps by which the formation of the yarn is achieved differ somewhat between the three routes.

Worsted Processing The worsted system has the most steps in its processing sequence, and better quality, long, sound wools are generally required. Fine and medium wools are favoured for fine yarns. The wool is first passed through a carding step, in which a series of rotating, toothed rollers open the tufts of wool, separate the fibres and mix them thoroughly. Inevitably some fibres break in carding, which is the most severe textile process. However, fibre breakage is minimised by spraying the wool with a lubricating mixture of water and oil prior to carding. The carded wool is removed for the next stage as a thick ribbon of fibre, called a sliver.

The sliver is next passed through a gilling step, where a series of pins is drawn through the sliver to straighten and align the fibres into a parallel arrangement. The gilled sliver is then combed to remove short fibres, neps (or little balls of fibre) and vegetable matter. The sliver is gilled again to restore the parallel alignment to form a top . The top is drafted (or drawn out) to form a thin ribbon, or roving , before being twisted and further drafted in spinning to form a worsted yarn.

As a result of (1) the removal of short fibres (2) the parallel arrangement of the fibres presented for spinning and (3) the high degree of twist inserted, a worsted yarn is sufficiently strong to require a minimum of 40 fibres in the cross-section. Hence, fine, even, firm yarns with satisfactory strength can be spun.

In the main, worsted-spun yarns are used in high-quality woven suiting fabrics, and hand and machine knitting yarns. In these products it is important that the yarn be free from faults such as neps, slubs (clumps), vegetable matter and protruding fibres. Short fibres may cause prickliness, while long protruding fibres have a tendency to form pills. Woollen Processing The woollen system is the least complex route, and it tends to be used to process blends of wools which vary in length and fibre diameter. The system is capable of handling the poorer types of wools, especially those that are short and tender (i.e. have low strength).

In the woollen system the wool passes through a two-stage carding machine to ensure a thorough opening of the tufts and mixing of fibres, and the removal of contaminants. At the end of the card, the thin, carded web of fibres is separated into narrow strips, which are condensed by rubbing into a thin ribbon called a slubbing. The slubbing is then spun into yarn by applying twist in a ring-spinning frame .

A woollen-spun yarn is characterised by a high proportion of short fibres, which are distributed very much at random throughout the yarn. Longer fibres often undergo reversals in direction and may protrude from the yarn, to contribute to a hairy appearance.

The protruding loops and ends of fibres have an important influence on the tactile and visual properties of a woollen-spun yarn. A fibre with reversals contributes less to the strength of a yarn than if it was fully extended without reversals, as tends to be the case in a worsted yarn. Therefore, a woollen yarn tends to have less strength than a worsted yarn of similar thickness. To obtain sufficient strength a minimum of about 200 fibres in the cross-section is required. Woollen-spun yarns tend to be of coarse count (i.e. thicker), spun to a low twist. Hence they are bulky, soft handling, relatively hairy, and less even than worsted yarns. The reversals and other irregularities in the path of fibres within the yarn create air spaces within the yarn and these also contribute to their soft, bulky handle.

In the main, woollen spun yarns are used in woven, knitted and tufted products such as carpets, blankets, tweeds and heavier woven and knitted apparel. Most of the large spinning plants in New Zealand produce woollen spun carpet yarns.

Semi-worsted Processing The semi-worsted system was developed to produce a yarn with greater strength than in the woollen system, but without the significant expense of having to remove short fibres in a combing step. Wool is passed through a carding machine, gilled three times to straighten the fibres, and then spun directly from a thin gilled sliver.

The semi-worsted system is best suited to sound wools of 100-120mm staple length (with a minimum length of at least 70mm). Because there is less opportunity for the removal of contaminants, the wools used must be virtually free of vegetable matter.

Semi-worsted yarns are intermediate in properties between those produced on the worsted and woollen systems. They are used mainly for manufacturing carpets and knitwear. Because of the greater fibre length and the degree of straightening produced by the gilling step, semi-worsted yarns tend to be less bulky than woollen yarns. Hence bulkier wools are sought for semi-worsted blends if a good fabric cover or a softer handle is required in products.

In all three systems it is usual to twist singles yarns from the spinning step into multiple plies, or folded yarns. Plying two or more singles yarns together in this way improves both the evenness and strength of the final yarn.

The three processing routes for wool are shown in the following flow diagram.