Threads from plants and animals are usually not more than a few centimetres long. To make a long, strong thread for weaving or knitting, they must be spun. A carding machine combs the fibres so that they are all lying in the same direction and form a loose rope. This rope is then gently drawn out into a thinner thread and twisted into yarn.
Spinning is the twisting techniques where the fiber is drawn out, twisted, and wound onto a bobbin.The yarn issuing from the drafting rollers passes through a thread-guide, round a traveller that is free to rotate around a ring, and then onto a tube or bobbin, which is carried on a spindle, the axis of which passes through a center of the ring. The spindle is driven (usually at an angular velocity that is either constant or changes only slowly) and the traveller is dragged around a ring by the loop of yarn passing round it. If the drafting rollers were stationary, the angular velocity of the traveller would be the same as that of the spindle and each revolution of the spindle would cause one turn of twist to be inserted in the loop of yarn between the roller nip and the traveller. In spinning, however, the yarn is continually issuing from the rollers of the drafting system and, under these circumstances, the angular velocity of the traveller is less than that of the spindle by an amount that is just sufficient to allow the yarn to be wound onto the bobbin at the same rate as that at which it issues from the drafting rollers.
Each revolution of the traveller now inserts one turn of twist into the loop of yarn between the roller nip and the traveller but, in equilibrium, the number of turns of twist in the loop of yarn remains constant as twisted yarn is passing through the traveller at a corresponding rate.
Artificial fibres are made by extruding a polymer through a spinneret into a medium where it hardens. Wet spinning (rayon) uses a coagulating medium. In dry spinning (acetate and triacetate), the polymer is contained in a solvent that evaporates in the heated exit chamber. In melt spinning (nylons and polyesters) the extruded polymer is cooled in gas or air and sets. All these fibres will be of great length, often kilometers long.
Natural fibres are from animals (sheep, goat, rabbit, silkworm), minerals (asbestos), or plants (cotton, flax, sisal). These vegetable fibres can come from the seed (cotton), the stem (known as bast fibres: flax, hemp, jute) or the leaf (sisal). Many processes are needed before a clean even staple is obtained. With the exception of silk, each of these fibres is short, only centimetres in length, and each has a rough surface that enables it to bond with similar staples.Artificial fibres can be processed as long fibres or batched and cut so they can be processed like a natural fibre.
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