How Yarn is Produced

Yarn consists of several strands of material twisted together. Each strand is, in turn, made of fibers, all shorter than the piece of yarn that they form. These short fibers are spun into longer filaments to make the yarn. Long continuous strands may only require additional twisting to make them into yarns. Sometimes they are put through an additional process called texturing.

The characteristics of spun yarn depend, in part, on the amount of twist given to the fibers during spinning. A fairly high degree of twist produces strong yarn; a low twist produces softer, more lustrous yarn; and a very tight twist produces crepe yarn. Yarns are also classified by their number of parts. A single yarn is made from a group of filament or staple fibers twisted together. Ply yarns are made by twisting two or more single yarns. Cord yarns are made by twisting together two or more ply yarns.

Raw Materials

About 15 different types of fibers are used to make yarn. These fibers fall into two categories, natural and synthetic. Natural fibers are those that are obtained from a plant or an animal and are mainly used in weaving textiles. The most abundant and commonly used plant fiber is cotton, gathered from the cotton boil or seed pod when it is mature. In fact, cotton is the best-selling fiber in America, outselling all synthetic fibers combined.

Fibers taken from the plant leaf or stern are generally used for rope. Other plant fibers include acetate (made from wood pulp or cotton linters) and linen, made from flax, a vegetable fiber. Animal fibers include wool, made from sheep hair, and mohair, made from angora goats and rabbits. Silk is a protein extruded in long, continuous strands by the silkworm as it weaves its cocoon.

Synthetic fibers are made by forcing a thick solution of polymerized chemicals through spinneret nozzles and hardening the resulting filament in a chemical bath. These include acrylic, nylon, polyester, polyolefin, rayon, spandex, and triacetate. Some of these fibers have similar characteristics to the natural fibers without the shrinkage problems. Other fibers have special properties for specific applications. For instance, spandex can be stretched over 500% without breaking.

The Manufacturing Process

There are three major spinning processes: cotton, worsted or long-staple, or wool. Synthetic staple fibers can be made with any of these processes. Since more yarn is produced with the cotton process than the other two, its manufacture is described below.

Preparing the fibers

• 1 Fibers are shipped in bales, which are opened by hand or machine. Natural fibers may require cleaning, whereas synthetic fibers only require separating. The picker loosens and separates the lumps of fiber and also cleans the fiber if necessary. Blending of different staple fibers may be required for certain applications. Blending may be done during formation of the lap, during carding, or during drawing out. Quantities of each fiber are measured carefully and their proportions are consistently maintained.

Carding

• 2 The carding machine is set with hundreds of fine wires that separate the fibers and pull them into somewhat parallel form. A thin web of fiber is formed, and as it moves along, it passes through a funnel-shaped device that produces a ropelike strand of parallel fibers. Blending can take place by joining laps of different fibers.

Combing

• 3 When a smoother, finer yarn is required, fibers are subjected to a further paralleling method. A comblike device arranges fibers into parallel form, with short fibers falling out of the strand.

Drawing out

• 4 After carding or combing, the fiber mass is referred to as the sliver. Several slivers are combined before this process. A series of rollers rotating at different rates of speed elongate the sliver into a single more uniform strand that is given a small amount of twist and fed into large cans. Carded slivers are drawn twice after carding. Combed slivers are drawn once before combing and twice more after combing.

Twisting

• 5 The sliver is fed through a machine called the roving frame, where the strands of fiber are further elongated and given additional twist. These strands are called the roving.

Spinning

• 6 The predominant commercial systems of yarn formation are ring spinning and open-end spinning. In ring spinning, the roving is fed from the spool through rollers. These rollers elongate the roving, which passes through the eyelet, moving down and through the traveler. The traveler moves freely around the stationary ring at 4,000 to 12,000 revolutions per minute. The spindle turns the bobbin at a constant speed. This turning of the bobbin and the movement of the traveler twists and winds the yarn in one operation.

• 7 Open-end spinning omits the roving step. Instead, a sliver of fibers is fed into the spinner by a stream of air. The sliver is delivered to a rotary beater that separates the fibers into a thin stream that is carried into the rotor by a current of air through a tube or duct and is deposited in a V-shaped groove along the sides of the rotor. As the rotor turns, twist is produced. A constant stream of new fibers enters the rotor, is distributed in the groove, and is removed at the end of the formed yarn.