A History of Yarn

2. Any fibre, as wool, silk, flax, cotton, nylon, glass, etc., spun into strands for weaving, knitting, or making thread

Background

Yarn consists of several strands of material twisted together. Each strand is, in turn, made of fibres, all shorter than the piece of yarn that they form. These short fibres 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 fibres during spinning. A fairly high degree of twist produces strong yarn; a low twist produces softer, 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 fibres 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.

History

Natural fibers—cotton; silk, and wool—represent the major fibres available to ancient civilizations. The earliest known samples of yarn and fabric of any kind were found near Robenhausen, Switzerland, where bundles of flax fibres and yarns and fragments of plain-weave linen fabric, were estimated to be about 7,000 years old.

Cotton has also been cultivated and used to make fabrics for at least 7,000 years. It may have existed in Egypt as early as 12,000 B.C. Fragments of cotton fabrics have been found by archaeologists in Mexico (from 3500 B.C.)., in India (3000 B.C.), in Peru (2500 B.C.), and in the southwestern United States (500 B.C.). Cotton did not achieve commercial importance in Europe until after the colonization of the New World. Silk culture remained a specialty of the Chinese from its beginnings (2600 B.C.) until the sixth century, when silkworms were first raised in the Byzantine Empire.

Synthetic fibers did not appear until much later. The first synthetic, rayon, made from cotton or wood fibres, was developed in 1891, but not commercially produced until 1911. Almost a half a century later, nylon was invented, followed by the various forms of polyester. Synthetic fibres reduced the world demand for natural fibers and expanded applications.

Until about 1300, yarn was spun on the spindle and whorl. A spindle is a rounded stick with tapered ends to which the fibres are attached and twisted; a whorl is a weight attached to the spindle that acts as a flywheel to keep the spindle rotating. The fibres were pulled by hand from a bundle of carded fibres tied to a stick called a distaff. In hand carding, fibers are placed between two boards covered with leather, through which protrude fine wire hooks that catch the fibers as one board is pulled gently across the other.

The spindle, which hangs from the fibres, twists the fibres as it rotates downward, and spins a length of yarn as it pulls away from the fibre bundle. When the spindle reaches the floor, the spinner winds the yarn around the spindle to secure it and then starts the process again. This is continued until all of the fibre is spun or until the spindle is full.

A major improvement was the spinning wheel, invented in India between 500 and 1000 A.D. and first used in Europe during the Middle Ages. A horizontally mounted spindle is connected to a large, hand-driven wheel by a circular band. The distaff is mounted at one end of the spinning wheel and the fibre is fed by hand to the spindle, which turns as the wheel turns. A component called the flyer twists the thread just before it is wound on a bobbin. The spindle and bobbin are attached to the wheel by separate parts, so that the bobbin turns more slowly than does the spindle. Thus, thread can be twisted and wound at the same time. About 150 years later, the Saxon wheel was introduced. Operated by a foot pedal, the Saxon wheel allowed both hands the freedom to work the fibers.

A number of developments during the eighteenth century further mechanized the spinning process. In 1733, the flying shuttle was invented by John Kay, followed by Hargreaves' Spinning Jenny in 1766. The Jenny featured a series of spindles set in a row, enabling one operator to produce large quantities of yarn. Several years later Richard Arkwright patented the spinning frame, a machine that used a series of rotating rollers to draw out the fibers. A decade later Samuel Crompton’s' mule machine was invented, which could spin any type of yarn in one continuous operation.

The ring frame was invented in 1828 by the American John Thorp and is still widely used today. This system involves hundreds of spindles mounted vertically inside a metal ring. Many natural fibres are now spun by the open-end system, where the fibres are drawn by air into a rapidly rotating cup and pulled out on the other side as a finished yarn.

Raw Materials

About 15 different types of fibers are used to make yarn. These fibres fall into two categories, natural and synthetic. Natural fibres 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 fibre is cotton, gathered from the cotton boil or seed pod when it is mature. In fact, cotton is the best-selling fibre in America, outselling all synthetic fibers combined.

Animal fibres include Wool, made from sheep hair, and Mohair made from Angora goats and rabbits. Silk is a protein extracted 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 fibres without the shrinkage problems. Other fibres 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 fibres 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

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

Carding

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

Combing

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

Drawing out

• After carding or combing, the fibre 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

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

Spinning

• 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.

• Open-end spinning omits the roving step. Instead, a sliver of fibres 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 fibres enters the rotor, is distributed in the groove, and is removed at the end of the formed yarn.