Drafting Device

one of the basic components of spinning and rover machines. It drafts (stretches) the product to the required thickness (tex, or number), with simultaneous straightening and lining up of the threads. For centuries weavers performed this process by hand.

The simplest form of drafting device appeared in the first half of the 18th century. Devices of various construction are used for different fibers, but all of them have the same essential element—two or more drafts consisting of grooved metal cylinders that are pressed upon from above by pressure rollers, which usually have an elastic outer covering. The upper rollers are pressed to the cylinders by a loading device or by their own weight. The product, which is pressed between the cylinder and the roller, moves forward with a speed virtually equal to that of the cylinder. To achieve drafting, the circumferential speed of the cylinders increases as the product moves through, so that the fibers, as they pass successively under various drafts, increase their speed and thereby slip and are straightened in the product being processed. The drafting of the product between two pressure sets is numerically equal to the ratio of the cylinders’ circumferential speed of revolution, or to the ratio of the length of the stretched product to the initial length. In practice, the magnitude of total stretching varies from 10 to 200.

Various apparatus, including transporting belts, packers, combs, and auxiliary rollers, increase the device’s stretching capacity and improve control of the speed of the moving fibers and their parallelization in the fabric. When spinning wool, bast fibers, and silk, whose fiber length is markedly greater than that of cotton, drafting devices with multiple combs are utilized. The distance between stretching pairs in such devices is greatly increased, and needles are used to control fiber motion and to improve parallelization between cylinders.

In the USSR and abroad, drafting devices have been developed that are fed by a thin ribbon or fine roving, making possible extreme stretching, on the order of 200-800. The use of such drafting devices permits the elimination of roving machines and improves the economic indicators.