Weaving is performed on modern looms, which contain similar parts and perform similar operations to simple hand-operated looms. Fabrics are formed from weaving by interlacing one set of yarns with another set oriented crosswise. Satin, plain and twill weaves are the most commonly used weave patterns (see picture to the left). In the weaving operation, the lengthwise yarns that form the basic structure of the fabric are called the warp and the crosswise yarns are called the filling, also referred to as the weft. While the filling yarns undergo little strain in the weaving process, warp yarns undergo much strain during weaving and must be processed to prepare them to withstand the strain (Corbman, 1975).
Once size is applied, the wound beam is mounted in a loom. Shuttle looms are rapidly being replaced by shuttleless looms, which have the ability to weave at higher speeds and with less noise. The operation of a traditional shuttle loom is discussed in this section to illustrate the weaving process.
The major components of the loom are the warp beam, heddles, harnesses, shuttle, reed and takeup roll. In the loom, yarn processing includes shedding, picking, battening and taking-up operations.
Shedding. Shedding is the raising of the warp yarns to form a shed through which the filling yarn, carried by the shuttle, can be inserted. The shed is the vertical space between the raised and unraised warp yarns. On the modern loom, simple and intricate shedding operations are performed automatically by the heddle frame, also known as a harness. This is a rectangular frame to which a series of wires, called heddles, are attached. The yarns are passed through the eye holes of the heddles, which hang vertically from the harnesses. The weave pattern determines which harness controls which warp yarns, and the number of harnesses used depends on the complexity of the weave (Corbman, 1975).
Picking. As the harnesses raise the heddles, which raise the warp yarns, the shed is created. The filling yarn in inserted through the shed by a small carrier device called a shuttle. The shuttle is normally pointed at each end to allow passage through the shed. In a traditional shuttle loom, the filling yarn is wound onto a quill, which in turn is mounted in the shuttle. The filling yarn emerges through a hole in the shuttle as it moves across the loom. A single crossing of the shuttle from one side of the loom to the other is known as a pick. As the shuttle moves back and forth across the shed, it weaves an edge, or selvage, on each side of the fabric to prevent the fabric from raveling.
Battening. As the shuttle moves across the loom laying down the fill yarn, it also passes through openings in another frame called a reed (which resembles a comb). With each picking operation, the reed presses or battens each filling yarn against the portion of the fabric that has already been formed. Conventional shuttle looms can operate at speeds of about 150 to 160 picks per minute.
With each weaving operation, the newly constructed fabric must be wound on a cloth beam. This process is called taking up. At the same time, the warp yarns must be let off or released from the warp beams (Corbman, 1975).
Because the shuttle can cause yarns to splinter and catch, several types of shuttleless looms have been developed. These operate at higher speeds and reduced noise levels. By the end of 1989, shuttleless looms represented 54 percent of all looms installed, up from 15 percent in 1980. Shuttleless looms use different techniques to transport cut pieces of fill yarn across the shed, as opposed to the continuous yarn used in shuttle looms.
Some of the common shuttleless looms include water-jet looms, air-jet looms, rapier looms, and projectile looms.
Water-jet looms transport the fill yarn in a high-speed jet of water and can achieve speeds of 400 to 600 picks per minute. Water jets can handle a wide variety of fiber and yarn types and are widely used for apparel fabrics.
Air-jet looms use a blast of air to move the fill yarn and can operate at speeds of 800 to 1,000 picks per minute. Air looms, although limited in the types of filling yarns they can handle, are increasing in commercial use. Yarn is drawn from the yarn package (1) by the measuring wheel and drive roller arrangement (2). Between the yarn package and the measuring wheel is a tube through which an air current flows in opposite direction to the yarn. This maintains a straight even feed of yarn. The yarn then forms a loop (3) which shortens as the pick penetrates further into the shed. The main jet (4) is the major projecting force for the yarn, although supplementary jets (5) are activated to prevent the pick from buckling.
Rapier looms use two thin wire rods to carry the fill yarn and can operate at a speed of 510 picks per minute. Rapiers are used mostly for spun yarns to make cotton and woolen/worsted fabrics. In a double rapier loom, two rods move from each side and meet in the middle. The fill yarn is carried from the rod on the fill side and handed off to the rod on the finish side of the loom.
Projectile looms use a projectile to carry the fill yarn across the weave. Shuttleless looms have been replacing the traditional fly-shuttle loom in recent years.