Drawing-In & Warp Tying
When a new denim style is put on a weaving machine, it is necessary to draw or insert the warp yarns through various elements, including the stop motion devices, weave design control devices, and a filling beat-up device.
Each end of yarn must have its own individual drop wire and heddle and be inserted into the correct dent in the reed. This procedure can be done manually or automatically on drawing-in machines. Of course, manual drawing-in is much more time-consuming. When the same end count and draw is to follow on a loom with a depleted warp, then a full beam of yarn can be tied to the yarns of the old beam. This can be done by a tying-in machine, which automatically selects an end of yarn from the old beam and ties it to the appropriate end on the new beam.
Warp yarns are fed from the loom beam and pass over a whip roll or rollers, which help to control variation in yarn tension during weaving. The yarns are then directed through drop wires, heddles, and a comb-like device called a reed. The spaces between the reed wires across the width of the reed are called dents. Each reed will have a specific number of dents per inch — 12 to 18 for most denim and denim-type fabrics. The reed number and the number of warp ends determine the woven width of the fabric.
Basic Weaving Motions
Four basic motions are required to weave a fabric, such as denim — warp control (let-off and take-up), shedding, filling insertion, and beat-up. The warp control determines the rate the fabric will be made. The shedding determines the design, the filling insertion determines the range of speeds, and the beat-up pushes the inserted filling yarn into the fabric.