Welcome to Mechanical Finishing where you will learn about “Drying”, “Compaction”, “Calendering”, and “Sanding, Napping, and Shearing.”
Drying is, of course, used to remove moisture from the fabrics; however, the way in which the heated air is applied can have more far-reaching effects. Controlling the mechanical action of the drier, including the air velocity and other mechanisms, can result in bulking of the fabric and shrinkage control. High temperatures after drying can be used for heat setting of thermoplastic fibers. Various types of dryers are used in the textile finishing house.
A fabric’s tendency to shrink is affected by its structure, with more open structures having a greater propensity to shrink. Compaction, a mechanical process, can be used to reduce fabric length shrinkage by mechanically compressing the structure of the fabric. Compacting machines are available in various designs for knit and woven fabrics.
Calendering is a mechanical finishing process typically used to produce special fabric effects, such as high luster, smoothness, or even embossing. In this operation, primarily used on knitted and woven goods, the fabric is passed between heated rolls under heavy pressure.
Sanding, Napping, and Shearing
In contrast to calendering, sanding makes knit or woven fabrics feel softer and appear more textured. Sanding can be used to make the fabric surface resemble sueded leather. Typically, the fabric surface is subjected to one or more rolls of abrasive material (usually sandpaper) moving at a much higher surface speed than the fabric. In the napping process, typically used on woven flannel and knit fleece, wire points are used to lift fibers from the surface of a fabric. The shearing process uses a very sharp rotating cylinder with shearing blades and a straight fixed ledger blade to cut off surface fibers or yarn loops.