This process comes from the need to assemble or combine two or more yarns. Such a composite yarn is made of a central part called the core and an outside part called the cover. Very often, the core is a spandex fiber or natural rubber, which gives the wrapped yarn its elastic properties.
Covers may be natural fibers (eg cotton or wool) or synthetic (eg polyamide or polyester), which are first wound off onto flanged bobbins and then placed on a hollow spindle into which the core is fed.
A covering cycle, during which a spindle produces 600gr of covered yarn, may last from two hours (eg thick yarns used in industry and agriculture) to four weeks (eg fine counts for hosiery).
There are different types of yarn covering:
- Conventional covering to produce single or double-covered yarns (one or two covers over a core).
- Air covering to produce yarns that are simply intermingled.
- Air and two-for-one covering, which provides a high resistant yarn, especially for warp (weaving).