It will be apparent that raw fibers are usually better than waste fibers because waste contains processed and therefore stressed fibers. Furthermore, since waste fibers have experienced differing numbers of machine passages, they differ from each other in their characteristics. For example, lap web is very compressed, but waste from thread break suction systems is barely compressed at all.
Random and uncontrolled feeding of such fiber material back into the normal spinning process is to be avoided at all costs, since considerable count variation will result along with quality variations. It is preferable that:
- a constant, fixed percentage of waste fibers should be added to the fiber blend; and
- within this fixed proportion of waste, there should be a constant, fixed percentage of waste fibers of different sorts.
All of the clean waste arising in the mill can be returned to the same blend from which it arose; comber waste is used mostly in the rotor spinning mill; recycled fibers can be returned in limited quantities to the blend from which they arose. Rieter gives the following average amounts of recycled fibers that can be added to the normal blend:
- carded up to 5%
- combed up to 2.5%
- coarse up to 20%
- medium up to 10%
- fine up to 5%
As regards fibers from hard waste, only roving is used. When such fibers are used at all, they are often not returned to the blend from which they came but to a lower quality blend, and even then only in the smallest possible quantities.