Spun yarns of synthetic staple fibers have been produced by cutting continuous filaments into staple fibers, which are then assembled into yarn in the same manner as fibers of cotton or wool. A simpler direct spinning process is also used wherein parallel continuous filaments are stretch-broken and drafted between input rolls and delivery rolls in a drafting zone to form a sliver of discontinuous fibers which is thereafter twisted to form a spun yarn as disclosed, for example, in New U.S. Pat. No. 2,721,440 or Preston U.S. Pat. No. 2,784,458. A true twisting operation is inherently slow. Higher speeds can be obtained by using a false-twisting device, as disclosed in Tissot et al. U.S. Pat. No. 2,946,181 or Field, Jr. U.S. Pat. No. 3,079,746. Tissot et al. teaches that the use of gelatin size will provide adequate strength for weaving or knitting. However, the yarn lacks strength after the size is removed during fabric finishing. Field, Jr., teaches the use of a twisting jet to produce a yarn having surface fibers wrapped about a core bundle which is substantially free of true twist. However, improvements in this product are desirable to make it even more like a conventional spun yarn.
Bunting, Jr., et al. U.S. Pat. No. 3,110,151 discloses at column 23, lines 33-52, a process in which staple fibers averaging 7.6 centimeters long and 2 denier per filament were fed as a roving to drafting rolls and then through an entangling jet device, referred to therein as an interlacing jet, for entangling into yarn. Such products are not comparable to conventional spun yarns in strength, cleanness (freedom from neps and slubs), and uniformity.