18—some Aspects of Yarn Structure

Yarn geometry, when the number of constituent filaments is small, is studied here with particular reference to yarn configuration, retraction, diameter, and packing factor. It is shown how, for twist factors within the range 20–40, yarn configuration and therefore yarn diameter remain more or less constant. A new approach to the definition of yarn diameter is put forward and corroborated by experimental evidence. A new formula for yarn retraction on twisting is determined for yarns having filament numbers in the range 1–37, and experimental evidence is given to show how it is more applicable than Treloar's formula when the number of filaments is fewer than 37. Two new definitions of packing factor are considered.