Measuring Yarn/Package Friction During Over-End Unwinding

The magnitude and uniformity of withdrawal tension during over-end unwinding depends on the coefficient of friction between the yarn and package. Current friction measurement techniques do not have the high speed and package surface roughness characteristics of yam-on-package friction. This research develops a new measurement technique for yam-package friction that uses simultaneously captured tension data and images of the yam sliding on the package surface during actual unwinding. An algorithm combines a mathematical model of the sliding motion with experimental data to produce estimates of the yarn/package coefficient of friction. Packages of equivalent denier, textured and fully drawn polyester yams are tested with a measurement uncertainty of less than 10%. The coefficients of friction increase from 0.40 to 0.48 and 0.23 to 0.35 over the speed range of 500 to 1000 m/min for the textured and fully drawn yams, respectively. A simpler measurement method with an Instron tensile tester can be used for comparative coefficient of friction measurements, but it provides quantitative agreement with the in-situ measurements only at low tension.