Felting and Ratchet Action of Wool Fibers

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Abstract
Frictional contacts between crossing fibers consist of a true frictional component and a ratchet component that causes fiber migration. The saw-tooth shaped profile of a Merino wool fiber operates as a ratchet on the curved surface of crossing fibers up to a radius of curvature of the crossing fiber of about 50 microns: ' An apparatus and method for the measurement of the longitudinal rubbing force between a mounted glass fiber and a wool fiber is described that gives a reproducible record showing each scale edge traversed. A convenient method is described for the analysis of these records to show the effectiveness of the fiber scales for different ampli tudes of fiber-to-fiber movement during felting processes. The results obtained agree with the theory developed for ratchet-action, of particular interest being the decrease to zero of the directional frictional effect as the amplitude of movement is reduced from a distance equal to that between neighboripg scale edges to zero. To limit the extent of against-scale slippage of resilient fibers under strain during felt formation, it is desirable to have some energy loss, i.e., a true frictional component, in the ratchet system.

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