Coefficients of friction between cereal grain and various silo wall materials

Abstract

The coefficients of friction of 7 materials which could be used in the construction of agricultural silo walls (or as linings) were determined for wheat and barley at different moisture contents within a range of 10 to 20% (w.b.). In general the coefficients increased with increasing moisture content, and varied between approximately 0·11 for Teflon on the driest barley to nearly 0·5 for concrete on the wettest wheat. The coefficient with wheat was up to 0·1 higher than with barley at corresponding moisture contents. With certain materials minima occurred at 15% m.c. or below. Tests were carried out by rotating annular plates on the grain surface, using both an open tray and an annular tray only slightly larger than the plate to prevent any flow of the grain in a radial direction. The coefficients obtained by the former method were approximately 0·04 less than those obtained by the latter. Additional tests carried out to compare the difference between the shear stress at the initial yield point and the maximum shear stress due to friction showed the former to be about 0·02 less than the latter.