Four methods of determining the angle of repose of free flowing powders have been critically compared using graded samples of glass balls, lead shot and silver sand. The method used influenced the result. Results of all methods have been correlated graphically and values for static and dynamic interparticulate friction have been assessed for the materials used. It was found that results for spheres could be correlated on one graph, irrespective of type of material and an explanation is given to account for this.
A punch penetration shear test has been used to support the theory of orientation of layers within the crystal lattice as the lubricating mechanism of laminar solids. Under high applied loads, this orientation is prevented, thereby causing a high value of the shear strength. The increased shear strength is manifest in an increased coefficient of friction under high loads, as found experimentally in the die pressing of solid plugs of talc and graphite. The use of these solids as lubricants in compaction processes cannot be justified at high constraining loads, where the relative density of the compact is high.
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