An experimental study on the producing mechanism of ultra fine powders in the initial wear region was carried out by a rotating friction mill devised to produce submicron powders by mutual friction grinding of two specimens of marble. The following results were obtained.
(1) The frequency distribution of inclination of a tiny surface protuberance showed the shape of a log-normal distribution and the relation of Hmax/tanθ=a·Hmax+b was obtained between the average inclination and surface roughness of specimens.
(2) The frequency distribution of diameter of contact protuberance area showed also the shape of a log-normal distribution and the average diameter agreed with the theoretical value.
(3) The number of contact point of a tiny surface protuberance increased as the surface roughness decreased.
(4) The standard deviation of a roughness distribution curve increased with the surface roughness of specimens.
(5) Two theories of cohesive wear and abrasive wear were examined as the producing mechanism of ultra fine powders in the initial wear region by mutual friction grinding. When the surface roughness of a specimen was under about 10μ, the formation of powders was predominated by the cohesive wearing mechanism and over about 10μ powers was produced by the abrasive wearing mechanism. It is concluded that the surface roughness of a specimen is an extremely important factor in mutual friction grinding.
