Abstract
Some properties of powder beds, i.e.“viscosity”of powder in a vibrating state, their packing density, the angle of repose and shearing stress, were measured at a range from room temperature to about 300°C. α-alumina powders with several kinds of particle sizes and spherical glass powder were used as the samples.
Increasing the temperature in the range higher than 100°C, in which moisture was considered not to be effective upon the adhesive properties of these powders, the“viscosity”and the angle of repose increased and the packing density decreased. These results suggest that the attractive force between the particles increases with the increase of temperature as has been verified by the shearing tests.
The theoretical calculation of sedimentation volume, which was studied by Nakagaki et al. for the packing density in relation to the adhesive probability of particles, P, was applied to the packing density in a heated state in order to obtain the quantitative relation between the attractive force and temperature. On the basis of an assumption that P was given as a function of kαD/mv, where k, α, D, m and v were respectively shape factor, temperature factor, particle size, mass of the particle and sedimentation velocity of particle in hot air, the relation between α and absolute temperature T was obtained in the following equation.
logα=aT/Tm-b
In this equation, Tm was the absolute temperature of melting point of the sample. The constant a was found to be the same one for α-alumina and glass powder.
The effects of temperature upon the angle of repose and the“viscosity”of powder were systematically interpreted in terms of the temperature factor α obtained from the above equation.
