Effect of high-speed loading conditions on the pressing mechanism

In the high-speed pressing of powders it is possible to distinguish several processes with differnt operative mechanisms of powder particle deformation. Deformation mechanisms are determined by a complex criterion whose value depends on the mass velocity, since, thermal diffusivity, density, and hardness of particles. An understanding of the particle deformation mechanisms is of practical value. In the pressing of fine powders it is best to employ a quasistatic process represented by field II. To obtain compacts of high density and strength, use should be made of coarse powder fractions or pregranulated fine fractions in order to create conditions corresponding to field III. Incidentally, granulation not only increases the size of particles but also lowers their hardness, which is desirable in the case of difficult-to-press materials. Of particular interest is the pressing of rapidly quenched powders, which do not readily lend themselves to heat treatment. In such a case parameters corresponding to field IV should be chosen, and strength will then be imparted to compacts by melting and rapid solidification of the particle surfaces.