RADIAL PRESSURES IN POWDER COMPACTION

AbstractA simple theory is advanced to explain the variation of radial (die-wall) pressure during compaction in conventional dies. The theory predicts that, during the application and release of pressure by the punch, the radial pressure should follow a characteristic cycle whose form is determined by the elastic properties and by the yield stress in shear of the material being pressed. The theory is supported by experimental radial-pressure determinations on a range of materials.The theory accounts for the residual radial pressures that dies continue to exert on compacts after removal of the punch pressure; according to the theory, these residual pressures arise through shearing of the pressed material, and have maximum values which are determined by the shear strength of the material. The mechanism of production of capping and laminar cracks by residual radial pressures is discussed in detail.An apparatus for the measurement of radial pressures and powder/die friction coefficients at moderately high tem...