POWDER SEGREGATION DURING DIE FILLING

A study of powder segregation during die filling with two-component mixes of Pb particles has shown that: (1) Segregation occurs by fines filtering down through the moving powder mass. This effect builds up an inner mound of fines-rich material on the bottom of the die and an excess of coarse particles in the periphery of the die cavity. This is termed normal segregation. (2) For a particular size of large component, reducing the size of the small component increases segregation up to the point at which the average relative size difference between coarse and fine is 0.7. When the fines are smaller than this their flow is restricted and so segregation is reduced. (3) Particle shape and density in the mixtures studied have little effect upon segregation. (4) Increasing the rate of die filling decreases opportunity for segregation. (5) Increasing the height from which the powder falls into the die causes mixing and decreases segregation. (6) Inverse segregation, which is an excess of fines in the periphery of the die cavity, occurs in coarse particle systems containing a high percentage of fines. This is because the relatively few coarse particles are Lindered from flowing within the matrix of fines towards the rim of the die cavity. © 1969.