Question : What are the meaning of “true density” and “packing density” of media?
Answer :
(1) 1. For the same material, higher true density means fewer pores inside the body. Meanwhile, better physical properties including wear resistance. The following pictures and experiment prove the correlation between true density and wear resistance.
SEM picture of cross section of poor density YSZ bead ( 1mm, N-brand )
SEM picture of cross section of high density YSZ bead (1mm, EE-TEC)
After 80 hours of milling in pure water, N-brand seriously contaminates the water (left) while EE-TEC beads keep water clean.
(2) Packing density : media weight per specified volume
Except for calculate packing volume in the milling chamber, the packing density reveal the following important Properties :
- True density. Media has higher packing density has higher true density.
- Roundness of the media. As the pictures below , bead with perfect roundness has highest packing density (left) while elliptic bead has loose packing.
