We have written about correct definition the hardness group of grinding balls in the article. Here, we would like to pay your attention for nuances in hardness measurement of grinding balls with high volumetric hardness.
For conformity grinding ball to the fifth hardness group needs to prepare a flat surface platform by removing metal from grinding ball to R (radius) depth on the one side and to a 0.5 R depth on the other side (Picture 1).
Picture 1. Platform preparation for hardness measuring of Ø40mm grinding ball on R depth
Hardness measuring all radius parts of grinding ball carried out in accordance with Picture 2.
Picture 2. Performance scheme of hardness measurement on a grinding ball platform (depth R)
Volumetric Hardness (VH) determined as sum of grinding ball measured values on surface hardness (Тsurf); hardness at 0,25 R (Т0,25); hardness at 0,5R (Т0,5); hardness at 0,75 R (Т0,75) and hardness in the center(Тc). Volumetric hardness (VH) calculated by formula:
VH= 0,289 Тsurf+ 0,436 Т0,25 + 0,203Т0,5 + 0,063Т0,75 + 0,009 Тc