It has been pointed out that properties of the magnetic keeper may change from original condition after casting. In this study, to evaluate the effect of the casting and the heat treatments for the casting alloy on the property of the keeper, hardness test and light microscopic observation were carried out.
Two kinds of keepers (HICOREX Slim, Hitachi Metals, Japan and Magfit 600, Aichi Steel, Japan) were investigated in this study. These keepers were cast on with gold-silver-palladium alloy (Castwell MC, GC, Japan). Then homogenization heat treatment and hardening heat treatment for gold-silver-palladium alloy were performed on the casting-on specimens. After casting-on and each heat treatment, hardness test and microscopic observation on the keepers were performed. Before these experiments, non-heated keepers were estimated as control.
The results for casting-on samples showed a decrease in hardness for both keepers. Furthermore, after each heat treatment, a decrease in hardness was found as compared to the control for both keepers (p<0.01, ANOVA).
In both keepers, microscopic findings showed that grains became larger than those of control and grain boundaries became distinguished.
The results showed that heat treatments for the casting alloy should be avoided because the properties of keepers were adversely affected.
