Abstract
Seven experimental investments distributing the three grain sizes of crushed electrically fused calcia powder, i.e., coarser powder (100-200 mash), medium-sized powder (200-325 mash) and finer powder (325 meth pass) were prepared and the manipulatory characteristics, the strength of set investments and the surface texture of titanium castings were investigated. Calcia investments containing 75-90 wt% of the finer powder, 5-15 wt% of the mediumsized powder and 5-10 wt% of the coarser powder had better manipulatory characteristics with methanol and set completely within 24 hours at 23℃. The green strength of these investments was 9.1-10.5 Mpa and the fired strength, 10.0-10.9 MPa. Titanium castings with all experimental investments showed a glossy surface that did not react with the mold in spite of the high mold temperature of 1000℃. Especially the castings with calcia investments containing 75-90 wt% of the finer powder had an excellent surface, which had a roughness of 1.07-1.14 μm(Ra).
