Studies of Titanium Casting Using Commercial Investments with Quick Heating

Objectives: The purpose of this study was to investigate the possibility of titanium casting using commercial investments with the quick heating method (QHM). Methods: Two commercial phosphate-bonded investments for titanium (TV: Tancovest, Bego, and RT: Rematitan plus, Dentaurum) were examined. Green strengths (GSs) were measured by a compressive test at 30 and 40 minutes after the start of mixing. Fired strengths (FSs) were determined using specimens described as follows: specimens with the QHM were directly sintered at 30 minutes after mixing to a elevated temperature of 950 (TV) or 1000 degrees Celcius (RT) for 30 minutes, then cooled to room temperature; specimens with the conventional heating method (CHM) were heated and cooled according to manufacturer's suggestions. GSs and FSs were analyzed using two-way ANOVA at p<0.05. A crown wax pattern was prepared using a metal mold. The casting molds were heated with the QHM and the CHM. Five titanium castings from each casting condition were obtained using an argon-arc-melting casting machine (Cyclarc II, Morita). Results: The GSs significantly increased with longer measuring time; the GSs at 30 and 40 minutes of TV were 4.4 and 7.9 MPa, and those of RT, 10.3 and 12.2 MPa, respectively. FSs with QHM of TV (17.6 MPa) and RT (13.8 MPa) were significantly greater than those with the CHM of TV (15.4 MPa) and RT (13.2 MPa), respectively. The cracks of one TV mold with the QHM were so severe that the mold could not to be cast, and the top of three TV molds with the QHM were fractured; however this did not produce any defects on the casting surface. On the other hand, the remained mold did not show any crack or defects of casting. Conclusion: These results suggest that RT possesses practically acceptable properties even when the QHM was employed.