Effect of Casting Force on Mold Filling of Titanium

Objectives: This study examined the effect of the casting force on the castability (mold filling capacity) of commercially pure titanium (CP Ti: ASTM grade 2). Methods: Two types of wedge-shaped acrylic patterns were prepared with either 15° or 30° angles and invested with a MgO based investment material (Selevest CB, Selec Co., Japan). The molds were cast using a centrifugal casting machine (Ticast Super R, Selec) at rotational speeds of 600, 1000, 1250, 1500, or 3000 rpm. The castings (n=6) were sliced perpendicular to the triangular surface into four specimens, and the area near the tip of each specimen was photographed with a scanning electron microscope (25x). Mold filling was determined by measuring the distance between the tip of the cast wedge and the theoretical acute tip of the triangle. Results were statistically analyzed by one-way ANOVA and multiple tests (a=0.05). Results: The mold was filled out for experimental conditions except for the 15° mold at 600 rpm. The determination of filling [mean (SD), mm] is listed below:

	600	1000	1250	1500	3000	rpm
30°Ð	361(75)c	292(105)bc	214(102)ab	218(64)ab	151(60)a
15°Ð	-	843(281)d	401(226)e	342(132)e	301(207)e

Identical letters indicate no significant differences (p>0.05). For each corresponding speed, the mold filling of the 30° angle was smaller than that of the 15° angle (p<0.05). In each angle, the means tend to reduce with the increase in the rotational speed. In the 15° angle, the mold filling was more pronounced with the change in speed. Conclusions: In order to fill CP Ti at a sharp margin in centrifugal casting, a rotational speed ³1250 rpm is needed. This study was partially funded by NIH/NIDCR grant DE 11787 and the Baylor Oral Health Foundation.