MULTIDIMENSIONAL INTERNAL SETTING EXPANSION OF A PHOSPHATE-BONDED CASTING INVESTMENT MEASURED WITH STRAIN-GAUGES

Strain gauges were used to determine the setting expansion of phosphate-bonded casting investments. The gauges were placed at the approximate site of the wax pattern. The isotropy of the expansion was evaluated with multidirectional strain gauges that measured the difference in expansion in two orthogonal directions. A large difference was found between the setting expansion measured externally (1% to 1.5%) and the method described here (0.01%). For casting rings lined with a nonasbestos layer, no statistically significant differences were found in the setting expansion parallel to the long axis of the ring and the expansion in the direction perpendicular to the long axis. © 1990 The C. V. Mosby Company.