A study of solder investment setting expansion and thermal contraction: Part 2

In this study, which won the NBC Fellowship Project, the author measured expansion and contraction in two soldering and six casting investments to determine which are most accurate (defined as marginal gap less than 50 micrometers and lack of movement with alternating finger pressure) under a number of manipulated parameters, including water/powder ratio, setting time, span length and burnout temperature. It was determined that all investments demonstrated slight expansion between initial and final set. Substantial contraction occurred in all investments when subjected to heat. Vestra, CB-30 and Cera-Fina demonstrated the greatest contraction at 1500 degrees F. Hi-Heat (soldering), Quick Set, High Span, Vivest, and Hi-Temp (casting) demonstrated greatest contraction at 2000 degrees F. The purpose of the study and the methods and materials used were explained in part one, published in March. The results and conclusions are presented here. An introduction to elevated fixturing and a verification of the study results will be presented in part three.