Abstract
To evaluate the cushioning effects of dry casting ring liners on the hygroscopic expansion of investment materials, cushioning ability was determined for fifteen ceramic liners (A : rockwool type, B : ceramic fiber low temperature type, C : ceramic fiber standard type, D : ceramic fiber low temperature standard type, E : kaolin type). Dry liners were seated inside the sliding frame of an apparatus for expansion measurement, and then the hygroscopic expansion was measured for 120 min. Cushioning effects were calculated by differences between the hygroscopic expansion with and without a liner. The cushioning effect of liners increased with time and peaked at 20 min, then markedly decreased by 25〜40 min, and changed only slightly thereafter. In only three liners in the D group, the cushioning effect showed a positive value by 120 min starting 15 min after the water was poured. The maximal cushioning effects of fifteen liners were noted in D group liners. The cushioning ability of three liners in D group on the hygroscopic expansion was sufficient.
