Machinable glass ceramic contg. mica - having graded workability and strength, prodn. comprising controlled colling and heating

摘要

Machinable mica-contg. glass ceramic, (I) having graded workability and strength contains by wt. 15-35% Al2O3, 5-15% K2O, 1-15% F, 0-5% Li2O, 0-5% Fe2O3, 0-5% TiO2, 0-3% MnO, 0-5% CaO and in addn. 35-65% SiO2, 5-22% FeO, 0-10% Na2O, where =15% FeO may be replaced by an equiv. quantity of MgO, and K2O + Na2O =15%. (I) can be used as metal substitutes. The FeO replacement by MgO improves machinability and reduces crystallisation-tendency of FeO-contg. melts. Slow heating rates favour strength, whereas quick heating rates favour machinability. (I) are chemically stable, have higher bending strength than glass and a low heat-expansion coefft.