Method of reducing the tendency of tempered glass articles to yield under their internal stresses

摘要

482,914. Tempering glass. SADDAN, R. (Corning Glass Works) Dec. 24, 1936, No. 35419. [A Specification was laid open to inspection under Sect. 91 of the Acts, July 1, 1937.] Drawings to Specification. [Class 56] A method of increasing the stability of tempered glass articles consists in tempering the articles to produce a high degree of stress in the glass, and then subjecting them to heat treatment at a temperature, and for a time, adapted to reduce the stress to a predetermined value. The method is suitable for treating tempered glass articles which are subjected to heat in service. For example, a cooking-dish made of a glass composed of 60À5 per cent of silica, 21À4 per cent of alumina, 0À6 per cent of sodium oxide, 8À7 per cent of magnesium oxide, and 1-5 per cent of fluorine is highly tempered. It is then heated to a temperature of 535‹ C. for two hours, or to 510‹C. for seven hours. The compositions of a number of glasses to which the method may be applied are given in the Specification, and the effect of the treatment of the glass is illustrated by diagrams.