Manufacture of glassware articles of improved strength

Abstract

An article of glassware, particularly a glass container, of increased strength is made by a process in which the parison is treated in a manner which will cause the glass in the outer surface layer of the formed glassware article to be in a state of compression. Preferably a glaze having a coefficient of thermal expansion lower than the coefficient of thermal expansion of the glass of the parison is applied to the outer surface of the parison. Advantageously, the glaze is applied to the parison by a flame spray method or by dipping the parison into a fluidized bed containing powdered glaze. As an alternative, the glaze applied to the outer surface of the parison may be capable of being at least partially crystallized, after the glassware article has been formed from the parison, to produce an outer surface of the glassware article having a lower coefficient of thermal expansion than the base glass of the glassware article. Alternatively to the application of a glaze, glass in the outer surface of the parison may be chemically changed so that the surface glass in the parison has a higher transformation temperature than the remainder of the glass in the parison. Additionally, the interior surface of the parison may be treated by a material producing active gases so that a compressive layer is produced on the internal surface of the final glassware article, at least partially balancing the compressive layer in the outer surface of the glassware article.