Chovani formového materialu ve styku se sklem

A new testing method and apparatus for determining sticking temperature as well as hot corrosion and wear of mold materials to be used in glass industry has been developed. The testing procedure simulates the molding process in glass container manufacturing by pressing a large number of gobs (soda-lime glass) from a melting crucible under defined non-isothermal conditions. As function of pressing parameters, especially mold temperature, molding pressure and service time of the mold specimens, the sticking behavior, surface structure of the molded glass objects and corrosion and wear of the mold surfaces are analyzed. The intensity of sticking at each mold temperature underlies a statistical distribution, and is quantified by recording the time interval necessary for separating the glass blank from the mold surface using a well defined debonding procedure. The duration of sticking increases steeply with mold temperature within a narrow temperature interval of 20-50 K. The sticking characteristics of each tested material (stellite, cast iron, coated steel, bronze) can be described by two values: the lower and the upper sticking temperatures. A definition for each is given in the presented work. For the lower sticking temperatures a nearly linear dependence on the thermal diffusivity of the mold materials was found. The upper sticking temperature depends additionally on chemical and structural properties of the mold surfaces. Corrosion and wear of the mold materials are monitored by analyzing abraded particles on the molded glass surfaces and by stylometry. Due to carrying out these experiments at and above the lower sticking temperature (i.e. well above mold temperatures run in industrial processes), significant differences in corrosion behavior in short time laboratory experiments are obtained.