Glass in contact with mould materials for container production

Abstract

The high-temperature behaviour of various mould materials and coatings was studied by subjecting to cychc temperature changes in oxidizing atmosphere and to contact with a soda-lime-sihca glass melt at 1050°C. In a cyclic immersion test the influence of the type of mould material, type of coating, surface roughness and of temperature on the tendency of sticking to the glass melt was investigated. In the base materials the corrosive attack mainly occurred along grain boundaries and in softer phases of the materials, starting from the surfaces. Defects in the moulded glass surfaces, worn-off particles from the moulds and microcracks due to adhesion were found to depend on the type of oxide layer formed on the mould surface. Some ceramic nitride PVD films proved highly resistant to oxidation and abrasion, and caused no detectable damage of the glass. The sticking behaviour of the glass to the various mould materials was investigated by measuring the separation forces. They were found to increase exponentially with temperature up to permanent adhesion. All of the mould materials investigated showed the same dependency of separation forces on temperature. Only in the case of a specific coating containing boron nitride a shift to distinctly higher temperatures was observed.