GLASS IN CONTACT WITH MOLD MATERIALS FOR CONTAINER PRODUCTION

The high-temperature behaviour of various mould materials and coatings was studied by subjecting to cyclic temperature changes in oxidizing atmosphere and to contact with a soda-lime-silica glass melt at 1050 d egrees C. In a cyclic immersion test the influence of the type of moul d material, type of coating, surface roughness and of temperature on t he tendency of sticking to the glass melt was investigated. In the bas e materials the corrosive attack mainly occurred along grain boundarie s and in softer phases of the materials, starting from the surfaces. D efects in the moulded glass surfaces, worn-off particles from the moul ds and microcracks due to adhesion were found to depend on the type of oxide layer formed on the mould surface. Some ceramic nitride PVD fil ms proved highly resistant to oxidation and abrasion, and caused no de tectable damage of the glass. The sticking behaviour of the glass to t he various mould materials was investigated by measuring the separatio n forces. They were found to increase exponentially with temperature u p to permanent adhesion. All of the mould materials investigated showe d the same dependency of separation forces on temperature. Only in the case of a specific coating containing boron nitride a shift to distin ctly higher temperatures was observed.