Measurement and mathematical modelling of the heat transfer in the glass forming process, in consideration of the heat transfer coefficients and radiation influences

Abstract

During forming, glass to mould contact temperatures are the significant factor for the final glass surface quality. For a good characterization of this contact condition the heat transfer by conduction and radiation needs to be described in detail. A laboratory testing unit was set up to investigate the influence of radiation emitted by different glass composidons and the influence of different mould materials used during forming. To support the experimental results, heat transfer conditions and temperatures were modelled at given boundary conditions using the CFD-Code FLUENT software program applying discrete models. Measurement and modelling results show that the radiation influence on heat transfer is strongly dependent on the spectral absorption coefficient of the glass which affects heat flux densities and surface temperatures. Results show up to 15 % higher heat flux density for amber glass compared to flint glass. In addition, internal glass temperature distributions are strongly affected. If glass throughput, type of forming tools and mould cooling settings are carefully adapted to the optical characteristics of the glass, an optimal surface quality and physical strength can be achieved, which may lead to significant economic benefits. Due to the complex interactions of the parameters which influence glass to mould heat transfer mathematical modelling proves to be essential for future developments in forming technology.