Development of a Computer Simulation Model for Blowing Glass Containers

In glass container manufacturing (e.g. production of glass bottles and jars) an important process step is the blowing of the final product. This process is fast and is characterized by large deformations and the interaction of a hot glass fluid that gets into contact with a colder metal, the mould. The objective of this paper is to create a robust finite element model to be used for industrial purposes that accurately captures the blowing step of glass containers. The model should be able to correctly represent the flow of glass and the energy exchange during the process. For tracking the geometry of the deforming inner and outer interface of glass, level set technique is applied on structured and unstructured fixed mesh. At each time step the coupled problem of flow and energy exchange is solved by the model. Here the flow problem is only solved for the domain enclosed by the mould, whereas in the energy calculations, the mould domain is also taken into account in the computations. For all the calculations the material parameters (like viscosity) are based on the glass position, i.e. the position of the level sets. The velocity distribution, as found from this solution procedure, is then used to update the two level sets by means of solving a convection equation. A re-initialization algorithm is applied after each time step in order to let the level sets reattain the property of being a signed distance function. The model is validated by several examples focusing on both the overall behavior (such as conservation of mass and energy) and the local behavior of the flow (such as glass-mould contact) and temperature distributions for different mesh size, time step, level set settings and material parameters. NOMENCLATURE A Lakatos coefficients B K Lakatos coefficients cp J/kgK specific heat of glass f m/s 2 body force (gravitation) kc W/mK conductivity of glass p Pa pressure q W/m 2 heat flux t sec time T K glass temperature TL K Lakatos coefficients U m/sec velocity η m/s dynamic viscosity ρ kg/m density σ Pa Cauchy stress tensor INTRODUCTION Glass is a material used in many products such as windows, bottles, art articles, etc, which all have their own unique manufacturing process. In the past, glass technology has been a craft mainly based on empirical knowledge and hands on experience. Over the last twenty years there has been significant progress in understanding and modeling the glass manufacturing process [1,2]. This paper concentrates on modeling the blowing stage of the forming process of glass containers. In particular it is interested in the accurate representation of the glass-air interface during blowing [3]. For glass containers manufacturing, the forming process is typically comprised of two stages: a pressing stage (Figure 1a) and a blowing stage (Figure 1b). As the glass flows down entering the forming machinery it is cut into gobs. At the start of the process the pressing mould is open from above and a gob of molten glass falls from the gobbing device into the mould then the plunger is pushed up by a piston (Figure 1a). This mould usually produces an intermediate form, called the preform or parison. This preform is then transferred into a