Compressibility of Air in Casting Mould Evaluated by Finite Element Method and the Stream Function Model

Casting is a manufacturing process for making complex shapes of metal materials. Casting has two stages – filling process requiring a gating system and solidification process requiring a riser. The air in the mould cavity during casting is displaced through the riser by the molten metal in a very rapid manner necessitating the need to determine its compressibility as it exit through the riser. The finite element method and the stream function model were used to analyze the flow of air through the top risers of casting mould. Results show that the velocity profile at any cross section is parabolic in shape with the maximum velocity at the centre. Comparing the finite element solutions with the exact solutions showed that the solutions converged towards the exact solutions. Further comparing of finite element solutions and experimental results with the local speed of sound (Mach number) showed that the Mach number was greater than one, which established that the air in the mould cavity during casting is compressible as it is displaced by the molten metal. Before now all researches did was to develop empirical equations and optimized molten metal flow in casting mould. This work has gone further to establish the compressibility of airflow in casting mould.