A New Sand Casting Process with Accelerated Solidification Rate

Abstract

In order to solve the problems involved in coarse grains, macro and micro porosities initiated by low solidification rate in sand casting, an innovative counter-gravity sand casting process, Casing under Adjustable Pressure with Accelerated Solidification (CAPAS) was put forward in this paper. The hydrodynamics of mold filling for CAPAS is based on Bernoulli's principle. The mold and crucible were placed separately in the upper and lower chambers, with the feed tube connected between them. High-speed jet flow of air made negative pressure in the upper chamber. In this way, pressure differential was created between the two chambers. Thereby the molten metal in the crucible was forced to flow upward smoothly to fill the mold cavity. After mold filling, cold air was introduced into sand mold through aisles that are set within the mold, which results in strong convective heat exchange at the casting/mold interface. So solidification rate of casting increased dramatically. The microstructures of the aluminum castings were compared between CAP (Low pressure sand casting) and CAPAS by optical microscope. The results showed that the microstructure of CAPAS aluminum casting was much finer than that of CAP casting and tensile strength markedly increased.