New Possibilities to Control the Interaction Process between Liquid Alloys and Sand Mould

摘要

The present sand moulds cannot simultaneously insure optimum values of the main factors that govern the reactions between the liquid alloy and the mould wall (moistening angle, heat resistance, porosity, reducing atmosphere, coefficient of heat accumulation, exogenous gas pressure). The authors promote the use of the combined moulds technology which have bi-layered walls: active layer and support layer. The active layer (pattern layer) with a small thickness (up to 30mm) contains- along with its usual components of sand and binder - a certain amount of pyrocarbon precursors. Only a pyrocarbon film of up to 3% deposited on the surface of the sand granules has the ability to effectively change all the factors of influence listed. Only the vacuum-hardened support layer can determine the decrease of the exogenous gas pressure. These values can be adjusted within wide limits, even during the pouring process. The method is flexible and can be adjusted according to the alloy composition, the casting configuration and the running system, etc. It has important economic and environmental features. The applied use of these moulds does not require any special investments. It was conceived as a small and medium batch production foundry, but additional research will definitely prove that it can be compatible with high batch production.