The influence of the parameters of lost foam process on the quality of aluminum alloys castings

Abstract

This paper presents the research results of application of Lost foam process for aluminum alloys castings of a simple geometry. The process characteristic is that patterns and gating of moulds, made of polymers, stay in the mould till the liquid metal inflow. In contact with the liquid metal, pattern intensely and in relatively short time decomposes and evaporates, which is accompanied by casting crystallization. As a consequence of polymer pattern decomposition and evaporation a great quantity of liquid and gaseous products are produced, which is often the cause of different types of casting errors. This paper presents the results of a research with a special consideration given to detecting and analyzing the errors of castings. In most cases the cause of these errors are defects of polymer materials used for evaporable patterns production, as well as defects of materials for refractory coatings production for polymer patterns. The researches have shown that different types of coatings determine properties of the obtained castings. Also, the critical processing parameters (polymer pattern density, casting temperature, permeability of refractory coating and sand, construction of patterns and gating of moulds) significantly affect on castings quality. During the research a special consideration was given to control and optimization of these parameters with the goal of achieving applicable castings properties. The study of surface and internal error of castings was performed systematically in order to carry out preventive measures to avoid errors and minimize production costs. In order to achieve qualitative and profitable castings production by the method of Lost foam it is necessary to reach the balance in the system: evaporable polymer pattern - liquid metal - refractory coating - sandy cast in the phase of metal inflow, decomposition and evaporation of polymer pattern, formation and solidification of castings. By optimizing the processing parameters castings of required structural and mechanical characteristics could be achieved, casting defects characteristic for this process could be avoided with the result of the production costs saving. The presented results can be useful to define parameters of Lost foam process and its application in practice with objective to obtain castings with in advance specified quality

Synthesis of the new lost foam refractory coatings based on talc

“…4,5 Unlike sand mould casting, where liquid metal flows into the "mould cavity", with the lost foam process, the patterns and pouring systems made of polymers are retained in the mould until a liquid metal has flown in ("full mould casting"). 1,[6][7][8][9] In contact with a liquid metal, polymer patterns degrade, evaporate and simultaneously the castings solidification takes place. As a consequence of the degradation and the evaporation of the polymer pattern, a large amount of liquid and gas products is released.…”

“…If subcooling is considerably fast, a fine tiny-grained structure is formed on castings. 1,7,13 The pattern degradation and the evaporation rate depend on…”