Research And Development Of Quantitative Determination Technology Of Trapped Gases In Aluminum Die Casting

Die casting is a cost-effective technology widely used to produce components withhigh precision and high productivity for automotive and other industries. A disadvantageof this process is the gas entrapment due to the turbulent flow of metal during the filling.The entrapped gas remains in the casting which hinders the casting’s suitability forwelding or heat treatment and deteriorates the casting quality. Gas content in a casting isan effective indicator of casting quality and provides a good indication of the suitabilityfor post casting processing. A number of methods may be used to quantify the gas level inthe castings. Vacuum fusion is a more accurate method to determine the gas content. Avacuum melting equipment designed with vacuum system and vacuum chamber wasdescribed in the paper, together with measuring principle, process and application.In the vacuum melting equipment, the part is placed in a vacuum chamber and heateduntil molten. The gas in the part is then released and the gas content can be quantifiedfrom the pressure increase in the vacuum chamber by gas standard curve which calculateoccluded gas quantity as a function of the pressure increments. The vacuum systemconsists of an oil diffusion pump and rotary vane pumps. Vacuum chamber comprises acavity and a cover. The cooling pipes are arranged around the cavity. The holes are openedin the cover and expanded to a plurality of interfaces, each for vacuum, quantitative gasinjection and temperature measurement.The vacuum system of the equipment can reach9.7×10-4Pa, to meet themeasurement requirements. The temperature of vacuum chamber and the furnace weretested by the thermocouple. Heating and holding by stages can as soon as possible make astable indoor temperature of vacuum between600℃-660℃. Gas standard curve with asignificant linear relationship are plotted through gas injection tube to releasequantification gas into the vacuum chamber. The curve shows that the slope only dependson temperature of vacuum chamber during the gas liberating instead of on its pressure invacuum.Finally, we present the results of a quantitative test of the gas level of a clutch housing.The gas release from the part may occur in several times and at different instants. At any case, it was found that all the gas was released from the casting parts about660℃. Theequation of gas standard curve under660℃is ΔP(Pa)=8.4683V(ml). After the increasedpressure caused by the leakage is removed, gas content of the casting section near theoverflow, runner section and biscuit were7.1ml/100g,4.31ml/100g,8.34ml/100g.