Massive venting and vacuum

摘要

As it happens, porosities caused by air trapped in castings (blowholes) account for a large share of rejects in pressure die casting. The defects, found after machining, tapping, and tightness testing, cost foundries a lot of money. The vacuum technique in pressure die casting has been in existence for a very long time; a few companies were pro posing installations as early as 1960. Many foundrymen are still wondering about the effectiveness of the vacuum. The demand for very low customer return levels, even zero, and weldability constraints are encouraging foundrymen to make the process more reliable and to increase the capacity and reliability of the machines and tooling. For this reason, pressure die casting tests were performed to measure the effect of application of a vacuum on the castings made. Two studies were conducted. The first (A. Badal, Y. Longa, P Hairy) was performed on a test casting and demonstrated the utility of the vacuum and of massive venting. The second (J. de Ruffray, D. Bihan, P. Girot) was perlbrmed on an industrial casting in collaboration with the THEVENIN foundry (S31 group) in order to confirm the utility of massive venting and determine its advantages and limitations.