The Absorption of Gas in Aluminium Casting by the Mould Reaction
1965 Volume 29 Issue 7 Pages 708-714
Details
1965 Volume 29 Issue 7 Pages 708-714
Samples were prepared by casting molten aluminium in a CO2-process mould, a oil sand mould, a permanent mould and green sand moulds of different moisture content.
The authors measured the density and the gas content by the vacuum fusion extraction method, and then studied the effect produced by the mould reaction under these mould conditions.
The results were as follows:
(1) The mould reaction on green sand moulds was most remarkable, but the effect of the CO2-process mould was very small on account of the small moisture content. In case of the oil sand mould, however, the effect of the mould reaction was negligible, with no great difference from that of the permanent mould.
(2) The mould reaction effect was very marked at the portion near the surface, where the resulting defects caused by gas absorption were mainly observed. However, with increase of the runner length these defects tend to appear in the central portion. Most of the defects caused by the gas were observed along the grain boundary, and they were hardly observable in the grains.
(3) Under the mould reaction, the molten aluminium absorbed the gas in excess. The factors having the greatest effect on this reaction were the casting temperature and the moisture content in the mould. Accordingly, the quantity of the gas extracted in green sand moulds was much more than that from the samples in other sorts of moulds, but the relation between the gas content and the moisture in the moulds could not determined.
(4) The gas content in the samples depended on the synthetic effect of the mould reaction in each part of the mould. However, most of the gas absorbed by the sample were what was generated in the mould around the sample itself.
The effect of the runner length was found to be relatively small. Further, the gas from the mould reaction at the gate portion was distinctly marked only in the sample with the shortest runner length, while the effect became weaker with the increase in the runner length.
