Abstract
In general it is considered that the unsoundness of pure copper castings is mainly caused by the steam generated by the reaction between hydrogen and oxygen absorbed in molten copper. In the present work, the behavior of oxygen and hydrogen in the melting and pouring processes of pure copper was quantitatively analysed and the effects of gases on the soundness of castings were determined.
When molten copper (1,230°C) was oxidized in the atmosphere, the oxidation rate was in good agreement with the previously reported values for the 25min from the start of oxidation. The flux cover on the surface of molten copper was necessary to keep the oxygen content at a minimum and the graphite cover was best. Oxygen content in molten copper was 0.34% in weight when the flux was not used, 0.072% when a strongly oxidizing flux powder was used and 0.004% when graphite powder was used.
In general, when phosphorus was added, hydrogen content was high while oxygen content was low. However, the melt with oxidizing flux cover showed low hydrogen content even with low oxygen content.
The density of sand mold castings increased with pouring distance, due to the evolution of hydrogen during the pouring process. When phosphorus was not added, the densities of sand and permanent mold castings depended on the hydrogen content. Both castings gave low figures when the hydrogen content increased up to 0.00007%. When phosphorus was added, the density of sand mold castings depended upon the hydrogen content and low figures were obtained when the hydrogen increased up to 0.00015%. However, the density of permanent mold castings was not affected by hydrogen content.
