Removal of Aluminium from Copper-based Alloys to Ensure Pressure-Tight Castings

The preserce of aluminium is harmful in gunmetal
particularly meant for the production of
pressure-tight castings, because aluminium, if
present in gunmetal even in traces, causes leakage;
but the metal is sometimes introduced into the alloy
along with the used scraps which may contain
aluminium varying from 0.5 to 2.5 per cent., viz.
naval parts, impellers, propellers, etc. The passing of dry compressed air under 100 lb./sq. in. through the melt containing different proportions of intentionally added aluminium caused .the removal of even traces of the metal practically without any loss of zinc or tin, as aluminium has the tendency for preferential oxidation. The extent of its removal has been shown to depend on its percentage
in the melt and the amount of compressed air passed through it.