State, with reasons, suitable material for the manufacture of each of the following, giving the approximate composition :
(a) a brass for deep pressed containers; (b) a brass for small machined bolts ; (c) a bronze for the impeller of a sea-water pump.
(a) The suitable brass for deep pressed containers is the admiralty brass containing copper and zinc in the proportion of 7 to 3, with 1% of tin.
The addition of tin to the basic cartridge brass (70% copper, 30% zinc), gives improved resistance to corrosion, renders the material less prone to season cracking, and could possibly lessen the number of interstage annealings. This material is very ductile.
(b) The brass used for small machined bolts is free cutting brass with composition: 61.5% copper, 35.5% zinc, and 3% lead.
This material is basically a leaded Muntz metal, the addition of lead imparts the highest machinability to the brass.
(c) The suitable bronze for the impeller of sea water pump is admiralty gun metal having composition of 85% copper, 13% tin, and 2% zinc.
It produces sound casting and has excellent resistance to salt-water corrosion. Machinability could be improved by addition of lead, but this has to be balanced against a lower resistance to corrosion.