(a) What is the main difference between a brass and a bronze ?
(b) State the composition, and two common uses of a bronze commonly used in engineering.
(c) What is the general effect of adding a small proportion of (1) phosphorus, (ii) lead, to a bronze ?
(a) A brass is an alloy of copper and zinc, the major constituent being copper. A bronze is an alloy of copper and tin, the major constituent being copper.
(6) A bronze commonly used in engineering and commonly known as 'eighty-fives', three fives' consists of 85% of copper, with 5% each of tin, zinc and lead. Because of its improved machining qualities, it has replaced the traditionally used admiralty gun metal,
It is used for low pressure pipe fittings and small pump castings where reasonable corrosion resistance is desired.
(c) (i) If phosphorus is added in very small quantities, often only a trace, improves fluidity of casting. If the phosphorus ranges from about 0.05 to 0.25% as in a phosphor-bronze, it forms cuboids which resist wear and can carry heavy loads. It thus becomes an excellent bearing material.
(ii) Lead is distributed throughout a bronze as globules. It allows chip cracks to propagate easily and hence the addition of lead improves machining qualities.