Bronzes: Bronze is a common alloy of copper and tin. The alloys of copper and tin are generally termed as bronzes. The wide range of composition of these alloys comprise of 75 to 95% copper and 5 to 25% tin.
Properties of bronzes: Bronze has higher strength, better corrosion resistance than brasses. It is comparatively hard and resists surface wear and can be shaped or rolled into wire, rods and sheets very easily. It has antifriction or bearing properties. Bronze is costlier than brass. The tensile
strength of bronze increases gradually with the amount of tin, reaching a maximum when tin is about 20%. However the percentage of tin content if increases beyond this amount, the tensile strength decreases very rapidly. Bronze is most ductile when it contains about 5% of tin. As the amount of tin increases about 5%, the ductility gradually decreases and practically disappears with about 20% of tin. Whereas presence of zinc in the bronze increases fluidity of molten metal, strength and ductility.
Some of the common types of bronzes are discussed as under:
Phosphor Bronze: When bronze contains phosphorus in very small amount, then phosphor bronze is produced.
A common type of phosphor bronze has the following composition.
Cu = 89 to 94%
Sn = 6 to 10%
P = 0.1 to 0.3%
Properties: Tensile strength, ductility, elasticity, soundness of castings, good wearing quality and resistance to fatigue of phosphor bronze increases with increase of phosphorus in bronze. This material possesses good corrosion resistance especially for sea water, so that it is much used for propeller blades. Phosphor bronze of proper composition can be easily casted, forged, drawn, and cold rolled.
Applications: Phosphorus bronze is used making for bolts, electric contact springs, bearings, bushes, gears, ship sheathing, valve parts, propeller blades, worm wheels, gears, nuts for machine lead screws, pump parts, linings and for many other purposes. It is also suitable for making springs and corrosion resistance mine cables.
Silicon bronze: Silicon bronze contains
Cu = 96%
Si = 3%
Mn or Zn = 1%
Silicon bronze has good general corrosion resistance of copper combined with higher strength. It can be cast, rolled, stamped, forged and pressed either hot or cold and it can be welded by all the usual methods.
Applications: Silicon bronze is widely used for making boilers, tanks, stoves or where high strength and good corrosion resistance is required. It is used also for making screws, tubing’s, pumps etc.
Beryllium bronze: Beryllium bronze is a copper base alloy contains
Cu = 97.5%
Br = 2.5%
Beryllium bronze possesses higher tensile strength than other bronzes. It possesses excellent corrosion resistance. It is having high yield point and high fatigue limit. It is having good hot and cold resistance. This can be heat treated by precipitation hardening. It possesses excellent formability in soft condition, and high fatigue and creep resistance in hardened condition. However it involves high cost.
Applications: Beryllium bronze is particularly suitable material for making springs, tubes, diaphragms and electrical contacts, heavy duty electrical switches, cams and bushings. This is used for it is used for making chisels and hammers using for such conditions where spark might cause explosion. It has a film forming and a soft lubricating property, which makes it more suitable as a bearing metal. Since the wear resistance of beryllium copper is five times that of phosphorous bronze, therefore it is used as a bearing metal in place of phosphor bronze.
Manganese bronze: Manganese bronze is an alloy of copper, zinc and little percentage of manganese. The usual composition of this bronze is
Copper = 60%
Zinc = 35%
Manganese = 5%
Manganese bronze is highly resistant to corrosion. It is stronger and harder than phosphor bronze.
Applications: Manganese bronze is mainly used for bushes, plungers, feed pumps, rods etc. Worm gears are frequently made from this bronze.
Aluminium Bronze: Aluminium bronze possesses
Cu = 85 to 88%
Al = 8 to 11%
Fe = 3%
Sn = 0.5%
Properties: The aluminium bronze with 8% aluminium possesses very good cold working properties. When iron is added to this metal, its mechanical properties are greatly improved by refining the grain size and improving the ductility. The maximum tensile strength of this alloy is 450
MPa with 11 % aluminium. This material possesses good resistance to corrosion and it is somewhat difficult to cast due to oxidation problem.
Applications: Aluminium bronze is generally used for making fluid connection fittings, gears, propellers, air pumps, bushings, tubes, slide and valves etc. Cams and rollers are commonly produced using this alloy.
Bell Metal: Bell metal generally contains
Cu = 66.7%
Sn = 33.3%
Bell metal is very strong. It possesses resistance to corrosion water and atmosphere. It is used to make bells.