Bronzes

Bronze is basically an alloy of copper and tin. In general, it possesses superior mechanical properties and corrosion resistance than brass. Those containing upto 8% tin are called working bronzes. They can be easily cold worked, rolled, formed and drawn. They are available in various forms, as strip, wire and sheet etc. With the increase in tin content, its strength and corrosion resistance increase. It is then known as hot working bronze. Small addition of phosphorus further improves its strength, ductility and bearing properties. The amount of phosphorus added is 0.5%. This is then known as phosphor bronze.

Phosphor bronze

Various compositions of this alloy are available for different uses. That having about 0.5% P is widely used for different types of springs in electrical instruments. Its drawn tubes are used in fuel systems and instruments. Cast phosphor bronze is used for bearings and gears. Bearing bronze contains 10% tin and small addition of lead. Gear bronze contains 13% tin for greater strength. Phosphor bronze can be sand cast, centrifugally cast, or cast through lost wax process. It carries good load bearing capacity, enough plasticity and good wear resistance, which make it an ideal bearing metal.

Gun metal

It is a phosphor bronze having 2 to 5% Zn. Small amount of lead is also added to improve castability and machinability. It is used for bearing bushes, glands, pumps and valves etc.

Bell metal

It is a straight bronze having 20 to 25% tin. It can be readily cast and is generally used for casting of bells.

Speculum metal

Another straight bronze containing 30% tin. It is a hard alloy and takes good polish. It is largely used for decorative work and vacuum plating.

Aluminium bronze

It contains upto 14% A1 and the rest Cu, with sometimes a little addition of iron. It possesses good strength, high corrosion resistance and good heat resistance.

One variety, containing upto 8% A1, is known as cold working Al-bronze. It is available in the form of tubes for condensers, heat exchanges and steam and chemical plants. It is also used for springs. Although variety, called hot working Al-bronze, contains 8% to 14% Al. It can be readily forged, extruded, stamped, sand and gravity die-cast and otherwise hot worked. It is used for a large range of cast and forged parts, such as gears, pinions, valve seats, guides in I.C. engines, cams and roller, etc.

Silicon bronze

It contains 1 to 4% Si, 0.25 to 1.25% Mn, 0.5 to 1% iron (if added) and the rest copper. Small addition of upto 0.5% Pb will improve machinability. It has high strength, toughness and corrosion resistance. It can be readily hot worked. With low silicon content it can be safely cold worked also. It is widely used for boiler parts, tanks, marine hardware and similar other items.

Manganese bronze

It contains 55 to 60% Cu, 38 to 42% Zn, upto 1.5% tin, upto 2% iron, upto 1.5% Al and upto 3.5% Mn. It has superior mechanical properties and high corrosion resistance. It has poor response to cold working, but can be readily hot worked. It is used for such parts where high strength and corrosion resistance are desired, such as in ship propellers and rudders, etc.