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Bronzes are alloys of copper and tin, with commercial grades usually containing between 2 and 13 percent of tin. They are also called phosphor bronzes because phosphor is added to the alloy as a deoxidizing agent for casting. Phosphor additions usually vary between 0.01 and 0.5%.
Bronzes were the first metal alloys, developed about 4000 years ago – that period was named the Bronze Age. While they are probably best known for their historical uses, they are also useful for engineering applications.
- High strength
- High hardness
- Good ductility
- Good corrosion resistance
- High resistance to fatigue and corrosion-fatigue
- Low coefficient of friction with most other metals and alloys
- High immunity to season cracking
Lead is added to bronze. It is insoluble in the bronze, so cooling of the alloy during casting must be carefully controlled to ensure lead particles are evenly distributed throughout the casting. The actual tin and lead contents are tailored to suit the strength and lubricity of the application.
Self-lubricating bearings and bushes can also be made from porous bronze. Porous bronze is made via powder metallurgy. In simple terms, this involves mixing and pressing together copper and tin powders, followed by sintering. This results in a porous bronze which is not as strong as cast bronze. However, the pores can be impregnated with oil after sintering or graphite prior to pressing to produce a self-lubricating material.
Pumps, Valves, and Fittings
These items are typically made from phosphor bronze which contains 4 to 12% tin and 0.02 to 0.5% phosphorus, which increases hardness and wear resistance, but reduces ductility and toughness. These alloys also possess good corrosion resistance.
Gunmetals containing from 3 to 10% tin and 3 to 8% zinc. They have good corrosion resistance and cast-ability and can be used for pumps, valves and, bearings. Leaded gun metals with 3 to 5% lead are also suited to these applications.
Wrought and work hardened phosphor bronzes (see pumps, valves, and fittings) possess excellent spring properties making them highly suited to electrical contact applications and switch parts.
Bronzes are used for spring manufacture for applications where the material requires high resistance to repeated stresses, corrosion, and fatigue.
Condensers, pressure vessels, aircraft fuel pumps, mine water pump, bellows, diaphragms, springs, general purpose bearings and heavily loaded high-speed bearings, bushings, clutch plates, gears, valve guides, rolling mill screw down nuts, castings.
Sources and Further Reading
This article was updated on 25th April, 2019.