Bronzes are alloys of copper and tin, with commercial grades usually containing between 2 and 13% tin. They are also called phosphor bronzes because phosphor is added to the alloy as a deoxidising agent for casting. Phosphor additions usually vary between 0.01 and 0.5%. 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 co-efficient of friction with most other metals and alloys
• High immunity to season cracking
Self Lubricating Bearings
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 contains4 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 castability and can be used for pumps, valves and bearings. Leaded gunmetals 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 a high resistance to repeated stresses, corrosion and fatigue.
Condensers, pressure vessels, bellows, diaphragms, springs, bearings, bushings, clutch plates, gears, castings.
Primary Author: Dr. Agnes Segal
Source: Materials Information Service, “Using copper and copper alloys” edited by Justin Furness.
For more information on this source please visit The Institute of Materials