Gunmetal

Gunmetal is the trade name for a group of casting materials that are now standardised as copper-tin-zinc-lead alloys (CuSnZnPb) according to DIN EN 1982 (formerly DIN 1705).

The multi-component alloy was developed in England in the 19th century and called gun metal and modified several times (Ruebel-Bronze, Uchatius-Bronze).

Besides the main alloy components copper (80 to 90 %), tin (1.5 to 11 %) zinc (1 to 9 %), lead up to 8 %, nickel contents up to 2 % are allowed (restriction: drinking water area). 
The most commonly cast alloy is CuSn7Zn4Pb7 (formerly: Rg7).

Gunmetal is relatively wear-resistant and cavitation-resistant, which is why it was also called "machine bronze" as early as the 19th century.  The tensile strength is 150 to 300 N/mm². Gunmetal is still used today for gear parts, gear wheels and in the broad field of gunmetal fittings for heating and water supply technology. In the latter, however, with the restriction that only a lead content <3.0 % and <0.6 % nickel are permitted in the alloys used for fittings and pipe connectors in the drinking water sector.

Gunmetal, as a copper-lead-tin alloy, is also classified as a bearing material (bearing metal). Plain bearings made of this material are not very sensitive to temporary lubrication failure and thus have good emergency running properties.