Bronze and Gunmetal

Materials ·

Bronze (copper-tin alloys) and gunmetal (copper-tin-zinc, typically RG5/CC491K) are traditional pump materials offering excellent corrosion resistance in seawater and potable water, good machinability, and natural antimicrobial properties, making them the preferred choice for marine, shipboard, and water utility pump impellers, wear rings, and casings.

History

Bronze pump components date to ancient Rome, where lead-bronze was cast for aqueduct distribution valves and small force pumps circa 100 AD. The term gunmetal derives from its use in cannon founding from the 14th century onward in Europe. In the 19th century, gunmetal (the Ounce Metal composition of 85% Cu, 5% Sn, 5% Zn, 5% Pb) became the universal material for municipal water pump fittings throughout Britain and its colonies. The Hydraulic Research Association standardized gunmetal grades for water works pumps in the United Kingdom in 1952.

Key Properties

  • Density: 8.7 to 8.9 g/cm3
  • Tensile strength: 260 to 350 MPa
  • Hardness: 70 to 90 HB
  • Excellent seizure resistance — natural lubricity provided by tin addition
  • Good machinability with lead-containing grades
  • Natural biocidal and antimicrobial properties (oligodynamic effect of copper)

Corrosion and Chemical Resistance

  • Excellent resistance to seawater, brackish water, and freshwater service
  • Resistant to dilute non-oxidizing acids at ambient temperature
  • Susceptible to dezincification in high-zinc brasses — not an issue with gunmetal (Zn below 5 percent)
  • Vulnerable to ammonia, amines, and strong oxidizing acids — avoid these media
  • Do not use in contact with acetylene or concentrated nitric acid
  • Dealloying (selective tin leaching) can occur in aggressive soft water — specify lead-free grades

Grades and Standards

  • Gunmetal RG5 (CC491K): 85% Cu, 5% Sn, 5% Zn, 5% Pb — ISO 1338 and BS EN 1982
  • Lead-free gunmetal CC480K: DZR-resistant grade for potable water (WRAS approved)
  • ASTM B584 C83600 (Ounce Metal) — North American equivalent of RG5 for pump castings
  • ASTM B62 — tin bronze C90300 for impeller castings
  • DIN EN 1982: pump castings for marine and water utility service

Applications

  • Seawater cooling pump impellers and wear rings on ships and offshore platforms
  • Marine fire fighting pump components and valve bodies
  • Potable water utility pump casings where lead-free grade is specified
  • Hydraulic turbine guide vane bearings
  • Pump shaft sleeves and bearing bushings in water service
  • Navy and coast guard vessel bilge and ballast pump internals

Advantages

  • Outstanding natural seawater corrosion resistance without protective coatings
  • Inherent biocidal property inhibits biofilm formation in drinking water systems
  • Excellent bearing properties — compatible with steel shafts without galling
  • Long service track record since Roman times with predictable performance
  • Pressure-tight castings achievable without porosity defects

Limitations

  • Lead-containing grades not compliant with REACH and RoHS for potable water in many jurisdictions
  • Significantly more expensive than cast iron per kilogram of finished casting
  • Lower tensile strength than steel limits use in high-pressure applications
  • Heavy compared to polymer and aluminium pump alternatives
  • Supply chain subject to copper and tin commodity price volatility

Selection Criteria

  • For potable water service specify CC480K (lead-free) with WRAS approval confirmation
  • For seawater service specify RG5 (CC491K) or ASTM B584 C83600
  • For high-velocity seawater above 3 m/s use naval brass or nickel aluminium bronze instead
  • Check local regulations for permissible lead content limits in drinking water contact materials
  • For wear rings and shaft sleeves specify bronze even when casing material is cast iron — prevents galling

Top 10 Manufacturers

  • 1. Wieland-Werke AG (Germany) — ~14% of bronze pump component market; wrought and cast copper-tin alloys
  • 2. KME Group (Germany/Italy) — ~12%; copper-tin alloy castings for pump manufacturers worldwide
  • 3. Hubbell Power Systems (USA) — ~8%; C83600 bronze pump castings for utility and marine applications
  • 4. National Bronze Mfg. Co. (USA) — ~7%; cast bronze pump impellers and casings to order
  • 5. Atlas Bronze (USA) — ~6%; tin bronze pump bushings and wear rings for various industries
  • 6. Luvata Oy (Finland) — ~6%; copper alloy semifinished products for pump component manufacturers
  • 7. Concast Metal Products (USA) — ~5%; continuous cast bronze bar for machined pump components
  • 8. Alaskan Copper and Brass (USA) — ~5%; cast and wrought bronze pump components and forgings
  • 9. PMX Industries (USA) — ~4%; specialty copper alloy strip and shapes for pump internals
  • 10. Ningbo Zhenhai Casting (China) — ~4%; gunmetal pump body castings for OEM pump supply