Cast Iron

Materials ·

Cast iron is an iron-carbon alloy containing 2 to 4 percent carbon, used extensively for pump casings, impellers, and bearing housings in water, sewage, and general industrial applications due to its low cost, good machinability, and adequate corrosion resistance in mild environments.

History

Cast iron pump components date back to the early industrial revolution. The first notable cast iron pump was produced around 1700 by Thomas Savery and Thomas Newcomen for mine drainage in England. By 1850, cast iron had become the dominant material for municipal water supply pump casings throughout Europe and North America. The introduction of nodular (ductile) iron in 1948 by Keith Millis at International Nickel Company dramatically improved impact toughness, expanding cast iron use to high-pressure pump applications.

Key Properties

  • Density: 7.1 to 7.3 g/cm3
  • Tensile strength: 150 to 400 MPa (grey to ductile iron)
  • Hardness: 150 to 300 HB
  • Thermal conductivity: 40 to 60 W/mK
  • Good vibration damping — superior to steel and most other metals
  • Excellent castability for complex volute shapes
  • Low material cost compared to any steel or alloy alternative

Corrosion and Chemical Resistance

  • Suitable for fresh water, wastewater, and mild alkaline solutions
  • Susceptible to accelerated corrosion in acidic environments (pH below 6)
  • Graphitic corrosion can occur in aggressive soils or seawater
  • Epoxy or bitumen coatings often applied for extended service life
  • Not recommended for acids, chlorinated solvents, or saline water without protective lining

Grades and Standards

  • Grey iron: ASTM A48 Class 20 to 50 (DIN EN 1561: EN-GJL-150 to EN-GJL-350)
  • Ductile iron: ASTM A536 Grade 65-45-12 (DIN EN 1563: EN-GJS-400-15)
  • Austempered ductile iron (ADI): ASTM A897 for high-strength applications
  • ISO 1083 covers spheroidal graphite cast iron globally

Applications

  • Municipal water supply and distribution pump casings
  • Sewage and wastewater treatment pump bodies
  • Irrigation and drainage system pump casings
  • HVAC circulating pump bodies
  • Fire suppression system pump casings
  • General industrial cooling water pumps

Advantages

  • Lowest cost of all metallic pump materials per kilogram
  • Excellent castability — complex volute and casing shapes achievable
  • Self-lubricating graphite flakes reduce wear on sliding surfaces
  • Good vibration and noise damping in rotating equipment
  • Widely available globally from multiple foundries in all continents

Limitations

  • Low tensile strength compared to steel limits high-pressure applications
  • Brittle — susceptible to cracking under thermal shock or mechanical impact
  • Poor resistance to acids and aggressive chemicals without coating
  • Heavier than aluminium or polymer alternatives
  • Grey iron is not weldable; ductile iron requires preheating procedures

Selection Criteria

  • Choose grey cast iron (ASTM A48 Class 30 or higher) for standard water service below 16 bar
  • Choose ductile iron (ASTM A536 Grade 65-45-12) for higher-pressure or impact-loaded applications
  • Apply internal coatings for potable water or mildly corrosive service environments
  • Avoid in pH below 6 or in chloride-rich environments without a protective lining
  • Specify nodular (ductile) iron for pump casings subject to hydraulic shock or water hammer

Top 10 Manufacturers

  • 1. Sulzer Ltd. (Switzerland) — ~18% of cast iron pump market; centrifugal and axial-flow pumps for water and wastewater
  • 2. Flowserve Corporation (USA) — ~12%; extensive range of grey and ductile iron volute casings for process service
  • 3. KSB SE (Germany) — ~10%; cast iron pump bodies for building services and process industries
  • 4. Grundfos A/S (Denmark) — ~9%; cast iron circulators and multistage pump casings
  • 5. ITT Inc. (USA) — ~7%; Goulds brand grey iron process pump casings and impellers
  • 6. Ebara Corporation (Japan) — ~7%; cast iron pumps for municipal water systems across Asia
  • 7. Xylem Inc. (USA) — ~6%; grey iron submersible and vertical turbine pump casings
  • 8. Weir Group PLC (UK) — ~5%; ductile iron slurry pump liners for mining applications
  • 9. Pentair PLC (Ireland/USA) — ~4%; grey iron pump bodies for pool and HVAC applications
  • 10. WILO SE (Germany) — ~3%; cast iron heating circulation pump bodies for building services