Bushings & journal bearings
Pump shafts, rotating equipment, hydraulic actuators. The default plain-bearing material across heavy industry.
Bearing bronze · SAE 660 · UNS C93200
C932 Bearing Bronze
Leaded tin bronze — the bearing-bushing default. Self-lubricating from the lead content, dimensionally stable, and corrosion-resistant in marine environments. The bushing material that just works.
UTS
240 MPa
Density
8.9 g/cc
Hardness
65 HB
Mach.
70 /100
When to use
Pick C932 when steel slides on it.
C932 (also called SAE 660) is the bushing-and-bearing default. The 7% lead content provides natural lubrication at the wear interface, the 7% tin gives it strength and corrosion resistance, and the bronze base resists galling against steel shafts. Plain bushings in C932 outlast many rolling-element bearings in dirty or shock-loaded applications.
The leaded chemistry also makes it excellent to machine — chips break short, surface finish is clean, and tool life is good. The catch: lead is RoHS-restricted in many products, so for European markets check whether a lead-free bearing bronze (e.g. C89320) or C954 aluminum bronze is required instead.
Strengths
Why bushings are bronze.
- Self-lubricatingLead microstructure smears at the wear interface — provides break-in lubrication and reduces galling.
- Anti-galling vs steelWon't seize against steel shafts the way aluminum or unlubricated bronze can.
- Marine corrosion resistantTin content provides good resistance to seawater, brine, and brackish exposure.
- Excellent machinability70/100 — chips break clean, sharp turning finish, fast cycle times.
- Dimensionally stableLow CTE for a bronze. Good fit retention on press-fit installations.
- Good fatigueStandard for cyclically loaded plain bearings (engine, pump, hydraulic).
Trade-offs
What you watch for.
- Lead content + RoHS7% lead content. Restricted under EU RoHS in many product categories. Use a lead-free bearing bronze (e.g. C89320) or C954 aluminum bronze for European markets.
- Density penalty8.9 g/cc — heavier than steel. Bushings are usually small enough this doesn't matter.
- Lower strength than alloy steelUTS 240 MPa — design for the bearing function, not as a structural element.
- Cost$8-15/lb — multiples of stainless. Justified for the bearing function, less so for general parts.
- Soft65 HB. Steel shafts dominate the wear contact. Bronze gives up; that's the design intent.
- Galvanic vs aluminumStandard galvanic precaution if assembly sees moisture. Use isolation washers.
Specs
Mechanical, physical & chemical data.
Mechanical
Properties (sand cast)
| Ultimate tensile strength | 240 MPa (35 ksi) |
|---|---|
| Yield strength (0.5% extension) | 125 MPa (18 ksi) |
| Elongation at break | 20% |
| Modulus of elasticity | 100 GPa |
| Hardness | 65 HB / 65 HV |
| Compressive yield (0.1% set) | 150 MPa |
| Compressive yield (10% set) | 375 MPa |
| Charpy impactat 21 °C | 11 J |
Source: Copper Development Association. Continuous-cast bar properties slightly higher across the board.
Physical & thermal
At room temperature
| Density | 8.9 g/cc (0.322 lb/in³) |
|---|---|
| Melting range | 857 – 999 °C |
| Specific heat | 0.376 J/g·°C |
| Thermal conductivity | 60 W/m·K |
| CTE (20–300 °C) | 18.0 µm/m·°C |
| Electrical conductivity | 12% IACS |
| Coefficient of friction (vs steel, lubricated) | 0.05 – 0.15 |
| Magnetic | Diamagnetic |
Lower thermal conductivity than pure copper — chemistry is mostly Cu but alloy additions reduce it. Still better than most steels.
Composition
Chemistry, weight %
| Copper (Cu) | 81.0 – 85.0 |
|---|---|
| Tin (Sn) | 6.3 – 7.5 |
| Lead (Pb) | 6.0 – 8.0 |
| Zinc (Zn) | 1.0 – 4.0 |
| Iron (Fe) | 0.20 max |
| Nickel (Ni) | 1.0 max |
| Antimony (Sb) | 0.35 max |
| Sulfur (S) | 0.08 max |
The 6-8% Pb is the bearing function; lead-free bearing bronzes (e.g. C89320) trade some self-lubrication for RoHS compliance.
Specifications
Common purchase specs.
ASTM B584
Continuous casting / sand casting bronze
ASTM B22
Bronze for bridge bearings
ASTM B505
Continuous-cast bronze bar
AMS 4860
Bronze bar — leaded tin
SAE 660
Equivalent designation (most common)
UNS C93200
Unified numbering
EN CC493K / 2.1090
European equivalent (CuSn7Zn4Pb7-C)
MIL-B-16541
Military bronze spec
Machining
Machining considerations.
C932 is one of the easier materials to machine. Sharp tools, generous feed, and reasonable speeds — chips break short and clean. The lead content makes it more forgiving than C110 copper or C260 brass.
Cutting speed
300–500 SFM with carbide. HSS works well at 200–300 SFM for low volume.
Feed rate
Aggressive constant feed. C932 doesn't work-harden — keep it cutting.
Tooling
Polished or coated carbide. Sharp edges; positive rake.
Coolant
Flood with water-soluble. Some shops run dry on plain turning.
Bored bushings
Hold ID with a ground reamer or single-point bore. Tolerance under 0.0005″ achievable in turning.
Press-fit allowance
Standard interference: 0.001-0.002″ per inch of bore diameter for steel housings.
Threading
Threads readily — but the soft material can strip under repeated assembly. Use thread inserts for fasteners.
Lead dust caution
Machine with proper ventilation and dust collection — leaded chips are a long-term respiratory concern.
Applications
Where C932 shows up.
Valve guides
Engine valve guides, hydraulic valve trim. Self-lubricating contact against steel valve stems.
Marine hardware
Propeller shafts, deck fittings, pump impellers. The seawater-corrosion resistance is good without paint.
Compare
Related materials.
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