Bearing Bronze—also commonly known as Phosphor Bronze or Tin Bronze—is a high-performance copper-based alloy primarily used in heavy-duty bearing applications.
It contains copper as the base metal with additions of tin, phosphorus, and sometimes lead to improve machinability.
This alloy is widely preferred for its excellent wear resistance, high load-carrying ability, and self-lubricating properties, making it ideal for components that operate under friction, high pressure, or limited lubrication.
Bearing Bronze is especially known for its reliability, durability, and long service life in both industrial and mechanical environments.
Composition
The typical composition of C93200 bearing bronze is:
| Element | Typical Range (wt%) | Function |
|---|---|---|
| Copper (Cu) | 81.0 – 85.0 | Base metal; provides ductility, conductivity, and corrosion resistance. |
| Tin (Sn) | 6.3 – 7.5 | Improves hardness, strength, and wear resistance. |
| Lead (Pb) | 6.0 – 8.0 | Acts as a solid lubricant, dramatically reducing friction and improving conformability/embeddability. |
| Zinc (Zn) | 2.0 – 4.0 | Improves fluidity and casting characteristics. |
| Nickel (Ni) | ≤ ~1 | Can enhance corrosion resistance. |
| Phosphorus (P) | Typically ≤ ~1.5 | Can improve wear and hardness. |
| Trace impurities | Fe, Sb, S, etc. | Controlled for quality. |
Key Mechanical & Physical Properties
Mechanical Properties
| Property | Typical Value |
|---|---|
| Tensile Strength | ~35 ksi (≈ 241 MPa) minimum |
| Yield Strength | ~20 ksi (≈ 138 MPa) minimum |
| Elongation | ≥ 10 % |
| Hardness | Varies, moderate (typical bronze range) |
| Impact / Ductility | Adequate for bearing loads |
Physical Properties
| Property | Typical Value |
|---|---|
| Density | ~0.322 lb/in³ (~8.9 g/cm³) |
| Modulus of Elasticity | ~14,500 ksi (≈ 100 GPa) |
| Coefficient of Thermal Expansion | ~10×10⁻⁶ /°F (~18×10⁻⁶ /°C) |
| Thermal Conductivity | ~33.6 Btu/ft-hr-°F (~58 W/m·K) |
| Electrical Conductivity | ~12 % IACS (relative to pure copper) |
Metallurgical Behavior & Strengthening
🧬 Microstructure
Bearing bronze typically exhibits a multi-phase microstructure:
α-Cu solid solution matrix — provides strength and toughness.
Tin-rich intermetallics (δ phases) — enhance hardness and wear resistance.
Lead particles — discrete soft solid lubricant sites that reduce friction.
The lead does not dissolve into the copper matrix but remains as fine dispersed particles that smear under load, forming a tribological film that lowers friction.
Strengthening Mechanisms
Solid solution strengthening from tin and zinc.
Dispersion of lead and intermetallics enhancing wear performance and internal lubrication.
Fine grain size control during casting/refinement improves toughness.
Bearing bronzes are not typically heat-treatable for additional hardening like steels; most performance tuning comes from composition and solidification control.
Refining & Processing Properties
Casting
Bearing bronzes (especially C93200) are excellent casting alloys:
Good molten fluidity, allowing sand, centrifugal, and permanent-mold casting.
Controlled solidification reduces shrinkage and porosity.
Machining
Lead content significantly enhances machinability, making cutting easier with standard tools.
Considered a free-machining bronze compared to lead-free bronzes.
Fabrication & Joining
Good soldering/brazing performance.
Welding generally not recommended due to lead and tin content.
Broadly, the alloy is designed to be manufacturing-friendly for precise bearing and bushing fabrication.
Available Forms
Cast bars, billets, and blooms for machining.
Rods, tubes, flats, squares in mill stock form.
Near-net shapes for reduced machining effort.
Custom castings for complex bearing housings and components.
Key Characteristics
| Feature | Benefit |
|---|---|
| Low friction/self-lubrication | Lead particles act as internal solid lubricant, reducing wear and friction. |
| Good wear resistance | Tin & intermetallic phases resist surface degradation. |
| Excellent machinability | Lead improves cutting behavior and tool life. |
| Good load-carrying capacity | Suitable for moderate radial/axial loads. |
| Thermal conductivity & stability | Heat is efficiently dissipated, preventing bearing overheating. |
| Corrosion resistance | Bronze matrix resists corrosion in many environments. |
Applications
Industrial & Machinery
Sleeve bearings & bushings in motors, presses, pumps, and gearboxes
Thrust washers & bearings where axial loads apply
Machine tool bearings and guides requiring smooth motion
Automotive
Engine bearings, water & fuel pump bushings, linkage bushings.
Marine & Harsh Environments
Bearings in pumps, cylinders, and other submerged or corrosive exposure.
General Engineering
Wear plates, wear rings, and custom components requiring low friction.
Advantages & Why Choose Bearing Bronze
Low Friction, Less Wear
Lead inclusions smear to create a built-in lubricant film, reducing bearing wear and improving efficiency.
Self-Lubricating Behavior
Even with marginal lubrication, bearings operate smoothly because of the alloy’s internal lubrication characteristics.
Excellent Machinability
Compared to lead-free bronzes and many steels, bearing bronze is easier to machine with reduced tool wear and better surface finish.
Balanced Mechanical Performance
Good strength, ductility, and wear resistance makes it suitable for a wide range of service conditions.
Good Thermal Behavior
Efficient heat dissipation helps maintain dimensional stability and prevents bearing overheating.
Corrosion Resistance
Bronze’s natural resistance to environmental corrosion enhances durability in marine and industrial settings.
Limitations & Considerations
Not for very high loads/speeds — heavier alloys like aluminum bronze may be better for extreme conditions.
Lead content restrictions — some regions limit lead-containing alloys for environmental or health reasons.
Welding challenges — lead and tin reduce weldability compared to other bronzes or steels
Summary
Bearing bronze (especially C93200) is a lead-enhanced tin bronze alloy optimized for sliding contact, low friction, wear resistance, and machinability.
It combines solid lubrication from lead, wear-resistant matrix phases, and good mechanical strength to deliver long service life in bearings, bushings, thrust washers, and other tribological components across industrial, automotive, marine, and general engineering applications.