Leaded Bronze Bearings and Bushings

The Engineer’s Guide to Leaded Bronze Bearings and Bushings

For engineers and designers tasked with creating custom bearings, bushings, and wear parts, material selection is everything. The ideal material must be strong enough to handle operational loads, durable enough to resist wear, and—critically for custom parts—easy to machine into precise shapes. For decades, one family of alloys has proven to be the undisputed champion in meeting these needs: leaded bronze.

Leaded Tin Bronze Bearing and Bushing

Properties: Good strength and wear resistance, excellent machinability due to the presence of lead, and moderate corrosion resistance.

C93700, C92710, C93500, 937B, 930D, 935B, LB2, LB3, LB4, SAE 64, CuPb10Sn, CuPb5Sn, C93200, SAE660, CuSn7ZnPb

This technical guide provides an in-depth look at this essential group of materials, covering the key alloys known by designations like C93200 (SAE 660), C93700 (SAE 64), C92710, C93500, 937B, LB2, CuPb10Sn, and CuSn7ZnPb. We will explore why their unique composition makes them the premier choice for self-lubricating components.

The Secret Ingredient: Why Lead is Essential

The defining characteristic of this bronze family is the intentional addition of lead. Unlike other elements added to create strength, lead is introduced for two distinct and vital purposes related to performance and manufacturability.

1. Inherent Self-Lubrication: The lead is distributed throughout the bronze matrix as soft, microscopic particles. During operation, as friction occurs, a minuscule amount of this lead is drawn to the surface, smearing into a thin, lubricating film. This film prevents metal-to-metal contact between the bushing and the shaft, drastically reducing friction and preventing seizure. This is especially critical during start-up, shut-down, or in instances of intermittent lubrication where a traditional oil film might fail.

2. Unmatched Machinability: For anyone who has ever machined metal, leaded bronze is a pleasure to work with. The soft lead particles act as a natural chip-breaker. As the material is cut, the chips break off into small, manageable pieces instead of forming long, stringy, and hazardous swarf. This results in a faster, safer machining process, reduced tool wear, and an exceptionally smooth surface finish—a critical requirement for high-quality bearing surfaces.

Core Properties for Reliable Performance

These alloys offer a balanced profile perfectly suited for bearing applications.

Good Strength & Wear Resistance: The foundation of the alloy—the copper-tin bronze matrix—provides the structural integrity and hardness needed to support significant loads and resist deformation. The lead enhances this by providing a low-friction surface, which results in excellent wear resistance. The material is designed to wear slowly and predictably over a long service life.

Excellent Machinability: As mentioned, the lead content makes these alloys arguably the easiest-to-machine bearing materials available. This advantage cannot be overstated when manufacturing custom, tight-tolerance parts, as it directly translates to lower production costs and higher quality components.

Moderate Corrosion Resistance: Leaded bronzes offer good, reliable resistance to corrosion from atmospheric conditions and many industrial fluids. They perform well in most operating environments, though they are not intended for use with harsh acids or in severe marine saltwater applications.

A Guide to the Alloy Grades

The many designations can be confusing, but they generally fall into a few key categories based on their lead content. Choosing the right one depends on the specific demands of your application.

Note: These values are typical and can vary based on the specific casting method and specifications.

Application Spotlight: Where Leaded Bronze Excels

The unique blend of properties makes these alloys indispensable across a vast range of machinery:

• General Machinery: The most common use is for custom-machined bearings, bushings, and wear plates in pumps, motors, conveyor systems, and industrial presses.

• Automotive & Equipment: Used for components like wrist pin bushings, transmission parts, and fittings in agricultural and construction equipment.

• Hydraulics: Utilized for piston components and glands where lubricity and wear resistance are critical.

• Any application involving sliding contact under moderate load and speed.

Conclusion: The Engineer’s Choice for Custom Bearings

When an application calls for a custom-made bearing or bushing, leaded bronze alloys are the superior choice. They provide a robust and reliable solution that balances mechanical strength with exceptional wear resistance. More importantly, their unparalleled machinability empowers engineers and workshops to produce high-precision, cost-effective components tailored to any design. By understanding the differences between grades like the all-purpose C93200 (SAE 660) and the high-speed C93700 (SAE 64), you can specify the perfect material to ensure long life and flawless performance in your machinery.