Self-lubricating bearings with embedded solid lubricants, such as graphite, are a critical component in many mechanical systems where maintenance and lubrication are challenging. These bearings are designed to release lubricant as they wear, providing a consistently low friction surface. The choice of base material for these bearings significantly affects their load carrying capacity, making the selection process crucial for optimal performance and durability. Here’s an overview of the four copper-based alloys you mentioned, which are used as base materials in graphite bronze bearings:

1. CuSn5Pb5Zn5

• Composition: This alloy consists of copper, 5% tin, 5% lead, and 5% zinc.
• Properties: It offers good corrosion resistance and moderate strength. The presence of lead and zinc provides improved machinability and wear resistance.
• Applications: Suitable for moderate load applications where some corrosion resistance is required.

2. CuSn12

• Composition: This alloy is made up of copper with 12% tin.
• Properties: It has excellent wear resistance and good corrosion resistance, making it suitable for high-load applications.
• Applications: Ideal for heavy-load bearings used in slow to moderate speed applications, such as worm wheels and bushings.

3. CuSn10Pb10

• Composition: This alloy contains copper, 10% tin, and 10% lead.
• Properties: The high lead content enhances its machinability and embeddability, which helps in accommodating foreign particles and reducing friction.
• Applications: Excellent for bearings under medium to high loads and where the embedding of dirt particles and debris is possible.

4. CuNi4Al10Fe4

• Composition: Comprising copper, 4% nickel, 10% aluminum, and 4% iron.
• Properties: This is a high-strength, corrosion-resistant alloy, with the added nickel and aluminum providing increased toughness and resistance to wear and fatigue.
• Applications: Suitable for high-load, high-speed applications, and where excellent wear resistance is crucial, such as in aerospace and marine environments.

Selection Considerations

The selection of the right alloy for self-lubricating bearings depends primarily on:

• Load Carrying Capacity: Higher tin, lead, or specific additives like nickel and aluminum can enhance the bearing’s ability to support heavier loads.
• Speed of Operation: Alloys with better wear resistance are preferable for higher speeds to minimize wear and friction.
• Environment: Corrosion resistance is critical in harsh environments, making certain alloys more suitable than others.
• Compliance and Availability: Some applications may have restrictions on materials like lead, influencing the choice of alloy.

Each of these materials has unique properties that make them suitable for specific applications within various industries. The choice should align with the operational requirements and environmental conditions of the bearing’s application.

The hardness of bearing materials is a crucial factor in their performance, particularly in terms of wear resistance, load-carrying capacity, and their interaction with mating materials. Here’s a brief overview of the materials you mentioned, along with their typical hardness values:

1. Gun Metal

• Hardness: Greater than 165 HB (Brinell Hardness)
• Composition: Typically a type of bronze – usually a mix of copper, tin, and zinc.
• Properties: Gun metal is known for its good sliding properties, corrosion resistance, and ability to conform to irregularities.
• Applications: Used in steam and hydraulic castings, valves, gears, and bearings where moderate loads and speeds are anticipated.

2. Tin Bronze

• Hardness: Greater than 210 HB
• Composition: Primarily copper with a significant amount of tin (around 12% is common).
• Properties: Offers excellent resistance to corrosion, high wear resistance, and low friction coefficient. Tin bronzes are stronger than most other bronzes, making them suitable for heavy loads.
• Applications: Commonly used in high-load bearings, heavy-duty gears, and marine applications.

3. Lead-Tin Bronze

• Hardness: Greater than 180 HB
• Composition: This alloy combines copper with significant percentages of lead and tin, enhancing its machinability and wear properties.
• Properties: The presence of lead in the alloy allows for excellent machinability and also helps in embedding small impurities that might otherwise cause damage to the shaft.
• Applications: Ideal for use in applications where there are intermittent loads and where the bearing must accommodate impurities.

4. Ni-Al Bronze

• Hardness: Greater than 270 HB
• Composition: Alloy of copper with nickel, aluminum, and iron.
• Properties: This is a high-strength alloy, with excellent resistance to wear, corrosion, and fatigue. The nickel and aluminum in the composition not only increase the hardness but also improve the overall toughness of the material.
• Applications: Used in high-load applications such as aircraft, marine hardware, and under-the-hood automotive components, where high strength and resistance to shock and wear are necessary.

Considerations for Matching Bearing and Mating Materials

• Compatibility: The hardness of the bearing material should be compatible with that of the mating shaft material to prevent excessive wear or galling. Typically, the shaft material should be slightly harder than the bearing material.
• Wear and Fatigue: Harder materials generally offer better resistance to surface wear and can handle higher loads. However, they are also less tolerant to misalignment and contamination.
• Operating Conditions: Environmental factors like temperature, humidity, and exposure to corrosive elements should also be considered when selecting bearing materials.

The selection of the right bearing material will depend not only on its hardness but also on the specific operational and environmental conditions expected in its application.