Commonly Used Bearing Materials You Need To Know

Metal Materials

Bearing alloys, bronze, aluminum-based alloys, zinc-based alloys, and more are categorized as metallic materials. Among them, bearing alloys, also known as white metal alloys, are primarily composed of lead, tin, antimony, or other metals. They exhibit properties such as good wear resistance, high ductility, favorable running-in performance, excellent thermal conductivity, adhesion resistance, and good oil adsorption. However, due to their higher cost, they are usually cast onto bronze, steel, or cast iron bearing shells to form thin coatings.

(1) Bearing Alloys (Commonly known as Babbitt or White Metal)

Bearing alloys are alloys of tin, lead, antimony, and copper, with tin or lead serving as the matrix and containing hard crystal grains of antimony-tin (Sb-Sn) and copper-tin (Cu-Sn). The hard crystal grains provide anti-wear functionality, while the soft matrix enhances material ductility. Bearing alloys have low elastic modulus and elastic limit. Among all bearing materials, they exhibit the best embeddability and friction compliance, making them easily adaptable for mating with shaft journals, resistant to adhesive wear. However, their strength is relatively low, making them unsuitable for standalone bearing production. Instead, they are affixed as bearing linings onto bronze, steel, or cast iron bearing shells. Bearing alloys are suitable for heavy loads and medium-high-speed applications, albeit being costlier.

(2) Copper Alloys

Copper alloys possess high strength, good anti-friction properties, and wear resistance. Among these, bronze, with better performance than brass, is the most commonly used material. Types of bronze include tin bronze, lead bronze, and aluminum bronze, with tin bronze being widely applied due to its superior anti-friction properties. However, tin bronze is harder than bearing alloys, leading to poorer running-in and embeddability. It is suitable for heavy loads and medium-speed applications. Lead bronze exhibits strong anti-adhesive capabilities, making it suitable for high-speed and heavy-duty bearings. Aluminum bronze, with higher strength and hardness, has weaker anti-adhesive properties and is suitable for low-speed, heavy-duty bearings.

(3) Aluminum-Based Alloys

Aluminum-based bearing alloys feature excellent corrosion resistance and high fatigue strength, along with good friction performance. These qualities have led aluminum-based alloys to replace more expensive bearing alloys and bronze in certain fields. Aluminum-based alloys can be made into single-metal components such as bushings and bearings, as well as bimetallic parts where aluminum-based alloys serve as the bearing lining and steel as the backing.

(4) Gray Cast Iron and Wear-Resistant Cast Iron

Ordinary gray cast iron or wear-resistant gray cast iron containing alloying elements like nickel, chromium, and titanium, as well as ductile iron, can be used as bearing materials. The flake or spheroidal graphite in these materials, when present on the material surface, forms a lubricating graphite layer, resulting in decent anti-friction and wear-resistant properties. Additionally, graphite can adsorb hydrocarbons, aiding in boundary lubrication. Therefore, when using gray cast iron as a bearing material, lubricating oil should be added. Due to cast iron's brittleness and poor running-in properties, it is only suitable for low-speed applications with light loads, not subjected to impact loads.

Non-Metal Materials

The most commonly used non-metallic materials are various plastics (polymer materials), such as phenolic resin, nylon, and polytetrafluoroethylene (PTFE). Polymers possess characteristics such as non-reactivity with many chemicals, strong corrosion resistance, a degree of self-lubrication, the ability to operate without lubrication, and lubrication ability at high temperatures. They also exhibit good embeddability, anti-friction, and wear-resistant properties.

When selecting polymer materials as bearing materials, several factors must be considered. Due to the significantly lower thermal conductivity of polymers compared to steel, the dissipation of frictional heat must be taken into account. This strictly limits the working speed and pressure of polymer bearings. Additionally, due to the much larger linear expansion coefficient of polymers compared to steel, the clearance between polymer bearings and steel shaft journals should be larger than that of metal bearings. Moreover, the strength and yield limit of polymer materials are lower, limiting the loads they can withstand during assembly and operation. Additionally, since polymer materials exhibit creep under normal temperature conditions, they are not suitable for producing bearings with strict clearance requirements.

Carbon-graphite can be used as a bearing material in adverse environments. The higher the graphite content, the softer the material and the lower the friction coefficient. Metals, polytetrafluoroethylene, or molybdenum disulfide can be added to carbon-graphite materials, and liquid lubricants can also be impregnated. Carbon-graphite bearings possess self-lubrication properties, which depend on the amount of adsorbed water vapor. Carbon-graphite materials have an affinity for lubricants containing hydrocarbons, enhancing their boundary lubrication properties. Furthermore, they can be used as water-lubricated bearing materials.

Rubber is primarily used in environments with water as a lubricant, especially in dirty and contaminated conditions.

Wood has a porous structure and can be improved using fillers. Filling polymers can enhance wood's dimensional stability, reduce moisture absorption, and increase strength. Bearings made from wood can operate in heavily dust-laden conditions.

Porous Metal Materials

These are bearing materials made from different metal powders that are compressed and sintered. These materials possess a porous structure, with pores accounting for approximately 10% to 35% of the volume. Before use, the bearing shell is immersed in hot oil for several hours to saturate the pores with lubricating oil. As a result, bearings made from this material are often referred to as oil-impregnated bearings.

These bearings exhibit self-lubricating properties. During operation, the rotation of the shaft journal and the expansion of oil due to bearing heating result in lubricating oil being drawn into the friction surface, providing lubrication. When not in operation, capillary action draws the oil back into the bearing interior, enabling the bearing to function well even without the addition of lubricating oil for an extended period. For optimal performance, periodic oil supply is recommended. Due to its relatively low toughness, porous metal materials are suitable for smooth, low-impact loads, and medium-low-speed conditions. Commonly used materials include porous iron and porous bronze. Porous iron is often used to produce mill bushings, machine tool oil pump liners, internal combustion engine camshaft bushings, and more. Porous bronze is commonly used for turntables, electric fans, textile machinery, and automobile generator bearings. In China, there are specialized factories manufacturing oil-impregnated bearings, and suitable choices can be made based on design manuals when needed.

Porous Metal Materials

Porous metal materials are composed of metal powders of various types, compressed and sintered into bearing materials. This type of material has a porous structure, with porosity accounting for 10% to 35% of the volume. Prior to use, the bearing shells are immersed in hot oil for several hours to fill the pores with lubricating oil. Therefore, bearings made from this type of material are referred to as oil-impregnated bearings.

These bearings possess self-lubricating properties. During operation, the rotation of the shaft journal and the expansion of oil due to bearing heating result in lubricating oil being drawn into the friction surface, providing lubrication. When not in operation, capillary action draws the oil back into the bearing interior, enabling the bearing to function well even without the addition of lubricating oil for an extended period. For optimal performance, periodic oil supply is recommended. Due to its relatively low toughness, porous metal materials are suitable for smooth, low-impact loads, and medium-low-speed conditions. Commonly used materials include porous iron and porous bronze. Porous iron is often used to produce mill bushings, machine tool oil pump liners, internal combustion engine camshaft bushings, and more. Porous bronze is commonly used for turntables, electric fans, textile machinery, and automobile generator bearings. In China, there are specialized factories manufacturing oil-impregnated bearings, and suitable choices can be made based on design manuals when needed.

Summary

In summary, the choice of bearing materials depends on factors such as working conditions, loads, and speeds. Metallic materials like bearing alloys, copper alloys, and aluminum-based alloys are suitable for various applications. Non-metallic materials like plastics, rubber, and wood are used in specific environments. Porous metal materials exhibit self-lubricating properties and are suitable for specific speeds and load conditions. Making the right choice of bearing materials can improve equipment performance and longevity.