What is a bearing retainer? What materials are bearing retainers made ofs?

1. What is a bearing retainer?

A bearing retainer, also known as a cage, is one of the key components of a bearing. Its function is to enclose and isolate the rolling elements, allowing them to move with them and often guiding them. The cage withstands stresses caused by friction, strain, and inertia, as well as chemical corrosion from lubricants, lubricant additives, substances produced by aging, organic solvents, and coolants. Therefore, the cage's design and material are crucial to its performance and bearing reliability.

A bearing retainer maintains an appropriate distance between rolling elements, preventing contact and reducing friction; it evenly distributes the rolling elements, thereby evenly distributing the load; and it guides the rolling elements in the unloaded zone, improving rolling conditions in the bearing and preventing damaging sliding.

2. What materials are used for bearing retainers?

Common retainers are categorized by material into metal and non-metallic cages. Composite materials are also available. Cage materials include: mild steel and stainless steel, bakelite/plastic (nylon), and brass/bronze/aluminum alloy. Bearing cages for special purposes must also meet specific operating requirements, such as high-temperature resistance, corrosion resistance, self-lubrication (for use in vacuum), or non-magnetic properties.

1. Steel Cage Materials

Steel cages are widely used in rolling bearings due to their high strength, toughness, and ease of processing. They are typically cold-stamped from 08 and 10 carbon steel sheets. Other machining methods can also be used as needed. Commonly used steel cage materials include 20, 30, 45, 0Cr18Ni9, 1Cr18Ni9Ti, 40CrNiMo, ML15, and ML20. Steel cages are generally heat-treated to relieve stress and restore plasticity, including high-temperature tempering and recrystallization annealing. To reduce the friction coefficient of steel cages, surface treatment may be necessary.

2. Brass Cages

Both stamped and solid steel cages are available. Stamping is only suitable for small and medium-sized applications. Brass sheet, brass casting, or brass forging. Brass has high tensile strength and comparable mechanical strength to stamped steel cages, but has a lower density and a higher maximum speed. It is unaffected by lubricants, including synthetic oils and greases. Brass cages should not be used in applications above 300°C or in ammonia (for example, in cooling), as ammonia can cause seasonal cracking of the brass. Operating temperatures should be below 300°C.

3. Non-ferrous Metal Cage Materials

Unlike steel, non-ferrous metals have unique properties. For example, aluminum alloys offer low density, good thermal conductivity, and excellent corrosion resistance. Copper alloys offer excellent thermal conductivity, low friction coefficient, good formability, and high operating temperature. Zinc-aluminum alloys offer advantages such as low cost, low density, and excellent performance.

4. Non-metallic Cage Materials

Non-metallic cage materials primarily include polymers and their composites, including nylon, phenolic tape, and polytetrafluoroethylene. Polymer materials offer a good balance of strength and elasticity. The excellent sliding properties of polymer cages ensure minimal friction when moving relative to lubricated rolling element surfaces, minimizing bearing heat and wear. Even in lubricant-starved conditions, polymer cages maintain excellent kinematic characteristics, ensuring continued bearing operation for a period without damage. Due to the low density of polymers, cages made from them exhibit low inertia.

In addition to being manufactured from pure materials, cages can also be modified, filled, or reinforced with other materials.

Different bearing cage materials have their own unique properties, advantages, and disadvantages. When choosing a bearing cage, consider not only economic factors but also practical needs.