Special Material for Bearings

The bearing industry uses different materials for the production of the various bearing components. The bearing materials are processed to achieve desirable properties to maximize bearing performance , life and minimize cost . 

Chrome Steel - SAE 52100, 100Cr6 , SUJ2

The most common material used to produce the load carrying components in precision ball bearings, roller bearings, and tapered roller bearings is high carbon chrome steel. These components are the bearings inner and outer rings, balls and rollers. Using controlled processing and heat-treating methods the finished bearing components have high strength to resist cracking and a hard surface to resist subsurface rolling contact fatigue. The typical surface hardness for bearing components made from this material ranges from 60- 64 on the Rockwell hardness C scale (Rc).

Martensitic stainless steels S400 Series

Stainless steel materials are used to make bearing components because it is more resistant to surface corrosion due to the higher content of chromium (~18%) with the addition of nickel. The chromium reacts with oxygen to form a layer of chromium oxide on the surface, creating a passive film.

Austenitic Stainless Steel Bearings AISI300 Series

Bearing components made from 300 series stainless steel materials have greater corrosion resistance and are non-magnetic because of the low carbon content. However, the tradeoff is that this material cannot be hardened so the bearings can only operate under low loads and speeds. The surfaces of the bearing undergo a chemical reaction with the oxygen called a passivation process; the passive film developed on the surface protects the bearing from corrosion. The corrosion resistance is best when the bearing is not completely submerged in liquid (such as underwater applications). Bearings made from this material are usually special order items requiring minimum quantities; in addition they are more expensive.

Medium Carbon Alloy Steel Bearings

Bearings made from medium or low carbon alloy steel material are typically called “semi-precision” or “commercial grade” bearings. The typical materials are AISI8620 or AISI4320. The inner and outer rings are surface hardened in a heat-treating process call case hardening or carburizing. Bearings made from these materials cannot carry high loads or operate at high speeds and they do not have corrosion resistance. The bearings made from these materials are usually low cost.

Low Carbon Alloy Steel Bearings

Low carbon steel is used in the production of bearing cages, metal shields and metal washers around which rubber is molded for seals. Common materials are AISI C1008 and C1010. The material needs to be protected from corrosion with a coating of oil/grease (cages) or by plating (shields). Additional information on Retainers and Closures can be found in the respective technical bulletins.

Plastics and Non-Metallic Materials

A little likely to austenitic stainless steel S300 series , bearings made of plastic can only operate under lower loads and speeds , but this kind of bearings are much cheaper and suitable for furniture , light load conveyer system……

Cages

Plastic materials are sometimes used for bearing cages. The most common is molded nylon plastic but molded acetal (POM) is also used. Other polymers are used in special bearing designs where specific performance requirements such as high speed, or low torque or low noise are identified.

Cages made from phenolic (phenol-formaldehyde) materials are most common in high speed ball bearings used in machine tool equipment spindles. The phenolic cages are lightweight and have high strength. The cost of processing this material has led to an increase use of plastics in its place. Additional information is contained in the Cages technical bulletin. any chemicals 

Seals

The most common seal material is nitrile rubber or Buna rubber. It has good mechanical properties, can be used across a wide temperature range, is resistant to many chemicals and is low in cost. Materials such as Viton and Silicone are expensive elastomers and they’re usually used when an application requires their unique properties.

Ceramic Materials

Bearings made with ceramic materials fall into a specialty niche in the bearing industry. The most common arrangement is a hybrid bearing, usually with stainless steel rings and ceramic balls. The most common ceramic material used is silicon nitride. Balls made from this material are hard, up to Rc78, and have a very smooth surface. Hybrid bearings are more expensive than all stainless steel bearings.

Coating , Hybrid

Sometimes bearing components will be coating with Zn / Ni / Cr / Ti / Cr2O3 / PTFE ..........for some special applications , or made Hybrid bearings , such as steel rings + ceramic balls . 

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