Ceramic vs. Insulated Bearings: Key Differences and Applications

Comparison of Hybrid Ceramic Bearings and Insulated Bearings

In certain special applications or specific products, both insulated bearings and ceramic bearings offer electrical insulation properties. However, due to differences in their applicable scenarios, each type has its own distinct advantages. The detailed comparison is as follows:

Insulated bearings achieve insulation through a special coating applied to either the inner or outer ring of the bearing. A layer of alumina (Al₂O₃), approximately 100 micrometers thick, is applied to the bearing surface, allowing it to withstand up to 1000V DC. Internally, the structure remains the same as that of standard bearings. Alumina is an inorganic compound known for its high hardness, excellent thermal resistance, and strong chemical stability, and is widely used in industries such as manufacturing, healthcare, environmental protection, and daily life. The firm bond between the alumina layer and the bearing surface ensures the insulated bearing maintains the same rigidity as a standard bearing, without compromising the dimensional accuracy required for precise fits.

Thanks to the reliable continuity and adhesion of the alumina coating, insulated bearings effectively break the shaft current path, making them widely used in electric motor applications where shaft current needs to be eliminated. Additionally, their identical dimensions to standard bearings eliminate the need to redesign mating components.

Insulated bearings are categorized into two types: outer-ring insulated and inner-ring insulated. In outer-ring insulated bearings, the insulation layer is applied to the external surface of the outer ring (which fits into the bearing housing). In contrast, inner-ring insulated bearings have the insulation layer on the outer surface of the inner ring (which fits onto the shaft). The latter typically offers better insulation performance due to its smaller coating surface area, which results in higher impedance.

The uniqueness of ceramic bearings lies in the use of silicon nitride (Si₃N₄) ceramic rolling elements. Silicon nitride exhibits exceptional properties such as high hardness, self-lubrication, excellent wear resistance, thermal oxidation resistance, and the ability to withstand thermal shocks (resisting cracking under rapid temperature changes). Bearings using silicon nitride balls are lightweight and offer both electrical insulation and high-speed performance. In applications involving high rotational speeds but relatively low shaft voltages, hybrid ceramic bearings (where only certain components are ceramic) are often more suitable.

From a purely electrical insulation perspective, insulated bearings offer better performance. However, ceramic bearings excel under high-speed conditions. Therefore, the selection between the two should be based on the specific requirements of the application.