Analysis of the Causes Affecting the Grinding Metamorphic Layer of FAG Bearings
Source: China Bearing Network | Date: March 29, 2014
The grinding metamorphic layer in FAG bearings is a critical factor that affects their performance and longevity. This layer is primarily influenced by two main factors: grinding heat and grinding force. Understanding these causes can help prevent premature bearing failure and improve overall quality. During the grinding process, the contact area between the grinding wheel and the workpiece generates a significant amount of energy, leading to high temperatures within the grinding zone. These temperatures can reach up to 1000–1500°C in a very short time (0.1 to 0.001 milliseconds). Such extreme conditions can cause various changes in the surface layer of the bearing, including oxidation, amorphous structures, high-temperature tempering, secondary quenching, and even cracking. 1. **Grinding Heat Effects** - **Oxide Layer Formation**: The high temperature can cause oxygen from the air and the steel itself to form a thin oxide layer on the surface, typically 20–30 nm thick. This layer is closely related to the grinding process and serves as an indicator of grinding quality. - **Amorphous Structure**: At such high temperatures, the surface may melt and solidify rapidly, forming a very thin amorphous layer (around 10 nm) with high hardness. However, this layer can be easily removed during fine grinding. - **High-Temperature Tempering**: If the temperature exceeds the tempering range but does not reach the austenitizing temperature, it can lead to a reduction in hardness. The higher the temperature, the more pronounced the softening effect. - **Secondary Quenching**: When the surface reaches above the Ac1 temperature, it can transform into martensite during cooling. This can result in a secondary quenching layer, which often requires a high-temperature tempering layer beneath it. - **Cracking**: Secondary quenching can induce stress in the surface, creating tensile stresses in certain areas. These stresses can lead to cracks, especially along grain boundaries, and severe cases can result in full-scale surface cracking. 2. **Grinding Force Effects** - **Cold Plastic Deformation Layer**: As the abrasive grains cut or plow the surface, they can cause plastic deformation, especially when the grinding wheel becomes dull or the feed rate increases. - **Thermoplastic Deformation**: High temperatures from grinding can reduce the elastic limit of the material, causing further deformation under pressure from the grinding wheel. This deformation is not fully reversed during the process. - **Work Hardening Layer**: In some cases, the surface layer becomes harder due to plastic deformation, which can be detected using microhardness testing or metallography. Additionally, decarburization layers formed during casting or heat treatment, if not fully removed during subsequent processing, can also affect the surface properties of the bearing. These residual layers may lead to softening and early failure. In summary, the formation of the grinding metamorphic layer in FAG bearings is a complex phenomenon influenced by both thermal and mechanical factors. Proper control of the grinding process is essential to minimize these effects and ensure the reliability and performance of the bearings.
Related Bearing Knowledge: - SKF Double Row Roller Bearing Features and Application of Sliding Bearings - TIMKEN Bearing Fault Diagnosis and Solutions - INA Flange Bearing Temperature Rise – Critical Analysis This article was originally published on China Bearing Network. Link: http://www.chinabearing.net Please cite the source when reusing this content. Previous: The Manufacturing Process of the Primary Part of a Bearing Next: How to Identify Bearing Faults by Sound
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