**How to Extend the Life of Rolling Mill Bearings?**
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Source: China Bearing Network | Time: March 3, 2013
Improving the service life of rolling mill bearings is essential for maintaining efficiency and reducing maintenance costs in industrial applications. The key lies in controlling various factors that influence bearing performance, including material composition, heat treatment processes, and surface treatments. Below are some effective methods to enhance bearing longevity.
1. **Optimize the Microstructure Before Quenching**
Controlling the initial microstructure of the steel before quenching is critical. High-temperature austenitizing at around 1050°C followed by isothermal normalization at 630°C can produce a fine pearlitic structure, which improves the mechanical properties. Alternatively, isothermal treatment at 420°C can yield a bainitic structure. Wrought waste heat blast annealing can also be used to achieve a fine-grained pearlitic arrangement, ensuring uniform carbide dispersion and better overall performance.
2. **Control Quenching Parameters**
The carbon content in martensite, retained austenite, and undissolved carbides depend heavily on the quenching temperature and time. Increasing the quenching temperature typically reduces undissolved carbides but increases retained austenite. Hardness initially rises with temperature, peaks, and then decreases. Prolonged austenitizing times help reduce undissolved carbides and increase retained austenite, but this effect diminishes over time.
3. **Achieve Optimal Microstructure After Quenching**
For GCr15 steel, the ideal post-quenching microstructure includes about 7% undissolved carbides, 9% retained austenite, and cryptocrystalline martensite with a uniform carbon content of approximately 0.55%. This balance ensures high hardness and wear resistance. Fine carbides in the original structure allow for a lower quenching temperature and shorter austenitizing time, improving the final mechanical properties.
4. **Avoid Excessive Austenitizing Time**
If the original microstructure contains fine carbides, prolonged austenitizing may cause them to coalesce and grow, degrading the material’s properties. Therefore, it's recommended to use rapid heating and austenitizing techniques to maintain the desired microstructure and enhance mechanical performance.
5. **Enhance Surface Compressive Stress**
Introducing a carburizing or nitriding atmosphere during quenching can increase surface compressive stress, significantly improving fatigue resistance. For example, GCr15 steel quenched in a carburizing atmosphere showed 1.5 times longer life compared to non-carburized samples due to higher residual compressive stress on the surface.
6. **Ensure High-Purity Steel**
Bearings require high-purity materials with low levels of oxygen, nitrogen, phosphorus, and oxides. Techniques like electroslag remelting or vacuum arc remelting can reduce impurities to below 15 ppm, ensuring better performance and durability.
By focusing on these aspects—microstructure control, precise heat treatment, surface modification, and material purity—industrial operators can significantly extend the life of rolling mill bearings, leading to improved productivity and cost savings.
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