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Rolling mill bearings smooth and sealed
**Rolling Mill Bearings: Lubrication and Sealing**
Home > Bearing Knowledge > Rolling Mill Bearings Lubrication and Sealing
Source: Bearing Network | Date: March 28, 2013
Lubrication is a critical factor in the effective operation of rolling mill bearings. In fact, lubricants are often referred to as the "fifth major component" of the bearing system. Over 40% of bearing failures in rolling mills are caused by poor lubrication conditions. To reduce maintenance costs and extend the service life of bearings, it's essential to select the right lubrication method and high-quality lubricant that matches the application environment. Additionally, proper sealing must be ensured to prevent contaminants such as water, scale, and debris from entering the bearing.
Currently, rolling mill bearings are typically lubricated using grease or oil-gas methods. Most manufacturers use simple grease lubrication due to its ease of implementation and convenience for replacement. However, adopting an oil-gas lubrication system can significantly improve performance by maintaining optimal lubrication conditions under aspiration. This not only enhances bearing efficiency but also reduces long-term costs.
1. **Grease Lubrication Method**
Grease lubrication is straightforward and widely used. It should be selected based on factors like operating temperature, rotational speed, load, sealing requirements, and grease supply. High-performance greases with good thermal resistance, high viscosity, extreme pressure additives, and water resistance are recommended. For rolling mill bearings, 2#, 3# lithium-based greases with EP additives or polyurea greases are commonly used.
Although high-quality grease may have a higher initial cost, it requires less volume and extends bearing life, leading to lower overall costs. It’s important to fill the grease properly and avoid mixing different brands. The appearance of the bearing should always maintain a stable oil film for optimal performance.
2. **Grease Filling and Maintenance**
During installation, the inner space of the bearing should be fully filled with grease. For vertical or inclined rolls, each bearing housing’s top and bottom covers should be adequately filled. After each roller change, check the grease for signs of hardening, discoloration, contamination, oxidation, or emulsification. If any of these issues are found, the grease should be replaced immediately, along with any damaged seals. If the grease remains in good condition, it can continue to be used.
3. **Oil-Gas Lubrication**
Oil-gas lubrication is an advanced method where compressed air periodically delivers small drops of lubricating oil into the bearing. The oil stays inside the bearing, while the air helps dissipate heat and prevents external contaminants like moisture and dust from entering. This method is environmentally friendly as it avoids oil atomization and pollution.
4. **Sealing Solutions**
Proper sealing is crucial for maintaining internal lubrication and protecting bearings from harmful elements such as cooling water, iron oxide scale, and impurities. Seal failure is one of the main causes of bearing damage, especially in areas close to the roll. Bearings often suffer from contamination, grease loss, wear, or even fracture, particularly in cold strip mills where emulsions accelerate grease degradation.
There are two main types of bearing seals: self-contained and external. External seals usually combine labyrinth and contact designs. A higher number of labyrinth stages (at least two) and smaller gaps provide better sealing. The radial gap should be between 0.6–1.5 mm, and the axial gap around 4–6 mm.
Contact-type lip seals are commonly used in rolling mills. They are directional and cannot be reversed. Hot rolling mills typically use two seals, with both lips positioned outside the bearing housing to block external dirt. Cold strip mills often use three seals, with one lip facing inward to prevent grease from contaminating the rolled material. Care must be taken to avoid damaging the seal lip during installation.
RBR type sealing rings are another option. These rubber lip seals are designed for axial sealing and are widely used in modern rolling mills. Their lip adheres to the gland base, allowing old grease to escape while blocking external contaminants. They are easy to use and do not interfere with the bearing housing during roller changes.
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This article is sourced from China Bearing Network. For more information, visit [http://www.chinabearing.net](http://www.chinabearing.net).
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