During the actual operation of bearings, a large amount of heat will be generated due to metal friction, resulting in an excessively high temperature of the bearings, which in turn affects the operation of the bearings. Therefore, lubricating oil or lubricating grease is generally used for lubrication. Under normal circumstances, for spindle bearings with rolling bearings, lubricating oil is usually selected as the main lubricant. So, how should we choose the bearing lubricating oil properly? Below, the editor of Guoyang Precision Machinery has sorted out the performance requirements and selection methods of bearing lubricating oil for your reference.  

I. Performance Requirements of Bearing Lubricating Oil

1. Moderate Viscosity: When the lubricating oil is used under low-temperature conditions, viscosity, viscosity index, and pour point are very important.

2. Oxidation Stability: When used continuously for a long time or intermittently for a long time, or when used under high-temperature or other conditions that make the lubricating oil prone to oxidation and deterioration, it is very important for the lubricating oil to have good oxidation stability and/or thermal stability.

3. Anti-rust Property: If there is steam or moisture at the workplace, the machine is likely to get damp and rust. In this case, the lubricating oil needs to have good anti-rust property.

4. Anti-foaming Property: When the lubricating oil is agitated or circulated in the oil circuit system, some foam will naturally form due to mechanical movement. However, if there is too much foam, it may lead to insufficient oil supply to the bearings and cause the lubricating oil to overflow from the oil tank. At this time, an adequate amount of anti-foaming agent needs to be added to the lubricating oil.

5. Oil-water Separation Property (Anti-emulsification): If a large amount of water enters the lubricating oil, it is important that the lubricating oil can resist emulsification and easily separate the water. Generally speaking, mineral oil without any additives can also have good oil-water separation property and anti-emulsification performance.

6. Extreme Pressure Property: In some cases of large loads and low speeds, it is difficult to maintain a sufficient thickness of the oil film and ensure that the lubricating oil remains in a liquid state solely relying on its viscosity. This makes the bearings prone to seizure. At this time, it is necessary to add oily additives to maintain oil supply and improve the extreme pressure property.

7. Cleanliness: The temperature of the bearings of internal combustion engines and paper-making machinery will rise very high, and the lubricating oil is prone to oxidation and deterioration, resulting in the easy generation of residues. Therefore, in order to ensure that the residues do not adhere to the bearings or the oil supply system, in addition to having good oxidation stability and thermal stability, the lubricating oil must also have good cleanliness.

II. Selection Methods of Bearing Lubricating Oil

For the lubricating oil of spindle bearings using rolling bearings, it is generally comprehensively considered according to parameters such as the product of the bearing inner diameter d and the spindle speed n, that is, the speed factor dn, the bearing operating temperature T, and the load P borne by the bearing.

1. When the bearing operating temperature is between -30°C and 0°C, for ordinary loads (3MPa), the applicable oil viscosity (at 40°C) is 18 to 32mm²/s, and the viscosity grades are 22 and 32; for heavy loads or impact loads (from 3MPa to 20MPa), the applicable oil viscosity (at 40°C) is 18 to 50mm²/s, and the viscosity grades are 32 and 46.

2. When the bearing operating temperature is between 0°C and 60°C and the speed factor (dn value) is below 15000mm.r/min, for ordinary loads, the applicable oil viscosity (at 40°C) is 32 to 70mm²/s, and the viscosity grades are 32, 46, and 68; for heavy loads or impact loads (from 3MPa to 20MPa), the applicable oil viscosity (at 40°C) is 70 to 192mm²/s, and the viscosity grades are 68, 100, and 150.

3. When the speed factor (dn value) is between 15000 and 75000mm.r/min, for ordinary loads, the applicable oil viscosity (at 40°C) is 32 to 50mm²/s, and the viscosity grades are 32 and 46; for heavy loads or impact loads (from 3MPa to 20MPa), the applicable oil viscosity (at 40°C) is 42 to 90mm²/s, and the viscosity grades are 46, 68, and 100.

4. When the speed factor (dn value) is between 75000 and 150000mm.r/min, for ordinary loads, the applicable oil viscosity (at 40°C) is 15 to 32mm²/s, and the viscosity grades are 15 and 32; for heavy loads or impact loads (from 3MPa to 20MPa), the applicable oil viscosity (at 40°C) is 32 to 42mm²/s, and the viscosity grade is 32. When the speed factor (dn value) is between 150000 and 300000mm.r/min, for ordinary loads, the applicable oil viscosity (at 40°C) is 9 to 12mm²/s, and the viscosity grades are 5, 7, and 10; for heavy loads or impact loads (from 3MPa to 20MPa), the applicable oil viscosity (at 40°C) is 18 to 32mm²/s, and the viscosity grade is 15.

5. When the bearing operating temperature is between 60°C and 100°C and the speed factor (dn value) is below 15000mm.r/min, for ordinary loads, the applicable oil viscosity at 40°C is 110 to 192mm²/s (at 100°C is 9.3 to 12.5mm²/s), and the viscosity grade is 150; for heavy loads or impact loads (from 3MPa to 20MPa), the applicable oil viscosity (at 40°C) is 195 to 240mm²/s (at 100°C is 15 to 24mm²/s), and the viscosity grade is 150.

6. When the speed factor (dn value) is between 15000 and 75000mm.r/min, for ordinary loads, the applicable oil viscosity at 40°C is 70 to 120mm²/s (at 100°C is 5.6 to 9.3mm²/s), and the viscosity grades are 68 and 100; for heavy loads or impact loads (from 3MPa to 20MPa), the applicable oil viscosity (at 40°C) is 110 to 192mm²/s, and the viscosity grade is 150. When the speed factor (dn value) is between 75000 and 150000mm.r/min, for ordinary loads, the applicable oil viscosity at 40°C is 50 to 90mm²/s (at 100°C is 5.6 to 9.3mm²/s), and the viscosity grades are 46, 68, and 100; for heavy loads or impact loads (from 3MPa to 20MPa), the applicable oil viscosity (at 40°C) is 70 to 120mm²/s, and the viscosity grade is 100.

Regarding how to select the bearing lubricating oil, the above are the performance requirements and selection methods of the lubricating oil sorted out by the editor of Guoyang Precision Machinery for you. I hope it can be helpful to you. In fact, not only the conventional spindle bearings need lubrication, but also the precision bearings with other special requirements also need to do a good job of lubrication, so as to ensure the accuracy of the bearings.