The lubrication of SKF bearings plays a critical role in determining the fatigue life, friction, wear, temperature, and vibration of rolling bearings. Without proper lubrication, bearings cannot function effectively. Studies on bearing failure show that approximately 40% of damage is directly related to inadequate lubrication. Therefore, maintaining good lubrication is essential for reducing friction and wear, and it also provides additional benefits such as heat dissipation, rust prevention, sealing, and shock absorption.
The main functions of bearing lubrication include:
a. Creating an oil film between contacting surfaces to reduce friction and wear.
b. In oil lubrication, especially with circulating or mist systems, the lubricant helps remove heat generated inside the bearing.
c. Grease can act as a seal, preventing contaminants like dust from entering the bearing.
d. Lubricants protect metal components from corrosion.
e. Proper lubrication significantly extends the fatigue life of the bearing.
When using grease lubrication, it's important to choose the right type based on operating conditions. Grease consists of base oil, thickener, and additives, and performance varies widely between brands. Common types include calcium-based, sodium-based, lithium-based, and molybdenum disulfide greases. The filling amount should be about 1/2 to 1/3 of the internal space, and at high speeds, this should be reduced to 1/3 to avoid excessive heating.
For SKF bearings, grease selection depends on several factors. At higher temperatures, the dropping point of the grease should be at least 10–20°C above the operating temperature. Synthetic greases are recommended when the temperature is 20–30°C below the dropping point. For heavy loads, a grease with low penetration and high oil film strength is preferred. In humid environments, calcium-based grease is suitable due to its water resistance.
Oil lubrication is often used in high-speed or high-temperature applications where grease may not be sufficient. Viscosity is a key factor, with the ideal range being 12–15 cSt at operating temperature. Higher speeds require lower viscosity, while heavier loads need higher viscosity. Common oils include machine oil, turbine oil, and compressor oil.
Lubrication methods for SKF bearings include:
a. Oil bath lubrication – suitable for low to medium speed bearings, where part of the bearing is immersed in oil.
b. Drip lubrication – delivers oil drop by drop, typically one drop every 3–8 seconds.
c. Circulating oil lubrication – uses a pump to deliver filtered oil, which is then cooled and reused.
d. Spray lubrication – mixes oil with compressed air to create an oil mist, ideal for high-speed, high-temperature bearings.
e. Injection lubrication – injects high-pressure oil into the bearing, ensuring proper coverage even at very high speeds.
In special cases, solid lubricants such as molybdenum disulfide can be added to grease or incorporated into materials like plastics or powder metallurgy to create self-lubricating bearings. These provide additional protection under extreme conditions such as high temperature, vacuum, or corrosive environments. Solid lubricants can also be applied directly to raceways or cages to form a protective film, reducing friction and extending service life.
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