As we all know, bearing is a pivotal component in contemporary mechanical equipment. Its main function is to support the mechanical rotating body to reduce the friction coefficient of the mechanical load during the transmission of the equipment. Therefore, it is particularly important to choose a suitable lubricant. So, how should the rolling bearing lubricant be selected, and what are the methods?
The lubricants used in rolling bearings are divided into two types: grease and lubricating oil.
One, grease.
Grease is made by mixing lubricating oil, thickener and additives at high temperature. According to the type of thickener, grease can be divided into calcium-based grease, sodium-based grease, calcium-sodium-based grease, lithium-based grease, aluminum-based grease, and molybdenum disulfide grease.
The main performance indicators of grease are penetration, dropping point, mechanical stability, oxidation stability and corrosion resistance. The choice of grease should be based on the working conditions, temperature and load of the bearing.
Dropping point is generally used to evaluate the high-temperature performance of grease. The actual working temperature of the bearing should be 10-20℃ lower than the dripping point of the grease, and the use temperature of synthetic grease should be lower than 20-30℃. Penetration refers to the hardness or bearing capacity of the grease. Bearings that work under heavy loads should use grease with low penetration. Calcium-based grease is not easy to dissolve in water and is suitable for working environments with humid and high water content. Sodium-based grease is easily soluble in water and is suitable for dry and low-moisture working environments.
Generally, grease is often used in bearings. The advantages of lubricating grease are: high oil film strength; good grease adhesion, not easy to lose, and long use time; simple sealing, which can prevent dust, moisture and other debris from entering the bearing. The disadvantage is: when the speed is higher, the friction loss power is larger.
Insufficient or excessive grease will cause the temperature rise and wear of the bearing to increase during the operation of the bearing, so the filling amount of grease should be moderate. Generally, it is appropriate to fill 1/3 to 1/2 of the space between the bearing and the housing.
Two, lubricants.
lubricants include special mineral oil, vegetable oil and synthetic lubricants.
The performance indicators of lubricating oil include viscosity, viscosity-temperature characteristics, acid value, corrosiveness, flash point, freezing point, etc.
Viscosity: Refers to the frictional resistance of the relative movement of the lubricating oil. The viscosity directly affects the fluidity of the lubricating oil and the ability to form a lubricating oil film between the friction surfaces. Therefore, viscosity is an important basis for choosing lubricating oil.
Bearings working under high speed or high temperature conditions are generally lubricated by oil. The advantages of oil lubrication are: reliable lubrication, low friction coefficient, good cooling and cleaning effects, and a variety of lubrication methods can be used to adapt to different working conditions. The disadvantage is that it requires complicated sealing devices and oil supply equipment.
When the bearing is immersed in oil (oil valley lubrication), the height of the oil level should not exceed the center of the rolling element under *. When the speed is high, drip oil or oil mist lubrication should be used.
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