Lubrication has an important impact on the fatigue life and friction, wear, temperature rise, vibration and so on of rolling bearings. Without normal lubrication, bearings cannot work. Analysis of the causes of bearing damage shows that about 40% of bearing damage is related to poor lubrication. Therefore, good lubrication of bearings is an effective measure to reduce bearing friction and wear. In addition, bearing lubrication has a variety of functions, such as heat dissipation, rust prevention, sealing, easing impact and so on. The role of bearing lubrication can be briefly explained as follows:

A. A layer of oil film is formed between the two rolling surfaces or sliding surfaces in contact with each other to separate the two surfaces and reduce friction and wear of the contact surface.

B. When oil lubrication is used, especially when circulating oil lubrication, oil mist lubrication and oil injection lubrication are used, the lubricating oil can take away most of the friction heat inside the bearing and play an effective role in heat dissipation.

C. When lubricating with grease, it can prevent dust and other foreign matters from entering the bearing and play a sealing role.

D. Lubricants can prevent metal from rust.

E. Prolong the fatigue life of bearings.

Lubrication methods of bearings can be roughly divided into grease lubrication and oil lubrication. In order to give full play to the function of bearings, it is important to use lubrication methods according to the use of reduction and use purposes. Table 4-2 shows the advantages and disadvantages of grease lubrication and oil lubrication.

Grease is a lubricant consisting of base oils, thickeners and additives. When choosing, we should choose grease which is very suitable for the use conditions of bearings. Because of different trademarks, there will be a great difference in performance, so attention must be paid to the selection. The commonly used grease for bearings are calcium base grease, sodium base grease, calcium sodium base grease, lithium base grease, aluminum base grease and molybdenum disulfide grease. The amount of filling grease in the bearing is appropriate to fill 1/2 to 1/3 of the internal space of the bearing. It should be reduced to 1/3 at high speed. Excessive grease raises the temperature.

When selecting grease according to working temperature, the main indexes should be drop point, oxidation stability and low temperature performance. Drop point can generally be used to evaluate high temperature performance. The actual working temperature of bearings should be lower than drop point 10-20℃. The use temperature of synthetic grease should be 20-30℃ lower than the drop point. When selecting grease according to bearing load, grease with small needle insertion should be selected for heavy load. In addition to small needle penetration, it also has high oil film strength and extreme pressure performance under high pressure. When grease is selected according to environmental conditions, calcium base grease is not easily soluble in water and is suitable for dry and less moisture environment.

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