(1) The role of bearing lubrication

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.

(2) Comparison of grease lubrication and oil lubrication

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.

(3) the grease 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.

(4) the choice of grease

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.

(5) oil lubrication

Under the condition of high speed and high temperature, oil lubrication can be used when grease lubrication is not suitable. Through the circulation of lubricating oil, a lot of heat can be taken away.

Viscosity is an important characteristic of lubricating oil. The viscosity directly affects the fluidity of lubricating oil and the thickness of oil film formed between friction surfaces. The viscosity of lubricating oil at bearing working temperature is generally 12-15CST. The higher the speed, the lower the viscosity, and the heavier the load, the higher the viscosity. Commonly used lubricating oil are mechanical oil, high-speed mechanical oil, turbine oil, compressor oil, transformer oil, cylinder oil and so on.

Oil lubrication methods include:

A. Oil bath lubrication

Oil bath lubrication is the most common lubrication method, suitable for low and medium speed bearing lubrication, bearing part immersed in the groove, the lubricating oil by rotating bearing parts, and then flow back to the oil groove oil surface should be slightly lower than the center of the lowest rolling body.

B. Lubrication with oil drops

Drop oil lubrication is suitable for the bearing parts that need to be supplied with lubricating oil quantitatively. It is advisable to drop one drop of oil every 3-8 seconds. Too much oil will cause the bearing temperature to increase.

C. Circulating oil lubrication

The filtered oil is conveyed to the bearing parts by the oil pump, and then filtered and cooled by the lubricating oil after the bearing. Because circulating oil can take away a certain amount of heat to cool the bearing, this method is suitable for bearing parts with high speed.

D. Spray lubrication

Dry compressed air is mixed with lubricating oil through a sprayer to form oil mist. In the spray bearing, the airflow can effectively cool the bearing and prevent the invasion of impurities. This method is suitable for lubrication of high speed and high temperature bearing parts.

E. Spray lubrication

The high pressure oil is shot into the bearing through the nozzle with an oil pump, and the oil shot into the bearing flows into the oil groove through the other end of the bearing. When the bearing rotates at a high speed, the rolling body and the cage also form a flow of air around it at a very high rotation speed. It is difficult to send the lubricating oil to the bearing with general lubrication method. At this time, the lubricating oil must be sprayed to the bearing by high-pressure injection.

(6) solid lubrication

Used in some special conditions, adding a small amount of solid lubricant grease, such as add 1 of 3-5% molybdenum disulphide can reduce wear and improve the compressive strength heat-resistant ability, for high temperature, high, high vacuum, corrosion resistance, resistance to radiation, and extremely low temperature and other special conditions, the solid lubricant in engineering plastics and powder metallurgy material, Can be made into bearing parts with self-lubricating performance, such as using binder to bond solid lubricant on the raceway, cage and rolling body, forming a lubricating film, to reduce friction and wear has a certain effect.

(7) Lubricant supplement and replacement

A. Filling interval of grease

Due to the increase of mechanical action, aging and pollution, the lubrication base filled in the bearing configuration will gradually lose its lubrication performance. Therefore, lubrication rank needs to be constantly supplemented and updated. The interval time of lubricant supplement will be different due to the formation, size and speed of bearings, etc., and the approximate interval time of grease supplement is required according to the operation time. In addition, when the bearing temperature exceeds 70 ° C, every 15 ° C rise in bearing temperature, it is necessary to use grease to reduce the interval by half. Double-sided closed bearings have been loaded with grease when manufacturing, “HRB” in these products is standard grease, the total operating temperature range and other properties suitable for the specified occasions, and the amount of grease is also corresponding to the size of the bearing, the service life of grease can generally exceed the bearing life, except for special occasions, do not need to add grease.

B. Lubricating oil replacement cycle

Lubricating oil replacement cycle due to the use of different conditions and oil, generally speaking, in the operating temperature of 50℃ below, less dust in a good environment, replace once a year, when the oil temperature reaches 100℃, to 3 months or less time to replace once.