1、 Function of bearing lubrication
Lubrication has an important influence on the fatigue life, friction, wear, temperature and vibration of rolling bearing. Without normal lubrication, the bearing can not work. The analysis of the causes of bearing damage shows that about 40% of bearing damage is related to poor lubrication. Therefore, good bearing lubrication is an effective measure to reduce bearing friction and wear. In addition, bearing lubrication has many functions, such as heat dissipation, rust prevention, sealing, impact mitigation and so on.
a. An oil film is formed between the two rolling surfaces or sliding surfaces in contact with each other to separate the two surfaces and reduce the friction and wear of the contact surface.Bearing lubrication
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.Bearing lubrication
c. When grease lubrication is used, it can prevent external dust and other foreign matters from entering the bearing and play a sealing role.Bearing lubrication
d. Lubricants can prevent metal corrosion.Bearing lubrication
e. Prolong the fatigue life of bearings.Bearing lubrication
2、 Comparison between grease lubrication and oil lubrication
The lubrication methods of bearings are roughly divided into grease lubrication and oil lubrication. In order to give full play to the function of the bearing, it is important to adopt the lubrication method according to the use reduction and use purpose. Table 4-2 shows the advantages and disadvantages of grease lubrication and oil lubrication.
3、 Grease lubrication
Grease is a lubricant composed of base oil, thickener and additives. When selecting, the lubricating grease that is very suitable for the service conditions of the bearing should be selected. Due to different trademarks, there will be great differences in performance, so we must pay attention to it when selecting.Bearing lubrication
Common lubricating greases for bearings include calcium base grease, sodium base grease, calcium sodium base grease, lithium base grease, aluminum base grease and molybdenum disulfide grease.Bearing lubrication
The amount of grease filled in the bearing should be 1 / 2-1 / 3 of the internal space of the bearing. It should be reduced to 1 / 3 at high speed. Too much grease will increase the temperature rise.Bearing lubrication
4、 Selection of lubricating grease
When selecting lubricating grease according to the working temperature, the main indicators should be the drop point, oxidation stability and low-temperature performance.Bearing lubrication
The drop point can generally be used to evaluate the high-temperature performance, and the actual working temperature of the bearing should be 10-20 ℃ lower than the drop point. The service temperature of synthetic grease shall be 20-30 ℃ lower than the dropping point.Bearing lubrication
When selecting the grease according to the bearing load, the grease with small penetration should be selected for the heavy load. When working under high pressure, in addition to small penetration, it also has high oil film strength and extreme pressure performance.Bearing lubrication
When selecting grease according to environmental conditions, calcium based grease is not easy to dissolve in water and is suitable for dry and less water environment.
5、 Oil lubrication
Under the conditions of high speed and high temperature, oil lubrication can be used when grease lubrication is no longer 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 should be selected, and the heavier the load, the higher the viscosity should be selected. The commonly used lubricating oils include machine oil, high-speed machine oil, turbine oil, compressor oil, transformer oil, cylinder oil, etc.
Oil lubrication methods include:
a. Oil bath lubrication
Oil bath lubrication is a common lubrication method, which is suitable for the lubrication of low and medium speed bearings. Part of the bearing is immersed in the groove, and the lubricating oil is brought up by the rotating bearing parts and then flows back to the oil groove. The oil surface should be slightly lower than the center of the low rolling element.
b. Drip lubrication
Oil dripping lubrication is suitable for bearing components requiring quantitative supply of lubricating oil. The amount of oil dripping is generally one drop every 3-8 seconds. Excessive amount of oil will increase the bearing temperature.
c. Circulating oil lubrication
The filtered oil is delivered to the bearing parts by the oil pump, and the lubricating oil after passing through the bearing is filtered and cooled before use. Because the circulating oil can take away a certain amount of heat and cool the bearing, this method is suitable for bearing parts with high speed.
D. spray lubrication
The dry compressed air is mixed with the lubricating oil through the sprayer to form an oil mist. In the jet bearing, the airflow can effectively cool the bearing and prevent impurities from invading. This method is suitable for the lubrication of high-speed and high-temperature bearing parts.
e. Jet lubrication
Use the oil pump to shoot the high-pressure oil into the bearing through the nozzle, and the oil injected 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 element and cage also form airflow in the surrounding air at a fairly high rotation speed. It is difficult to send the lubricating oil to the bearing by general lubrication method. At this time, the lubricating oil must be sprayed into the bearing by high-pressure injection method, and the position of the nozzle should be placed between the inner ring and the center of the cage.
6、 Solid lubrication
Under some special use conditions, adding a small amount of solid lubricant to the grease, such as adding 3 ~ 5% molybdenum disulfide 1, can reduce wear and improve the compression and heat resistance. For special conditions such as high temperature, elegance, high vacuum, corrosion resistance, radiation resistance and extremely low temperature, adding solid lubricant to engineering plastics or powder metallurgy materials can make bearing parts with self-lubricating performance, If the solid lubricant is bonded to the raceway, cage and rolling body with adhesive to form a lubricating film, it has a certain effect on reducing friction and wear.
7、 Supplement and replacement of lubricant
a. Grease replenishment interval
Due to the increase of mechanical action, aging and pollution, the lubricating base filled in the bearing configuration will gradually lose its lubricating performance. Therefore, the lubrication rank needs to be continuously supplemented and updated. The interval of lubricant replenishment varies with the formation, size and speed of the bearing. Figure 4-1 shows the approximate interval of grease replenishment according to the operation time.
In addition, in Figure 4-1, when the bearing temperature exceeds 70 ℃, the replenishment interval of lubricating grease should be reduced by half for every 15 ℃ rise in the bearing temperature.
The double-sided closed bearing has been filled with grease during manufacturing. “HRB” uses standard grease in these products. The common operating temperature range and other properties are suitable for the specified occasions, and the grease filling amount is also corresponding to the size of the bearing. The service life of the grease can generally exceed the service life of the bearing. Except for special occasions, it is not necessary to supplement grease.
b. Replacement cycle of lubricating oil
The replacement cycle of lubricating oil is different due to service conditions and oil quantity. Generally, when it is used in a good environment with operating temperature below 50 ℃ and less dust, it shall be replaced once a year. When the oil temperature reaches 100 ℃, it shall be replaced once in 3 months or less.