First, the role of bearing lubrication Lubrication has a significant impact on the fatigue life of rolling bearings and friction, wear, temperature, vibration, etc., without normal lubrication, the bearing can not work. Analysis of the cause of bearing damage indicates that about 40% of bearing damage is associated with poor lubrication. Therefore, good lubrication of the bearings is an effective measure to reduce bearing friction and wear.
In addition, the lubrication of the bearing also has various functions such as heat dissipation, rust prevention, sealing, and shock mitigation.
The effect of bearing lubrication can be briefly explained as follows:
a. Forming a gap between two rolling surfaces or sliding surfaces that are in contact with each other The oil film separates the two surfaces, reducing friction and wear on the contact surfaces.
b. When using oil lubrication, especially when using circulating oil lubrication, oil mist lubrication and fuel injection lubrication, the lubricating oil can take away most of the friction heat inside the bearing and play an effective heat dissipation effect.
c. When grease lubrication is used, it is possible to prevent foreign matter such as dust from entering the bearing and sealing.
d. Lubricants have the effect of preventing metal corrosion.
e. Extend the fatigue life of the bearing.
Second, grease lubrication and oil lubrication comparison of bearing lubrication methods are roughly divided into grease lubrication and oil lubrication.
In order to fully utilize the function of the bearing, it is important to use a lubrication method depending on the purpose of use reduction and use. 3. Grease Lubricating Grease is a lubricant composed of a base oil, a thickener and an additive. When selecting, you should choose a grease that is very suitable for the conditions of use of the bearing. Due to the different trademarks, there will be great differences in performance, so you must pay attention when choosing.
Commonly used greases for bearings include calcium-based greases, sodium-based greases, calcium-sodium-based greases, lithium-based greases, aluminum-based greases, and molybdenum disulfide greases.
The amount of grease filled in the bearing is preferably 1/2-1/3 of the internal space of the bearing. It should be reduced to 1/3 at high speed. Excessive grease will increase the temperature rise.
Fourth. Selection of grease
When selecting grease according to working temperature, the main indicators should be dropping point, oxidation stability and low temperature performance. The dropping point can generally be used to evaluate high temperature performance. The actual working temperature of the bearing should be lower than the dropping point of 10-20 °C. . Synthetic grease should be used at a temperature below the drop point of 20-30 °C.
When selecting the grease according to the bearing load, the grease with a small penetration should be selected for the heavy load. When working under high pressure, in addition to the small penetration, it also has higher oil film strength and extreme pressure performance. When selecting grease according to environmental conditions, calcium-based grease is not easily soluble in water and is suitable for drying and low moisture environments.
Fifth. Oil lubrication Under the conditions of high speed and high temperature, oil lubrication can be used when grease lubrication is not suitable. A large amount of heat can be taken away by the circulation of the lubricating oil. Viscosity is an important characteristic of lubricating oil. The viscosity directly affects the fluidity of the lubricating oil and the thickness of the oil film formed between the friction surfaces. The viscosity of the lubricating oil at the working temperature of the bearing is generally 12-15 cst. The higher the speed, the lower the viscosity, and the heavier the load, the higher the viscosity. Commonly used lubricating oils include mechanical oil, high-speed mechanical oil, turbine oil, compressor oil, transformer oil, cylinder oil, and the like. Oil lubrication methods include:
a. Oil bath Lubricating oil bath lubrication is the most common lubrication method. It is suitable for the lubrication of low and medium speed bearings. Part of the bearing is immersed in the groove. The lubricating oil is taken up by the rotating bearing parts and then flows back to the oil groove. Should be slightly below the center of the lowest rolling element.
b. Drip oil lubrication Drip lubrication is suitable for bearing parts that need to supply lubricating oil quantitatively. The amount of oil dripping is generally one drop every 3-8 seconds. Excessive oil quantity will cause the bearing temperature to increase.
c. Circulating oil lubrication The oil pump delivers the filtered oil to the bearing components, and the oil after passing through the bearings is filtered and cooled for use. Since the circulating oil can take a certain amount of heat to cool the bearing, this method is suitable for bearing parts with higher rotational speed.
d. Spray lubrication The dry compressed air is mixed with the lubricating oil by a sprayer to form an oil mist. In the injection bearing, the air flow can effectively cool the bearing and prevent the intrusion of impurities. This method is suitable for the lubrication of high speed, high temperature bearing components.
e. Injection lubrication The oil pump shoots the high pressure oil through the nozzle into the bearing, and the oil injected into the bearing flows into the oil groove through the other end of the bearing. When the bearing rotates at high speed, the rolling elements and the cage also form a gas flow at the relatively high rotation speed of the surrounding air. It is difficult to send the lubricating oil to the bearing by the general lubrication method. At this time, the lubricating oil must be sprayed by the high-pressure injection method. In the bearing, the position of the nozzle should be placed between the inner ring and the center of the cage.
Sixth. Solid Lubrication Solid Lubrication Under some special conditions, a small amount of solid lubricant is added to the grease. For example, adding 3 to 5% of Molybdenum Disulfide No. 1 can reduce wear and improve resistance to pressure and heat. For high temperature and elegance. Special conditions such as high vacuum, corrosion resistance, radiation resistance, and extremely low temperature. Adding solid lubricants to engineering plastics or powder metallurgy materials can produce bearing parts with self-lubricating properties, such as solid lubricants with binders. Bonded to the raceway, cage and rolling elements to form a lubricating film that has a certain effect on reducing friction and wear.
Seventh.Replenishment and replacement of lubricants a. Replenishment interval of grease Due to mechanical action, aging and pollution increase, 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 between lubricant replenishment will vary depending on the formation, size, and rotational speed of the bearing. Figure 4-1 shows the approximate interval between refilling the grease based on the operating time. In addition, when the bearing temperature exceeds 70 ° C, for every 15 ° C rise in the bearing temperature, the supplemental interval of the grease is reduced by half. Double-sided closed bearings have been filled with grease at the time of manufacture. “HRB” uses standard greases in these products. The total operating temperature range and other properties are suitable for the specified conditions, and the amount of grease is also corresponding to the bearing size. The service life of the grease can generally exceed the bearing life. Except for special occasions, no grease needs to be replenished. b. Lubricating oil replacement cycle The replacement period of the lubricating oil varies depending on the conditions of use and the amount of oil. Under normal circumstances, when the operating temperature is below 50 ° C and the dust is used in a good environment, it is replaced once a year. When it reaches 100 °C, it should be replaced in 3 months or less.