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What is the role of bearing lubrication

Update:29 Sep 2020
Summary:

1. The role of bearing lubrication    Lubrication has a […]

1. The role of bearing lubrication
   Lubrication has an important influence on the fatigue life and friction, wear, temperature, vibration, etc. of rolling bearings. Without normal lubrication, the bearing 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 the bearing is an effective measure to reduce bearing friction and wear. In addition, bearing lubrication also has multiple functions such as heat dissipation, rust prevention, sealing, and impact mitigation. The role of bearing lubrication can be briefly described as follows:
   A. An oil film is formed between the two rolling surfaces or sliding surfaces that are in contact with each other to separate 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 oil spray lubrication, the lubricating oil can take away most of the friction heat inside the bearing and play an effective role in heat dissipation.
   C. When using grease lubrication, it can prevent foreign matter such as external dust from entering the bearing and play a sealing role.
   D. Lubricants have the effect of preventing metal corrosion. e. Extend the fatigue life of the bearing.
  
   2. Comparison of grease lubrication and oil lubrication
  
   Bearing lubrication methods are roughly divided into two types: grease lubrication and oil lubrication. In order to give full play to the function of the bearing, it is important to adopt a lubrication method according to the use adjustment and the purpose of use. 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 choosing, you should choose a grease that is very suitable for the bearing conditions. Due to different trademarks, there will be great differences in performance, so you must pay attention when choosing.
   The commonly used greases for bearings include calcium-based grease, sodium-based grease, calcium-sodium-based grease, lithium-based grease, aluminum-based grease, and molybdenum disulfide grease.
    The amount of grease filled in the bearing should be 1/2-1/3 of the inner space of the bearing. Should be reduced to 1/3 at high speed. Too much grease will increase the temperature rise. Fourth, the choice of grease When selecting grease according to the 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 10-20 ℃ lower than the dropping point. . The use temperature of synthetic grease should be 20-30℃ lower than the dropping point.
    When selecting grease based on bearing load, select grease with low penetration for heavy loads. In addition to low penetration when working under high pressure, it also has higher oil film strength and extreme pressure performance.
    When selecting grease based on environmental conditions, calcium-based grease is not easily soluble in water, and is suitable for dry and low-water environments. Five, oil lubrication
   Under high-speed and high-temperature conditions, 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 size of 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 12-15cst. The higher the speed, the lower the viscosity, the heavier the load, the higher the viscosity. Commonly used lubricants include mechanical oil, high-speed mechanical oil, turbine oil, compressor oil, transformer oil, and cylinder oil. 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, and the lubricating oil is picked up by the rotating bearing parts and then flows back to the oil surface of the oil groove. Should be slightly lower than the center of the lowest rolling element.
   B. Drop oil lubrication    Drop oil lubrication is suitable for bearing parts that require a quantitative supply of lubricating oil. The amount of oil dripping is generally one drop every 3-8 seconds. Excessive oil will cause the bearing temperature to increase.
   C. Circulating oil lubrication    Use an oil pump to deliver the filtered oil to the bearing parts, and then filter and cool the lubricating oil after passing through the bearing. Since circulating oil can take away a certain amount of heat and cool the bearing, this method is suitable for bearing parts with higher speeds.
   D. Spray lubrication    uses dry compressed air to be mixed with lubricating oil through a sprayer to form an oil mist. Injecting the bearing, the airflow can effectively cool the bearing and prevent the intrusion of impurities. This method is suitable for the lubrication of high-speed and high-temperature bearing components.
   E. Jet lubrication   Use an oil pump to inject high-pressure oil into the bearing through a 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 elements and the cage also make the surrounding air form an airflow at a relatively high rotation speed. 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 high-pressure injection. In the bearing, the position of the nozzle should be placed between the inner ring and the center of the cage.