Do you really understand bearing grease lubrication and oil lubrication?

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This post was last edited by yinkuilin6868 on 2015-11-23 08:39. The methods of lubricating bearings generally fall into two categories: grease lubrication and oil lubrication. To fully utilize the functions of bearings, it is important to adopt appropriate lubrication methods based on their operating conditions and intended use. Bearing grease Grease is a lubricant composed of base oil, thickeners, and additives. When selecting, a lubricant that is highly suitable for the bearing’s operating conditions should be chosen. Since different brands of lubricants vary greatly in performance, careful attention must be paid when making this selection. 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 lubricating grease filled in the bearing should be such that it fills 1/2 to 1/3 of the internal space of the bearing. At high speeds, it should be reduced to 1/3. Excessive grease can easily raise the temperature of bearings in operation. Selection of grease: When choosing grease based on the operating temperature, the key parameters are the dripping point, oxidation stability, and low-temperature performance. The dripping point is generally used to assess high-temperature performance, and the actual operating temperature of the bearing should be 10–20°C lower than the dripping point. The operating temperature for synthetic grease should be 20-30°C below its drip point. When selecting grease based on the bearing load, a grease with a low penetration value should be chosen for high loads. When operating under high pressure, in addition to a low penetration value, it is also necessary to have high film strength and extreme pressure properties. When selecting grease based on environmental conditions, calcium-based grease is insoluble in water and is suitable for dry environments with low moisture levels. Lubricant for bearings: Under high-speed and high-temperature conditions, when grease lubrication is no longer suitable, oil lubrication can be used. Through the circulation of lubricating oil, a large amount of heat can be removed. Viscosity is an important property of lubricating oils; its value directly affects the fluidity of the oil as well as the thickness of the oil film formed between the friction surfaces. At the operating temperature of bearings, the viscosity of lubricating oils is generally 12-15 cSt. The higher the rotational speed, the lower viscosity should be chosen; the greater the load, the higher viscosity should be chosen. Commonly used lubricants include machine oil, high-speed machine oil, turbine oil, compressor oil, transformer oil, cylinder oil, etc. Lubrication methods Oil bath lubrication: Oil bath lubrication is the most common method of lubrication; it is suitable for lubricating bearings operating at low to medium speeds. Part of the bearing is submerged in the oil tank, and the lubricating oil is carried away by the rotating bearing components before flowing back into the tank. The oil level should be slightly below the center of the lowest rolling element. 　　Drip lubrication: Drip lubrication is suitable for bearing components that require a fixed amount of lubricant; it is generally appropriate to apply one drop every 3–8 seconds. An excessive amount of oil can cause the bearing temperature to rise. 　　Circulating oil lubrication: A oil pump is used to deliver the filtered oil to the bearing components; the lubricating oil that passes through the bearings is then filtered and cooled before being reused. Since the circulating oil can carry away a certain amount of heat, thereby cooling the bearings, this method is suitable for bearing components with high rotational speeds. 　　Spray lubrication: Dry compressed air is mixed with lubricant using a sprayer to form an oil mist, which is then sprayed into the bearings. The airflow helps to cool the bearings effectively and prevents impurities from entering them. This method is suitable for lubricating high-speed, high-temperature bearing components. 　　Jet lubrication: A high-pressure oil is pumped through a nozzle into the bearing, and the oil that enters the bearing flows to the oil sump through the other end of the bearing. When the bearing rotates at high speed, the rolling elements and cage also rotate at a very high speed, creating air currents around them. It is difficult to deliver lubricant to the bearing using conventional lubrication methods; in such cases, high-pressure spraying is required to inject the lubricant into the bearing, with the nozzle positioned between the inner ring and the center of the cage.