What are some ways to lubricate bearings?
In addition to making the bearing rotate better, bearing lubrication also has other functions. Different lubrication methods are suitable for different working situations. The properties of bearing lubricants also help predict and control surface friction, wear, and corrosion, which can significantly reduce material fatigue damage, resist violence, and prevent material scaling.
Bearing lubrication methods are mainly divided into seven types: oil cup drip lubrication; oil bath lubrication; splash lubrication; circulating oil lubrication; oil mist lubrication; oil spray lubrication and oil-air lubrication.
1. Oil cup dripping oil lubrication
A lubrication method that drips oil into the bearing through the oil-saving port in the oil cup. The advantages of oil cup dripping lubrication are simple structure, easy use, and fuel saving. Moreover, the amount of oil supply can be adjusted by the oil saver. Generally, the amount of oil dripping is one drop every 3-8 seconds, because too much oil will cause the temperature rise of the bearing to increase. The disadvantage is that there are certain requirements for the viscosity of the lubricating oil. Lubricating oil with high viscosity cannot be used and it has no heat dissipation function. Oil cup dripping lubrication is suitable for low speed, light load and low operating temperature situations.
2. Oil bath (oil immersion) lubrication
A lubrication method in which the bearing part is immersed in lubricating oil and the oil is brought into other parts of the bearing after the bearing is running. Oil bath lubrication is one of the most common and simple lubrication methods.
Considering the stirring loss and temperature rise during oil bath lubrication, for horizontal shafts, the height of the bearing part intruding into the lubricating oil should be limited. Generally, the oil level is controlled near the center of the lowest rolling element of the bearing. Oil bath (oil immersion) lubrication is sufficient, but the oil supply is not easy to adjust. If there is no filter device in the oil tank, it is easy to bring impurities into the inside of the bearing and damage the bearing. Oil bath (oil immersion) is generally suitable for low-speed or medium-speed situations. It is commonly used on low-speed bearings.
Lesson learned: Separable reinforcing ribs can be installed at the bottom of the bearing housing to reduce agitation and/or dissipate heat. The static oil level should be slightly lower than the center of the lowest rolling element of the bearing applied to the horizontal axis. For the vertical axis, the static oil level should cover 50%-80% of the rolling elements. If the bearing temperature is relatively high when using an oil bath system, you can use a dripping, splashing or circulating oil system instead.
3. Splash lubrication
A lubrication method in which oil is splashed and brought into the bearing through other running parts.
The oil supply amount of splash lubrication is not easy to adjust, and the lubricating oil level cannot be too high, otherwise it is easy to cause stirring loss and temperature rise, and it is also easy to bring impurities in the oil tank into the inside of the bearing and damage the bearing.
In splash lubrication, oil is splashed onto the bearing by a rotating body (impeller or "slinger") mounted on the shaft, and the bearing is not immersed in oil.
Experience: In gearboxes, gears and bearings often share an oil tank with the gear that serves as an oil slinger. Since the viscosity of the gear oil may be different from the bearing requirements and the oil contains wear particles from the gears, a separable lubrication system or method can be used to improve bearing life.
4. Circulating oil lubrication
A lubrication method in which the lubricating oil is sucked from the oil tank through an oil pump and transported to the parts of the bearing that need lubrication, and then returned to the oil tank through the oil return port, filtered and reused.
Circulating oil lubrication is sufficient, the oil supply is easy to control, and it has strong heat dissipation and impurity removal capabilities. Circulating oil lubrication is suitable for situations where the purpose is to dissipate heat or remove impurities, as well as high-speed, high-temperature, heavy-load situations, and has high reliability. Circulating oil lubrication is an ideal lubrication method. However, it requires an independent oil supply system and the manufacturing cost is relatively high. The oil supply system consists of an oil pump, cooler, filter, oil tank, oil pipeline, etc. Circulating oil lubrication includes oil injection lubrication, forced lubrication, and spray lubrication. The angles of their classification are different.
5. Oil mist lubrication
A lubrication method in which lubricating oil is mixed with a small amount of lubricating oil in an oil mist generator using compressed air to form oil mist, which is then delivered to the bearing lubrication part.
Oil mist lubrication has small stirring loss and temperature rise, saves fuel, and has less impurities in the oil. Moreover, the airflow generated when the oil mist is sprayed has a certain cooling effect, and can also effectively prevent the intrusion of impurities or discharge impurities. However, the cost of the lubrication device is high, and there are certain requirements for the viscosity of the oil used. Generally, it should not be higher than 340㎜2/s, otherwise, the atomization effect will not be achieved. In addition, if the sealing is not tight during lubrication, some oil mist may escape into the air and pollute the environment. If necessary, an oil and gas separator should be used to collect the oil mist. Oil mist lubrication is suitable for high-speed applications.
6. Oil injection lubrication
A lubrication method that uses high-pressure injection to inject lubricating oil into the bearing to lubricate the bearing. When the bearing is running at high speed, the rolling elements and cage also rotate at a very high speed, thus forming an air vortex around the bearing. If normal lubrication is used, it is difficult for the lubricating oil to reach the lubrication part. On the other hand, due to the centrifugal force generated at high speed, it is difficult to keep lubricating oil in the lubricated parts. In order to ensure that sufficient but not excessive lubricating oil is supplied to high-speed bearings, lubricating oil must be forced into the bearing from one end for lubrication, and then flow back into the oil tank from the other end.
When designing the lubrication system, the high-pressure nozzle should be positioned between the inner ring and the center of the cage, and the lubricating oil should be thrown toward the outer raceway through centrifugal action. In order to effectively lubricate the bearings, the injection speed of lubricating oil should not be less than 15m/s.
From the perspective of operating speed, oil injection lubrication is often used for bearings running at higher speeds under low or medium loads; from the direction of bearing force, oil injection lubrication is often used for bearings on vertical or inclined shafts, and lubricating oil is usually directly injected into the bearings.
7. Oil and gas lubrication
Oil-gas lubrication is usually suitable for situations where bearings run at high speeds. The oil-gas lubrication system mixes a small amount of lubricating oil with gas at a certain pressure and then supplies it to the bearings. This method is suitable for high-speed applications, such as machine tools, and is generally less used in the refining and chemical industries.
