Bearing lubrication and sealing
Typical varieties of bearings
Bearings are divided into two categories according to their structure: rolling bearings and sliding bearings. Rolling bearings can be divided into radial bearings, thrust bearings and hybrid bearings.
Rolling bearings
Radial bearings
Radial bearings, also known as deep-groove ball bearings, are the most widely used type of rolling bearings. It consists of an inner ring, an outer ring and a number of rolling elements between them, which can bear radial loads, axial loads or combined loads, and can limit the relative axial displacement and speed of the shaft to a certain range.
Thrust bearings
Thrust bearings are mainly used to bear axial loads. It consists of a shaft ring, a seat ring, and a rolling element assembly composed of a cage and a rolling element. It can bear one-way or two-way axial load, limited speed, limit axial displacement of the relative shaft, and can also be used as low-speed end support components.
Hybrid bearings
Hybrid bearings are composed of steel rings and ceramic rolling elements. Since the ceramic material has a much higher hardness than the steel material, the rolling contact surface of the hybrid bearing is suitable for heavy load rolling. Under the same radial load, the bearing capacity of the hybrid bearing is 3-4 times that of the ordinary bearing, which can reduce the size of the bearing and save space.
Sliding bearings
Plain bearings
Plain bearings are widely used in transmission machinery, rarely subjected to radial loads, and usually used to carry alternating or intermittent axial or combined loads. According to their structure, plain bearings can be divided into single-row rolling bearings, double-row rolling bearings and thin wall bearings.
Sleeve bearings
Sleeve bearings are widely used in automobiles, motorcycles and engineering machinery. They are mainly used for journal bearings, main shaft bearings, gearbox bearings and gearbox bearings, etc. Usually, the geometric accuracy and the surface roughness of the shaft and the bearing seat are required to be high, which can ensure the running accuracy and reduce the noise of the bearing.
Lubrication of rolling bearings
Lubrication is an important part of bearing management, which directly affects the working performance and service life of bearings. The purpose of bearing lubrication is to reduce the friction coefficient of bearing rotation and reduce the bearing surface temperature generated when the bearing rotates, so as to extend the service life of the bearing. Bearings are lubricated with oil, grease and dry film.
Oil lubrication
Oil is the most widely used lubricant for bearings. When circulating in the bearing, the minimum film thickness needs to be maintained to reduce the contact area between the rolling elements and the raceway, which reduces the friction and wear between the two.
Oil tightness of the bearing
The internal space of the bearing is in a sealed or semi-sealed state, so it is necessary to ensure the inner tightness of the bearing. It is generally divided into contact case seal and non-contact case seal. The contact case seal is directly in contact with the bearing raceway. It is mainly used for high speed and high temperature occasions. Non-contact case seals are not directly in contact with the bearing raceway, so they are mainly used for slow speed occasions.
Sealing of sliding bearings
In order to effectively prevent dust, particles, water and other impurities from entering the bearing and to prevent bearing lubricants from spilling out. Sliding bearings are usually sealed by mechanical seals, brush seals and labyrinth seals.
Mechanical seals
Mechanical seals are composed of metal parts, usually flats and grooves, which form a connection between the moving parts, so that when the contact surfaces are placed together, they are sealed. This kind of seal is usually applicable to the bearing rotating at high speed.
Brush seals
Brush seals are mainly composed of synthetic brush and contact ring. It is installed in the gap between the two parts to be sealed, by relying on the elastic force of the brush fibers and the viscosity of the lubricant to achieve tightness. This kind of seal has the characteristics of low friction coefficient and long service life, which is suitable for low speed occasion.
Labyrinth seals
Labyrinth seals are mainly composed of sealing grooves, which are distributed and arranged in staggered installation. The clearance between the grooves and the adjacent cover surface and the oil leakage inside the grooves form a multi-phase and airtight structure. This kind of seal is usually used for low speed occasions, which has the characteristics of low cost, simple structure and good tightness.
In conclusion
Bearing lubrication and sealing play important roles in bearing operation and service life. Bearing lubrication is to reduce the friction and temperature between the bearing and its inner space, so as to ensure the bearing has a good working performance; sealing is to ensure the inner space of the bearing is sealed, prevent impurities from entering and leaking of lubricants. Different bearing types need to be matched with different lubricants and seals.
