Precautions for installation of rolling bearing
Rolling bearing is the most widely used general part in all kinds of rotating machinery. It is one of the most easily damaged parts of the machine. Once the rolling bearing fails, it will have a great impact on the normal operation of the machine. Therefore, the correct installation of rolling bearings is an important guarantee to reduce bearing faults and prolong the service life of bearings. According to statistics, 16% of the bearing failures are caused by improper installation. Therefore, when installing the bearing, it must be carried out in strict accordance with the operating specifications.
Installation method of rolling bearing
(1) Make clear the model of bearing
The bearing model can represent the basic size, original clearance, cage type, sealing form, lubrication requirements, etc. Therefore, it is necessary to determine whether the bearing model is correct before installation.
(2) Selection of bearing lubrication
It has an important impact on the lubrication of rolling bearing, such as friction, wear, temperature rise, vibration and fatigue life. Without normal lubrication, the bearing can not work. The bearing damage related to poor lubrication accounts for about 40%. Therefore, the effective measures to wear, prolong bearing life and reduce bearing friction are to maintain good lubrication of the bearing; In addition, bearing lubrication has the functions of cooling, vibration absorption, sealing and rust prevention. There are two common lubricants for rolling bearings: grease and lubricating oil. Bearings with high operating temperature or high speed are lubricated with lubricating oil, which has good heat dissipation and lubrication effect, but the lubricating oil is easy to lose, so it is necessary to ensure sufficient oil supply during operation.
(3) Selection of installation method
1. Hand hammer and mounting sleeve method
This method is applicable to small cylindrical bore bearings (bearing diameter less than 80mm), especially deep groove ball bearings, which are installed by hammering. Care should be taken because the hardened collar of the bearing is sensitive to hammering. In any case, it is forbidden to directly knock the inner and outer rings with a hammer, and it is forbidden to advance them with the transmission force from the outer ring to the inner ring and from the inner ring to the outer ring. It is best to use a flat end and soft steel sleeve for installation. In this way, the hammering force can be evenly distributed on the whole circumference to avoid the deflection and crimping of the ferrule.
2. Hot charging method
Heating installation method when the inner diameter of the bearing is greater than 70mm or the fit interference is large, the heating method is used to expand the bearing hole, so as to save labor and time in installation and avoid damage caused by excessive force.
At this time, the heating temperature needs to be controlled. Generally, the bearing is heated to 80 ℃ and the maximum temperature is 100 ℃. If the temperature exceeds 120 ℃, the bearing will be tempered, which will reduce the hardness and accuracy of the ferrule. Common heating methods include:
1). Electric heating plate heating method
The bearing can be placed on an electric heating plate with a temperature of 100 ℃ for a few minutes. This method is the most simple. For example, turning over several times can make the bearing bear heat evenly, and the efficiency is also high. This method can be used for large and small bearings.
2). Electric furnace heating method
The bearing is heated in a closed automatic temperature control electric furnace, which has the advantages of uniform heating, accurate temperature control and fast heating. It is suitable for heating many bearings in a batch.
3). Induction heating method
The induction heater can quickly, reliably and cleanly heat the bearing to the required temperature, which is especially suitable for the tight fit of the inner ring. Because only the inner ring is heated and the outer ring is rarely heated, it can be easily installed on the shaft and in the seat hole.
4). Electric bulb heating method
Using 50W electric lamp bulb to heat the bearing can ensure that the heating temperature is about 100 ℃. The smaller bearing can be directly placed on the bulb, and the larger bearing can be placed in the conical cover of the bulb. The conical cover can prevent the heat loss of the bulb and make the heating uniform. The conical cover can be adjusted up and down, which can adapt to heating bearings of different sizes within a certain range. If a far-infrared bulb is used, note that the direction of the bulb should be downward to avoid infrared rays being harmful to people’s eyes. This kind of light bulb can save energy. The bulb heating method is suitable for less quantity and less frequent use; In case of bearing heating, the bulb can also be used for lighting at ordinary times. In addition, no other equipment is required.
5). Oil tank heating method
This is a widely used traditional heating method. A metal mesh is set at the place 50-70mm from the bottom of the oil tank, the bearing is placed on the mesh, and the large bearing should be lifted with a hook. The bearing should not be placed directly at the groove bottom to prevent local heating of the bearing part contacting the groove bottom, or dirt deposited at the groove bottom from entering the bearing. The key points of oil tank heating method are as follows. Mineral oil with non corrosivity and good thermal stability shall be used, preferably transformer oil. The oil and container shall be kept clean. The capacity of the oil groove shall be determined by the size and oil quantity of the heated bearing. If the container is too small, the oil temperature will drop quickly as soon as it is put into the bearing during continuous operation, and the effect is not good.
6). Key points of heating installation method
- ① The heating temperature should be controlled properly. If the temperature is too high, the bearing will be damaged. If the temperature is too low, the expansion of the ferrule is insufficient, and the effect is not significant. The amount of thermal expansion of the inner diameter of the inner ring obtained at a heating temperature of 80-100 ° C is sufficient for bearings with general interference.
- ② As soon as the required heating temperature is reached, the installation shall be carried out as soon as possible to avoid installation difficulties due to cooling.
- ③ When the bearing is cooled, it also shrinks in the width direction. Therefore, during installation, a certain pressure shall be applied to compress the inner ring to the shoulder. After cooling, a very thin feeler gauge shall be used to test whether there is a gap between the end face of the inner ring and the shaft shoulder. In short, the operation requires proficiency, speed and accuracy.
3. Press installation method
When the bearing diameter increases and the interference increases, the press can be used to press and install the bearing on the shaft first, and then install the shaft into the bearing seat hole. Together with the bearing, the assembly sleeve made during press installation shall be padded with a layer of soft metal material (copper or soft steel) on the end face of the bearing inner ring. The matching pipe shall have an inner diameter slightly larger than the diameter of the journal and an outer diameter slightly smaller than the retaining edge of the bearing inner ring, Avoid being pressed on the holder. The bearing seat fits tightly with the bearing outer ring hole. When the shaft and inner ring fit loosely, the bearing can be pressed into the bearing seat hole first. At this time, the sleeve with the outer diameter of the assembly sleeve slightly smaller than the diameter of the seat hole should be selected. If the seat hole and the shaft are tightly matched with the bearing ring, the seat hole and the shaft shall be pressed into the outer ring and the inner ring at the same time. The structure of the assembly sleeve shall be able to press the end faces of the bearing inner ring and the outer ring at the same time. When assembling the bearing, the maintenance personnel of the company rarely install the inner and outer rings of the bearing according to the requirements for convenience, but only install the inner or outer rings of the bearing. This is very dangerous and must be eliminated!
4. Bearing clearance pre tightening and adjustment
The clearance of rolling bearing includes radial clearance and axial clearance. Its main function is to ensure the normal operation, lubrication and compensation of thermal elongation of rolling element. If it is a rolling bearing with adjustable clearance, the axial clearance is generally proportional to the radial clearance. During installation, in order to obtain the required radial clearance, only the axial clearance needs to be adjusted, and they are installed in pairs at one or both ends of the shaft, so only the axial clearance of one bearing can be adjusted. There are two commonly used adjustment methods: one is to adjust the position of the outer ring by using screws through the bearing outer ring gland, move the outer ring position, and loosen it with nuts after adjustment; The other is to adjust by adding or subtracting the gasket thickness between the machine body and the bearing cover. Pre tighten the rolling bearing by giving a certain axial pressure to the bearing and making the ring raceway and rolling element in a proper pre compression state during bearing installation. The rotation accuracy and stiffness of the bearing can be improved by preloading to reduce the vibration of the shaft during operation. Angular contact bearings and tapered roller bearings are used in pairs and side by side. Generally, this method should be adopted for assembly. The commonly used preloading methods include adding preload between ferrules, grinding narrow ferrules and adding preload and gasket.
Precautions for installing rolling bearing
(1) Check carefully before assembly
The bearing shall be cleaned before assembly, and the inner and outer race, rolling element and cage of the bearing shall be carefully checked to see if there is rust, burr, bruise and crack; Check whether the bearing clearance is appropriate, whether the rotation is light and free, and whether there is jamming; Check whether the dimension and dimensional tolerance, cylindricity, roundness and other geometric tolerances of bearing seat L and shaft diameter meet the requirements, and check whether the surface has burrs and unevenness.
(2) Understand the positioning mode of bearing
For a shaft to run smoothly, it needs at least two fulcrums for axial and radial support, and each fulcrum has at least one or more bearings. In general, one bearing plays a positioning role, and the other bearing does not play a positioning role. In special cases, two bearings play the role of positioning at the same time. Locating bearings provide radial support and axial guidance. Therefore, the positioning bearing must be fixed on the shaft and the bearing chamber at the same time. Deep groove ball bearings, spherical roller bearings, double row angular contact ball bearings and paired single row angular contact ball bearings can all be used as positioning bearings; Paired tapered roller bearings can also be used as positioning bearings; Cylindrical roller bearing without flange and thrust bearing with radial clearance can also be used as positioning bearing. Non locating bearings provide only radial support and must be movable in the axial direction.
(3) Pay attention to reasonable assembly
Improper assembly can lead to various bearing faults.
1. The proper assembly method requires that the rolling element is not stressed. When the cold pressing method is adopted for assembly, the assembly force on the end face of the ferrule shall act uniformly and symmetrically. It is best to press in with a press if conditions permit. Be sure to operate properly. If you drive it with a hammer, otherwise the seat ring will be deformed and cracked. If you hit it with a hammer on the seat ring without interference fit, the bearing will be damaged indirectly or the rolling element and raceway will be indented.
2. If the assembly temperature is well controlled, the assembly temperature must be well controlled. When the heating method is adopted for assembly, the heated oil temperature shall be controlled at 80 ℃ – 100 ℃ and shall not be higher than 120 ℃ at most. After heating the bearing on the journal, quickly take it out and suit it. If the temperature is not controlled properly and the temperature is too high, the hardness will be reduced. Due to the tempering of the bearing, the bearing is easy to peel off, wear and even crack during operation.
3. Adjust the bearing clearance. For rolling bearings with non adjustable clearance or adjustable clearance, the axial clearance shall be adjusted well. During assembly, when the temperature rises, the length of the shaft shall be compensated, so as to ensure the normal operation of the rolling element. If the axial clearance is too large, it will produce vibration, bath sound and even damage the cage; If the axial clearance is too small, it will cause the bearing to rotate and crawl, jam, heat, and even damage the rolling element. The following examples illustrate the importance of gap pre tightening and adjustment:
Example 1: for the installation of the vibration exciter bearing of the pellet thermal vibrating screen of our company, due to the excessive preload of the workers during installation, and the thermal vibrating screen is in a high-temperature environment, the bearing is damaged due to the temperature rise (thermal expansion and cold contraction) shortly after the installation and operation of the thermal vibrating screen, affecting the production.
Example 2: the company’s 3#10t grab crane often has the problem of trolley rail gnawing. After the problem analysis, it is found that the main reason for rail gnawing is that the bearings are not pre tightened and adjusted during the installation of trolley wheels, resulting in wheel gnawing because the running track cannot be guaranteed.
(4) Ensure good bearing lubrication, and pay attention to two problems when using grease for lubrication:
First, generally, the bearing is only filled with 1/3 – 1/2 of the clearance volume. An appropriate amount of grease should be added to the bearing. Too much is not only useless, but also increases the resistance when running the bearing to heat up.
Second, select the appropriate brand of grease according to the requirements of the manual. For example, due to the poor water resistance of sodium grease, the water pump bearing cannot be selected. General bearings can be coated with an appropriate amount of grease on the bearing. Otherwise, it will not only affect the heat dissipation effect and cause waste, but also affect the braking performance and make the grease overflow when heated. This phenomenon is particularly common in our equipment. Please pay attention!
(5) Carefully test run and check the bearing. After the rolling bearing is installed, carefully test run the bearing to see whether the temperature of the bearing installation part is too high and whether there are hidden troubles such as noise during bearing operation.
- 1. The bearing temperature is too high. During the test run, the bearing part with a certain temperature is allowed. When touching the bearing, the normal condition should be that it does not feel hot. Otherwise, it indicates that the bearing temperature is too high. The reasons for high bearing temperature are: the quality of lubricating oil does not meet the deterioration or requirements, and the salary of lubricating oil is too high; Rotate the bearing race on the shaft or in the housing; The bearing rolling element or cage is broken; Bearing assembly is too tight, etc.
- 2. During operation, the rolling bearing is allowed to make slight running noise. If there is impact sound or abnormal noise or the noise is too loud, it indicates that the assembly of the bearing is abnormal. The noise of newly installed rolling bearings is mainly caused by dry friction, insufficient bearing lubrication, or abnormal noise due to bearing breakage. Try to eliminate it during operation. If any hidden trouble is found.
Common errors and taboos in bearing installation
- 1. It is forbidden to knock the inner ring and outer ring of the bearing at will, or transfer force by the outer ring or inner ring. Prevent the transmission of force through the roller or ball of the bearing from damaging the bearing.
- 2. It is forbidden to heat the bearing directly with open fire. If the temperature of open flame heating flame is too high, it will cause annealing, reduce the hardness of bearing and affect its service life.
- 3. Prevent the site from being unclean. If there are iron filings, burrs, dust and other foreign matters in the bearing, the bearing will produce noise and vibration during operation, and even damage the raceway and rolling element. Conclusion: in short, a series of problems such as installation, inspection and maintenance of rolling bearings are described in detail in this paper. The correct installation of rolling bearings is an important guarantee to reduce bearing faults and prolong the service life of bearings.
Source: China Bearing Manufacturer – Yaang Pipe Industry (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
If you want to have more information about the article or you want to share your opinion with us, contact us at firstname.lastname@example.org