Basic knowledge of rolling bearings

2021-06-26 17:00

Bearings are closely related to the lives of modern people and are essential key components in people’s lives. From bicycles and electric vehicles to various automobiles, trains, airplanes, heavy machinery, and production equipment, they are inseparable from bearings. Bearings Has penetrated into thousands of households.


Bearings are used to fix and reduce the friction coefficient of load during mechanical transmission. They play a pivotal role in contemporary mechanical equipment. Its main function is to support the mechanical rotating body to reduce the friction coefficient of the mechanical load during the transmission of the equipment. Bearings can be divided into rolling bearings and sliding bearings. Today we will talk about rolling bearings in detail.


Rolling bearing is a kind of precision mechanical component that changes the sliding friction between the rotating shaft and the bearing seat into rolling friction, thereby reducing friction loss. Rolling bearings are generally composed of four parts: inner ring, outer ring, rolling elements and cage. The function of the inner ring is to cooperate with the shaft and rotate with the shaft; the function of the outer ring is to cooperate with the bearing seat and play a supporting role; The cage evenly distributes the rolling elements between the inner ring and the outer ring, and its shape, size and quantity directly affect the performance and life of the rolling bearing; the cage can evenly distribute the rolling elements, prevent the rolling elements from falling off, and guide the rolling elements Rotation plays a role of lubrication.


Rolling bearing features

1. Specialization


In the processing of bearing parts, a large number of special bearing equipment is used. For example, ball mills, grinders and other equipment are used for steel ball processing. Specialization is also reflected in the production of bearing parts, such as a steel ball company specializing in the production of steel balls and a miniature bearing factory specializing in the production of miniature bearings.


2. Advancement


Due to the large-scale requirements of bearing production, it is possible to use advanced machine tools, tooling and technology. Such as CNC machine tools, three-jaw floating chucks and protective atmosphere heat treatment.


3. Automation


The specialization of bearing production provides conditions for its production automation. In the production, a large number of fully automatic, semi-automatic dedicated and non-dedicated machine tools are used, and the production automatic line is gradually popularized and applied. Such as automatic heat treatment line and automatic assembly line.


Classified by structure type


According to the structure of rolling element and ferrule, it can be divided into:


Deep groove ball bearings, needle roller bearings, angular contact ball bearings, self-aligning ball bearings, self-aligning roller bearings, thrust ball bearings, thrust self-aligning roller bearings, cylindrical roller bearings, tapered roller bearings, with seat outer spherical surface Ball bearings and so on.


According to the structure, rolling bearings can be divided into:


1. Deep groove ball bearings


Deep groove ball bearings are simple in structure and easy to use. They have the largest production batch and the widest application range. It mainly bears radial load, but also can bear certain axial load. When the radial clearance of the bearing is enlarged, it has the function of angular contact bearing and can bear larger axial load. Used in automobiles, tractors, machine tools, motors, water pumps, agricultural machinery, textile machinery, etc.


2. Needle roller bearings


Needle roller bearings are equipped with thin and long rollers (the length of the roller is 3-10 times the diameter, and the diameter is generally not greater than 5mm), so the radial structure is compact, and its inner diameter and load capacity are the same as other types of bearings. The smallest diameter, especially suitable for supporting structures with limited radial installation dimensions. According to different applications, bearings without inner ring or needle roller and cage components can be selected. At this time, the journal surface and shell hole surface matching the bearing are directly used as the inner and outer rolling surfaces of the bearing, in order to maintain the load capacity and running performance Same as the bearing with ring, the hardness of the surface of the shaft or housing hole raceway. The machining accuracy and surface and surface quality should be similar to the raceway of the bearing ring. This kind of bearing can only bear radial load. For example: universal joint shafts, hydraulic pumps, sheet rolling mills, rock drills, machine tool gearboxes, automobile and tractor gearboxes, etc.


3. Angular contact bearing


Angular contact ball bearings have a high limit speed, which can bear radial load and axial load at the same time, and can also bear pure axial load. Its axial load capacity is determined by the contact angle and increases with the increase of the contact angle. Mostly used in: oil pumps, air compressors, various transmissions, fuel injection pumps, printing machinery.


4. Self-aligning ball bearing


The self-aligning ball bearing has two rows of steel balls, the inner ring has two raceways, and the outer ring raceway is an inner spherical surface, which has the performance of self-aligning. It can automatically compensate for the coaxiality error caused by the bending of the shaft and the deformation of the housing, and it is suitable for parts where strict coaxiality cannot be guaranteed in the support seat hole. The middle bearing mainly bears radial load. While bearing radial load, it can also bear a small amount of axial load. It is usually not used for bearing pure axial load. For example, bearing pure axial load, only one row of steel balls is stressed. It is mainly used in agricultural machinery such as combine harvesters, blowers, paper machines, textile machinery, woodworking machinery, traveling wheels and drive shafts of bridge cranes.


5. Spherical roller bearings


Spherical roller bearings have two rows of rollers, which are mainly used to bear radial loads and can also bear axial loads in any direction. This kind of bearing has high radial load capacity, especially suitable for working under heavy load or vibration load, but cannot bear pure axial load; it has good centering performance and can compensate the same bearing error. Main uses: papermaking machinery, reduction gears, railway vehicle axles, rolling mill gearbox seats, crushers, various industrial reducers, etc.


6. Thrust ball bearings


Thrust ball bearing is a separable bearing, the shaft ring "seat washer can be separated from the cage" steel ball components. The shaft ring is a ferrule matched with the shaft, and the seat ring is a ferrule matched with the bearing seat hole, and there is a gap between the shaft and the shaft. Thrust ball bearings can only handle axial loads, one-way thrust ball bearings can only bear axial loads in one room, and two-way thrust ball bearings can bear axial loads in two directions. The thrust ball cannot limit the longitudinal movement of the shaft, and the limit speed is very low. The one-way thrust ball bearing can limit the axial displacement of the shaft and the housing in one direction, and the two-way bearing can limit the axial displacement in two directions. Mainly used in automobile steering mechanism and machine tool spindle.


7. Thrust roller bearing


Thrust roller bearings are used to withstand the combined longitudinal load of the shaft with the main axial load, but the longitudinal load shall not exceed 55% of the axial load. Compared with other thrust roller bearings, this type of bearing has a lower friction factor, higher speed, and has the ability to adjust the center. The rollers of type 29000 bearings are asymmetric spherical rollers, which can reduce the relative sliding of the stick and the raceway during work, and the rollers are long, large in diameter, and the number of rollers is large, and the load capacity is large. They are usually lubricated by oil. Grease lubrication can be used at low speeds. When designing and selecting, it should be preferred. Mainly used in hydroelectric generators, crane hooks, etc.


8. Cylindrical roller bearings


The rollers of cylindrical roller bearings are usually guided by the two ribs of a bearing ring. The cage, the roller and the guide ring form an assembly, which can be separated from the other bearing ring and is a separable bearing. This kind of bearing is more convenient to install and disassemble, especially when the inner and outer ring and the shaft and the shell are required to be interference fit. This type of bearing is generally only used to bear radial load. Only single row bearings with ribs on the inner and outer rings can bear small steady axial loads or large intermittent axial loads. Mainly used for large motors, machine tool spindles, axle boxes, diesel crankshafts and automobiles, etc.


9. Tapered roller bearings


Tapered roller bearings are mainly suitable for bearing combined radial and axial loads based on radial loads, while large cone angle tapered roller bearings can be used for bearing combined radial and axial loads based on axial loads. This type of bearing is a separable bearing, and its inner ring (including tapered rollers and cage) and outer ring can be installed separately. In the process of installation and use, the radial and axial clearance of the bearing can be adjusted. It can also be pre-interference installed for automobile rear axle hubs, large-scale machine tool spindles, high-power reducers, axle bearing boxes, and rollers for conveying devices. .


10. Spherical ball bearing with seat


The outer spherical ball bearing with seat is composed of a sealed outer spherical ball bearing on both sides and a cast (or stamped steel plate) bearing seat. The internal structure of the outer spherical ball bearing is the same as that of the deep groove ball bearing, but the inner ring of this kind of bearing is wider than the outer ring. The outer ring has a truncated spherical outer surface, which can automatically adjust the center when matched with the concave spherical surface of the bearing seat. Generally, there is a gap between the inner hole of this kind of bearing and the shaft, and the inner ring of the bearing is fixed on the shaft with a jack wire, an eccentric sleeve or an adapter sleeve, and rotates with the shaft. The bearing with seat has compact structure, convenient loading and unloading, perfect sealing, suitable for simple support, and is often used in mining, metallurgy, agriculture, chemical industry, textile, printing and dyeing, conveying machinery, etc.


Sort by size


Bearing size according to its outer diameter


(1) Miniature bearings-bearings with a nominal outer diameter range of 26mm or less.


(2) Small bearings-bearings with a nominal outer diameter range of 28-55mm.


(3) Small and medium-sized bearings-bearings with a nominal outer diameter range of 60-115mm.


(4) Medium and large bearings-bearings with a nominal outer diameter range of 120-190mm.


(5) Large bearings-bearings with a nominal outer diameter range of 200-430mm.


(6) Extra-large bearings-bearings with a nominal outer diameter range of 440-2000mm.


(7) Heavy-duty bearings-bearings with a nominal outer diameter range of more than 2000mm.


advantage


1. Low friction resistance, low power consumption, high mechanical efficiency and easy start;


2. The size is standardized, interchangeable, easy to install and disassemble, and easy to maintain;


3. Compact structure, light weight, and reduced axial size;


4. High precision, large load, small wear and long service life;


5. Some bearings have self-aligning performance;


6. It is suitable for mass production, with stable and reliable quality and high production efficiency;


7. The transmission friction torque is much lower than that of hydrodynamic bearings, so the friction temperature rise and power consumption are lower;


8. Starting friction torque is only slightly higher than rotating friction torque;


9. The sensitivity of bearing deformation to load changes is less than that of hydrodynamic bearings;


10. Only a small amount of lubricant is needed for normal operation, and lubricant can be provided for a long time during operation;


11. The axial size is smaller than the traditional hydrodynamic bearing;


12. It can bear combined radial and thrust loads at the same time;


13. In a large load-speed range, the unique design can obtain excellent performance;


14. Bearing performance is relatively insensitive to fluctuations in load, speed and operating speed.


shortcoming


1. Loud noise.


2. The structure of the bearing seat is more complicated.


3. Higher cost.


4. Even if the bearings are well lubricated, installed correctly, dust-proof and moisture-proof, and running normally, they will eventually fail due to the fatigue of the rolling contact surface.


Daily maintenance


1. Are there requirements for the installation surface and installation site?


Yes. If there are iron filings, burrs, dust and other foreign objects in the bearing, it will cause noise and vibration when the bearing is running, and even damage the raceways and rolling elements. Therefore, before installing the bearing, you must ensure that the installation surface and the installation environment are clean.


2. Must the bearing be cleaned before installation?


The bearing surface is coated with anti-rust oil. You must carefully clean it with clean gasoline or kerosene, and then apply clean, high-quality or high-speed and high-temperature lubricating grease before installation. Cleanliness has a great influence on bearing life and vibration and noise. But what we want to remind you in particular is: fully enclosed bearings do not need to be cleaned and refueled.


Third, how to choose grease?


Lubrication has an extremely important impact on the operation and life of bearings. Here is a brief introduction to the general principles of choosing lubricating grease. Grease is made of base oil, thickener and additives. The performance of different types and different grades of the same type of grease varies greatly, and the allowable rotation limit is different. Please pay attention to it when choosing. The performance of grease is mainly determined by the base oil. Generally, low-viscosity base oils are suitable for low temperature and high speed, and high-viscosity base oils are suitable for high temperature and high load. Thickeners are also related to the lubricating performance, and the water resistance of the thickener determines the water resistance of the grease. In principle, greases of different brands cannot be mixed, and even greases with the same thickener will have a bad influence on each other due to different additives.


Fourth, when lubricating the bearing, should the more grease be applied, the better?


When lubricating a bearing, the more grease is applied, the better. This is a common misconception. Excessive grease in the bearing and the bearing chamber will cause excessive stirring of the grease, resulting in extremely high temperatures. The amount of lubricant filled in the bearing should be 1/2 to 1/3 of the inner space of the bearing, and it should be reduced to 1/3 at high speed.


Five, how to install and remove?


Do not directly hammer the end face and non-stressed surface of the bearing during installation. Press blocks, sleeves or other installation tools (tools) should be used to make the bearing evenly stressed. Do not install through the transmission force of the rolling elements. If the installation surface is coated with lubricating oil, the installation will be smoother. If the interference is large, the bearing should be installed in mineral oil and heated to 80~90℃ as soon as possible. The oil temperature should be strictly controlled not to exceed 100℃ to prevent the tempering effect from reducing the hardness and affecting the size recovery. When the disassembly is difficult, it is recommended that you use the disassembly tool to pull out and carefully pour hot oil onto the inner ring. The heat will expand the inner ring of the bearing and make it easier to fall off.


6. Is the radial clearance of the bearing as small as possible?


Not all bearings require the smallest working clearance, you must select the appropriate clearance according to the conditions. In the national standard 4604-93, the radial clearance of the rolling bearing is divided into five groups-2 groups, 0 groups, 3 groups, 4 groups, and 5 groups. The basic radial clearance group is suitable for general operating conditions, normal temperature and common interference fit; bearings that work under special conditions such as high temperature, high speed, low noise, low friction, etc. should use large radial clearance; Bearings for precision spindles and machine tool spindles should be selected with a smaller radial clearance; for roller bearings, a small amount of working clearance can be maintained. In addition, there is no such thing as clearance for separate bearings; finally, the working clearance of the bearing after installation is smaller than the original clearance before installation, because the bearing has to bear a certain load rotation, and there is also bearing coordination and load. The amount of elastic deformation.