Bearing is a component that fixes and reduces the friction coefficient of load in the process of mechanical transmission. It plays an important role in contemporary mechanical equipment. Its main function is to support the mechanical rotating body to reduce the mechanical load friction of the equipment during the transmission process. coefficient. Bearings can be divided into two types: rolling bearings and sliding bearings. This article will explain those things about rolling bearings for you!
What is a rolling bearing?
A rolling bearing is a precise mechanical element that converts the sliding friction between the running shaft and the shaft seat into rolling friction, thereby reducing friction loss. Rolling bearings are generally composed of four parts: inner ring, outer ring, rolling body 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; Because the cage evenly distributes the rolling elements between the inner ring and the outer ring, its shape, size and quantity directly affect the performance and life of the rolling bearing; the cage can make the rolling elements evenly distributed, prevent the rolling elements from falling off, and guide the rolling elements. Rotation acts as lubrication.
1. Characteristics of rolling bearings
In the processing of bearing parts, a large number of special equipment for bearings are used. Such as steel ball processing using ball mills, grinding machines and other equipment. The characteristics of specialization are also reflected in the production of bearing parts, such as steel ball companies specializing in the production of steel balls, and miniature bearing factories specializing in the production of miniature bearings.
The use of advanced machine tools, tooling and processes is made possible by the high volume scale requirements of bearing production. Such as CNC machine tools, three-jaw floating chuck and protective atmosphere heat treatment.
The specialization of bearing production provides conditions for its production automation. A large number of fully automatic, semi-automatic dedicated and non-dedicated machine tools are used in production, and automatic production lines are gradually popularized and applied. Such as automatic heat treatment line and automatic assembly line.
Second, the structure of rolling bearing:
Rolling bearings include raceways (inner ring and outer ring), rolling elements (balls or rollers) and cages. The cages keep the rolling elements at a certain interval and fix them in the correct position for rolling motion.
Raceway (inner and outer ring) or raceway surface
The surface in contact with the rolling elements is called “raceway surface”, and this contact surface bears all the loads of the bearing.
Usually the inner ring is fixed on the shaft, and the outer ring is fixed on the bearing housing.
The rolling elements are divided into balls and rollers according to their shapes, and the rollers are divided into four categories: cylindrical rollers, needle rollers, tapered rollers and drum spherical rollers.
Geometrically speaking, the contact between the rolling elements and the inner and outer ring raceways is point (ball) or line (roller) contact.
Theoretically, the rolling elements roll on the rolling surfaces of the inner and outer rings and rotate separately.
The rolling element and the ring support the load borne by the bearing with the contact surface of the raceway surface, and the cage does not directly bear the load. It is only used to maintain the correct position and spacing of the rolling elements, while preventing the rolling elements from falling off when the bearing is installed. The types of cages are classified according to the way of production, including press-in, car-type and formed cages
3. Classification of rolling bearings
1. Classification by structure type
According to the structure of rolling elements and ferrules, it can be divided into:
Deep Groove Ball Bearings, Needle Roller Bearings, Angular Contact Bearings, Spherical Ball Bearings, Spherical Roller Bearings, Thrust Ball Bearings, Thrust Spherical Roller Bearings, Cylindrical Roller Bearings, Tapered Roller Bearings, Spherical Ball bearings, etc.
Rolling bearings can be divided into:
1) Deep groove ball bearings
Deep groove ball bearings have a simple structure and are easy to use. They are the type of bearing with the largest production volume and the widest application range. It mainly uses one to bear radial load, and can also bear certain axial load. When the radial clearance of the bearing increases, it has the function of an angular contact bearing and can bear a large 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 rollers is 3-10 times the diameter, and the diameter is generally not more than 5mm), so the radial structure is compact, and its inner diameter and load capacity are the same as other types of bearings. The outer diameter is the smallest, especially suitable for supporting structures with limited radial installation size. Depending on the application, a bearing without an inner ring or a needle roller and cage assembly can be selected. At this time, the surface of the journal and the surface of the housing hole matched with 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. As with the bearing with ring, the hardness, machining accuracy and surface and surface quality of the raceway surface of the shaft or housing hole should be similar to the raceway of the bearing ring. This type of bearing can only bear radial loads. For example: universal joint shafts, hydraulic pumps, sheet mills, rock drills, machine tool gearboxes, automobile and tractor gearboxes, etc.
3) Angular contact bearings
Angular contact ball bearings have a high limit speed and can bear both warp and axial loads, as well as pure axial loads. The axial load capacity is determined by the contact angle and increases with the increase of the contact angle. Mostly used for: oil pumps, air compressors, various transmissions, fuel injection pumps, printing machinery.
4) Self-aligning ball bearings
The self-aligning ball bearing has two rows of steel balls, two raceways in the inner ring, and an inner spherical raceway in the outer ring, 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 shell, and is suitable for parts where the bearing seat hole cannot guarantee strict coaxiality. The middle bearing mainly bears radial load, while bearing radial load, it can also bear a small amount of axial load. Usually, it is not used to bear pure axial load. If it bears pure axial load, only one row of steel balls is stressed. Mainly used in agricultural machinery such as combine harvesters, blowers, paper machines, textile machinery, woodworking machinery, overhead crane wheels and drive shafts.
5) Spherical roller bearings
Spherical roller bearings have two rows of rollers, which are mainly used to withstand radial loads, and can also withstand axial loads in either direction. This kind of bearing has high radial load capacity and is especially suitable for working under heavy load or vibration load, but cannot bear pure axial load; it has good self-aligning performance and can compensate for 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 bearing
Thrust ball bearing is a separable bearing, the shaft washer “seat ring” can be separated from the cage “steel ball” components. The shaft ring is a ferrule matched with the shaft, 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 take out the axial load, one-way thrust ball bearings can only bear the axial load of one room, and two-way thrust ball bearings can bear the axial load in two directions. The thrust ball can not limit the longitudinal direction of the shaft to move, and the limit speed is very low. One-way thrust ball bearings can limit the axial displacement of the shaft and housing in one direction, and two-way bearings can limit the axial displacement in two directions. Mainly used in automobile steering mechanism, machine tool spindle.
7) Thrust roller bearings
Thrust roller bearings are used for shafts mainly bearing axial loads. Combined radial loads, but the radial loads shall not exceed 55% of the axial loads. Compared with other thrust roller bearings, this kind of bearing has lower friction factor, higher speed and self-aligning ability. The rollers of the 29000 type bearing are asymmetric spherical rollers, which can reduce the relative sliding of the stick and the raceway during operation, and the rollers are long and large in diameter, the number of rollers is large, and the load capacity is large. Low speed conditions can be greased. In the design and selection, it should be preferred. Mainly used in hydraulic generators, crane hooks, etc.
8) Cylindrical roller bearings
The rollers of cylindrical roller bearings are usually guided by two ribs of one bearing ring. The cage. The rollers and the guide ring form a combination, which can be separated from the other bearing ring and belong to a separable bearing. This kind of bearing is easy to install and disassemble, especially when the inner ring, the outer ring and the shaft and the housing are required to be interference fit. Such bearings are generally only used to bear radial loads, and only single-row bearings with ribs on both the inner and outer rings can bear a small steady axial load or a large intermittent axial load. Mainly used for large motors, machine tool spindles, axle boxes, diesel engine crankshafts, and automobiles, such as gearboxes.
9) Tapered roller bearings
Tapered roller bearings are mainly suitable for bearing combined radial and axial loads dominated by radial loads, while tapered roller bearings with large taper angles can be used to withstand combined radial and axial loads dominated by axial loads. This kind of bearing is a separable bearing, and its inner ring (including tapered rollers and cage) and outer ring can be installed separately. During installation and use, the meridional clearance and axial clearance of the bearing can be adjusted, and it can also be pre-interfered to be installed for the rear axle hub of the automobile, the main shaft of the large machine tool, the high-power reducer, the axle bearing box, and the roller of the conveying device. .
10) Outer spherical ball bearing with seat
The spherical insert ball bearing with seat consists of an insert spherical ball bearing with seals on both sides and a cast (or steel plate stamped) 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 be automatically aligned with the concave spherical surface of the bearing seat. Usually, 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 top 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, commonly 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 2000mm or more.
Fourth, the advantages and disadvantages of rolling bearings:
- Small friction resistance, low power consumption, high mechanical efficiency, easy to start;
- The size is standardized, interchangeable, easy to install and disassemble, and easy to maintain;
- Compact structure, light weight, and reduced axial size;
- High precision, large load, small wear and long service life;
- Some bearings have self-aligning performance;
- Suitable for mass production, stable and reliable quality and high production efficiency;
- The transmission friction torque is much lower than that of the hydrodynamic bearing, so the friction temperature rise and power consumption are lower;
- The starting friction torque is only slightly higher than the rotating friction torque;
- The sensitivity of bearing deformation to load changes is less than that of hydrodynamic bearings;
- Only a small amount of lubricant is needed for normal operation, and lubricant can be provided for a long time during operation;
- The axial dimension is smaller than that of traditional hydrodynamic bearings;
- It can bear radial and thrust combined loads at the same time;
- In a large load-speed range, the unique design can obtain excellent performance;
- Bearing performance is relatively insensitive to fluctuations in load, speed and operating speed.
- The noise is loud.
- The structure of the bearing seat is more complicated.
3, the cost is higher.
- Even if the bearings are well lubricated, installed correctly, tightly protected against dust and moisture, and operate normally, they will eventually fail due to fatigue of the rolling contact surfaces.
- Daily maintenance of rolling bearings
- Are there requirements for the installation surface and installation site?
Yes. If there are foreign objects such as iron filings, burrs, dust, etc. in the bearing, it will cause noise and vibration during the operation of the bearing, and even damage the raceway and rolling elements. Therefore, before installing the bearing, you must ensure that the installation surface and installation environment are clean.
2. Does the bearing have to 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 high-temperature lubricating grease before installation and use. The impact of cleanliness on bearing life and vibration noise is very large. But we would like to remind you that: the fully enclosed bearing does not need to be cleaned and refueled.
3. How to choose grease?
Lubrication has a very important influence on the operation and life of bearings. Here is a brief introduction to the general principles of grease selection. Grease is made of base oil, thickener and additives. The performance of different types and different brands of greases of the same type is very different, and the allowable rotation limits are different. Be careful when choosing. The performance of lubricating grease is mainly determined by the base oil. Generally, the low-viscosity base oil is suitable for low temperature and high speed, and the high-viscosity base oil is suitable for high temperature and high load. The thickener is 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 adverse effects on each other due to different additives.
4. When lubricating bearings, is it better to apply more grease?
It is a common misconception that when lubricating bearings, the more grease the better. Excessive grease in the bearing and bearing chamber will cause excessive agitation of the grease, resulting in extremely high temperatures. The amount of lubricant filled in the bearing is suitable to fill 1/2-1/3 of the inner space of the bearing, and it should be reduced to 1/3 at high speed.
5. How to install and remove?
When installing, do not directly hammer the bearing end face and non-stressed surface. Use pressure blocks, sleeves or other installation tools (tools) to make the bearing evenly stressed, and do not install through rolling element transmission force. If the mounting surface is lubricated, the installation will be smoother. If the interference is large, the bearing should be heated to 80-90℃ in mineral oil and installed as soon as possible, and 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. In case of difficulty in disassembly, it is recommended that you use the disassembly tool to carefully pour hot oil on the inner ring while pulling outwards. The heat will expand the inner ring of the bearing, making it easier to fall off.
6: Is the radial clearance of the bearing as small as possible?
Not all bearings require a minimum working clearance, you must choose the appropriate clearance according to the conditions. In the national standard 4604-93, the radial clearance of rolling bearings is divided into five groups – group 2, group 0, group 3, group 4, and group 5. The clearance values are from small to large, and group 0 is the standard clearance. The basic radial clearance group is suitable for general operating conditions, normal temperature and commonly used interference fit; bearings working under special conditions such as high temperature, high speed, low noise and low friction should choose a large radial clearance; Small radial clearance should be selected for precision spindles, machine tool spindle bearings, etc.; a small amount of working clearance can be maintained for roller bearings. In addition, there is no clearance for separate bearings; finally, the working clearance after the bearing is installed is smaller than the original clearance before installation, because the bearing has to bear a certain load to rotate, and the bearing fit and load are generated. amount of elastic deformation.