Bearings are components that fix and reduce the coefficient of friction of the load during mechanical transmission. It plays a pivotal role in contemporary machinery and equipment. Its main function is to support the mechanical rotating body to reduce the mechanical load friction coefficient of the equipment during the transmission process. Bearings can be divided into two types: rolling bearings and plain bearings. Today we will talk about rolling bearings in detail.
A rolling bearing is a precision mechanical component that changes the sliding friction between the running shaft and the shaft seat into rolling friction, thereby reducing friction loss. The rolling bearing is generally composed of an inner ring, an outer ring, a rolling body and a cage. The inner ring is matched with the shaft and rotates together with the shaft; the outer ring acts to cooperate with the bearing seat to support the rolling body; The rolling element is evenly distributed between the inner ring and the outer ring, and its shape and quantity directly affect the service 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 Rotate for lubrication.
Rolling bearings can be divided according to structure:
1.Deep groove ball bearing
The deep groove ball bearing has a simple structure and is easy to use, and is a type of bearing with the largest production batch and the widest application range. It is mainly used to withstand radial loads and also to withstand certain axial loads. When the radial clearance of the bearing is increased, the function of the angular contact bearing can withstand large axial loads. Used in automobiles, tractors, machine tools, motors, pumps, agricultural machinery, textile machinery, etc.
2. Needle bearing
Needle roller bearings are equipped with thin and long rollers (the length of the roller is 3 to 10 times the diameter and the diameter is generally not more than 5 mm), so the radial structure is compact, and the inner diameter and load capacity are the same as those of other types of bearings. The smallest diameter, especially suitable for support structures with limited radial mounting dimensions. Depending on the application, bearings or needle roller and cage assemblies without inner ring can be used. The journal surface and the housing hole surface that match the bearing directly serve as the inner and outer rolling surfaces of the bearing to maintain load capacity and running performance. As with ferrule bearings, the hardness of the raceway surface of the shaft or housing bore. The machining accuracy and surface and surface quality should be similar to the raceway of the bearing ring. This type of bearing can only withstand radial loads. For example: universal joint shafts, hydraulic pumps, sheet mills, rock drills, machine tool gearboxes, automotive and tractor gearboxes.
3. Angular contact bearing
Angular contact ball bearings have a high limit speed and can withstand both longitudinal and axial loads, as well as pure axial loads. The axial load capacity is determined by the contact angle and increases with increasing contact angle. Used for: oil pumps, air compressors, various types of 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 has an inner spherical shape, which has self-aligning performance. The coaxiality error due to the winding of the shaft and the deformation of the casing can be automatically compensated, and is suitable for the components in which the support seat hole cannot ensure strict coaxiality. The middle bearing is mainly subjected to radial load, and can bear a small amount of axial load while being subjected to radial load. It is usually not used to withstand pure axial load, such as bearing a pure axial load, and only one row of steel balls is stressed. Mainly used in agricultural machinery such as combine harvesters, blowers, paper machines, textile machinery, woodworking machinery, bridge cranes and drive shafts.
5. Spherical roller bearings
Spherical roller bearings have two rows of rollers that are primarily used to withstand radial loads and can also withstand axial loads in either direction. This kind of bearing has high radial load capacity, especially suitable for working under heavy load or vibration load, but can not bear pure axial load; good self-aligning performance can compensate the same bearing error. Main uses: paper machine, speed reducer, railway vehicle axle, rolling mill gear box seat, crusher, various industrial speed reducers, etc.
6. Thrust ball bearing
The thrust ball bearing is a split type bearing, and the collar "seat can be separated from the cage" steel ball assembly. The shaft ring is a ferrule that cooperates with the shaft, and the seat ring is a ferrule that cooperates with the bearing housing hole, and has a gap between the shaft. Thrust ball bearings can only draw axial load. One-way thrust ball bearings can only bear the axial load of one room. Two-way thrust ball bearings can bear axial loads in two directions. The thrust ball can not restrain the warp direction of the shaft to move, 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 both directions. Mainly used in automotive steering mechanisms, machine tool spindles.
7. Thrust roller bearing
Thrust roller bearings are used to support the axial load-based shaft. The warp joint load, but the warp load must not exceed 55% of the axial load. Compared with other thrust roller bearings, this type of bearing has a low friction factor, a high rotational speed, and a self-aligning capability. The roller of the 29000 type bearing is an asymmetric spherical roller, which can reduce the relative sliding of the stick and the raceway during the work, and the roller has a long diameter, a large diameter, a large number of rollers and a large load capacity, and is usually oil lubricated. Low speed conditions can be lubricated with grease. When designing the selection, it should be preferred. Mainly used in hydroelectric generators, crane hooks, etc.
8. Cylindrical roller bearing
Rollers for cylindrical roller bearings are usually guided by two ribs of a bearing ring. The cage. The roller and the guide ring form a combination that can be separated from the other bearing ring and is a detachable bearing. Such a bearing is easy to install and disassemble, especially when the inner ring and the outer ring are required to have an interference fit. These bearings are generally only used to withstand radial loads. Only single-row bearings with inner and outer rings with ribs can withstand small constant axial loads or large intermittent axial loads. Mainly used for large motors, machine tool spindles, axle axle boxes, diesel crankshafts and automobiles, lock boxes, etc.
9. Tapered roller bearings
Tapered roller bearings are mainly suitable for bearing radial and axial combined loads with radial loads, while large taper tapered roller bearings can be used to withstand axial loads and axial combined loads. The bearing is a separate bearing, and the inner ring (including the tapered roller and the cage) and the outer ring can be separately installed. The bearing's meridional clearance and axial clearance can be adjusted during installation and use. It can also be pre-interference mounted for the rear axle hub of the car, large machine tool spindle, high power reducer, axle bearing housing, and roller of the conveyor. .
10. With spherical ball bearings
The outer spherical ball bearing is composed of a sealed outer spherical ball bearing and a cast (or steel stamped) bearing housing. 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 the bearing is wider than the outer ring. The outer ring has a spherical outer surface and can be self-aligning with the concave spherical surface of the bearing seat. Usually, there is a gap between the inner hole of the bearing and the shaft, and the inner ring of the bearing is fixed on the shaft by a top wire, an eccentric sleeve or a clamping sleeve, and rotates together with the shaft. The bearing with compact structure, convenient loading and unloading, perfect sealing, suitable for simple support, often used in mining, metallurgy, agriculture, chemical, textile, printing and dyeing, conveying machinery, etc.
Routine maintenance
First, what are the requirements for the installation surface and installation site?
Yes. If foreign matter such as iron filings, burrs, dust, etc. enters 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 bearings, you must ensure that the mounting surface and the installation environment are clean.
Second, must the bearings be cleaned before installation?
The surface of the bearing is coated with anti-rust oil. You must clean it with clean gasoline or kerosene, and then apply it with clean high-quality or high-speed high-temperature grease. The effect of cleanliness on bearing life and vibration noise is very large. But we must remind you that the fully enclosed bearings do not need to be cleaned and refueled.
Third, how to choose grease?
Lubrication has a very important impact on the operation and life of the bearing. Here is a brief overview of the general principles for selecting grease. Grease is made of base oil, thickener and additives. The grease performance of different types and different grades varies greatly. The allowable rotation limit is different. Be careful when selecting. The performance of grease is mainly determined by the base oil. Generally, the low viscosity base oil is suitable for low temperature, high speed and high viscosity for high temperature and high load. The thickener is also related to the lubricating properties, and the water resistance of the thickener determines the water resistance of the grease. In principle, the different greases of the brand cannot be mixed, and even the grease of the same thickener may have a bad influence on each other due to the different additives.
Fourth, when lubricating the bearing, the more grease is 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 bearing chambers will cause excessive agitation of the grease, resulting in extremely high temperatures. The amount of bearing filling lubricant should be 1/2 to 1/3 of the internal space of the bearing, and should be reduced to 1/3 at high speed.
Five, how to install and disassemble?
Do not directly hammer the bearing end face and the non-stress surface during installation. The bearing should be evenly stressed by the clamp, sleeve or other installation tools (tooling), and should not be installed by the rolling body transmission force. If the mounting surface is coated with oil, it will make the installation smoother. If the interference is large, the bearing should be placed in mineral oil and heated to 80~90 °C and installed as soon as possible. Strictly control the oil temperature not to exceed 100 °C to prevent the tempering effect from decreasing and affecting dimensional recovery. When disassembling is difficult, it is recommended that you use the disassembly tool to pull outward while carefully pouring hot oil onto the inner ring. The heat will cause the inner ring of the bearing to expand, making it easier to fall off.
Sixth, the smaller the radial clearance of the bearing, the better?
Not all bearings require a minimum working clearance and you must select the appropriate clearance depending on the conditions. In GB 4604-93, the radial clearance of rolling bearings is divided into five groups - 2 groups, 0 groups, 3 groups, 4 groups, 5 groups. The clearance values are from small to large, and 0 is the standard clearance. The basic radial clearance group is suitable for general operating conditions, conventional temperature and common interference fit; bearings with high temperature, high speed, low noise, low friction and other special conditions should use large radial clearance; Small radial clearance should be used for precision spindles and bearings for machine tool spindles; a small amount of working clearance can be maintained for roller bearings. In addition, there is no play for the separate type of bearing; finally, the working clearance after the bearing is installed is smaller than the original clearance before installation, because the bearing is subject to a certain load rotation, as well as the bearing fit and load. The amount of elastic deformation.