Focus on the Bearing Industry for 20 Years!
Bearings can be divided into radial bearings and thrust bearings according to the direction of load. Radial bearings are mainly used to bear pure radial loads, such as deep groove ball bearings, cylindrical roller bearings, needle roller bearings, etc. Thrust bearing is mainly used to bear pure axial load, such as thrust ball (roller) bearing, etc. For the bearing that needs to bear the combined radial and axial load at the same time, the bearing with contact angle shall be selected according to the direction (or angle) and size of the load. Its load bearing capacity changes with the change of contact angle. The larger the contact angle is, the greater the axial bearing capacity is, while the radial bearing capacity decreases.
Generally, when the load angle of the bearing is less than 45 °, Select angular contact ball bearing or tapered roller bearing, etc. when the load angle is greater than 45 “When selecting thrust angular contact bearings, the axial load capacity of such bearings is generally greater than the radial load capacity. When selecting the bearing contact angle, the theoretical contact angle should be greater than the load angle. Due to the existence of clearance, deep groove ball bearings can also bear a certain amount of axial load; cylindrical roller bearings with retaining edges on the inner and outer rings can also bear a certain axial load through special design Load capacity. In the actual selection of bearings, combined bearings of various structures can also be selected to meet the requirements of radial and axial load carrying capacity or speed at the same time.
Deep groove ball bearing or angular contact ball bearing can be selected for high speed and light load, and cylindrical roller bearing or tapered roller bearing (with axial load) can be selected for high speed and heavy load The thrust bearing generally has a low speed due to structural constraints. The limit speed given by the bearing sample is applicable to the class 0 tolerance bearing with small load and normal lubrication and cooling conditions. This value can be referred to when selecting the bearing speed. The working speed of the general bearing should be lower than this value. According to the application experience, the high working speed can be taken as 0.8 times of the limit speed.
The bearings with light diameter and narrow width can be selected when the radial installation size is small and the rotating speed is high. Needle roller bearings can be selected when the load is large and the rotating speed is low. Single ring or non ring bearings can also be selected. Under the premise of ensuring the application characteristics of bearings, reducing the overall size of bearings or combining them with supporting components into units is one of the development trends of bearings at present. Another problem to be considered in size selection is the fatigue life of the bearing. Generally, the larger the overall size of the bearing, the longer the corresponding fatigue life. However, one-sided demand for long life will increase the volume of the machine and increase the manufacturing cost. Too low service life will bring trouble to use.
Under the same overall dimensions, the load capacity of roller bearing is greater than that of ball bearing. If it is subjected to pure radial (axial) load, centripetal (thrust) bearing shall be selected. When bearing combined load, angular contact ball bearing or tapered roller bearing with contact angle less than 45 ° can be selected when radial load is greater than axial load, and thrust angular contact bearing can be selected when axial load is greater than radial load. When there is impact load, cylindrical roller bearing, tapered roller bearing or self-aligning roller bearing can be selected.
In the case of low speed and large load, full loaded roller bearings can be selected. Double row or four row bearings can also be selected for heavy load.
Because the length of the shaft will elongate or shorten with the change of temperature, one end of the shaft is generally fixed and the other end can swim freely in the axial direction. The fixed end bearing is usually subject to combined load, and the bearing that can bear a certain axial force should be selected. The axial swimming support bearing only bears radial load. Therefore, the radial bearing should be selected to avoid the additional axial force generated by the bearing itself and affect the axial swimming. This kind of bearing mainly includes cylindrical roller bearing and needle roller bearing. If axial swimming is required in both directions, the bearing with inner ring or outer ring without flange can be selected. If the axial swimming is large, clearance fit can be adopted for the inner or outer ring according to the load nature. To limit the axial travel in one direction, select the bearing with single stop edge on the inner ring or outer ring.
For the occasions where the main engine requires high rotation accuracy, high speed, difficult maintenance and high reliability, it is necessary to select bearings higher than Class 0 tolerance. The accuracy and stiffness of the shaft and housing shall be improved to match it.
The bearing clearance includes original clearance, installation clearance and working clearance. Generally, the original clearance is large and the working clearance is small. Clearance has a great influence on the use of bearings. Therefore, the clearance should be reasonably selected to make the performance of bearing such as rotation accuracy, temperature rise, vibration and service life in a good state. When selecting the bearing clearance, the smaller clearance group can be selected for the occasions with light load, high speed, high precision and low bearing working temperature, and the larger clearance group can be selected for the occasions with heavy load, impact load and high working temperature.
The elastic deformation of imported bearings is very small, and rigidity does not need to be considered in most applications. Only in the occasions requiring high rotation accuracy, such as spindle bearing, sheet mill and other bearings, the stiffness is required. Under the same size, the stiffness of roller bearing is greater than that of ball bearing. When the bearing structure is certain, the stiffness can also be improved by applying the preload, but the added preload should be calculated by setting I 10. Excessive preload has an impact on the temperature and fatigue life of the bearing. The bearings that can apply preload include tapered roller bearings, angular contact ball bearings, thrust bearings, etc.
In order to meet the needs of detection and maintenance, bearings need to be installed or removed frequently in some applications. At this time, bearings with separable inner and outer rings can be selected to facilitate installation and disassembly. Separable bearings include cylindrical roller bearings, tapered roller bearings, needle roller bearings, thrust bearings, etc. For the occasions where it is inconvenient to install and disassemble the bearing, the bearing with high bearing capacity and high precision shall be considered when selecting the bearing.
When the inner and outer rings of the bearing are deflected due to manufacturing error or installation and positioning error, the use will be affected due to excessive local stress. Therefore, when selecting bearings, for the occasions with large support span, multi fulcrum shaft, relatively low support accuracy and large shaft deformation, self-aligning bearings and outer spherical bearings can be selected.
The heat of the bearing comes from two parts. One part is the heat generated by the friction and heating of the bearing itself, and the other part is the heat VO generated by the overflow conduction or radiation of the bearing working environment. When the service temperature of the bearing exceeds a certain limit, the material organization and size of the bearing will change, resulting in the decrease of material hardness, dimensional accuracy and matching amount of parts Clearance reduction and other problems. Therefore, if the bearing needs to work at high temperature for a long time, the bearing with high temperature tempering treatment shall be used when selecting the bearing. Bearing parts can also be made of heat-resistant steel.
When selecting bearings, price is also an important factor to be considered. The price of bearings is mainly reflected in the structure, variety and quality of materials, production batch, manufacturing accuracy, etc. Ball bearings of the same size are cheaper than roller bearings. The more complex the bearing structure, the more parts, and the higher the price. The variety and quality of materials are different, and the price is also different. The higher the precision, the higher the price, and the higher the manufacturing precision. The price of a grade is increased by about 40%. Therefore, when selecting imported bearings, they can meet the use requirements to avoid waste.
1. Correctly select the imported bearings that can meet the constraints, including: reasonably select the bearings and check whether the selected bearings can meet the constraints of strength, speed and economy;
2. Carry out the combination design of imported bearing parts
The selection of imported bearings includes: reasonable selection of bearing type, size series, inner diameter, tolerance grade, special structure, etc.
When selecting imported bearings, the first thing is to select the type of imported bearings. When selecting the type of bearing, the working conditions of the bearing, the characteristics of various bearings, price and other factors shall be considered. Like the general part design, the scheme of bearing type selection is not, and there can be a variety of options. When selecting, a variety of feasible schemes shall be put forward first, and then a better bearing type shall be selected after in-depth analysis and comparison. Generally, the main problems to be considered when selecting imported bearings are:
1. The magnitude, direction and nature of the load on the bearing. This is the main basis for selecting the bearing type.
(1) Magnitude and nature of load
Generally, because the contact between the main components of ball bearing is point contact, it is suitable for working under small and medium load and small load fluctuation; The contact between the main components of roller bearing is line contact, which should be used to bear large load;
(2) Load direction
If the bearing bears pure axial load, thrust bearing is generally selected; If the pure axial load is small, the thrust ball bearing can be selected; If the pure axial load is large, the thrust roller bearing can be selected; If the bearing bears pure radial load, deep groove ball bearing, cylindrical roller bearing or needle roller bearing are generally selected; When the bearing bears not only radial load but also small axial load, deep groove ball bearing or angular contact ball bearing or tapered roller bearing with small contact angle can be selected. When the axial load is large, angular contact ball bearing or tapered roller bearing with large contact angle can be selected, or the structure of radial bearing and thrust bearing can be selected, Bear radial load and axial load respectively.
Generally, when the speed is high, the load is small or the rotation accuracy is required to be high, the ball bearing should be selected; When the speed is low, the load is large or there is impact load, roller bearing should be selected.
The limit speed of thrust bearing is very low. When the working speed is high, if the axial load is not large, the angular contact ball bearing can be used to bear the axial load.
When the center line of the shaft does not coincide with the center line of the bearing seat and there is an angle error, or when the shaft is bent or tilted due to force, the axis of the inner and outer rings of the bearing will deviate. At this time, the self-aligning ball bearing or self-aligning roller bearing with certain self-aligning performance shall be adopted. For shafts with large fulcrum span, large shaft bending deformation or multiple fulcrum shafts, self-aligning bearings can also be considered. Cylindrical roller bearings, needle roller bearings and tapered roller bearings are sensitive to angular deviation. They should be used where the bearing and seat hole can ensure concentricity and high shaft stiffness. It is worth noting that the inclination angle of the inner ring axis of various bearings relative to the outer ring axis is limited. Exceeding the limit angle will reduce the service life of the bearing.
When the bearing seat has no split surface and the bearing components must be installed and removed along the axial direction, the bearings with separable inner and outer rings (such as cylindrical roller bearings, needle roller bearings, tapered roller bearings, etc.) shall be preferred. When the bearing is installed on the long shaft, in order to facilitate assembly and disassembly, the bearing with cone hole of 1:12 can be selected.
Generally, the price of deep groove ball bearings is low, and the price of roller bearings is higher than that of ball bearings. The higher the bearing accuracy, the higher the price. When selecting bearings, we must understand the prices of various bearings in detail and reduce the cost as much as possible on the premise of meeting the use requirements. Selection of size series, inner diameter, etc The size series includes diameter series and width (height) series. When selecting the size series of the bearing, the load borne by the bearing shall be mainly considered. In addition, the structural requirements shall also be considered.
For the diameter series, if the load is very small, you can generally choose ultra light or ultra light series; When the load is large, the heavy series can be considered; Generally, light series or medium series can be selected first, and then adjusted according to specific conditions after verification. For the width system, the normal series can be selected in general. If there are special structural requirements, other series can be selected according to specific conditions. The bearing inner diameter is related to the journal diameter, which can be preliminarily determined according to the journal diameter.
Tolerance grade: if there are no special requirements, grade 0 is generally selected. If there are special requirements, different tolerance grades can be selected according to specific conditions. Due to the complexity of design problems, the selection of bearings should not be expected to be successful at one time. Only through repeated analysis, comparison and modification in the whole process of selection, verification and even structural design can better bearings meet the design requirements be selected