Precision Manufactured Bearing

According to the ISO classification standards, precision bearings are divided into: P0, P6, P5, P4, P2. The grades are increased sequentially, among which P0 is the ordinary grade precision, and the other grades are precision grades. Of course, different types of bearings have different classification standards, and their classification methods are also different, but the meaning is the same. In terms of performance, precision bearings require the rotating element to have a high runout accuracy, high-speed rotation, limited friction and small friction changes.　　

The distinction between precision bearings and ordinary bearings should be distinguished from the following points: 　　

1. The size requirements are different. The size deviation (inner diameter, outer diameter, ellipse, etc.) of products with high accuracy grades is smaller than the value required for products with low accuracy grades; 　　

2. The required value of rotation accuracy is different. For products with high accuracy grade, the rotation accuracy (inner radial runout, outer radial runout, end face runout, etc.) is stricter than the required value for products with low accuracy grade. ; 　　

3. The required values of surface shape and surface quality are different. The surface shape and surface quality (surface roughness of raceway or groove, circular deviation, groove deviation, etc.) of products with high precision grade are required for higher strict than those are lower of the precision grade value. 　　

4. For products with particularly high accuracy grades, the material performance of the materials is better than that of products with general accuracy grades. In general, the precision grades of rolling bearing products are divided into the following six grades (from low to high): 0; 6; 6X; 5; 4; 2.　

The requirements of precision bearings for relative fitting parts

Because the precision of the precision bearing itself is within 1μm, it is required to have higher dimensional accuracy and shape accuracy with its matching parts (shaft, bearing seat, end cover, stop collar, etc.), especially the accuracy of the mating surface should be controlled to be the same as the bearing This point is crucial and most easily overlooked.　　

It must also be noted that if the parts matching the precision bearing do not meet the above requirements, it will make the precision bearing’s error several times larger than the original bearing error after installation, or even more than 10 times the error, thus the bearing will be not a complete precision bearing. The error of the matched parts is often not simply an error superimposed on the bearing, but an error added after being enlarged by different multiples.　

In order to ensure that the bearing does not produce excessive deformation after installation, it is necessary to do

(1) The roundness of the shaft and the seat hole and the verticality of the shoulder should be required in accordance with the corresponding accuracy of the bearing.　　

(2) It is necessary to accurately calculate the both interference between the rotating ring and the appropriate fit of the fixed ring.　　

The interference of the rotating ring should be smaller within the possible range. As long as we are ensured that the effect of thermal expansion at the working temperature and the effect of centrifugal force at the maximum speed, the creeping or sliding of the tight-fitting surface will not cause. According to the size of the working load and the size of the bearing, a very small clearance fit or interference fit is selected for the fixed ring. Too loose or too tight fit is not conducive to maintaining the original precise shape.　　

(3) If the bearing is running under high-speed conditions and the working temperature is relative high, the special attention should be paid that the fit of the rotating ring should not be too loose to prevent eccentric vibration, and there should be no gap in the fit of the fixed ring to prevent the ring from being Deforms under load and excites vibration.　　

(4) The condition of adopting small interference fit for the fixed ring is: that both sides of the mating surface should have high shape accuracy and small roughness, otherwise it will cause difficulty in installation and even more difficult disassembly. In addition, it is also necessary to consider the spindle, the effect of thermal elongation.　　

(5) Usually the main shaft that using paired double angular contact ball bearings bears a lighter load. If the fit interference is too large, the internal axial preload will be significantly larger, causing adverse effects. The main shaft of the double row short cylindrical roller bearing and the main shaft of the tapered roller bearing bear a relatively large load, so the fit interference is relatively large.　

In order to improve the actual matching accuracy of the bearing mounting, it is necessary to make use measuring methods and measuring tools that do not deform the bearing During the actual precision measurement of the matching surface size of the inner hole and outer circle of the bearing，the measurement of the inner diameter and outer diameter can be measured in all items of them, and a comprehensive analysis of the measured data can be done. Based on this, the size of the bearing installation part of the precision matching shaft and the seat hole can be determined. The actual measurement of the corresponding size and geometry of the shaft and the seat hole should be carried out under the same temperature conditions as the same time  as measuring the bearing.　　

In order to ensure a high actual matching effect, the roughness of the matching surface of the shaft and the seat hole and the bearing should be as small as possible.　　

When the above measurements are conducting, two sets of marks showing the direction of maximum deviation should be made on the outer circle and inner hole of the bearing, and on the corresponding surface of the shaft and the seat hole, on both sides close to the assembly chamfer. In the actual assembly, the maximum deviation of the two matching parties should be aligned in the same direction, so that the deviation of the two parties can be partially offset after assembly.　　

The purpose of making two sets of orientation marks for the deformation is that the compensation of deviation can be considered comprehensively, which not only to improve the rotation accuracy of each support at two ends, but also partially eliminate the coaxiality error of the seat hole between the two supports and the journal at both sides. The implementation of surface strengthening measures on the mating surface, such as sandblasting, can obtain by using a precision plunger with a slightly larger diameter to plug the inner hole once, etc., will help improve the accuracy of the mating.　

The requirements for some high-precision imported bearings are very high in the configuration

The precision bearings are usually used in machine tool spindles, which in the traditional application field. According to different processes, machine tool spindles have different requirements. Generally speaking, lathe spindles are used to cut metals at lower speeds and larger cutting loads. This type of spindle usually transmits drive torque through pulleys or gears. This means that the load on the drive end of the spindle is also considerable. This type of application does not require too high speed, and the more important parameters are stiffness and loading capacity. A very common method is to install a double row cylindrical roller bearing and a double row angular contact thrust ball bearing on the working end of the spindle, while a double row cylindrical roller bearing on the driving end of the spindle. This configuration can ensure a long working life and excellent rigidity, thereby producing high-quality workpieces. Moreover, from a view of kinematic point, the bearing can work stably, because the two types of bearings (radial and axial) respectively carry the load applied to the main shaft (in fact, in order to prevent the angular contact thrust ball from carrying the radial load, the outer diameter of outer ring has a special tolerance to ensure that it will never contact the bearing seat). When the designing of these types of spindles (this usually applies to heavy loads), a rule of thumb about where is the bearing located on the shaft, that is the distance between the center of the front and rear supports is 3-5 times than the inner diameter of the bearing.

When higher speeds are required (i.e., high-speed machining centers or internal grinding), different bearing solutions need to be found. Obviously, in these cases, a little concession is needed in terms of stiffness and carrying capacity. High-speed applications usually use a direct drive spindle which directly connected to moto.