**Abstract:** Aiming at the structure and characteristics of double row angular contact ball bearings, taking the inner ring separable bearing as an example, the measurement and assembly method of double row angular contact ball bearings is proposed. The load range leads to the problem of inability to measure, and a revised measurement calculation method is introduced, which solves this problem well.

Double row angular contact ball bearings are generally of inner ring separated type or outer ring separated type, which is equivalent to two sets of single row angular contact ball bearings assembled in a back-to-back (DB) or face-to-face (DF) manner and used together in pairs. When the bearing is installed, the axial preload is applied to eliminate the supporting radial clearance of the bearing and realize the preload of the bearing. After installation, for a double row angular contact ball bearing without a spacer in the middle, the final preload is the size of the two inner rings (inner ring separation type) or 2 outer rings (outer ring separation type) close to each other. It is determined by the degree of closeness of the non-reference end face; for a double-row angular contact ball bearing with a spacer in the middle, the final preload force can be adjusted by the width of the spacer.

It can be seen that the double row angular contact ball bearing is the same as the single row angular contact ball bearing during manufacture. The bearing should be assembled under a certain preload according to the user’s requirements, so as to give full play to the advantages of the double row angular contact ball bearing. sex.

**1 Assembly technology of double row angular contact ball bearings**

When assembling double row angular contact ball bearings, it is also necessary to accurately measure the amount of protrusion of the bearings participating in the assembly under a certain preload. The measurement of the protrusion of the angular contact ball bearing is carried out on the high-precision bearing protrusion measuring instrument, and the double row angular contact ball bearing must also be measured by the measuring instrument.

Due to the difference between the structure of the double row angular contact ball bearing and the single row angular contact ball bearing, the positioning and centering methods during measurement are completely different from those of the single row angular contact ball bearing. The protruding value of the two matched faces can be directly obtained by one measurement. Only the protruding values of the two reference end faces of the outer ring are measured respectively, and then converted to the two non-reference end faces of the matched inner ring ( Figure 1a), according to the needs, finally grind the width of the non-reference end face of one inner ring or two inner rings of the bearing to ensure the specified preload after the bearing is installed. The assembly process is much more complicated than that of single row angular contact ball bearings. . During measurement, it is also necessary to replace the accessories of the instrument according to the structure of the double row angular contact ball bearing to meet the measurement requirements.

The measurement principle of the protrusion of the double row angular contact ball bearing is shown in Figure 1b. The measurement principle is: place the reference ring (not shown in the figure, the position of the measured bearing in Figure 1b) in the combination of the centering ring and the centering seat, so that the end face of the reference ring and the end face of the positioning seat are in contact, and the measuring instrument The main shaft and the assembly apply a preload F0 to the reference ring in the axial direction, set the pointer of the measuring instrument to zero and lock it, take out the reference ring, and place the selected set of steel balls, cage and an inner ring I Install it into the channel on one side of the outer ring of the bearing, and place it in the assembly, apply a preload F0 to the inner ring of the bearing through the main shaft of the measuring instrument, the assembly and the outer ring, and rotate the outer ring of the bearing to obtain the protrusion indicated by the measuring instrument. The maximum value and the minimum value of the measurement, take the average value of the two as the protrusion value δI of the first measurement, then take out the bearing to be tested, turn the outer ring of the bearing upside down (rotate 180°), and place the selected other The set of steel balls, cage and another inner ring II are put into the channel on the other side of the bearing outer ring, and the above measurement process is repeated to obtain the second measured protrusion value δII (Figure 1a). Then the sum of the grinding amounts of the non-reference end face widths of the two inner rings of the double-row angular contact ball bearing is Δ=C-(B1+B2)-(δI+δII) (1) In the formula: C is the actual width of the outer ring; B1 is the actual width of inner ring I; B2 is the actual width of inner ring II. According to the above measurement method and the calculation result of formula (1), grind the non-reference end face of one inner ring or two inner rings of the bearing on the MG7340 high-precision horizontal shaft table surface grinder (if the reference end faces of both inner rings are ground , then the sum of the total grinding amount is Δ). After grinding, clean the bearing parts, and assemble the bearings according to the installation sequence during measurement, that is, to complete the assembly of double row angular contact ball bearings.

It should be pointed out that the theoretical maximum measurement load of the current high-precision bearing protrusion measuring instrument is 2kN. When the preload of the double row angular contact ball bearing pairing does not exceed 2kN, the pairing can be measured directly according to the above method. When the preload required for the double row angular contact ball bearing assembly is much larger than 2kN, it is beyond the measurement range of the current instrument, and the actual protrusion value of the bearing cannot be directly measured on the instrument. In this regard, a small measurement load (not exceeding the range of the instrument’s measurement load) is used for actual measurement, and then the difference between the paired preload and the deformation of the single set of bearings under the action of the measurement load can be corrected.

In the formula: δ0a, δ0 are the deformation of the single set of bearings under the action of the measurement load and the preload, respectively.

Where: δa is the axial deformation, mm; Fa is the axial load, N; Z is the number of steel balls; Dw is the diameter of the steel balls, mm; α is the bearing contact angle, (°). The calculation of δ0a and δ0 can be written in a computer program to speed up the calculation.

It should be pointed out that the contact angle of the bearing will change under the action of axial load. It can be seen from the actual calculation that the double row angular contact ball bearing with the original contact angle of 60° has a small difference between the δ0a and δ0 obtained from the actual contact angle and the δ0a and δ0 obtained from the original contact angle under the action of the axial load. can be ignored. Therefore, the influence of contact angle variation can be ignored when calculating δ0a and δ0. However, for bearings with a contact angle less than 45°, the smaller the initial contact angle, the greater the change of the actual contact angle under different axial loads. If the initial contact angle is directly substituted into the formula (3) to calculate δ0a and δ0 Therefore, for bearings with a contact angle less than 45°, the actual contact angle should be substituted into the formula (3) for calculation.

**2 instance computing**

The size of double row angular contact ball bearing ZYSF2575-2RS is Φ25mm×Φ75mm×28mm; the width deviation of inner and outer rings is ΔC=-20μm, ΔB1=-30μm, ΔB2=-35μm; Dw=7.144, Z=15 , F0=9410N, α=60°.

The measured load F0a=1000N is selected, and the protrusions measured on both ends of the bearing outer ring under the measurement load are δI=20μm, δII=32μm; under the action of the measurement load F0a=1000N and the preload F0=9410N, the computer program Calculated δ0a=4.7μm, δ0=21.1μm.

Then the total grinding amount of the non-reference end face width of the two inner rings

Δ=-20-(-30-35)-(20+32)-2×(21.1-4.7)=-39.8μm

In order to simplify the process and improve the efficiency, it is only necessary to grind the non-reference end face width of one of the inner rings to 39.8 μm, and the specified preload can be obtained after the bearing is assembled.

After the bearing assembly is completed, the following assembly can also be carried out according to the needs, that is, the double assembly of the double row angular contact ball bearing, as shown in Figure 2.

**3 Conclusion**

Double row angular contact ball bearings are equivalent to two sets of single row angular contact ball bearings assembled back-to-back or face-to-face and used in pairs. General technical conditions for the assembly of single row angular contact ball bearings. When the paired preload of the double row angular contact ball bearing is within the load range measured by the protrusion measuring instrument, the grinding protrusion can be calculated directly according to the formula (1) in the text and assembled. When the preload required by the assembly completely exceeds the measurement load range of the protrusion measuring instrument, the modified (2) formula can be used to calculate the protrusion that needs to be ground. The assembly of the inner ring separable double row angular contact ball bearing is introduced here. This method is also applicable to the assembly of the outer ring separable double row angular contact ball bearing and other similar bearings.