2023 July the Third Week KYOCM Technical Knowledge: Assembly Technology of Double Row Angular Contact Ball Bearings

Abstract: In view of the structure and characteristics of double row angular contact ball bearing, taking the inner ring separation type bearing as an example, the measuring group Completing the square method of double row angular contact ball bearing is proposed. In view of the problem that the preload required for the assembly is greater than the measuring load range of the protrusion measuring instrument, which leads to the inability to measure, a modified measuring calculation method is introduced, which solves this problem well.

Keywords: Double row angular contact ball bearing; Assembly; Projection amount; measure

Double row angular contact ball bearings are generally of the inner ring separation type or the outer ring separation 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 installing the bearing, axial preload is applied to eliminate the supporting radial clearance of the bearing and achieve pre tightening of the bearing. After installation, for a double row angular contact ball bearing without a spacer in the middle, the final amount of preload it bears is determined by the degree of non benchmark end face adhesion between two inner rings (inner ring separation type) or two outer rings (outer ring separation type); For double row angular contact ball bearings with a spacer in the middle, the final amount of preload they bear can be adjusted by the width of the spacer.

From this, it can be seen that when manufacturing double row angular contact ball bearings, like single row angular contact ball bearings, the bearings must be assembled according to user requirements under a certain preload, in order to fully utilize the advantages of double row angular contact ball bearings.

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 protrusion of the bearings participating in the assembly under a certain preload in advance. The measurement of the protrusion of angular contact ball bearings is carried out on a high-precision bearing protrusion measuring instrument, and the measurement of double row angular contact ball bearings must also be carried out with the help of this measuring instrument.

Due to the differences in the structure between double row angular contact ball bearings and single row angular contact ball bearings, the positioning and centering methods during measurement are completely different from those of single row angular contact ball bearings, which require positioning with the outer ring end face and centering with the outer diameter; Moreover, it is not possible to directly obtain the protrusion values of the two matched surfaces on the instrument through a single measurement. Only by measuring the protrusion values of the two benchmark end faces of the outer ring separately, and then converting them to the non benchmark end faces of the two matched inner rings (Figure 1a), can the width of one inner ring or two non benchmark end faces of the bearing be finally polished as needed to ensure that the specified preload is obtained after bearing installation, The assembly process is much more complex than that of single row angular contact ball bearings. When measuring, 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.

(a)protrusion       (b)measuring principle

1- Positioning seat; 2- Centering ring; 3- Centering seat; 4- Spindle; 5- Measuring instruments

Figure 1 Measurement principle of protrusion of double row angular contact ball bearings

The measurement principle of protrusion of double row angular contact ball bearings is shown in Figure 1b. The measurement principle is as follows: place the reference ring (not shown in the figure, at the position of the measured bearing in Figure 1b) in the combination body 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. Apply a preload F0 to the reference ring in the axial direction through the measuring instrument spindle and the combination body, set the pointer of the measuring instrument to zero and lock it tightly, take out the reference ring, and select a set of steel balls Install the cage and an inner ring I into the groove on one side of the bearing outer ring, and place them in the assembly. Apply a preload F0 to the bearing inner ring through the measuring instrument spindle, assembly, and outer ring, rotate the bearing outer ring, and obtain the maximum and minimum protrusion values indicated by the measuring instrument. Take the average of the two values as the protrusion value of the first measurement δ I, then take out the tested bearing, invert the outer ring of the bearing (rotate 180 °), and install the selected set of steel balls, cages, and another inner ring II into the groove on the other side of the bearing outer ring. Repeat the above measurement process to obtain the protrusion value of the second measurement δ II (Figure 1a). The sum of the grinding amounts for the non reference end face widths of the two inner rings of a double row angular contact ball bearing is

Δ =  C - (B1+B2) -（ δ I+ δ II)           (1)

In the formula: C is the actual width of the outer ring; B1 is the actual width of inner circle I; B2 is the actual width of inner ring II.

According to the above measurement methods and the calculation results of equation (1), grind one inner ring or the non reference end faces of two inner rings of the bearing on the MG7340 high-precision horizontal axis circular table surface grinder (if both reference end faces of the two inner rings are ground, the total amount of grinding is Δ) ， After grinding, clean the bearing parts and assemble the bearings according to the installation sequence during measurement, completing the assembly of double row angular contact ball bearings.

It should be pointed out that the theoretical maximum measurement load for high-precision bearing protrusion measuring instruments is 2 kN. When the preload of the pairing of double row angular contact ball bearings does not exceed 2 kN, the pairing can be directly measured using the above method. When the preload required for the assembly of double row angular contact ball bearings is much greater than 2 kN, it exceeds the measurement range of the current instrument and cannot directly measure the actual protrusion value of the bearing on the instrument. For this, a small measurement load (not exceeding the range of instrument measurement load) is used for actual measurement, and the difference in deformation of a single set of bearings under the paired preload and measurement load is corrected. The calculation formula for the sum of the grinding amounts of the non reference end face widths of the two inner rings of the bearing is

Δ =  C - (B1+B2) -（ δ I+ δ II) -2（ δ 0- δ 0a)                (2)

In the equation: δ 0a, δ 0 represents the deformation of a single set of bearings under measured load and preload.

δ 0a and δ 0 is calculated from the following equation

In the equation: δ  A is the axial deformation, mm; F a is the axial load, N; Z is the number of steel balls; Dw is the diameter of the steel ball, mm; α  Is the contact angle of the bearing, in degrees. δ 0a and δ The calculation of 0 can be accelerated by writing computer programs.

It should be pointed out that the contact angle of the bearing will change under the action of axial load. According to actual calculations, a double row angular contact ball bearing with an original contact angle of 60 ° is obtained from the actual contact angle under axial load δ 0a and δ 0 and obtained from the original contact angle δ 0a and δ The difference between 0 is very small and can be ignored. Therefore, the δ 0a and δ When calculating 0, the influence of contact angle changes can be disregarded. However, for bearings with a contact angle less than 45 °, the smaller the initial contact angle, the greater the change in actual contact angle under different axial loads. If the initial contact angle is directly substituted into equation (3) for calculation δ 0a and δ 0 will result in a significant error compared to the actual measurement results. Therefore, for bearings with a contact angle less than 45 °, the actual contact angle should be substituted into equation (3) for calculation.

2 Example Calculation

The dimensions of the double row angular contact ball bearing ZYSF2575-2RS are Φ 25 mm × Φ 75 mm ×  28 mm; The width deviation of the inner and outer rings is

Δ C=-20 μ M, Δ B1=-30 μ M, Δ B2=-35 μ M; Dw=7.144, Z=15, F0=9 410 N, α =  60 °.

Select the measurement load F0a=1000 N, and the protrusions measured on both ends of the bearing outer ring under the measurement load are:

δ I=20 μ M, δ II=32 μ M;

Calculated by a computer program under the action of measuring load F0a=1000 N and preload F0=9410 N δ 0a=4.7 μ M, δ 0=21.1 μ M.

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)=-39.8 μ M

To simplify the process and improve efficiency, only 39.8% of the non benchmark end face width of one of the inner rings needs to be polished off μ m. After the bearing is assembled, the specified preload can be obtained.

After the bearing assembly is completed, the following assembly can be carried out as needed, namely the two joint assembly of double row angular contact ball bearings, as shown in Figure 2.

Figure 2 ZYSF and ZYSN Bearing Assembly

3. Conclusion

Double row angular contact ball bearings are equivalent to using two sets of single row angular contact ball bearings in pairs after being assembled in a back-to-back or face-to-face manner. Therefore, when assembling double row angular contact ball bearings, like single row angular contact ball bearings, the general technical conditions for assembling single row angular contact ball bearings must be followed. When the preload of the paired double row angular contact ball bearing is within the range of the protrusion measurement instrument, the protrusion for grinding can be directly calculated according to equation (1) in the text for assembly. When the required preload for assembly completely exceeds the load range measured by the protrusion measuring instrument, the corrected equation (2) can be used to calculate the protrusion that needs to be polished. This article introduces the assembly of inner ring separated double row angular contact ball bearings. This method is also applicable to the assembly of outer ring separated double row angular contact ball bearings and other similar bearings.

More about KYOCM Thrust Ball Bearing:

Thrust ball bearings are designed to take axial (thrust) loads at high speeds, but they cannot take any radial loads. These bearings feature bearing washers with raceway grooves in which the balls move.

Thrust ball bearings are classified into “flat seat” and “aligning seat” types, based on the shape of the housing washer (outer ring seat), and as single-direction or double-direction. Spherical and aligning seat washers help to provide tolerance for mounting errors.