Abstract: This paper introduces the structural characteristics of a special-shaped double row full loaded cylindrical roller bearing, and expounds the causes and control measures of assembly clearance error of special-shaped double row cylindrical roller bearing according to the processing flow and assembly method.
Key words: cylindrical roller bearing; radial clearance; axial clearance; spring lock ring; error
1. Bearing structure
Figure 1 shows the structural diagram of a double row fully loaded cylindrical roller bearing with special-shaped structure. The two outer rings are NF type and the inner ring is NN type. During assembly, the two outer rings are locked by three spring locking rings to form an integrated double retaining edge outer ring. This kind of bearing has both radial and axial clearance requirements. Different processing technologies directly affect the clearance of the bearing.
Fig. 1 structural diagram of special-shaped double row cylindrical roller bearing
2. Error analysis of axial clearance Ga
According to the structure of the bearing, theoretically, the main factors affecting its axial clearance are the raceway width of the outer ring, the raceway width of the inner ring and the roller length. Therefore, for products with this type of structure, the axial clearance is allocated to the raceway width of the inner ring and outer ring according to the tolerance of each part of the influencing factors. In actual production, there are some errors. Here, the causes of axial clearance error are analyzed.
2.1 Influence of outer ring end face size
It can be seen from Figure 1 that the two outer rings are combined by the spring lock ring, which requires that the fit between the spring lock ring and the boss after the combination of the two outer rings is an interference fit. The size of the interference will directly affect the raceway width of the combined outer ring. Since the two outer rings are separated, even if the ring tank car is a true circle after processing, it will become an ellipse after grinding the end face, and the long axis of the ellipse is in the shape of a tip as shown in the view of La in the figure. This shows that the force on the spring lock ring is uneven, and the interference between the stub shaft and the spring lock ring is the key to affect the axial clearance.
Generally, the factors affecting the size of the boss elliptical stub shaft are: the processing size of the ring tank car and the end face grinding processing size. When determining the turning size of the inner diameter of the ring groove, although the influence of the grinding amount of the end face has been considered, because the end face is grinded according to the ideal equal allowance, the influence of the end face grinding mode on the elliptical stub shaft of the boss should be analyzed.
The equipment used for face grinding are M7675 and M7475. M7675 is a double face grinder, which is most suitable for grinding products with equal surface area at both ends of the ferrule. For products with different grinding areas, although the differential speed of two grinding wheels can be used for grinding, it is difficult to make the grinding amount of two end faces consistent. Therefore, M7475 single head vertical shaft surface grinder is used for this kind of products. The reference surface of a single outer ring of the bearing is the mating surface between the two outer rings. During plane grinding, the reference surface must be ground first, so as to effectively control the grinding amount of the reference end face within the design range, so as to meet the interference amount of the fit between the spring lock ring and the boss of the outer ring.
2.2 Influence of outer ring raceway width measurement
The outer race width tolerance is half of the bearing axial clearance minus the upper deviation of the inner race width and the lower deviation of the roller length (because the outer race width e is composed of two outer races). The raceway width of such products is very important, which directly affects the axial clearance of bearings, which requires that the smaller the cumulative error in measurement, the better. The measurement method of outer ring raceway width is shown in Figure 2. Therefore, a standard sample column with the same width as a single outer ring raceway is designed, and the retaining edge is taken as the positioning benchmark for measurement, that is, the influence of the outer ring end face width on the raceway width is ignored. At the same time, the raceway width can be obtained directly through the height difference between the sample column and the raceway width.
2.3 Influence of clearance measurement
From the analysis in 2.1, it can be seen that the interference between the spring lock ring and the outer ring boss is the main factor that directly affects the axial clearance. Therefore, the detection method of axial clearance after fitting is very key. Since the outer ring is separated when the spring lock ring is not installed, and the inner ring cannot be fixed, it can be measured only after the outer ring is fixed as a whole. If the outer ring is fixed and clamped on the axial clearance measuring device and the inner ring is pushed to measure the axial clearance, the measured value is affected by the clamping force of the outer ring and the error is large. Therefore, simulate the three-point clamping mode of spring lock ring, design the clamping block for locking the outer ring, and fix the outer ring into after integration, fix the inner ring and push the outer ring. At this time, the axial clearance obtained is basically the same as the actual axial clearance when installing the spring lock ring, and the error is only 0.02mm.
Fig. 2 structure diagram of single outer ring NNCD4936
3. Effect of spring lock ring on radial clearance Gr
The main factor affecting the radial clearance of ordinary bearing is the shape accuracy of each component. The radial clearance of the bearing is affected not only by the shape accuracy, but also by the spring lock ring. Next, take NNCD4936V as an example to analyze the influence of the spring lock ring on the radial clearance. Table 1 shows the measured values of the radial clearance of the front and rear bearing before and after installing the spring lock ring.
Table 1 measured radial clearance
It can be seen from table 1 that the radial clearance values before and after installing the spring lock ring are obviously different. The radial clearance value before installing the spring lock ring is close to the upper limit of the design requirements. After installing the spring lock ring, the radial clearance value becomes smaller, and there is a phenomenon of zero clearance. The variation of clearance value is 0.09-0.20mm. Theoretically, this phenomenon is caused by the radial relative displacement between the two outer rings after the spring lock ring is installed. Therefore, the bearing with zero clearance is measured by measuring the perpendicularity of its outer surface to the end face. The measurement results are 0.22, 0.25 and 0.26mm respectively. This shows that the relative displacement of the two outer rings of the zero clearance bearing exceeds the clearance value. In order to further prove that the relative displacement leads to the change of bearing radial clearance, several other bearing samples were measured. The measurement results are shown in Table 2.
Table 2 Difference between the front and rear surface of the spring lock
Correspondence of perpendicularity
Table 2 shows that the radial runout of the bearing is the relative displacement of the two outer rings. It can be seen that the relative displacement of the two outer rings caused by the installation of the spring lock ring leads to the change of the radial clearance of the bearing. Therefore, when allocating the diameter tolerance of the inner ring or outer ring of this type of bearing, the influence of the relative displacement of the two outer rings after installing the spring lock ring on the radial clearance of the bearing should be considered at the same time. During processing, the outer diameter of the two outer rings shall be consistent with the outer raceway size and the wall thickness shall be uniform; Ensure that the vertical locking clearance of the spring is not affected by the inclination of the clamp during installation, so as to avoid the influence of the locking clearance of the spring.
4. Conclusion
By analyzing the assembly clearance of special-shaped double row full loaded cylindrical roller bearing, it can be seen that the grinding amount control of the reference end face of a single outer ring is the key to affect the interference between the boss and the spring lock ring after the two outer rings are matched; At the same time, the control method and measurement method of the raceway width of a single outer ring are the theoretical guarantee for the axial clearance control. Therefore, the control of axial clearance and radial clearance should be strengthened by improving the processing technology (such as wire cutting and splitting the outer ring before the final processing).
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