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Analysis of the Reasons for Rolling Failure of Spherical Roller Bearings

wallpapers Environment 2020-10-27

There are three common structures of spherical roller bearings, two of which are shown in the following figure. The inner ring 02 has small ribs, which are distributed on both ends, and each has a roller gap, which is 180 degrees apart. The gap is used It is convenient to install suitable roller 04. The cage 46 or 66 of this type of structure generally uses brass. After assembling the finished product, it is necessary to check the bearing's rotational flexibility, but after rotating the outer ring 01, it is found that the roller has fallen off from the cage, or the roller is pulled out of the bearing along the gap with a little force.

Analysis of the cause of the roller falling off

The general process of assembly of spherical roller bearings : Put the cage 46 or 66 on the outer diameter of the inner ring 02, and install suitable rollers 04 from the roller gap of the small rib of the inner ring to form the inner ring assembly. Leave one or two cage pockets symmetrically in the row, and no rollers are installed first. Put the inner component into the outer ring 01, and reinstall the same set of rollers in the cage pocket from the gap. When checking the flexible rotation, some of the rollers fall off from the cage, or the rollers will come out of the gap with a little force by hand. Therefore, it is necessary to analyze the relevant parts of the bearing one by one. The analysis is summarized as follows:

01The influence of bearing ring processing

①The influence of the machining of the small sidewall of the bearing inner ring

The outer diameter of the small flange of the bearing inner ring machining is "-" tolerance according to the product drawing requirements, usually -0.35~-0.15mm, and the depth dimension of the designed notch is generally only the basic size without tolerance. The actual machining is controlled within ±0.2mm according to the current machine tool accuracy tolerance, and the notch deep mouth size measurement is measured on the basis of the outer diameter of the small rib (see Figure 2 below). The depth dimension tolerance of the oil groove is controlled by ±0.15mm according to the current processing industry standard, so that for small ribs with shallow depth (the distance from the outer diameter of the small rib to the center of the oil groove), the depth dimension usually does not exceed 3mm. The cumulative effect of tolerance may occur (the outer diameter of the rib and the depth of the notch are the smallest dimensions, and the depth of the oil groove is the maximum dimension), which will eventually result in the smallest contact area between the roller end face and the rib, and sometimes the contact part is even close to the oil groove. Therefore, push the roller out along the gap with a little force. As for the deeper ribs, due to its large contact area with the ribs, the tolerance effect is relatively small and sometimes even negligible.

②The influence of the grinding of the small rib of the bearing inner ring

The small ribs of the inner ring of the bearing are ground by the fixed-range method, and sometimes it is found that some small ribs have black skin after grinding. Due to the turning process, the grinding allowance of the small ribs is too small or the non-equal grinding of the surface grinding process causes the black skin after the grinding process. Usually, the black skin can be moved down normally if it is ground off, so that the thickness of the small rib is too small. For small ribs with shallow depth, the contact area between the roller end surface and the small ribs is small. After the small ribs are worn, the distance between the rollers along the axial direction of the inner ring increases, which makes the rollers easier to escape along the gap.

③The influence of bearing ring raceway grinding

The outer ring of the bearing is ground and the raceway is ground, and sometimes it is found that there are still black skins after individual grinding. Due to turning and heat treatment, the grinding allowance is too small or the outer raceway is deformed, resulting in black skin after grinding. Usually, the outer raceway is over-ground, and the black skin is worn off and it can move down normally. In this way, the inner raceway needs to be under-ground to achieve the normal assembly process. As a result, the center diameter of the roller set is generally outside, and the contact part between the roller and the rib is outside. After the gap is outside, the actual contact area is too small, so that the roller can easily escape along the gap.

02The influence of cage processing

Cage processing is usually drilled on a drilling machine, and the drilling is performed by positioning the equally divided mold. Because the mold itself is manufactured without special machine tool processing, the manufacturing accuracy is low. In addition, sometimes the flat end face process is processed by the cage base surface flatness is too poor, resulting in the pocket hole processing depth dimension is not uniform, generally adjust the machine tool to reposition the drilling, as a result The pocket hole is deeper and the pocket hole diameter is larger, so that after the roller is installed, the gap between the roller and the cage is large, and the amount of movement along the axis of the cage is large. Finally, after the roller is filled, the roller and the cage The overall gap is larger. In the test bearing rotation, it is easy for the rollers to fall out of the cage. In addition, the center diameter of the cage is measured, and the distance of the measuring column is controlled. The force of the caliper is different, and the skew degree of the column is also different (the position of the column in the pocket), so the final measurement size can only be used as a reference and cannot be effective Reflect the true measured value of the center diameter. For medium and large bearings, because the ribs are generally deep, this measurement method has less impact. For small bearings, because the ribs are shallower, the impact is greater. Sometimes the actual center diameter is too large, but it is qualified during measurement. This situation often occurs. After the center diameter is too large, the overall center of the roller set is outside, which causes the contact part of the roller and the small rib to be outside. After the gap is outside, the actual contact area is too small, and finally the roller comes out of the gap.


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