The Reason Why Self-aligning Roller Bearing Drop Roller

Time：2021.07.08  Source：Roller Bearings Suppliers

First of all we may know the three common structures of self-aligning roller bearings are all with small guards on the inner ring, which are distributed on both end faces, and each has a load of roller gaps, with an interval of 180 degrees. The role of the gaps is to facilitate the loading of appropriate rollers.Cages of this kind of structure may generally be made of brass.After finishing the assembly of the finished product, it is necessary to check the flexibility of bearing rotation, but after rotating the outer ring, it is found that the roller falls off from the cage, or if the hand pulls it out with a little force at the gap, the roller will leave the bearing along the gap.

Reason analysis of roller falling off:

The general assembly process of self-aligning roller bearing: on the outer diameter of the cage or sleeve inner ring, the roller loading notch on the small guard edge of the inner ring is loaded into the appropriate roller to form the inner ring component, but one or two cage pocket holes are left symmetrically in each row, and no rollers are installed at first.Put the inner component into the outer ring, and fill the same group of rollers from the gap in the cage pocket vacancy.When checking the flexibility of rotation, some rollers fall off from the cage, or if the hand is slightly applied at the gap, the rollers will come out from the gap. Therefore, it is necessary to analyze the relevant parts of the bearing one by one. The analysis is summarized as follows:

1. Influence of bearing ring processing

1)The influence of small flange turning processing of bearing inner ring

According to the requirements of the product drawings, the outer diameter of the small flange of the bearing inner ring machining is "-" tolerance, usually -0.35 ~ -0.15mm. 

However, the depth size of the designed notch is generally only the basic size without tolerance.The actual machining was controlled within ±0.2mm according to the current machine tool accuracy tolerance, while the notch deep orifice dimensions were measured on the outside diameter basis of the small flanges (Fig.2).The depth of the oil groove size tolerance according to the current processing industry standard press control + / - 0.15 mm, so the depth (small guard outside diameter to the distance to the center of the oil groove) shallow small guard, usually depth size no more than 3 mm, could produce tolerance accumulation effects in practical processing (guard outside diameter, depth of the gap size for minimum size, oil groove depth for the largest size).Finally, the contact area between the end face of the roller and the flange is the smallest, and sometimes the contact part is even close to the oil ditch.Therefore, a little force at the gap will roll out along the gap.But for the deep flange, because of its larger contact area with the flange itself, the tolerance effect is relatively small, and sometimes even can be ignored.

2) Influence of small flange grinding of bearing inner ring

The small flange of bearing inner ring grinding is grinded by fixed-range method, sometimes black skin is found after some small flange grinding.Due to the reason of turning machining, the allowance of small flange grinding is too small or the non-equal grinding in the grinding plane process, so that there is still black skin after grinding.Usually the black skin can be removed normally, so that the thickness of the small edge is small.However, for the small guard edge with shallow depth, the end face of the roller itself is small and its contact area is small. After the small guard edge is worn, the axial distance of the roller along the inner ring increases, so that the roller is easier to escape along the notch.Need WSBC 22218 E,click here to learn more.

3) The influence of bearing ring raceway grinding

Bearing outer ring grinding process raceway grinding, sometimes found after some individual grinding still have black skin.Due to the reasons of turning and heat treatment, the grinding allowance is small or the outer raceway is deformed, resulting in black skin after grinding.Usually, the outer raceway is ground, and the black skin can be moved down normally when it is ground off. In this way, the inner raceway needs to be underground to realize the normal assembly process.In this way, the overall center diameter of the roller group is deviated, and the contact part between the roller and the guard edge is deviated, and the actual contact area is smaller after the deviation at the notch, so that the roller is easier to detach along the notch.

2. the impact of cage processing

Cage machining is usually carried out by drilling holes on a drilling machine, and drilling is carried out by positioning the equal parts of the die.Due to the manufacturing without special machine tool processing, mold manufacturing precision is low, and sometimes even face process maintains a base surface flatness are super bad, cause pocket machining depth dimension is not unified, generally by adjusting the repositioning drilling machine tool, the result is deep hole, round hole diameter is larger, and after loading roller, roller and cage clearance is big,And the axial channeling momentum along the cage is large, and the overall gap between the roller and the cage is larger after the roller is filled eventually.It is easy for the roller to fall off from the cage during the test bearing rotation.Click here to learn more about WSBC 22224-E1.

In addition, to measure the center diameter of the cage, the caliper force is different and the skewness of the pillar is different (the position of the pillar in the pocket) through measuring the distance control of the measuring column. Therefore, the final measurement size can only be used as a reference and cannot effectively reflect the true measurement value of the center diameter.For medium and large bearings, the influence of this measurement method is small because the edge is generally deep.For small bearings,because of its shallow edge, the impact is greater, sometimes the actual center diameter is larger, and the measurement is qualified, this situation often occurs.When the center diameter is too large, the overall center of the roller group is outwardly oriented, which leads to the outwardly oriented contact area between the roller and the small guard edge. 

After the outwardly oriented contact area at the notch is outwardly oriented, the actual contact area is outwardly oriented, which ultimately leads to the unwinding of the roller from the notch.

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