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[case] Analysis on fracture characteristics of inner ring of rolling bearing

　　When the stress acting on the bearing ring is greater than the tensile strength of the material or the fatigue strength limit of the material, the ring will crack, and the crack will eventually expand to a certain extent, resulting in the complete separation of part, which is called cracking or fracture. The cause analysis will be carried out around the topic of fracture:

　　Taking the inner ring of four row cylindrical roller bearing as an example, the inner ring of the bearing needs interference fit with the roll shaft diameter to achieve the performance of high bearing capacity and high speed of the bearing. The inner ring fracture often occurs due to mismatching.

　　There are three main conditions for improper fitting, which can easily lead to inner ring fracture:
 

　　1. Excessive interference

　　When the interference between the inner ring and the shaft is too large, the inner ring cracks in two stages;

　　A: After the bearing is hot installed on the roll neck, it cracks before being used on the machine, that is, during the cooling process of the inner ring.

　　B: After the bearing is hot installed on the roll neck, it cracks during outer diameter grinding before being used on the machine

　　2. Small interference

　　When the interference between the inner ring and the shaft is too small, the inner ring cracking usually occurs in two stages;

　　A: During the use of the bearing on the machine, the inner ring and the shaft have relative sliding friction, resulting in the cracking of the inner ring.

　　B: During the operation of the bearing on the machine, the expansion of the inner ring at the initial stage is greater than that of the roll neck. When the rolling mill bites and throws steel, the impact load causes the inner ring to burst.

　　3. Friction of end fitting

　　C: During the use of the bearing on the machine, the inner ring and the distance ring have relative sliding friction, resulting in section cracks and inner ring cracks.

　　D: During the operation of the bearing on the machine, the inner ring, the moving labyrinth and the distance ring have relative sliding friction at the same time, resulting in section cracks and inner ring cracks.

　　In addition to the inner ring fracture caused by the above-mentioned unstoppable fitting, special attention shall be paid to the surface condition of the roller neck matched with the inner ring.

　　The inner ring of the bearing is fitted to the roll diameter by hot fitting. However, the surface defects of the roll diameter often lead to the destruction of the interference fit, resulting in inner ring cracking, bearing locking, roll diameter burning and other fault problems.

　　A: The roll neck surface sinks and the chamfer (non-contact stress area) bulges.

　　B: Irregular wear, irregular taper.