Research on the Causes of Bearing Ring Cracking

The bearing ring is one of the important parts of the bearing components. During the bearing use, the NSK bearing ring cracks and fractures are a common form of damage. Some bearings have cracks in the ring during early use, and some bearings It breaks due to fatigue during use. Based on the understanding of bearing knowledge, we can share common cracks in bearing rings in daily life and analyze the real cause of the cracks.

If the bearing cracks during use, contact fatigue spalling of the bearing ring will cause its instability. In addition to the high hardness and brittleness of the material, a one-time brittle fracture will begin to occur in the local spalling area, that is, a straight macro crack , The micro-fracture is relatively straight, showing rapid expansion of cleavage characteristics, and the rapid expansion area occupies most of the fracture section. The factors that cause contact fatigue include the structure of the material, the surface strengthening process, the surface roughness of the workpiece, the lubricant, and the stress.

Cracked bearing ring

1. Cracks on the raceway surface of the bearing outer ring and the reasons

After acid leaching a broken outer ring of a bearing, it can be seen by naked eyes that there are serious black burn marks on the surface of the channel. The horizontal cracks are basically perpendicular to the grinding direction, and the crescent-shaped burn layer appears on the broken fracture. It is in the shape of fine porcelain, and it starts to crack from the channel and quickly advances inward to complete fracture. Parallel cracks on the raceway surface of the bearing outer ring are typical grinding cracks, and the grinding cracks are mainly caused by factors such as excessive grinding and poor grinding process conditions; secondly, insufficient tempering of the bearing outer ring is also caused. Increased its susceptibility to grinding cracking. This phenomenon occurs even if the current intensity is relatively weak, and over time, the annular pit will develop into a corrugated groove. These corrugated grooves can only be found on the contact surface of the roller and the raceway of the ferrule, not on the steel ball, but the color becomes darker. These corrugated grooves are equidistant, and the bottom of the grooves on the raceway is darkened.

2. Cracks on the raceway surface of the bearing inner ring and the cause

After rough grinding of the raceway surface of the inner ring, magnetic particle inspection found that there were many small cracks on both sides of the raceway, especially near the oil ditch. In some rings, there were many deep, perpendicular to the grinding direction of the grinding wheel. Cracking and peeling phenomenon. After warp cutting, the whole piece of material falls off from the raceway surface. After hot pickling, it was found that there were cracks on the raceway surfaces on both sides of the inner ring of the bearing. The shape of the cracks was mostly net, and there were also straight cracks perpendicular to the grinding direction. In order to avoid the generation of grinding cracks, it is necessary to reduce the generation of grinding heat and accelerate the heat dissipation.