Why does the nup cylindrical roller bearing ring break?

NUP cylindrical roller bearing is mostly used in medium-sized machinery, and the fracture accident of cylindrical roller bearing ring is also one of the common problems during its use. The reason for the fracture of the cylindrical roller bearing ring is shared below, mainly by looking at the picture to introduce the specific situation of the fracture analysis of the bearing ring.

A. Some macro reasons for the fracture of the nup cylindrical roller bearing ring:

1. The outer wall of the nup cylindrical roller bearing ring has serious pitting corrosion and extrusion deformation.

2. The fracture of the nup cylindrical roller bearing ring has a transverse fracture and a longitudinal fracture. It can be seen from the fracture morphology that the cracks all start from the outer wall and extend to the tear on the inner wall, and the cracks are all located at the fatigue pitting or shedding of the outer wall, and a large area of pitting is also found on the outer wall at the fatigue spalling of the fragments. It can be seen that the fatigue pitting and shedding caused by excessive contact stress may be the source of cracking of the bearing ring. In addition, due to the axial thrust at the rib and the deep undercut groove, the stress concentration is relatively large, and it is also very easy to break at the rib.

3. A macroscopic crack was found on one fragment, which is a surface crack, a fatigue crack caused by contact stress, and a precursor to fatigue shedding. In the test, when we used a metallographic cutting machine to cut and sample the bearing ring fragments, due to vibration and external impact load, some fragments were further broken or cracked, and the cracks or cracks were located at the ribs, which shows that the material Hard and brittle, poor impact resistance, and the ribs are more likely to break due to high structural stress.

4. On the inner surface of the nup cylindrical roller bearing ring, many wear grooves and peeling blocks were also found, as well as macroscopically visible cracks. This shows that the bearing ring has relative sliding friction with the shaft. According to the working principle of the bearing, the bearing ring should have an interference fit with the shaft. When the shaft rotates, the bearing ring and the shaft rotate together, and the rollers roll between the bearing ring and the outer ring to reduce the vibration of the shaft. If the gap between the shaft and the bearing ring is too large, there will be relative sliding friction between the shaft and the bearing ring, which will cause the rollers to not roll normally, the ring will directly bear a large contact stress, and the bearing will be overloaded, resulting in fatigue pitting and corrosion. Fatigue falls off.

B. Fatigue damage analysis of damaged bearings

1. Fatigue pitting and fatigue shedding

For mechanical parts with high pair (that is, high pressure) contact, it is theoretically point and line contact, but in fact, after the elastic deformation of the material under load, the theoretical point and line contact becomes a small surface contact. Locally very high stress will be generated at the contact, such stress is called surface contact stress. In practice, the contact stress of high-level parts is cyclically changed. Under the action of contact cyclic stress, small micro-cracks are first formed on the metal surface, and then the cracks develop along the direction of an acute angle with the surface. When reaching After a certain depth, it goes beyond the surface of the part, and finally a small piece of metal peels off, forming a small pit on the surface of the part. This phenomenon is called fatigue pitting (pitting for short). Pitting corrosion is a failure mode under the action of contact stress, which belongs to fatigue damage. After pitting damage occurs to the bearing, strong vibration noise and heat generation usually occur during operation.

2. Influence of fatigue pitting and fatigue shedding on ferrule cracking

From the macroscopic analysis, it can be seen that, except for the fracture near the retaining ring, the position of most of the free surface of the fracture is accompanied by fatigue pitting and fatigue shedding. Fracture is intrinsically linked to fatigue pitting and shedding. The microcracks found in the microscopic observation of the cross-section of the pitting and the surface cracks found in the macroscopic view cause pitting and peeling, which greatly reduces the effective bearing area of the ferrule, and may also become a source of fracture, causing the ferrule to be damaged under the action of vibration. brittle fracture.

Contact: Grace
Email: ntn@llhbearing.com
Skype:+8618668903871
MP/Whatsapp: +8618668903871
Wechat:GraceXu1234