Do You Know The Three Main Factors Of Bearing Fracture And Cracking?

Bearings are vital parts in modern machinery production activities. If they fail to operate as required during assembly, testing, and use, the bearing cage is likely to break, and in severe cases, it will fall apart completely, or even more serious failures. .

Especially for high-voltage motors, it may also involve the erosion of the shaft voltage on the bearings, so special attention must be paid and relevant measures must be taken. So what exactly caused the bearing cage to break or even fall apart?

Let's take a look.....

Improper installation and use are the main causes of cage fracture

Three common bearing fracture and cracking factors:

Forced break

Keywords:

· Tensile Strength

· Overstress effect

The most common cause is rough handling (knocking) during bearing installation or removal. Hit the bearing ring with a hammer or chisel directly, which may cause small cracks. When the bearing is put into use, the fragments of the ring will break.

Large spherical roller bearing with cracked inner ring. Stop during operation and take out a roller to check the condition of the bearing raceway (lower row). Then "hammer" the roller back to its original position, causing part of the inner ring flange to fracture. The impact was transmitted by a roller in the other row, and part of the outer flange was also broken. At the same time, the sealing ring has broken.

The excessive interference fit on the tapered valve seat or sleeve is another cause of cracking of the inner ring. Tensile stress (hoop stress), as a result of excessive interference, is generated in the inner ring, and when cracks occur, the bearing is put into operation. (Compared with bainite, martensite hardened ferrules are more sensitive to this). When the bearing is heated and then installed in the shaft with wrong (extra-large) tolerances, the same result may also occur.

Forced fracture is two examples of stress concentration caused by local overload or overstress that exceeds the tensile strength of the material.

 Fatigue fracture

Keywords:

· Excessive bending fatigue strength

· Crack initiation/propagation

· Eventually force a break

· Inner ring and retainer

Start when the bending exceeds the fatigue strength. The crack started and then spread. Finally, the entire ferrule or retainer is cracked.

This usually occurs when the outer ring is not supported in a bearing chamber, so the outer ring has a certain degree of tolerance, or the outer ring has stress concentration points.

Heating fracture

Keywords:

· High slip and/or insufficient lubrication

· High frictional heat

· Cracks at right angles to the sliding direction

The sliding of the two surfaces generates frictional heat. If the sliding speed is high, thermal development causes cracks, which are generally at right angles to the sliding direction.

A typical example is a rotating inner ring equipped with a loose-fitting shaft and bearing axial loads. Due to creep, the side of the bearing will produce sliding motion on the abutment shoulder (or final gasket) on the shaft. Friction generates (a lot of) heat, which causes smearing and eventual cracking of the ferrule.

Rolling mill four-row tapered roller bearings (most) require clearance fit due to quick disassembly/installation. In order to avoid cracking, the inner ring is "case hardened", while the shoulder or final gasket is hardened.

Rolling mill four-row tapered roller bearings list