What are the forms of bearing ring breakage?

 

The common problem of bearing rings is fracture, and the fracture of bearing rings can be analyzed from two aspects, one is defect fracture, and the other is the use of fracture, which can be analyzed mainly from raw material problems and process processing, and the use of fracture is caused by fatigue transition and other reasons.

 

First of all, we can look at the causes of bearing ring defect fracture:

1. When defects such as raw material inclusion, looseness, brittle element segregation or carbide liquid precipitation, reticulation, banding, and unfortunate homogeneity and segregation are not eliminated or improved in the processing work, they will cause stress concentration, weaken the basic strength of the ferrule, and become the source of cracks.

 

Solution: The preventive measure is to adhere to the main channel supply, try to purchase stable and reliable quality steel, strengthen the warehousing inspection of the purchased steel, and check it from the source.

 

Second, there are cracks in the grinding process

 

Solution: Strengthen the monitoring of the grinding process, and the finished bearing ring is not allowed to have grinding burns and grinding cracks, especially on the mating surface of the inner ring to change the taper. If the ferrule is pickled, it should be fully inspected, and the burn product should be removed, and the severe burn can not be repaired or the repair is unqualified should be scrapped, and the ferrule with grinding burns is not allowed to enter the assembly process.

 

3. Improper heat treatment

 

Treatment method: In order to solve the defects such as soft spots of medium and large varieties of bearing rings, the composition and performance of quenching oil should be determined, and those that do not meet the requirements should be replaced in advance and replaced by rapid quenching oil to enhance the quenching ability of quenching medium and improve quenching cooling conditions. Strict tempering process. For the varieties with more fractures, the second tempering is carried out after the rough grinding of the ferrule, which can not only further stabilize the structure and size of the ferrule, but also reduce the grinding stress and improve the performance of the grinding metamorphic layer.

 

Bearing rings often break during use, and there are three main forms, namely: fatigue fracture, overload fracture and thermal fracture.

 

1. Fatigue fracture

 

Under the alternating load and impact load, the stress of the bearing ring (especially the outer ring) continuously exceeds the fatigue strength limit of the material, resulting in fatigue cracks, and the cracks eventually expand to a certain extent, resulting in fracture at the maximum stress of the part. It generally occurs in the bearing area of the outer ring, because the outer ring usually fits with the bearing box bore as a clearance fit, and the bearing box is a variable and elliptical part, which is easy to cause fatigue fracture under alternating load and impact load.

 

2. Overload breakage

 

Similar to fatigue fracture, when the stress acting on the bearing is greater than the tensile strength of the material, it causes cracks in the inner ring, usually due to improper installation, such as the tilt of the bearing installation, resulting in the eccentric load of the bearing, resulting in the fracture of the bearing caused by local overload; In addition, improper knocking during installation causes the bearing to crack and fall off, which is also classified as overload cracking. The most common is that when the bearing is installed with interference size, excessive interference will also lead to cracking of the bearing ring (mainly the interference fit of the inner ring of the four-row cylindrical bearing), and the interference is too large to cause the stress of the inner ring to be larger, especially the inner ring with thin cross-sectional thickness (cross-sectional thickness <12mm), and too much interference often leads to the axial cracking of the inner ring.

 

3. Thermal fracture

 

Thermal fracture is mainly due to the sliding friction between the parts matched with the end face of the bearing ring, under the action of axial force, the friction produces high heat, resulting in the end face accompanied by burns and discoloration, friction and high heat lead to cracks on the end face of the bearing ring, the crack is characterized by perpendicular to the direction of friction operation, and the same end face crack also has a greater impact on the inner ring with thin cross-section thickness (cross-sectional thickness <12mm), especially the heavy-duty high-speed or medium-speed rolling mill roll bearing.

 

The study of the ring fracture phenomenon should not only consider the defects generated in the material and production process, but also study and analyze the structural dimensions of the bearing parts, processing and measurement methods, processing technology, bearing service conditions and other factors.

 

1. Bearing structure and service conditions. Different structures are suitable for different service conditions; The structure of bearing parts is different, and its processing technology is not the same, which also affects its quality.

 

2. Strengthen process research, improve processing technology, improve processing quality, and reduce the possibility of defects in processing.

 

3. Improve processing monitoring methods and promote the improvement of processing quality.

 

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 be cracked, and the crack will eventually expand to a certain extent, resulting in a complete separation of a part of the part, which is called cracking or fracture.