Type of damage in plain bearings

Core Tips: 1. Scratch (two-body abrasive wear) The hard particles moving together with the shaft diameter are in contact with the friction surface, which is the lower contact stress between the particles and the metal surface, and they are drawn on the surface of the bearing pad.
1. Scratch (two-body abrasive wear)

The hard particles moving together with the shaft diameter are in contact with the friction surface, which is the lower contact stress between the particles and the metal surface, and they are drawn on the surface of the bearing pad; the hard particles semi-inlaid on the surface of the bearing pad are also on the surface of the shaft diameter. Lines are scarred and are called scratches. Scratch is a two-body abrasive wear, and the direction of the linear flaw is consistent with the direction of the shaft diameter.

The lubricating oil film is broken, and the hub peak on the shaft diameter surface will also scratch the bearing bush, and many linear scratches appear, which is also the two-body abrasive wear.

The hard particles are embedded in the surface of the bearing shell and fall off, causing scratches of the point-like scar.

Most of the above particles are iron and sand.

The scratching causes the surface of the friction pair to be roughened, thereby reducing the load bearing capacity of the lubricating oil film, and forming new hard particles and hub peaks that can scratch the friction surface, causing a vicious cycle.

2. (three-body) abrasive wear

The smaller hard particles entering the bearing gap migrate between the two friction surfaces, creating extremely high contact stress on the friction surface, forming a three-body abrasive wear, similar to the grinding action, causing the bearing pad and the shaft diameter surface to wear. The high contact stress between the hard particles and the friction surface causes plastic deformation or fatigue damage to the friction surface of the ductile metal, causing brittle fracture or peeling of the friction surface of the brittle metal.

The scratches of the abrasive wear are also linear, and the direction is also consistent with the direction of the shaft diameter.

When there is edge contact, lack of lubricating oil or cracking of the oil film, severe abrasive wear will occur. Abrasive wear will result in shaft diameter and/or bearing geometry and shape changes, loss of precision, and increased bearing clearance, causing the sliding bearing performance to deteriorate dramatically before the expected life.

3. Bite (gluing)

In the state where the lubricating oil film is broken or lacks oil, a large friction factor causes a large amount of frictional heat to be generated, and the bearing temperature rises. At high temperatures, the low melting point metal of one friction surface adheres to the other friction surface due to softening, and the adhered metal is detached from the original surface and transferred to the other friction surface due to the shearing action caused by the rotational movement of the shaft diameter. Causes obvious pits and raised scratches on the friction surface. This damage is adhesive wear.

When bite sticking occurs, the friction sharply increases and the bearing temperature further rises, forming a vicious circle. When the adhesion is serious, the power of the shaft diameter rotation can no longer cut the bonding point, the shaft diameter movement will be terminated, commonly known as the "holding shaft", and the bearing is completely damaged.

4. Fatigue wear

Fatigue wear is also called fatigue damage. Under the repeated action of the cyclic load, in the direction perpendicular to the sliding direction, the friction surface appears fatigue crack, and the crack develops perpendicularly to the surface of the bearing pad to the joint surface of the lining and the backing, and rotates to extend parallel to the friction surface. Eventually the material is peeled off from the friction surface, causing crater damage.

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Analysis of bearing failure

Core Tip: Bearings are precision mechanical foundations. Due to the rapid development of scientific and technological progress, customers are increasingly demanding the quality of bearing products. Manufacturers provide standards and meet host usability
Bearings are precision mechanical foundations. Due to the rapid development of scientific and technological progress, customers are increasingly demanding the quality of bearing products. It is important that manufacturers provide high-quality products that meet standards and meet host performance, but proper use of bearings is more important. In the technical work of special bearings for motorcycles in recent years, the author often encounters the problem that the bearings are qualified after testing, but the bearings are stuck after the installation or the early stop rotation is invalid when used. Mainly showing the rotation stuck, the working surface is severely peeled off, the cage is seriously worn and even twisted and broken. The failure result analysis shows that there are not many quality problems belonging to the bearing itself, and most of them are caused by improper installation and use. To this end, the author believes that it is necessary to make a superficial review of the failure modes and mechanisms common to bearings, in order to play a role in attracting jade.

First, the failure mechanism of the bearing
1. Contact fatigue failure
Contact fatigue failure refers to the failure of the working surface of the bearing subjected to alternating stress. Contact fatigue spalling occurs on the bearing working surface, often accompanied by fatigue cracking, first from the maximum alternating shear stress below the contact surface, and then extended to the surface to form different peeling shapes, such as pitting or pitting. Peeled into small pieces called shallow peeling. Due to the gradual enlargement of the exfoliation surface, it tends to expand deeper, and {TodayHot} forms a deep exfoliation. Deep exfoliation is a source of fatigue in contact fatigue failure.
2. Wear failure
Wear failure refers to the failure of the relative sliding friction between the surfaces resulting in the continuous wear of the metal on the working surface. Continued wear and tear will cause gradual damage to the bearing components and ultimately lead to loss of bearing dimensional accuracy and other related problems. Wear may affect the shape change. The increase of the clearance and the change of the surface of the working surface may affect the lubricant or cause the pollution to a certain extent, resulting in complete loss of the lubrication function, thus causing the bearing to lose the rotation precision or even the normal operation. Wear failure is one of the common failure modes of various types of bearings. It is usually classified into the most common abrasive wear and adhesive wear according to the form of wear.
Abrasive wear refers to wear caused by the intrusion of foreign hard particles or hard foreign matter or metal surface between the working surface of the bearing and the relative movement of the contact surface, often causing furrow-like scratches on the working surface of the bearing. Hard particles or foreign matter may come from inside the host or from other adjacent parts of the host system and be fed into the bearing by the lubricating medium. Adhesive wear refers to uneven friction of the friction surface due to microscopic protrusions or foreign matter on the friction surface. When the lubrication condition is seriously deteriorated, local friction occurs due to local friction, which may cause local deformation of the friction surface and friction micro-welding phenomenon. When the surface metal may be partially melted, the force on the contact surface tears the local friction weld from the substrate to increase the plastic deformation. This adhesive-tear-adhesive cycle constitutes adhesive wear. In general, slight adhesive wear is called scratching, and severe adhesive wear is called bite.
3. Fracture failure
The main cause of bearing fracture failure is defect and overload. When the applied load exceeds the material strength limit and the part is broken, it is called overload fracture. The main reason for the overload is the sudden failure of the host or improper installation. Defects such as microcracks, shrinkage cavities, air bubbles, large foreign objects, overheated tissue and localized burns of the bearing parts also cause breakage at the defects during impact overload or severe vibration, called defect fracture. It should be pointed out that in the manufacturing process, the {HotTag} bearing can correctly analyze whether the above defects exist through the instrument in the re-inspection of the raw materials, the quality control of the forging and heat treatment, and the process control, and the control must be strengthened in the future. However, in general, most of the bearing fracture failures that occur are overload failures.
4. Clearance change
During the operation of the bearing, due to the influence of external or internal factors, the original matching clearance is changed, the precision is reduced, and even the "biting death" is called the gap change failure. External factors such as excessive interference, inadequate installation, expansion caused by temperature rise, instantaneous overload, etc., internal factors such as residual austenite and residual stress are unstable, which are the main reasons for the failure of the gap change.

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