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 accuracy 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.
