Rolling bearings are one of the indispensable basic components of running machinery. Although the rolling bearing is small in size and low in cost, once the rolling bearing fails, the loss to the running machine and even the entire production equipment is enormous. With the rapid development of technology, enterprises are increasingly demanding the quality of rolling bearings. Especially for enterprises with automation and continuous production, the requirements for the reliability of rolling bearings are very strict. Therefore, how to improve the reliability of rolling bearings has become one of the major problems that rolling bearing manufacturers and customers need to solve urgently.
The reliability of the rolling bearing is closely related to the failure mode of the rolling bearing. To improve the reliability of the bearing, it is necessary to start from the failure mode of the bearing and carefully analyze the failure reason of the rolling bearing to find out the specific measures to solve the failure.
1. the failure mechanism of the bearing
(1) Contact fatigue failure
Contact fatigue failure refers to the material fatigue failure caused by the alternating working stress of the bearing working surface.
A common form of contact fatigue failure is contact fatigue spalling. Contact fatigue spalling occurs on the bearing working surface, often accompanied by fatigue cracks, first from the maximum alternating shear stress below the contact surface, and then spread to the surface to form different peeling shapes, such as pitting or pitting, peeling off In a small piece, it is called a shallow layer of peeling off. As the exfoliation surface gradually expands, it will slowly expand into the deep layer to form 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 problems. Wear failure is one of the common failure modes of various types of bearings. Generally, it can be divided into abrasive wear and adhesive wear according to the wear form.
Abrasive wear refers to the abrasion caused by the extrusion 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.
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.
(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 presence or absence of the above defects can be correctly analyzed by the instrument in the quality control of the incoming materials, the quality control of the forging and heat treatment, and the control of the processing. However, in general, most of the bearing fracture failures that occur are overload failures.
(4) Corrosion failure
Some rolling bearings inevitably come into contact with water, water vapor and corrosive media during actual operation, which can cause rust and corrosion of rolling bearings. In addition, the rolling bearing is also subjected to micro-current and static electricity during operation, causing current corrosion of the rolling bearing.
The rust and corrosion of the rolling bearing will cause the pit rust, the pit rust on the surface of the rolling element, the pear-like rust and the pit-like rust with the same rolling element spacing, and the overall rust and corrosion. Eventually caused the failure of the rolling bearing.
(5) Clearance change is invalid
In the work of rolling bearings, due to the influence of external or internal factors, the original matching clearance changes, the precision is reduced, and even the "biting death" is called the clearance change failure. External factors such as excessive interference, installation is not in place, expansion caused by temperature rise, instantaneous overload, etc.; internal factors such as residual austenite and residual stress are in an unstable state, etc., are the main causes of failure of clearance changes. .