1. Contact fatigue failure
Contact fatigue failure refers to the failure of the working surface of the NTN bearing due to the alternating stress. Contact fatigue spalling occurs on the working surface of NTN bearings, often accompanied by fatigue cracks, first from the maximum alternating shear stress below the contact surface, and then extended to the surface to form different spalling shapes, such as pitting or pitting , peeling off into small pieces called shallow peeling. Due to the gradual enlargement of the exfoliation surface, it tends to expand deeper and 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 NTN bearing parts and ultimately lead to loss of dimensional accuracy of the NTN bearing and other related problems. Wear and tear 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 NTN bearing to lose the rotation precision or even fail to operate normally. Wear failure is one of the common failure modes of various NTN bearings. It is usually divided into the most common 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 NTN bearing and the relative movement of the contact surface, which often causes a furrow-like scratch on the working surface of the NTN 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 NTN 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 NTN 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 matter, overheated tissue and localized burns of NTN bearing parts also cause breakage at the defect during impact overload or severe vibration, called defect fracture. It should be pointed out that in the manufacturing process, in the process of re-inspection of raw materials, quality control of forging and heat treatment, and process control, NTN bearings can be correctly analyzed by instruments to determine whether the above defects exist, and control must be strengthened in the future. However, in general, most of the NTN bearing fracture failures that occur are overload failures.
4. Clearance change
In the work of NTN bearing, due to the influence of external or internal factors, the original matching gap is changed, the precision is lowered, 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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