Manifestations Of Failed NTN Bearings

1. Contact fatigue failure
Contact fatigue failure refers to failure caused by alternating stress on the working surface of the bearing. Contact fatigue spalling occurs on the working surface of NTN bearings, and is often accompanied by fatigue cracks. It first occurs from the maximum alternating shear stress below the contact surface, and then expands to the surface to form different spalling shapes, such as pitting or pitting spalling. , peeling off into small flakes is called shallow peeling. Due to the gradual expansion of the peeling surface, it often extends to deep layers, forming deep peeling. Deep spalling is a fatigue source of contact fatigue failure.

2. Wear failure
Wear failure refers to the failure caused by the relative sliding friction between surfaces causing continuous wear of the metal on the working surface. Continuous wear will cause gradual damage to NTN bearing parts, and eventually lead to loss of bearing dimensional accuracy and other related problems. Wear may affect shape changes, increase the fitting clearance, and change the topography of the working surface. It may affect the lubricant or contaminate it to a certain extent, causing the lubrication function to be completely lost, thus causing the bearing to lose rotational accuracy or even fail to operate normally. Wear failure is one of the common failure modes of various types of bearings. According to the wear form, it can usually be divided into the most common abrasive wear and adhesive wear.
Abrasive wear refers to the wear caused by the squeeze of foreign hard particles or hard foreign matter or wear debris on the metal surface between the working surfaces of the bearing and the relative movement of the contact surfaces, 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 are sent into the bearing by the lubricating medium. Adhesive wear refers to the uneven stress on the friction surface due to microscopic protrusions or foreign matter on the friction surface. When the lubrication conditions seriously deteriorate, local friction heat is generated, which can easily cause local deformation of the friction surface and friction micro-welding. Serious The surface metal may be partially melted, and the force on the contact surface will tear the local friction welding point from the matrix and increase the plastic deformation. This adhesion-tear-adhesion cycle constitutes adhesive wear. Generally speaking, slight adhesive wear is called abrasion, and severe adhesive wear is called occlusion.

3. Fracture failure
The main reasons for NTN bearing fracture failure are defects and overload. When the applied load exceeds the strength limit of the material and causes the part to break, it is called overload fracture. The main reason for overload is sudden host failure or improper installation. Defects such as micro-cracks, shrinkage cavities, bubbles, large foreign matter, overheated tissue and local burns in bearing parts can also cause fractures at the defects during impact overload or severe vibration, which is called defect fracture. It should be pointed out that during the manufacturing process of bearings, instruments can be used to correctly analyze whether the above-mentioned defects exist during factory re-inspection of raw materials, forging and heat treatment quality control, and machining process control. Control must still be strengthened in the future. But generally speaking, most of the common bearing fracture failures are overload failures.

4. Failure of clearance change
During operation of NTN bearings, due to the influence of external or internal factors, the original fitting clearance changes, the accuracy decreases, and even causes “seizure”, which is called clearance change failure. External factors such as excessive interference, improper installation, expansion caused by temperature rise, instantaneous overload, etc., and internal factors such as unstable residual austenite and residual stress are the main reasons for clearance change failure.