NSK has developed the world's first high accuracy method for predicting the life of steel rolling bearings based on statistical data of non-metallic inclusions in the steel from ultrasonic testing. Non-metallic inclusions are typically the origin of rolling contact (flaking) fatigue.

This development has enabled NSK to revise up the basic dynamic load rating of applicable products to up to double the equivalent rolling contact fatigue life.

This technology contributes to carbon-neutrality by enabling a reduction in the frequency of component replacement and machine maintenance and also enabling downsizing of machinery.

NSK Ltd. has developed the world's first method to highly accurately predict the life of a rolling bearing based on statistical data (size and quantity) of non-metallic inclusions (impurities) in the steel.

This technology has enabled NSK to revise up the basic dynamic load rating of its bearings and further enables customers to design machines and vehicles that make full use of the long-life performance of high-quality NSK bearings.

NSK will initially begin to propose solutions based on this technology to select customers, followed by a broad revision of the basic dynamic load rating of its standard bearing lineup.

Background

NSK bearings are made of high-quality steel, which has been constantly improved by NSK researchers and engineers closely collaborating with steel manufacturers. As a result, the actual life of NSK bearings tends to be considerably longer than bearing life calculated in accordance with ISO standards.

In order to better enable customers to make full use of the long-life performance of NSK bearings in their machine design and pursue carbon neutrality, we needed a technology that could calculate rolling fatigue life with a high degree of accuracy.

Details

1. Advanced detection and analysis of non-metallic inclusions using Micro Ultrasonic Testing Method (Micro-UT Method)

The rolling contact fatigue life of bearings is closely related to the size and quantity of non-metallic inclusions in the steel. Depending on the steel, the amount and distribution of non-metallic inclusions can vary widely.

NSK's unique Micro-UT Method*1 can inspect a volume of steel 3,000 times larger in one-fifth of the time compared to conventional methods*2. This enables efficient collection and analysis of highly reliable statistical data on non-metallic inclusions in bearing steel.

2. NSK Digital Twin technology used to establish rolling bearing life calculation method based on non-metallic inclusion size.

To derive a bearing life calculation method based on the analysis of non-metallic inclusions, NSK developed a unique rotational testing method that involves introducing artificial defects simulating non-metallic inclusions of various sizes into rolling bearing raceways.

We succeeded in reproducing specific modes of failure as intended and further created a simulation*3 capable of reproducing and analyzing the stresses around the artificial defects to futher clarify the mechanism of flaking fatigue.

Based on this we sucessfully developed the world's first*4 method for calculating rolling contact fatigue life based on the size of non-metallic inclusions in steel.

Benefits

Highly accurate bearing life prediction using NSK's Micro-UT Method enables the long-life performance of NSK bearings to be calculated more accurately than before. This calculation method is applied to revise up the basic dynamic load rating of bearings, which is a vital parameter used in application life calculation. For example, for radial roller bearings, it is possible to revise up the basic dynamic load rating to double the equivalent rolling contact fatigue life.

Revised basic dynamic load ratings open up new possibilities for customers that want to capitalize on the long-life performance of NSK bearings in their machine design. This is expected to help customers reduce the frequency of component replacement and machine maintenance and potentially downsize machine and unit designs, thereby contributing to the realization of a carbon-neutral society.

Notes

*1: Micro-UT Method: Non-destructive testing using ultrasonic waves

*2: Compared to NSK's conventional analysis method

*3: Created through an open innovation project with Professor Hisao Matsunaga, Kyushu University

*4: Based on NSK examination of available literature