In a world first, NSK has introduced a new method of accurately predicting the
lifespan of rolling bearings based on their size and the amount of non-metallic
inclusions in the steel the bearings are made from. Going forward, NSK’s Angular
Contact Ball Bearings, Cylindrical Roller Bearings, Deep Groove Ball Bearings and
Tapered Roller Bearings will all see their lifespans increased, potentially even
doubled, by this optimisation of basic dynamic load ratings.
Load ratings are governed by the ISO 281:2007 standard, which states that when you test a batch of identical bearings, nine out of every ten need to make it through those million
revolutions without issue. ISO 281 does allow for an increase in the service life under
certain conditions, but in the past any modifications to the bearing had to be followed by a
further battery of tests. NSK, however, has developed a non-destructive testing method for
exactly these sorts of situations which makes it possible to dispense with further testing and allows the end user to benefit from a fundamental increase in the service life of their
bearings.
Generally speaking, most people use a manufacturer’s existing catalogue to calculate
bearing life. Alternatively they can usually input the external loads and the bearing
information into a calculation programme. The basic calculation, however, is still carried out
in accordance with ISO 281. This type of calculation has become the standard worldwide.
However, since the methods of determining a bearing’s lifespan were developed and
introduced (all the way back in 1962), material purity and manufacturing capabilities have
both come on leaps and bounds. As a result, the actual service lifespan of a bearing tends
to be quite a lot longer than that which is suggested by testing under ISO 281.
NSK’s solution has been to simplify things, bringing in computer-aided models alongside
empirical tests. The basic idea is that we use these models as a ‘digital twin,’ with the
ultimate aim of being able to dispense with service life tests with real, physical bearings and to determine changes to dynamic load ratings purely by means of digital evaluations.
NSK’s own internal research has shown that the composition and quality of bearing steel, in
particular the proportion of the steel which is made up of non-metallic impurities, has a huge impact on a bearing’s service life, indeed is actually a more accurate indicator of its lifespan than the above calculation methods. Our engineers realised that an evaluation method based on fracture mechanics (a field of mechanics concerned with the study of the
propagation of cracks in materials) could provide more meaningful insight.
The company worked with Kyushu University in Japan to develop a quantitative evaluation
method that could determine which factors influenced the process of crack propagation in a material, and to what extent. Notably, by combining the new method with an ultrasonic
inspection technique that scans the non-metallic inclusions in a large volume of steel, NSK
discovered it could predict the life of its bearings with much higher accuracy.
As a direct result, NSK has revised the basic dynamic load rating of many bearings with no
change in design or materials, while still applying the appropriate safety margin to any
uprated values. With this revision, the estimated life of radial roller bearings, for example, is up to twice that which it was before.
Even better, as the basic dynamic load ratings of bearings improves, they become suitable
for use in higher load conditions, meaning that company’s can opt for smaller bearings
which are still able to perform the same function of their larger counterparts. Obvious
benefits include machine downsizing and weight reduction.
End users can rely on the fact that the new bearing life values are determined on the basis
of a carefully studied methodology supported by an extensive empirical database. All new –
and fundamentally higher – values will be within the safe range. NSK’s researchers and
developers used a quantitative evaluation method to determine which factors or the number and size of impurities influence the process of crack propagation in a rolling bearing steel and to what extent. Computers with extreme computing power were used to run and analyse simulations.
Press picture Going forward, NSK’s Angular Contact Ball Bearings, Cylindrical Roller Bearings, Deep Groove Ball Bearings (pictured) and Tapered Roller Bearings will all see their lifespans increased.
About NSK Europe:
NSK Europe Ltd. is the European organisation of the Tokyo-based bearing manufacturer NSK, which was founded in Japan in 1916 and today employs nearly 25,600 people in its worldwide operations. The products and solutions provided by the industrial and automotive supplier can be found wherever things move. In addition
to nearly all types of rolling bearings, the company’s portfolio includes housed bearings, linear technology,wheel bearing units, transmission and engine bearings. The company is oriented to perfection in all of its business activities. Its aim is quality leadership in its industry, which it strives for through a continuous process of improvement, excellent product development, optimised production processes and customer-oriented service
processes. In fiscal year 2023, the more than 3,200 employees of NSK Europe Ltd. generated sales of over €662 million.
