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New treatment has bearing on longevity

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NSK has developed a new series of high performance HPS spherical roller bearings with a running life of up to double that of conventional bearings of same size.

In addition, its maximum limiting running speed has improved by as much as 20%.

The company says the new series of bearings will give users big benefits such as reducing their maintenance cost, downsizing their product design and saving energy.

Compared with other types of bearings, spherical roller bearings have a high load capacity and self-aligning feature that allows some misalignment of a shaft.

A spherical roller bearing has inner and outer ring raceways and rollers in a spherical profile, which gives the bearing self-aligning capacity. The geometrical form, however, produces slip at the contact surface between the raceway and roller while they are rotating. Slip generated causes fatigue from micro-structural changes, which eventually leads to flaking.

NSK says it has clarified the “long life” mechanism of spherical roller bearings by reducing the slip generated between the inner ring and rollers. The use of a special treatment on the surface of the outer ring is effective in improving the traction of the rollers, and has helped control the rotational speed of the rollers.

Theoretical analysis and bench tests verify that slip is reduced and this prolongs bearing operation life by up to twice or even longer than conventional spherical roller bearings.

The cage of a spherical roller bearing is an important component that largely affects the performance of the bearing. Therefore, the cage must be high in its dimensional accuracy, strength and function. NSK is now applying a special nitriding treatment on the surface of its cage, which it says drastically reduces cage wear in harsh operational applications.

The company says compared with usual nitriding method, its treatment forms a finer and harder surface with uniform hardness.

Since special treatments are generally conducted at high temperature, the dimensional accuracy of the cage can be affected. NSK says it has solved this difficult problem, and the high accuracy of its cage is now maintained unchanged after the treatment.

The problem of cage wear in long life applications at high speed, previously the bottleneck for increasing the limiting speed of a spherical roller bearing, is now solved.

The series of HPS spherical roller bearings are tough and will deliver high performance in diverse applications with reduced maintenance costs and more compact design.

NSK has improved the limiting speed by up to 20% compared with conventional bearings.

Initially, 42 sizes with bores from 40mm to 130mm are available.

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