NSK's HPS series of high-performance spherical roller bearings is interchangeable with standard bearing envelopes and is suitable for a variety of applications. The extended operating life and increased performance can extend maintenance schedules on machines where the bearings are fitted as a replacement and increase the performance of machines where the bearing is specified by the OEM manufacturer. These bearings can also be used to save weight and improve operational efficiency through some products being designed to be lighter more compact.
Spherical roller bearing (SRB) units typically offer a high load capacity and a self-aligning feature. The unitised design of the bearings enables easy handling and installation, making them popular across a wide range of industries including steel, pulp and paper, transportation, extraction and construction, which require durability and smooth running performance.
NSK researched the SRB design extensively in order to identify the limiting factors on bearing life, and sought to improve the design in order to address them and deliver the extended life of HPS bearings. Key to the self-aligning performance of SRB is the spherical profile of the bearing rollers acting in the bearing inner and outer ring raceways. However, the research showed that, under rotation, these geometrical forms interact to produce slippage at the contact surface points between the raceways and rollers.
Running life doubled
With its HPS design, NSK has clarified for the first time the mechanism that causes slippage and creates high friction on the surface, leading eventually to damage due to surface fatigue. NSK further verified, by theoretical analysis and bench testing, that the friction can be reduced by controlling the motion of rotating rollers and that a special surface treatment of the outer ring is effective in achieving this. Based upon these findings, NSK developed mass-production technology and bearings that can minimise slippage to prolong running life by more than twice that of conventional products. The cage of a spherical roller bearing is also an important component that plays a major role in the performance the bearing. Therefore, the cage must have high dimensional accuracy and functionality. NSK has applied a special nitriding surface treatment to the high-precision pressed steel cage of the HPS series, which can significantly reduce wear in harsh operating environments. Compared with usual nitriding, NSK's treatment forms a finer and harder surface with more uniform hardness.
Since the special treatment is conducted at high temperatures, the dimensional accuracy of the cage is inevitably affected. However, NSK has solved this difficult problem and has achieved a means of ensuring high accuracy of the cage after treatment. As a result, the problem of cage wear under conditions of continuous running at high speeds, which restricted any increase of the limiting speed of the bearing, has been solved. This is evidenced by the 20 per cent increase in limiting speed achieved by the HPS series design.
The high durability and superb running performance of the HPS series of spherical roller bearings are a result of consolidated technologies developed by NSK using new analysis technology, severity testing and refined production methods.
Initially 42 sizes with outside diameters ranging from 80-260mm will be marketed globally by NSK for a wide variety of industries and applications.
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