New HPS Series spherical roller bearings from NSK

NSK have developed new high-performance spherical roller bearings, the HPS Series, which are said to offer twice the running life compared with conventional bearings of the same size, as well as a maximum limiting running speed that has been improved by up to 20%.

Compared with other types of bearings, spherical roller bearings (SRBs) have a high load capacity and a self-aligning facility that allows for some misalignment of the axis of rotation. The unitized design of the bearings allows easy handling and installation, making them suitable for a wide range of industries, including quarrying and construction, where durability and smooth-running performance are required.

The key to the self-aligning performance of SRBs is the spherical profile of the bearing rollers acting in the bearing inner and outer ring raceways. However, under rotation these geometrical forms interact to produce slippage at the contact surface points between the raceways and rollers. With their HPS design, NSK say they have clarified, for the first time ever, the mechanism that causes slippage and creates high friction on the surface, leading eventually to damage due to surface fatigue. The company have further verified, by theoretical analysis and bench testing, that this friction can be reduced by controlling the motion of the rotating rollers, and that a special surface treatment of the outer ring is effective in achieving this. Based upon these findings, NSK have developed a bearing that minimizes slippage to prolong running life by more than twice that of conventional products.

The cage of an SRB is another important component that plays a major role in the performance of the bearing. NSK have applied a special nitriding surface treatment to the high-precision pressed-steel cage of the HPS Series, which significantly reduces wear in harsh operating environments. Because this special treatment is conducted at high temperatures, the dimensional accuracy of the cage is inevitably affected. However, NSK say they have achieved a means of ensuring high accuracy of the cage after treatment, as a result of which the problem of cage wear under conditions of continuous running at high speeds, which previously restricted any increase in the limiting speed of the bearing, has been resolved. This, they say, is evidenced by the 20% increase in limiting speed achieved by the HPS series design.

The NSK HPS Series of spherical roller bearings is currently available in 42 sizes with outside diameters ranging from 80mm to 260mm.

NSK UK Ltd, Northern Road, Newark, Notts NG24 2JF; tel: (01636) 605123.