NSK NJ208 ET Zylinderrollenlager (40x80x18)

As a cylindrical roller bearing, this bearing carries high radial loads with limited axial capacity. This NSK bearing measures 40x80x18 mm and weighs 0.373 kg; the specification table carries the supplementary technical details. Cylindrical rollers run on the raceways in line contact; that is where this design's high radial load capacity and its low deflection under load come from.

Line contact between roller and raceway spreads the load over the length of the roller instead of over a point; compared with a ball bearing of the same size this yields the higher radial load capacity and the lower deflection of the bearing position under load. A cylindrical roller bearing takes axial force through its ribs alone, and only as far as the rib arrangement provides for it at all: rib-free versions displace inside the bearing and work as a non-locating position with length compensation, versions guided by a rib on one side support in one direction, those guided on both sides in both.

That decision is made with the choice of design and not in service — it belongs at the start of the bearing arrangement layout, not at its end. Because the inner ring and the outer ring assembly are separable, both rings can be mounted independently and each executed with an interference fit, which eases the fitting and removal of heavy shafts; in return the bearing position must be aligned, since the roller row tolerates only a few angular minutes of misalignment before the contact pressure migrates to the roller ends.

A profiled roller surface mitigates this effect but does not replace the alignment of shaft and housing bore to one another. The lower load limit also has to be observed: if the bearing runs at high speed and virtually unloaded, the roller set can slide against the raceway instead of rolling on it. The open form leaves sealing, initial filling and relubrication to the surrounding construction; the normal radial clearance is matched to common fits and operating temperatures, at which the operating clearance settles within the intended range.