SKF NA4904 .2RS Nadellager (20x37x18)

As a needle roller bearing, this bearing carries high radial loads in a very compact section. The dynamic load rating of 19.4 kN characterises this bearing. The static load rating is 22.4 kN. The line contact of a needle reacts sensitively to hard particles; sealing on both sides addresses exactly that. In this design, the contact seal on both sides changes less about the load-carrying behaviour than about how the bearing position is operated.

A needle set works with long, narrow contact lines and a high contact pressure over a small area; hard particles leave indentations there which continue to act as local peaks in pressure. The seal keeps such particles away and the lubricant inside the bearing — both decisive at the typical mounting locations of this design, since connecting rods, rocker arms, joint pins and gearbox interiors can usually neither be cleaned nor conveniently relubricated after the fact.

The counterpart is an additional frictional torque at the rubbing lip; it generates heat, lowers the permissible speed relative to the open version, and makes the seal material the limit for operating temperature and media resistance. It should also be checked whether the sealed version provides for relubrication at all. The requirements of the design itself remain unchanged: without an inner ring of its own the shaft surface is the raceway and has to be executed accordingly in hardness, surface finish and tolerance; the bearing takes no axial force, so axial location has to be solved separately; and because the contact pressure is distributed over the length of the needle, the bearing position tolerates only slight misalignment before the load migrates to the needle ends.

The normal radial clearance is matched to common fits and operating temperatures. No separate catalogue attribute for the material of these items is available; the specification table of the individual item is what governs.