SKF 2304 M Self-Aligning Ball Bearing (20x52x21)

As a self-aligning ball bearing, this bearing compensates for misalignment and shaft deflection. The dynamic load rating of 18.2 kN characterises this bearing. The static load rating is 4.75 kN. The limiting speed is 19000 rpm. This design is intended for bearing positions at which misalignment cannot be structurally ruled out — with long shafts, bolted frames and separately machined pillow blocks.

The self-aligning ball bearing has two rows of balls in the inner ring and a common, spherically formed raceway in the outer ring. Because the centre of curvature of that raceway lies on the bearing axis, the inner ring unit with both rows of balls can swivel inside the outer ring; the bearing position thereby accommodates misalignment between the pillow blocks and a shaft deflected under load, without the contact pressure building up at an edge in the rolling contact.

That is exactly the application case: long shafts, welded or bolted frames, and constructions whose bearing seats are not bored in one setup — in materials handling, agricultural machinery, ventilation plant and textile machinery. The reverse side of the wide outer raceway is a low conformity between ball and raceway: the contact area stays small, the load rating lies below that of a rigid ball bearing of the same size, and friction in the rolling contact is low.

This design can take axial forces only to a modest extent; where the axial load predominates it belongs at a separate bearing position. It should also be noted that the alignment capability compensates for static misalignment — a misalignment that shifts with every revolution, by contrast, means a constant oscillating movement in the bearing and has to be allowed for in the lubrication design.

Rings and balls are made of through-hardened standard bearing steel. The open form brings no sealing element of its own, so sealing, initial filling and relubrication fall to the surrounding construction; the normal radial clearance is matched to a cylindrical seat with common fits.