SKF QJ308 MA Vierpunktlager (40x90x23)

As a four-point contact ball bearing, this bearing carries axial loads in both directions and moderate radial loads. The dynamic load rating of 71.5 kN characterises this bearing. The static load rating is 58.5 kN. The limiting speed is 14000 rpm. The design is laid out for axial load; any appreciable radial force belongs at a separate, radially carrying bearing position.

In the four-point contact ball bearing the raceways are of gothic-arch form, so each ball bears at four locations under axial load and a single row supports longitudinal forces in both directions; the split inner ring makes the high ball count and the separate mounting of the rings possible. The application profile follows directly from that: the design takes on the axial location of a shaft and replaces an adjusted pair, while the radial load falls to an adjacent radial bearing.

If it is loaded radially nonetheless, the contact moves into an unfavourable four-point condition with increased spin slip, which is why the outer ring is usually guided radially free in the housing. The normal radial clearance here also determines the contact angle that establishes itself, and with it the axial stiffness of the bearing position.

The open form leaves sealing and lubricant retention to the surrounding construction; for the design, axial force, the radial share and the fits should be assessed together.