SKF 6209/VA201 Kugellager (45x85x19)

The dynamic load rating of 31.5 kN characterises this bearing. The static load rating is 21.6 kN. This variant features extra-large radial clearance (C5). Very strongly increased clearance (C5) belongs at positions where a sustained temperature gradient between the rings consumes the greater part of the mounted clearance — on heated rolls, dryer sections or furnace equipment, for instance.

Very strongly increased clearance (C5) is the widest of the listed clearance classes, and it is not chosen for the fit alone but because heat is permanently supplied to the position from the inside. Where the inner ring is held at temperature by a hot shaft or a heated component while the outer ring cools through the housing, the inner ring expands permanently further, and the difference is taken directly out of the clearance.

If this allowance is set too small, the rolling contact is preloaded, the frictional torque rises, and the heat thereby generated closes the remaining clearance further — a course of events that reinforces itself. The opposite direction has to be assessed as well: in the cold state and at low radial load the full clearance is present, the load zone is narrow, and the ball set can slide on start-up before the operating temperature has established itself.

The open form suits this application picture, because heat removal can take place through the lubricant and the position is not tied to the temperature limit of a sealing material supplied with the bearing. The lubricant itself remains to be checked: it must withstand the same temperature that prompted the choice of clearance class, and relubrication intervals are to be set against that temperature rather than against a catalogue reference value.

Through-hardened standard bearing steel retains its hardness and dimensional accuracy only within the range stated for the series; whether a position may be operated above it is to be taken from the designation and the dimensional stabilisation data, and is not to be inferred from the clearance class.