NTN 6307 LLBC3/5K Kugellager (35x80x21)

This NTN bearing measures 35x80x21 mm and weighs 0.48 kg; the specification table carries the supplementary technical details. This variant features increased radial clearance (C3). Because the non-contact seal introduces no heat of its own, the temperature gradient at this position is determined from outside — and increased clearance (C3) therefore answers an environment, not the bearing.

This combination stands out in that its two features act independently of one another, which simplifies the design work. The non-contact seal follows the contour of the inner ring with an elastomeric sealing body down to a narrow distance without touching it: no load-independent frictional torque arises, no heat source at the inner ring and no wearing contact point, so the permissible speed lies close to that of the open form and the barrier effect is retained over the operating period.

Increased clearance (C3) holds an allowance ready for the shares that consume the mounted clearance in service — the interference fit on the shaft and the temperature gradient between a warmer inner ring and an outer ring coupled through the housing. Because the sealing takes no part in that gradient, it originates here in the surroundings of the position: in a hot shaft, an adjacent process or the power lost in a fast-running drive.

That makes the estimate of the residual clearance in the warm running state more direct than in a version sealing by contact, where part of the warming arises inside the bearing itself. It remains to be observed that the gap does not permanently hold back liquid and very fine dust, and that the grease charge is enclosed and dimensioned for the service life, so its ageing at the elevated operating temperature can become the limiting quantity.

At low radial load the wider clearance has to be taken into account, because the load zone turns out narrower. Through-hardened standard bearing steel sets the frame for hardness and dimensional accuracy; the temperature limit of the sealing material is to be taken separately from the designation.