NACHI 6902-2NSECM Kugellager (15x28x7)

For this NACHI bearing, 15x28x7 mm and a weight of 0.02 kg apply; the specification table holds the further technical particulars. This variant features a contact seal. At a sealed position the narrowed tolerance does not act on the frictional torque — that is set by the lip — but on stiffness, axial behaviour and vibration in the mounted state.

This version combines two features that concern different properties, and it is worth keeping them apart. The contact seal on both sides determines what enters the rolling chamber and what leaves it: it keeps moisture and fine dust away, holds the grease charge dimensioned for the service life inside the bearing, and in return produces a load-independent frictional torque and limits the permissible speed.

Normal radial clearance with narrowed tolerances, by contrast, determines none of that; it reduces the scatter of the clearance within the normal class and thereby acts on the properties that depend on the residual clearance — radial stiffness, axial mobility under load, vibration behaviour and the size of the load zone in the mounted state.

The frictional torque of this version is dominated by the lip and changes only slightly through the narrower clearance distribution; anyone seeking a reproducible breakaway force will find it here not in the clearance class but in the design of the seal. The combination makes sense where a closed, maintenance-free position is assembled in series and its mounted state can no longer be adjusted: the seal secures the ambient conditions, the narrowed tolerance secures the sameness of the units.

The choice of class itself is not replaced by it — interference fit, frictional heat of the seal and external temperature gradient still consume the same share as under the undivided normal clearance, and where that share is large, a wider clearance class remains the applicable answer. Through-hardened standard bearing steel supplies the hardness and dimensional accuracy on which a narrow distribution can rest at all; the temperature limit of the sealing material is to be taken from the designation.