NSK 6004 ZC3 Kugellager (20x42x12)

The principal dimensions are 20x42x12 mm at a weight of 0.068 kg; the further technical details are listed in the specification table. This variant features increased radial clearance (C3). Increased clearance (C3) belongs at positions that run warm — and a version shielded on one side is frequently found exactly where oil from the surrounding space reaches the rolling contact.

This version combines a directional design with an allowance in clearance, and both features act on the same process: the temperature in the rolling contact. On the closed side a non-contacting shield holds back coarse ingress without contributing a frictional torque; on the open side lubricant from the surrounding space can reach the rolling contact and carry frictional heat away with it.

It is precisely this passage that distinguishes the version from a doubly closed, grease-filled variant: the heat leaves the bearing not only through the rings but also with the lubricant, and that changes the temperature gradient between inner and outer ring. Increased clearance (C3) nevertheless holds an allowance ready, because at such positions several shares typically come together: the interference fit on the shaft, a heat flow supplied from outside and an ambient temperature above that of a free-standing drive.

What governs here too is the residual clearance in the warm running state, which should lead neither to a preloaded rolling contact nor to an unnecessarily narrow load zone. The asymmetry of the design also implies a mounting instruction: the shielded side belongs to the loaded surroundings, the open side to the interior supplied with lubricant, and this assignment is to be recorded in the assembly documents.

The gap of the shield holds back neither liquid nor fine dust; where these are to be expected, the sealing belongs in the surrounding design. Through-hardened standard bearing steel sets the frame for hardness, dimensional accuracy and the ratings listed in the catalogue.