ZEN SMF74 Kugellager (4x7x2)

The mounting dimensions are 4x7x2 mm and the weight is 0.001 kg; technical details beyond these are shown in the specification table. This variant features stainless steel. With no sealing element supplied, the surrounding medium reaches the rolling contact directly; corrosion resistance therefore has to come from the material of the rings and balls rather than from a barrier in front of them.

In this version the material takes on the task that a seal would otherwise perform. Because the open form leaves the rolling chamber exposed, moisture, cleaning agents and residues meet the raceway and the balls directly, and the resistance of those surfaces decides whether the position can survive the operating routine. Stainless steel forms a passive layer for this purpose, which slows the attack; that layer depends on a sufficient supply of oxygen and does not protect against every medium — chloride-bearing and acidic environments are to be assessed separately and not inferred from the material group alone.

The price of this material choice is mechanical: the attainable hardness lies below that of a through-hardened bearing steel, and with it the load ratings listed in the catalogue lie lower, so that at equal load a position means either a larger size or a shorter calculated service life. Which components the material statement covers is to be taken from the designation: rings and balls are the usual reference, while the cage and accessory parts may carry a material statement of their own — at a wet position it is precisely the cage material that has to be checked as well.

Normal radial clearance suits one interference-fitted ring and a moderate temperature difference; the differing thermal expansion and strength values of the stainless material are to be taken into account when selecting the fits. Lubrication and sealing rest entirely with the surrounding design, which in cleaning-intensive operations is also the reason for the open form: the rolling chamber can be flushed and deliberately refilled instead of having to enclose one grease charge for the whole service life.