ZEN SR4-2Z Kugellager (6,35x15,875x4,978)

The principal dimensions are 6.35x15.875x4.978 mm at a weight of 0.005 kg; the further technical details are listed in the specification table. This variant features stainless steel. In cleaning cycles a bearing position does not only become wet but also warm and cold again — the pressure change in the closed rolling chamber draws liquid inwards through every gap.

This version combines two protective effects that work on different levels. The shields on both sides close the rolling chamber across a non-contacting gap, keep the grease charge in the bearing and coarse contamination out without contributing a frictional torque; they are, however, no barrier against liquid, and in a flushed environment it must be expected that cleaning agents and water will reach the rolling chamber.

What counts after that is the material: stainless steel forms a passive layer that slows the attack on raceway and balls, and thereby takes on the share of protection that the geometry cannot provide. The alternation of operating states deserves particular attention, because a cleaning cycle warms the position and cools it again: the air enclosed in the closed rolling chamber contracts, and the resulting negative pressure draws liquid inwards through the gap, where it comes into contact with the grease charge.

The grease charge is enclosed by the shields and dimensioned for the service life, so relubrication is not foreseen; its resistance to the cleaning agents in use and its suitability for the respective industry are to be checked separately. The material choice has a mechanical cost: the attainable hardness lies below that of a through-hardened bearing steel, which is why the load ratings listed in the catalogue come out lower and a position under the same load has to be assessed accordingly.

Normal radial clearance is matched to one interference-fitted ring and a moderate temperature difference; the differing thermal expansion of the stainless material is to be taken into account when selecting the fits. Metal shields on both sides — Dimensional/form-fit equivalent — verify suffix-level details for critical applications. Matching suffixes are also listed by SKF (2Z), FAG (2Z), NSK (ZZ), NTN (ZZ) and NACHI (ZZE).