ZEN SF61801-2RS Kugellager (12x21x5)

The principal dimensions are 12x21x5 mm at a weight of 0.007 kg; the further technical details are listed in the specification table. This variant features a contact seal and stainless steel. A sealing lip ages, a material resistance does not; in wet environments it is therefore the material that decides what happens at the end of the seal's service life.

This version stages the protection in two steps that behave differently over time. The contact seal on both sides lays an elastomeric lip against the inner ring and thereby shuts splash water, cleaning agents and fine dust out of the rolling chamber — an effect that is present from the outset but declines with the ageing and wear of the lip, and which is bought with a load-independent frictional torque and a permissible speed lower than that of open versions.

The stainless steel of the rings and balls behaves the other way round: its passive layer is retained over the operating period and protects the raceways precisely when the first step has lost effect or a cleaning cycle has carried liquid past the lip. This staging is the actual reason for the combination; neither constituent replaces the other.

In the design three resistances are to be assessed separately, because they belong to different material groups: that of the ring material against the medium, that of the sealing material against cleaning agent and temperature, and that of the enclosed grease charge, which is dimensioned for the service life and cannot be renewed. Chloride-bearing and acidic environments are to be considered separately here and not inferred from the material group alone.

Mechanically, the lower attainable hardness of the stainless material has to be taken into account, which shows in reduced load ratings. Normal radial clearance is matched to one interference-fitted ring and a moderate temperature gradient; the frictional heat of the seal and the differing thermal expansion of the material enter into that consideration.

Contact seals on both sides (rubber lip seal) — Dimensional/form-fit equivalent — verify suffix-level details for critical applications. Matching suffixes are also listed by SKF (2RSH, 2RS1), FAG (2RSR), NSK (DDU), NTN (LLU) and NACHI (2NSE).