SKF W618/4 Kugellager (4x9x2,5)

The dynamic load rating of 0.449 kN characterises this bearing. The static load rating is 0.173 kN. The limiting speed is 85000 rpm. This variant features stainless steel. Stainless steel shifts the limit of this design from the sealing to the material: what matters is no longer what is kept out, but what the raceway may meet without damage.

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.