Special cases

In certain applications the speed limits are superseded in importance by other considerations.

Low speeds

At very low speeds it is impossible for an elasto-hydrodynamic lubricant film to be built up in the contacts between the rolling elements and raceways. In these applications, lubricants containing EP additives should generally be used; see section Grease lubrication -

Oscillating movements

With this type of movement the direction of rotation changes before the bearing has completed a single revolution. As the rotational speed is zero at the point where the direction of rotation is reversed, a full hydrodynamic film of lubricant cannot be maintained. In these cases it is important to use a lubricant containing an effective EP additive in order to obtain a boundary lubrication film that is able to support loads.
It is not possible to give a limit or a rating for the speed of such oscillating movements as the upper limit is not dictated by a heat balance but by the inertia forces that come into play. With each reversal of direction, there is a danger that inertia will cause the rolling elements to slide for a short distance and smear the raceways. The permissible accelerations and decelerations depend on the mass of the rolling elements and cage, the type and quantity of lubricant, the operational clearance and the bearing load. For connecting rod bearing arrangements, for example, preloaded bearings incorporating relatively small rolling elements with a small mass are used. General guidelines cannot be provided and it is necessary to analyse the movements more precisely in individual cases. It is advisable to contact the SKF application engineering service.
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