Preparations for mounting and dismounting
Before mounting, all the necessary parts, tools, equipment and data need to be at hand. It is also recommended that any drawings or instructions be studied to determine the correct order in which to assemble the various components.
Housings, shafts, seals and other components of the bearing arrangement need to be checked make sure that they are clean, particularly any threaded holes, leads or grooves where remnants of previous machining operations might have collected. The unmachined surfaces of cast housings need to be free of core sand and any burrs need to be removed.
The dimensional and form accuracy of all components of the bearing arrangement needs to be checked. The bearings will only perform satisfactorily if the associated components have the requisite accuracy and if the prescribed tolerances are adhered to. The diameter of cylindrical shaft and housing seats are usually checked using a stirrup or internal gauge at two cross-sections and in four directions (fig 1). Tapered bearing seats are checked using ring gauges, special taper gauges or sine bars.
It is advisable to keep a record of the measurements. When measuring it is important that the components being measured and the measuring instruments have approximately the same temperature. This means that it is necessary to leave the components and measuring equipment together in the same place sufficiently long for them to reach the same temperature. This is particularly important where large bearings and their associated components, which are correspondingly large and heavy, are concerned.
The bearings need to be left in their original packages until immediately before mounting so that they will not be exposed to any contaminants, especially dirt. Normally, the preservative with which new bearings are coated before leaving the factory does not need to be removed; it is only necessary to wipe off the outside cylindrical surface and bore. If, however, the bearing is to be grease lubricated and used at very high or very low temperatures, or if the grease is not compatible with the preservative, it is necessary to wash and carefully dry the bearing. This is to avoid any detrimental effect on the lubricating properties of the grease.
Bearings should be washed and dried before mounting if there is a risk that they have become contaminated because of improper handling (damaged packaging etc.).
When taken from its original packaging, any bearing that is covered by a relatively thick, greasy layer of preservative should also be washed and dried. This might be the case for some large bearings with an outside diameter larger than 420 mm. Suitable agents for washing rolling bearings include white spirit and paraffin.
Bearings that are supplied ready greased and which have integral seals or shields on both sides should not be washed before mounting.