Introduction

Bearings of all sorts are often crucial components of engineering devices. Sometimes they determine the life and reliability of those devices. The basic application is that of supporting some device that is mounted on and rotates with a circular shaft. This covers innumerable devices of all sizes running at all speeds. Perhaps the best known to most people and not just engineers is the electric motor where the armature rotates in bearings that are built into the frame. Figure 16-1 is of a small electric motor that has been dismantled. On the left is the armature on its highly-polished shaft in the part of the frame carrying the brushes and on the right, is the main body of the frame with the two permanent magnets. The bronze oil-less bearing is visible in the main body. The device being carried by the shaft is the armature with its windings and the commutator. Here we are concerned with the bearings and it is the high quality of the rubbing surfaces that should be noted. Electric motors may run in plain bearings or in ball races. I have shown some small ball and roller races in figure 16-2. In every case the balls or rollers are captured in a cage. It is often claimed that the cages are fitted to prevent the balls or rollers rubbing each other. There is a much more important reason for using a cage.

 

With the exception of bearings that are constructed by sintering a powder of perhaps leaded bronze to give a bush of the correct shape but with voids, up to 30% of the volume, that can be filled with liquid lubricant or graphite to give a long lasting “dry” bearing. All bearings use a lubricant that may be liquid or grease and it is that fact that leads to this chapter where the main thrust will be about bearings that use liquid lubricants.