The previous articles mainly dealt with the preloading methods carried out on single bearings. There are plenty of occasions where paired or duplex type of bearings is used. Some typical examples would be the spindle bearing assemblies in cylindrical grinding, surface grinding machines.
As discussed in the article to duplex bearings, various mounting arrangements of the bearings are possible. The back to back arrangement of the duplex bearings is one of the important arrangement of mounting of a duplex bearing.
As seen in the picture, the following points can be noticed in the back to back arrangement of the duplex bearing.
1. The inner race of the bearing are normally relieved for inducing the preload with a clearance between the inner races.
2. During mounting on the shaft and preloading, by means of the lock nut provided. The inner races of the two bearings are driven towards each other.
3. The load lines i.e. the lines that pass through the contact point of the rolling elements tend to converge or meet outside the bearing.
4. It is due to this converge of load lines outside the bearing, this method is termed as the back to back arrangement.
This type of arrangement finds it application in the following areas.
· It is applied in areas that require good alignment of the bearing housings and the shaft.
· This arrangement provides very good moment rigidity and hence in applied in such areas.
· This arrangement is used in areas where the shaft normally tends to be warmer than the housing.
This type of arrangement is used in the spindles of lathes, milling machines, etc.
This arrangement requires good amount of geometrical tolerances to be maintained in the mounting areas. Geometrical tolerances such as Cylindricity, Concentricity, Parallelism in the bores where the bearings are mounted, perpendicularity of the abutting edges of the bearings, etc must be ensured properly for the best performance of duplex bearings working in back to back arrangement.
We will look into the other type of duplex bearing arrangements in the forthcoming articles.