Duplex of paired bearings are two similar bearings of same type i.e. the bearings could be deep grove, angular or taper roller bearings. The bearings are arranged next to one another.
Duplex bearings can also be mounted with the provision of a small spacer in between them. This is done in some cases to increase the moment rigidity of the bearings.
Let us now see the advantages of using these bearings.
· Duplex bearings provide better axial and radial rigidity to the shaft. Thus it provided more stability to the shaft to rotate.
· Duplex Bearings have the capability to take up heavy bidirectional and unidirectional thrust loads.
· Duplex bearings are more easy to assemble expect for the care that must be taken during their preloading.
· Duplex bearings provide the least runout to the shaft on which they are mounted.
Apart from all these advantages, Duplex bearings tend to have the following drawbacks.
· An increased torque is required during startup condition to overcome the increased friction in the bearings.
· The bearings tend to have a reduced speed capacity due to their constructional aspects.
· Duplex bearings are highly sensitive to thermal expansion due to temperature rise. It is very important to have a control on the working temperature of the bearings.
· Duplex bearings require more of a lesser transition fit and cannot accept interference fits, which can damage them.
· These bearings are also poor in taking up misalignments and may lead to increased torque fluctuations in the bearing due to misalignment.
Duplex bearings are matched sets of bearings. The inner or the outer races of both the bearings are normally selectively relieved to induce an offset. This offset is utilized during the preloading of the bearings.
Care must be ensured during the mounting that only the relieved faces are facing each other. This is to ensure that the bearing gets preloaded properly. The duplex bearings are assembled in the following arrangements
1. Back to Back Arrangement.
2. Face to Face Arrangement.
3. Tandem Arrangement.
Each of the above arrangements is quite significant based on the type of they are designed to carry. We will look in detail on the mounting arrangements of duplex bearings in the forthcoming articles.