Bearings apart from being mounted on the shafts and housings have to be preloaded properly for their proper functioning. Preloading is the methodology by which we remove the internal clearance in the bearing by applying a permanent thrust load to it. In other terms we can say that we push the bearing to such an extent that it has to move only in the groove (raceway) and cannot move axially in either direction. We will look on when and how to preload bearings in this article.
Now let us look on why the need for preloading of bearing arises. It is mainly for the following reasons
· In order to eliminate the radial and axial play in the bearing which would be inherently present even after a bearing is mounted radially on a shaft.
· By preloading, we tend to eliminate all the unnecessary clearances, which induces a rigidity to the bearings and thus to the system the bearing supports.
· By reducing the clearances, we also tend to control the rotational accuracy of the bearing. Thus it helps to reduce the non-repetitive run out that could occur because of the clearances.
· By construction and definition, the rolling elements must always roll around in order to carry and distribute the load evenly. When a clearance is present, there is every chance for the rolling element to stop rotating and just skid on the raceway. Preloading the bearings thus helps in preventing the skidding of the balls on the raceway of the bearing.
There are also some negative effects when the bearings are preloaded beyond their limit. The effects are
· Excessive preloading of the bearings can cause increased heat generation in the bearings, which tends to reduce the speed capability and fatigue bearing life.
· Excessive preloading also causes the bearing to get loaded extremely, causing changes in the power requirement required to drive the system. A very high amount of torque is necessarily required to overcome this tightness in the bearing and thus increasing the energy or power demand for driving the system.
Various methodologies for the preloading of the bearings can be found. These methods of preloading are as important as the design and selection of the bearings.
We will look at the various preloading methods in the forthcoming articles.