1. What is concentricity (alignment) of Bearings?
Concentricity (alignment) of Bearings is when the surfaces of the inner ring (inner shift) and outer ring (outer shift) of the bearing are parallel to each other. In addition, for a thrust bearing, the blocking surface should be perpendicular to the center of the shaft.
2. What is the effect of eccentricity (non-alignment) on Bearings?
All Bearings have internal gaps that allow thermal expansion and a small acceptable amount of eccentricity when working. When the gap is insufficient, the bearing tempurature will increase, the metal parts rub together, reducing bearing life.
When Bearings lose its concentricity (out of alignment), it causes vibration and noise, great friction and over heat.
3. How to check eccentricity of Bearings
a. Attach the measuring gauge to measure the static and dynamic eccentricity of the outer ring with the shaft. The test is similar to the inner ring, with the gauge mounted on the body and the probe mounted on the inner ring, while rotating the shift.
The allowable deviation is 1.0 mil/inch (1.0 milliradian). That is, a diameter of 4 inches allows a deviation of 4.0 mil/ inch. Note that 1 mil = 0.025mm.
b. A simple way to gauge an off-center bearing is to rotae the shaft slowly to feel and use the stethoscope to hear. This approach is highly dependent on the experience of the maintainer.
Usually, manufactures contro eccentricity of bearings by controlling one or all of the following parameters:
- Tight fitting
- Assembly tolerance
- Tools and pressure when assembling
- The perpendicular angle of the shoulder shaft
- The accuracy of the machine body.