PSI - Issue 39

Nabam Teyi et al. / Procedia Structural Integrity 39 (2022) 333–346 Author name / Structural Integrity Procedia 00 (2019) 000–000

335

3

Fig. 1. Rotor defect due to misalignment.

Rotor defects due to bow: Here the axes of the bearings or bushings that support the shaft are perfectly in alignment, i.e. their axes are collinear, but, the shaft itself is not perfectly straight throughout its length (Fig. 2). Meaning, there is some bending of the shaft somewhere along its length, mostly around the middle portion. This may occur due to wrong manufacturing of the shaft or rough handling of the structure or overloading. Continued operation of such a bowed shaft is dangerous for the machine of which it is part of.

Fig. 2. Rotor defect due to bow. Rotor defects due to mass unbalance: Here the defect is due to mass unbalance due to non uniform distribution of mass of either the shaft material or the disc material or both. This is a common phenomenon in any material in its natural state of being (intrinsic) due to various inconsistencies and complexities in the manufacturing or extraction of the materials. This uneven distribution of mass in materials results in a little shift of the actual centre of mass from the geometric centre of the component. This small distance between the mass centre and the geometric centre is called eccentricity (Fig. 3). Also, during the life of the rotor in its static state there is a natural possibility of accumulation of dust or other substance on some locations on its surface, or chemical reactions on its surface due to environmental situations, which further accentuates mass unevenness. And during the rotor’s dynamic state, there is a natural phenomenon of wear due to friction adding to the mass unevenness.

Fig. 3. Rotor defect due to mass unbalance.