Simulation and Experimental Study to Investigate the Effect of Bent Shaft on Vibration Spectrum

Rotating system is the backbone of machinery. With the high speed demand of today’s machinery, it becomes more important than ever. There are many causes of bending of shaft. Shafts may bend during transportation, installation and also due to excessive heat. Bending of shaft results in high vibration which creates stress on bearings and couplings. If such fault is ignored, catastrophic failure will result. Therefore it is important to be able to diagnose this fault. Bent in the shaft can be identified by studying the vibration spectrum on the bearings. Researchers have reported that the dominant peak is observed normally at 1X if the bend is near the center of the shaft and at 2X if the bend closer to the coupling end. This data can be misinterpreted for misalignment but bent shaft frequency component is 1800 out of phase. The present study deals with the experimental investigation of detecting unique vibration signature for bent shaft having bent at coupling end. Experimental studies are performed on a rotor system test apparatus to predict the vibration spectrum for shaft bending. The rotor shaft vibrations are measured by using FFT analyzer. These acquired spectrums are compared with results obtained from simulation study by using ANSYS for confirmation of experiment results and these results are verified as reported in the literature.