A bent shaft (or bent rotor) is a phenomenon in which the shaft or rotor of a machine is curved or bent. This defect can be measurable outside the machine housing (bent shaft) or inside the machine (bent rotor). A bent shaft can occur, for example, as a result of the machine being idle for a long time. When we encounter a bent shaft, we observe increased vibrations in the radial (away from the axis of rotation) and axial (in the direction of the axis of rotation) direction. Axial vibrations can be higher than radial vibrations.
FFT analysis of the vibration spectrum will usually show 1X and 2X rotational frequencies. If the amplitude of 1X revolution is dominant, it indicates that the shaft bend is closer to the center of the shaft. Conversely, if the 2X RPM amplitude is dominant, then the bend is closer to the end of the shaft.
A bent shaft can have a negative impact on machine performance and can cause additional wear or damage to components. Therefore, it is important to identify this defect using vibration diagnostics and carry out the necessary repair or maintenance to minimize the negative effects on the machine.