Symptoms: 1X radial (V & H)
The technical way to describe unbalance is as a condition where "a shaft's geometric centerline and mass centerline do not coincide”, or where "the center of mass does not lie on the axis of rotation”. In other words, there is a heavy spot somewhere along the shaft.
Types of Imbalance / Unbalance
There are two types of unbalance: static and couple.
Static imbalance is characterised by:
We expect to see a high peak in the spectrum at 1X turning speed of the shaft. It is often higher in the horizontal direction compared with the vertical direction due to stiffness.
- Radial vibration @ 1x rpm.
- high axial as well as radial amplitudes
- often higher in the horizontal direction compared with the vertical direction due to stiffness
- The waveform should be very sinusoidal; if not there may also be misalignment, looseness or other fault condition
Phase is the best indicator. Compare vertical to horizontal phase – there should be a 90° phase shift. See also static and couple unbalance, and unbalance for vertical machines and overhung machines.
- 180 ° out of phase