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Imbalance / Unbalance 1x

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:

  • 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
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.
  • The waveform should be very sinusoidal; if not there may also be misalignment, looseness or other fault condition
  • 180 ° out of phase
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.

Severity - High

This condition is likely to cause catastrophic failures if levels are allowed to get high. Expect vastly reduced life of the asset and it component parts. expect cracks in welds and strure. bearings will fatigue quickly. - Rectify ASAP

Other Causes

The Links below can also be the cause of the problem and be confusable

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