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Different Causes of Vibration in Rotating Equipment

November 16, 2006
(Alignment and Balancing)

Each cause emits a different set of symptoms. Misalignment between a drive motor and shaft typically results in a dominant 2X harmonic component of vibration. Structural resonances can occur at 1X operating speed or at a harmonic frequency (2X, 3X, etc.) and the effect may vary depending on speed. Looseness in any mechanical connection between bearing caps, bearing pedestals, or foundations can cause excessive vibration levels or amplify a pre-existing unbalance problem. In most cases, a mechanically loose connection will yield harmonic levels of vibration (2X, 3X, etc.) and may also yield sub-harmonic levels of vibration (X/2, X/3, etc.). The common symptoms of a crack propagating in a fan are both an emergence and growth of a 2X component of vibration along with a change in the phase and amplitude of the 1X vibration component. Rotor mass unbalance is the most common cause of excessive vibration in most rotating equipment with a primary symptom being a high 1X vibration level.

Tip provided by:
LORD Corporation
Tel: 1-877-ASK-LORD


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