Rotor Rub
Rotor Rub produces similar spectra to Mechanical Looseness when rotating parts contact stationary components. Rub me be either partial or throughout the whole revolution. Usually generates a series of frequencies, often exciting one or more resonance's. Often excites integer fraction sub harmonics of running speed (1/2, 1/3, 1/4, 1/5, ....1/n), depending on location of rotor natural frequencies. Rotor rub can excite many higher frequencies (similar to wide-band noise when chalk is drug along a blackboard). It can be very serious and of short duration if caused by shaft contacting bearing Babbitt; but less serious when the shaft is rubbing a seal, an agitator blade rubbing the wall of a vessel, or a coupling guard pressing against a shaft.
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