ABSTRACT
However, the root cause of excessive unbalance-excited vibration can be other than the rotor being too far out of balance. As explained in Sec. 8, Chapter 9 an inadequately damped resonance condition can cause excessive vibration, even when the excitation force is not large, as Fig. 4 in Chapter 1 clearly shows. If for any reason the operating speed is quite near a critical speed, then the vibration levels can readily become excessive for continuous operation. A critical
error, component deterioration, or support/foundation changes over time. For similar causes, transient passage through a critical speed may exhibit vibration levels that are dangerously high even for a short-duration passage through critical speed, such as in a coast-down of the machine.
