A high pressure descaling pump was used to remove scale in a hot rolled band furnace. This pump was the key piece of equipment in this process which maintained the surface quality of the hot rolled band steel. Over a period of three years one pump continued to work normally, but the other pump vibrated vigorously. The motor, pump and the other system equipment were changed repeatedly, but the abnormal vibration was not eliminated. Vibration data from the two pumps was obtained, the modulation phenomenon existed in the vibration signal caused by the gear coupling misalignment was found, thus the envelope analysis based on the Hilbert transform was presented to demodulate the vibration signal. The frequency spectrum of the demodulated signal showed that the second order frequency characteristic was more obvious, which effectively revealed the fault information related with the gear coupling misalignment. It was found that the abnormal vibration was caused by coupling misalignment between the motor and the pump. After applying a more advanced alignment technique to thoroughly eliminate the misalignment in the coupling, the vibration was considerably reduced and the pump could work normally. This convincingly verified our analysis results and would dramatically reduce the ongoing maintenance cost for the descaling pump system.

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