Vibration problem

Excessive vibration in a fan

Centrifugal fan on foundation used to force heated air over drying malt Specification:

- 2.5 m dia impeller
- spherical roller bearings
- multiple v-belt drive
Operation problems:
- Pulsations, on closure of inlet vanes (flow control device)
- Excessive vibration levels in spite of careful impeller balancing.
- Prominent second and third harmonics in the frequency spectrum
- When run down, irregular knocking noises produced.

Also damage to machine identified on inspection:

-
Failure of two 24mm bolts holding steel pedestal to concrete foundation block
- Partial disintegration of grouting between pedestal & foundation
- Some damage to shaft surfaces where bearings attached.

Using accelerometers, vibration amplitude was measured at various heights down the pedestal and foundation:

Questions

1. What are the likely causes of the vibration problems?

2. What would you, as plant engineer, recommend to prevent recurrence?