Recent Question/Assignment

55 - 7947 Equipment Engineering and Design
Vibration problem (7947 PBL)
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?
Remember – study the example report and the assessment criteria. The solution is partly technical and partly management, as always!
All Theory and discussions must be directed and related to this problem. Lists of general/generic design issues, management techniques etc are not acceptable and will lose marks; all discussions must be related to the problem at hand.
Assessment criteria –PBL reports, module 7947 equipment engineering & design
See Marking Criteria sheet on Black Board.