Learning outcomes to be assessed:

• Analyse the performance and reliability of machines.
• Design systems for maintenance, reliability and good performance.
• Propose and justify measurement and monitoring systems for plant.
• Predict the behaviour of mechanical engineering systems
• Criticise the design and implementation of machine systems from cost and efficiency standpoints.

Task - (A) - Vibration Case Study

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.
 
Task - Part B - Structural Failure Case Study

Background

A 6 ton pressure vessel - see Figure 2 dimensioned drawing - was being lowered onto a "stillage" or temporary supporting structure for testing outside a factory in the open yard. The lower lugs were attached to the stillage and as the slings were being loosened by the crane operator, the vessel tilted slightly.

At this point one of the legs of the stillage collapsed. Luckily the slings had not been removed, so the vessel did not fall - but a serious accident was only narrowly averted.

figIt was subsequently noticed that the ground on which the vessel and stillage were being placed sloped at 5 degrees.

Problem

1. Why did the leg collapse? What effects or details did the designer ignore?

2. Redesign the stillage to avoid similar incidents in future, without increasing its footprint (width, length) since space is needed around it for testing.

3. Make recommendations on safe lifting and mechanical handling of the vessel.

Tips: work out the weight and the center of gravity of the vessel. Check the load on each leg. Estimate the collapse load using a suitable formula and relevant assumptions.

Also look up the rules for similar mechanical handling procedures.

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.

Attachment:- Equipment Eng.rar