Failure of Angular Contact Bearing on Newly Overhauled Motor - Conlusion
Written by Stephen H Shakeshaft
Monday, 07 June 2010 18:30
Page 3 of 3
Unfortunately the entire responsibility for the failure rested firmly with the contractor.
It was accepted that there were significant holes in their knowledge about bearing specifications.
The workshop had a good general reputation and this carried it through, but the client lost three days production from their plant. This loss dwarfed the cost of the motor failure.
The client however, can take some of the blame for not specifying in the work scope exactly what was to be done and what was to be supplied by the workshop nor was any guidance provided regarding bearings types or specifications.
In fact no written work scope was given except a shipping note saying "Please Overhaul the Motor and Return to Site".
The client could have been criticised for not having a spare motor, but it is impossible to carry spares for everything. The motor had given good service over many years and the case for tying up capital in what should have been a fairly low risk spare was probably weak.
I carried out a training course to familiarise all the office and shop floor staff with bearing designations.
A system of cross checking the bearings that came out of machines with the bearings that were ordered and went back into machines was implemented.
Overall, it was a serious failure but it highlighted a weakness that could catch out a large number of clients and contract repair workshops alike.
The work scope given to a repairer from the client should detail the exact sizes, suffix, clearance grade, cage material and desired make of rolling bearings. Anything less leaves the client open to the bearing being chosen by the contractor who may not either understand fully the requirements or may often choose to fit a cheaper bearing to save on costs.
Additionally, this particular motor was a flameproof design and the documentation process should generally as a whole have been much more robust when overhauling and re-certifying the motor to Ex standards.
Stephen H Shakeshaft IEng MIMechE MIET MIIE
20th May 2004.
Stephen H Shakeshaft Consulting Ltd
75 Mere Bank, Davenham, Northwich, Cheshire, CW9 8NB.
Tel 01606 331558
Mobile 07779 190087
Stephen H Shakeshaft is a Mechanical Engineer based in the United Kingdom. He is the Principal Consultant and Director of Stephen H Shakeshaft Consulting Ltd., an engineering consultancy specialising in optimisation of existing assets and engineering design of new build projects.
Stephen is a registered professional engineer in the UK and is a corporate member of both the Institution of Mechanical Engineers and the Institution of Engineering and Technology.
Stephen H Shakeshaft Consulting Ltd. can be found on the internet at the following URL www.shs-consulting.co.uk