Machine fault diagnosis

It has been suggested that this article or section be merged with Fault detection and isolation. (Discuss) Proposed since September 2010.

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2010)

Machine fault diagnosis is a field of Mechanical Engineering concerned with finding faults arising in machines. A particularly well developed part of it applies specifically to rotating machinery, one of the most common types encountered. To identify the most probable faults leading to failure, many methods are used for data collection, including vibration monitoring, thermal imaging, oil particle analysis, etc. Then these data are processed utilizing methods like spectral analysis, wavelet analysis, waveform analysis (in the time domain, because spectral analysis usually concerns only frequency distribution and not phase information) and others. The results of this analysis are used in a root cause failure analysis in order to determine the original cause of the fault. For example, if a bearing fault is diagnosed, then it is likely that the bearing was not itself damaged at installation, but rather as the consequence of another installation error (e.g., misalignment) which then led to bearing damage. Diagnosing the bearing's damaged state is not enough for precision maintenance purposes. The root cause needs to be identified and remedied. If this is not done, the replacement bearing will soon wear out for the same reason and the machine will suffer more damage, remaining dangerous. Of course, the cause may also be visible as a result of the spectral analysis undertaken at the data-collection stage, but this may not always be the case.

Data collection methods

Methods used to collect data include vibration measurement, thermal imaging, oil particle analysis and others.

Data analysis methods

Spectral Analysis, Wavelet Analysis, Time-domain Waveform Analysis, others.

Common faults diagnosed

When the machinery to be diagnosed includes rotating components, the most commonplace problems found are:

• Imbalance (Unbalance)
• Bent shaft
• Shaft misalignment
• Eccentricity
• Rub
• Resonance
• Soft foot
• Looseness
• Beat (acoustics)
• Sleeve bearing faults
• Belt problems
• Rolling-bearing faults
• Gear faults
• Machining vibrations

Schemes of applying diagnostics

Fault diagnostics in usual industrial practice need to be applied according to guidelines. This need arises from the fact that diagnostics on their own may be capable of saving a single machine if monitoring is adequate, but it is impossible to apply them to all the equipment. The investment needed to either install continuous condition monitoring sensors on all the machinery in a factory or to check enough samples from all machinery on a regular basis would be forbidding.

As a result, using fault diagnostics to meet industrial needs in a cost effective way, and to reduce maintenance costs without requiring more investments than the cost of what is to be avoided in the first place, requires an effective scheme of applying them. This is the subject of maintenance, repair and operations; the different strategies include:

• Condition-based maintenance
• Planned Preventative Maintenance
• Preventive maintenance
• Corrective maintenance (does not use diagnostics)
• Integrated Vehicle Health Management

See also

• Accident analysis
• Condition monitoring
• Diagnosis
• Maintenance testing
• Reliability centered maintenance
• Failure Analysis
• Failure
• Fault detection and isolation

References

• Taylor, James I. (1994), The Vibration Analysis Handbook (Second ed.), Vibration Consultants, ISBN 978-0-9640517-0-6 
• Taylor, James I. (2000), The Gear Analysis Handbook (First ed.), Vibration Consultants, ISBN 978-0-9640517-1-3 
• Taylor, James I. (2004), The Bearing Analysis Handbook (First ed.), Vibration Consultants, ISBN 978-0-9640517-3-7 
• Mobley, R. Keith (2002), An Introduction to Predictive Maintenance (Second ed.), Butterworth-Heinemann, ISBN 978-0-7506-7531-4 
• Mobley, R. Keith (2000), Vibration Fundamentals (First ed.), Butterworth-Heinemann, ISBN 978-0-7506-7150-7 
• Mobley, R. Keith (1999), Root Cause Failure Analysis (First ed.), Butterworth-Heinemann, ISBN 978-0-7506-7158-3 
• de Silva, Clarence W. (2007), Vibration Monitoring, Testing, and Instrumentation (First ed.), CRC, ISBN 978-1-4200-5319-7 
• Harris, C.M.; Piersol, A.G. (2002), Harris' Shock and Vibration Handbook (Fifth ed.), McGraw-Hill, ISBN 978-0-07-137081-3 
• Adams, M.L. (2001), Rotating Machinery Vibration - From Analysis to Troubleshooting (First ed.), Marcel Dekker, ISBN 978-0-8247-0258-8 
• SKF (2003), Vibration Diagnostic Guide (First ed.), SKF Inc. 
• Slavic, J; Brkovic, A; Boltezar, M (December 2011 vol. 17 no. 14 2164-2174), Typical bearing-fault rating using force measurements: application to real data, Journal of Vibration and Control, doi:10.1177/1077546311399949, http://lab.fs.uni-lj.si/ladisk/?what=abstract&ID=60 
• Luft, M. (1998), Machine Diagnostics: Quick and Easy through FFT Analysis (First ed.), PRUFTECHNIK AG 
• Smith, J.D. (2003), Gear Noise and Vibration (Second ed.), Marcel Dekker, ISBN 978-0-8247-6005-2 
• McMillan, R.B. (2004), Rotating Machinery: Practical Solutions to Unbalance and Misalignment (First ed.), Marcel Dekker, ISBN 978-0-8247-5052-7 
• Norfield, D. (2006), Practical Balancing of Rotating Machinery (First ed.), Elsevier, ISBN 978-1-85617-465-7 
• Muszynska, A. (2005), Rotordynamics (First ed.), Taylor & Francis, ISBN 978-0-8247-2399-6 
• Walker, D. (2003), Torsional Vibration of Turbomachinery (First ed.), McGraw-Hill, ISBN 978-0-07-143037-1 

External links

• Understanding and Reducing Fan Vibration