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How We Analyse Machine Failures

When machines experience a failure we recommend that you take a structured approach to solving the underlying problem.  By following these 6 stages we ensure that the real root cause is identified for our customers.

1. Collect Historical Failure Information

Gather as much technical information on the failure and operation of the machine as feasibly possible.  You will need to know an accurate account of the failure history but you will also need to fully understand how the machine operates.

2. Do a Site Evaluation

There’s nothing like a good ‘hands-on’ investigation on-site to evaluate the problem.  Make sure you are there when the machine is taken apart and take plenty of photographs.  If this is not possible, you can make conclusions on photographs alone – something we have successfully done for clients abroad on many occasions.

3. Perform a Macro-Analysis

Take a step back and take a broad overview of the situation rather than narrowing the approach to investigation of the apparent immediate problem.  Perform a macro-analysis of the machine by means of quick and often approximate calculations (Excel is a powerful and often under-utilised tool at this stage).  This often eliminates many of the possible causes of failure and enables you to focus on the key areas for more detailed investigation.

4. Undertake a Detailed Investigation / Micro-Analysis

Perform a micro-analysis now you are homed-in on the areas that could be the real root cause of the problem.  Do detailed calculations on the forces/loads on the components in question, check the drawings of these parts and any available measurement data.  Ask yourself the questions:

  • Did it fail by design (it was never going to operate for the design life)?
  • Were the parts made to drawing?
  • Were they installed correctly?

5. Consult Known Failure Modes

Our engineering team have a wealth of knowledge on machine and other Tribological failures.  We have distilled this knowledge into The Tribology Handbook, which is a quick concise guide to known failure modes of bearings, gears, cams etc.  Also review the pages in this section of our website on particular failures.

We suggest you start with these pages:

6. Conclude The Root Cause

By now you should have a fairly good idea as to what the root cause is and what the solution will be long term.  It is vitally important that your hard work is written up in a report rather than being communicated verbally – all too often these are valuable documents and critical conclusions can get either mis-interpreted or lost.  If you’re still stuck – help is at hand!  Please contact us and we’d be happy to help at any stage of the process.


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Failures That We Regularly Deal With

The rest of this page lists the typical types of failures observed when a machine fails.

General Failures

These failures are not machine-specific and can occur in all sorts of general purpose machinery.

  • Abrasion
  • Adhesion
  • Fatigue
  • Fretting
  • Friction
  • Half speed whirl
  • Lubrication
  • Oil whip
  • Pitting
  • Rotor Dynamics
  • Scuffing
  • Seizure
  • Vibration
  • Wear
  • Wiping

 

Plain bearing failures

The identification of the cause of damage or failure in plain bearings is crucial before remedial action can be taken to prevent further recurrence. The first step is a visual examination of the damaged component. The following photographs can then be used to find a match. “A picture is worth a thousand words.”

However, do not stop at this stage. More than one mechanism of failure can lead to superficially similar bearing damage. Moreover, once failure has been initiated, the original mechanism may lead to other failure mechanisms and it is essential to identify the original cause.

Typical failures observed in plain bearings are listed below:

  • Lubrication breakdown
  • Wear
  • Fatigue
  • Cavitation erosion
  • Fretting
  • Chemical effects
    • Thermal ratcheting
    • Electrical damage
    • Incompatible materials

     

    Click to see how to diagnose plain bearing failures

     

    Gear failures

    These classes of failure are more specific to gears and gearboxes.

    • Tooth breakage
    • Tooth pitting
    • Tooth scuffing
    • Plastic flow of teeth
    • Abrasive material in lubricant
    • Gear tooth corrosion
    • Crossed helical gears
    • Worm gears
    • Monitoring of gear tooth damage

       

      Click to see how to diagnose gear failures

       

      Rolling bearing failures

      Examination of failed components is a crucial element in failure diagnosis and is frequently the starting point in any failure analysis. It should not be overlooked, however, that the initial cause may lead to secondary damage that obscures the original event. Care and experience may be needed to separate primary and secondary effects.

      It is important to realise that rolling bearings have a finite life, the repeated high stressing at the contacts between rolling elements and tracks eventually resulting in fatigue damage to the surfaces. There are, however, a large number of other reasons why rolling bearings fail and it is crucial to distinguish between these and normal fatigue when investigating failures.

      Following are the main mechanisms of bearing damage and failure, but examination of used bearings that have not failed can still give valuable information on the conditions under which the bearing has been operating.

      • Track markings
      • Fatigue failure
      • Premature fatigue
      •  

      • Fitting damage
      • Lubrication failures
      • Loss of internal clearance
      •  

       

      • Wear
      • Fretting damage
      • Electrical damage

      Some Case Studies..

      We’ve put together some real-world examples of failures we’ve investigated and what the outcome was from our analysis.  Click the link below to see these case studies.

      Click to see case studies