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BEARING VIBRATION MONITORING


How to pinpoint bearing failure at an early stage


Envelope signal processing is a relatively new technique used to pinpoint bearing failure at an early stage. This relatively unknown technique can minimise the risk of machine damage and failure. Andy Pye reviews the work of Hansford Sensors


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n any manufacturing or processing plant, machine breakdown has significant consequences. Productivity and profitability are usually affected and there is also a health and safety risk. Surprisingly, however, the cause of the breakdown is rarely identified. Instead, the bearings that were damaged and failed are often simply replaced, in the hope that they may last longer next time. However, bearings don’t fail without reason. There is always an explanation for why they do, and it is usually for one of a number of reasons: the machine is running unbalanced, misaligned or at a critical speed; a bearing hasn’t


been fitted correctly; over- or under- lubrication has occurred; or maybe the wrong lubricant has been used.


VIBRATION ANALYSIS


When problems such as these occur in industrial equipment, sensitive accelerometers are used to detect and analyse the vibrations. This technique is known as vibration analysis and it can identify bearing failure in the very early stages – when there is a microscopic defect on the raceway, for example. This allows issues to be detected prior to machine breakdown and action can be taken proactively to minimise damage to assets. There is one important problem


❱❱ Critical vibration signals could be masked by other vibration components in industrial machinery


to note about this technique though: the identifying signal is usually drowned out in all the other noise produced by the machine.


WHAT IS ACCELERATION ENVELOPING? It is vital to catch bearing defects as early as possible, to stop them developing into more serious problems, and one way of achieving this is to use a signal processing technique called acceleration enveloping. It works by progressively filtering out unwanted parts of the vibration spectrum until the signal of a bearing defect can clearly be seen. Acceleration enveloping is most commonly used in roller bearing systems but can also be applied in areas such as electric motors and gearboxes. It is a key factor in the success of condition-based maintenance (CBM) programmes. Without acceleration enveloping,


DAQ, Sensors & Instrumentation 2017 /// 5


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