Vibration analysis of rotating machines

Vibration analysis is one of the methods used to monitor the health of rotating machines in operation. This is part of a predictive maintenance policy for industrial production equipment.

The objectives of this approach are to :

• reduce the number of breakdowns ;

• make production tools more reliable ;

• increase availability;

• better management of spare parts stock, etc.

Based on the vibrations regularly collected on a rotating machine, vibration analysis consists in detecting possible malfunctions and monitoring their evolution in order to plan or postpone a mechanical intervention.

Two technologies are available for vibration monitoring:

• by direct measurement of the displacement of rotating parts (machine shafts). These measurements, their interpretation and applications are not covered here. The technology involved is cumbersome. A common application is the monitoring of machines with hydraulic bearings (oil wedges). This monitoring is almost always carried out on-line, i.e. in real time. Sensors continuously measure shaft displacements, enabling alarms to be triggered immediately in the event of a malfunction;

• by measuring the acceleration undergone by fixed machine parts (casings). In this case, the means used are much more accessible to smaller structures. Using an accelerometer connected to a data collector, the technician collects the vibrations experienced by the machine casings. This technique lends itself equally well to on-line monitoring, as to periodic monitoring carried out during rounds according to a pre-established schedule.

Heavy industry, which generally uses turbomachinery, often uses a combination of the two technologies for high-performance vibration monitoring of its production equipment.

However, if the shafts of the machines being monitored are bearing-mounted (which is the case for the majority of them), periodic monitoring by measurement of the fixed parts enables a very detailed analysis of the condition of the machines. The objectives set out above are thus achieved, provided the activity is entrusted to competent, experienced personnel. In addition, the costs of preparation and implementation are considerably lower than those of eddy-current sensor technology, making periodic monitoring an attractive option for small and medium-sized businesses. Even if they don't have the skills in-house, they no longer hesitate to outsource the vibration monitoring of their rotating machinery.

The purpose...