Abstract:
Condition monitoring through the use of vibration analysis is an established and
effective technique for detecting loss of mechanical integrity of a wide range and
classification of rotating machinery. Equipment rotating at low rotational speeds present
an increased difficulty to the maintenance engineer, since conventional vibration
measuring equipment is not capable of measuring the fundamental frequency of
operation, also, component distress at low operational speeds does not necessarily show
an obvious change in vibration signature.
This thesis presents a study of high frequency stress wave analysis as a means of
detecting early stages of loss of mechanical integrity in slow speed machinery, the first
of its kind. Investigations were centred on the Rotating Biological Contactor (RBC)
which is used for sewage treatment in small communities and rotates between 0 .6 to 1
revolutions per minute.
The mechanism of stress wave generation was the relative movements between mating
components that were experiencing loss of mechanical integrity, for instance, the loss of
tightening torque between clamped components. Development of the stress wave
monitoring technique was accomplished by firstly, simulating a variety of mechanical
faults on the test-rig, and secondly, by numerous ‘on-site’ tests on operational RBCs and
their bearings. In application of this technique to operational RBCs and bearings, as well
as cataloguing evidence of mechanical deficiencies associated with RBCs operated
within the Severn Trent Water region, the author inspected 261 RBCs and covered over
35,000 miles, contributing to the uniqueness of this research programme.
This research has provided Severn Trent Water limited with a PC-based monitoring
system comprising an AE transducer, pre/post amplifiers, ADC board and software on
which all diagnosis was undertaken. Furthermore, during the process of investigating
reasons for the mechanical failures of the RBC, technical information was uncovered
thereby assisting Severn Trent Water in perusing a more robust design of RBC.
Moreover this work has assisted Severn Trent Water to maintain that envious reputation
that over a number of years not one of the RBC sewage treatment works has failed its
consent level as set by the Environmental Agency.