An investigation of pulsed eddy currents for the development of a profile gauging system suitable for aluminium hot rolling mills.
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Date
2012-01-27
Authors
Kibirige, Betty.
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Abstract
This study investigates the Pulsed Eddy Current (PEC) technique, as an alternative
method, to establish its performance in a profile gauging system
for aluminium hot rolling mills. Radiation gauges are the popular choice for
profile gauging. However, they present poor accuracy (+-0.1%), are not safe,
require frequent maintenance and axe very expensive. A PEC system model,
was developed using analytical methods in order to allow for specimen conditions
that could not be easily emulated, to be investigated thus giving a
complete assessment of the PEC system. 'l'he model was validated against
experimental data. The coil probe and specimen were characterised as lumped
resistance and inductance and the characterisation gave a good fit between
simulated results and results from experiments and was therefore useful to the
investigation. Results frorn experiments and simulations reveal that changes in
specimen temperature show a point of crossing in the received signal agreeing
with findings made by other researchers, for other parameters. Furthermore,
results indicate that relative motion between a small probe and a massive specimen
does not affect the signal at the probes and a quasi-static approximation
was assumed for the model.
The developed characterisation of the aluminium specimen used in conjunction
with the developed system model indicate that differences in thickness of up to
4 microns at the minimum nominal thickness of 2 mm required for the finishing
mill could be gauged. The signal processing method described in the study
indicates that at a crown and wedge definition of 0.2 %, accuracies of +- 0.04%
were achieved, showing PEC to have better accuracy than radiation gauges.
Temperature changes in the specimen were successfully eliminated from the
profile measurement.This was achieved by using the relationship observed between
the temperature point of crossing (TOC) and specimen thickness for
different specimen temperatures. A method for harnessing profile measurements
from the PEC signal was also developed. PEC system could therefore
have potential in profile gauging systems for aluminiunm hot rolling mills.