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Continuous on-line monitoring of industrial processes is a growing area of application for thermography, and the technique has become established in a number of industries.
Thermography is a non-contact technique and enables observations to be made whilst the plant is in operation and under load. The user can also make his inspection at a safe distance and it is often possible to carry it out with safety guards and fences still in position.
Some examples of continuous on-line monitoring are described below.
Glass Fiber Insulation
Glass Fiber Insulation is produced by atomising liquid glass through a nozzle to produce strands of glass which are deposited onto a conveyor.
The mat of fiber is then laid on a paper substrate and formed into rolls.
If gobs remain unatomised, they cool much more slowly than the remainder of the fiber and can cause ignition of the backing paper or process rolls, damaging the plant and causing lost production.
A thermal imager can be used to monitor the temperature of the fiber mat, giving an alarm if high temperature particles are detected to enable the operators to take action to prevent fires.
Radiographic Film Manufacture
During the manufacturer of radiographic film a thermal imaging system is used to control the application of the polymer liquid primer to polyester film prior to applying the X-ray sensitive coating.
It is essential that the primer covers the full width of the film to enable the sensitive coating to be applied reliably.
Thermal studies showed that there is a significant temperature difference between areas of the film where the primer has been applied and those where it has not.
The temperature pattern on the film is monitored continuously using a thermal imaging system and the inter-relationship of the average temperature within selected areas is used to indicate when the primer has not been correctly applied.
Continuous Condition Monitoring in the Steel Industry
Thermal imagers are used to monitor the condition of the refractories of hot metal ladles and other vessels in the steel industry.
In one particular application, the hot metal ladle is brought to an inspection station at which three thermal imagers provide a view of the complete periphery.
The temperature pattern is recorded and a data logging system enables information to be stored for individual ladles.
The trend of the temperature pattern over a period of time is observed and it is possible to forecast when repair or re-lining will become necessary.
The incidence of break-downs of hot metal is reduced but at the same time the actual frequency of repair work can also be reduced because knowledge of the state of the lining is available and accurate predictions of the urgency of repairs can be made.