Precision Control Systems ChamberIR E4 - Manual (Page 17)

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9.
Operation
General
The following paragraphs describe the general principles of Infrared Heating and the detailed
operation procedures for the Model E4 Quad Elliptical Heating Chamber.
Principals of Infrared Heating
General -
Heat energy from a resistance element is transformed into infrared radiant energy at the
surface of the heating element. Infrared radiant energy passes through the air (without heating
it) to the receiving object where it is absorbed and converted back into heat energy. The
receiving object then heats up. (Actually in an infrared installation, the air does heat up, but this
is due to convection heating from the work piece, reflector and lamp walls)
A substance ideally transparent to infrared energy converts none of the radiant energy to heat,
since the infrared energy passes through the substance. A surface with high infrared
absorptance characteristics converts almost all the infrared energy striking it into heat energy. A
surface having a low infrared absorptance characteristics reflect most of the radiant energy
striking it.
All materials absorb some infrared energy, and usually their absorptivity can be increased by
coating the surface with a material which is a good infrared absorber.
Temperature -
Maximum workpiece temperature is dependent on:
1. Heat Input Factors: Radiation to workpiece, area of workpiece being irradiated, and
absorptivity of workpiece.
2. Heat Loss Factors: Conduction to unheated masses, convection losses and radiation to
non-reflective surface.
Highest workpiece temperatures are attained when heat input factors are high, and heat loss
factors are held to a minimum. Overall efficiency is improved by blackening the heated side and
insulating the unheated side of the workpiece.
Workpiece -
For highest efficiency, the workpiece should have a dark, non-reflective (high absorptance to
infrared energy) surface; The workpiece should be located as close as possible to the focal line
of the heater.
Instrumentation -
Workpiece temperature can be monitored by a thermocouple attached directly to the specimen.
For measuring temperature on a moving web workpiece an optical pyrometer may be used.
Power Controls -
Section 5