Radiant Heater

Match the wavelength to the material, not to the wattage

Infrared is not one thing. A short-wave halogen lamp, a medium-wave quartz tube and a long-wave ceramic panel all put out the same watts and get absorbed very differently. Metals and dark coatings take short wave well. Water, most plastics and paint films absorb medium and long wave in the top fraction of a millimetre, which is exactly where drying and forming need the heat.

Getting this wrong is not a small loss. Energy at the wrong wavelength passes through the work or bounces off it and ends up warming the machine frame.

Line of sight is the whole design

A radiant heater only heats what it can see. A shadow behind a rib, a fixture, or the edge of a tray is a cold spot, and no amount of extra power fixes it. Lay the elements out over the work the way you would lay out lights over a bench: even spacing, overlapping coverage, and nothing between the element and the surface.

At the ends of a row the coverage always falls off, because the last element only radiates onto the work from one side. Either run the elements past the edge of the work or add reflectors at the ends.

Response time changes how it is controlled

A halogen heater reaches full output in under a second and goes cold almost as fast. That is a real advantage on a line that stops and starts — nothing scorches during a pause. But it demands proper control: a solid state relay or thyristor, and a sensor fast enough to keep up. A ceramic panel is the opposite. It takes several minutes either way, so it suits a steady process and is forgiving of a slow controller, but it will happily cook whatever is under it when the line stops.

Keep the reflector clean and the housing cool

The reflector is not decoration. In most radiant assemblies close to half the output reaches the work by way of the reflector, so dust, fumes and overspray on it come straight off the heating rate. Clean it on the same schedule as the rest of the machine.

The housing behind the reflector needs air moving over it, especially on halogen. Sealed into a box with no ventilation, the terminals and lead seals run far above what they were designed for, and they fail before the element does.

Ventilation is a process variable, not a comfort issue

If the process gives off water vapour or solvent, that vapour absorbs infrared before it reaches the work and it drifts. Extraction over a radiant drying tunnel is not only there for the operator; it keeps the heating consistent from the first part of the shift to the last.

Mounting and orientation

Halogen lamps have a preferred mounting position, usually horizontal, and life drops sharply if that is ignored. Quartz tubes need room to expand along their length — clamped rigidly at both ends they crack at the first heat cycle. Leave the fixings free to slide and support long tubes at the middle.