Heat transfer can be effected in three different ways, by conduction,convection and or radiation.
The propagation of heat by conduction occurs between two bodies placed in contact, without a transfer medium established between them.
When the transfer of heat is effected trought a medium (like air), we speak of propagation of heat by convection.
Heat is propagated by radiation when it is transmitted from a heat source in from of electromagnetic waves, known as infra-red waves.
Infra-red waves are not visible because they have a longer wavelength than visible light.
Infra-red heaters for extrusion cylinders and injection presses, plates for thermoforming machines as well as for a variety of other applications, are based on the principle of radiation heating with electromagnetic waves.
These heaters consist of a double-walled, insulated stainless steel casing, inside of which are arranged a variable number of quartz tubes wiyh internal heating spirals. When both ends of the spirals receive a voltage, the Joules effect causes them to become incandescent and emit radiation in the low to medium infra-red spectrum.