Halogen Heaters
The halogen heater consists of a bulb with an inlaid wolfram heating conductor protected from oxidisation by a gas mix containing halogen. The halogen heater emits IR radiation with a radiant power maximum in the short-wave IR range. The heating conductor is heated to temperatures of approximately 1,800 °C in a relatively short amount of time. As a result, visible light occurs outside of the IR range. An integrated thermocouple cannot be used with halogen heaters. The heaters are operated with integrated or external reflectors.
Due to its IR emission having a short-wave range, the halogen heater is useful for heating materials that absorb short-wave range IR radiation. This is not the case, however, with most materials. Using a halogen heater to heat a material that absorbs radiation predominantly outside of the range emitted by the halogen heater results in high efficiency losses. IR radiation not absorbed by the material causes the undesired heating of the material's surroundings.
Because halogen heaters also generate visible light, common industrial safety regulations often go unfulfilled (dazzling effect, cataracts). The amount of overall radiant power of halogen heaters emitted as visible light is 5–7 %, which makes no significant contribution to heating.
The additional following criteria are important in assessing a halogen heater:
The electrical operational life of halogen heaters is short compared to ceramic heaters of similar construction size if utilised where cyclic operations play a significant role in the heating unit. The frequent heating and cooling intervals hinder the chemical process of recombination between the heating conductor and the gas mixture inside the bulb.
Mechanical strength, e.g. with regard to vibration, impact, and collision with materials does not fulfil all requirements. Installation in a vertical position must be avoided to prevent compression of the coils and electrical short-circuiting.
Due to the comparatively high operating temperatures, it is necessary to construct high-quality reflectors, insulators and mechanical components and, if applicable, cooling devices such as electric fans.