INFRARED RAY THEORY

Heat is the result of agitation of atoms and molecules of a body. The temperature of a body rises when agitation of its particles increases. To increase agitation an input of energy is necessary. This energy can be transmitted by different systems:

• by CONDUCTION: When thermal energy is transferred by solid materials

• by CONVECTION: When thermal energy is transferred by a fluid

• by IRRADIATION: When thermal energy is transferred by Electro-magnetic waves

Excluding the system of heating by contact, in the car body painting sector, only two systems of heating for drying can be used:
1. Conventional heating (As in spray booths)
2. Infra-red ray heating

Infra-red radiation or infra-red rays belong to the large family of electromagnetic waves. Electromagnetic waves are rays that travel through a vacuum at a speed of 300,000 km/sec. and have a length of a few tens of kilometres to a fraction of a billionth of a millimetre.
Looking briefly at all the families of waves we find those used in radiotelegraphy of kilometric length, those for radio broadcasting of medium length of thousands and hundreds of metres, and for television and radar of a length of a few centimetres. Proceeding towards the shorter waves that is those with lengths of between 0.75 microns and 1,000 microns we find the bands of the so called thermal waves or infra-red rays.

Infra-red rays transport the energy necessary to agitate and thus heat the molecules of the body towards which it is directed. As light waves are not luminous in themselves, in the same way infra- red rays are not calorific in themselves. Their action is shown meeting with a receiving body which absorbs them and transforms them into heat, and becomes itself a source of emission.
Practically, all bodies that have a temperature of above zero emit electromagnetic waves and thus infra-red. Due to irradiation the infra-red rays that leave the warmer body are transferred and absorbed by the body with the lower temperature.

Irradiation is the means of heat transmission that allows the heating of a body without contact nor interposition of a physical means with the thermal source; in fact the sun heats the Earth through space and air. It consists of the passage of heat in the form of electromagnetic waves from the body of higher temperature to the one with lower temperature. The infra-red radiation (IR) that makes this heating possible is the portion of the electromagnetic spectrum comprised between the visible field and microwaves; it propagates itself through air without heating it and it is used for superficial heating of objects having a sufficiently regular form and without parts “in the shade.”
An infra-red emitter is a body that can be brought to a high temperature through the passage of electrical current or using catalytic panels fed on methane gas or liquid propane.

In the treatment of metallic, plastic and wood surfaces to paint, IR drying is preferable when quality finishes are required. In fact IR rays are able to penetrate through the layer of paint deposited before baking and act heating the support. Thus heat is transmitted by contact with the paint, which is heated from the inside towards the outside. In this way a safe and uniform anchorage is obtained with the elimination of the known problem of premature drying of the outermost layer , which impedes the exit of gases which develop with the baking of the paint, causing quality defects such as dotting and lumps once dry.

CLASSIFICATION OF INFRA-RED RAYS

As already shown, thermal or infra-red waves have a wave length of between 0.75 and 1,000 microns, and are thus subdivided:

•  SHORT WAVE: from 0.75 to 3 microns

•  MEDIUM WAVE: from 3 to 8 microns

•  LONG WAVE: from 9 to 1,000 microns

•  It is possible to distinguish:

- Short wave emitters composed of quartz lamps and tubes

- Medium wave emitters composed of quartz tubes and metal radiant tubes or catalytic panels

- Long wave emitters made with ceramic elements.


TYPES OF INFRA-RED RAY RADIATORS

Infra-red radiators can be classified:

• Electric radiators 2,000° C (SHORT WAVE)

Wolframio under vacuum resistance. Wave length 0.9/1.6 microns

• Electric radiators 1,200° C(SHORT WAVE)
Quartz resistance. Wave length 2.0-2.3 microns

• Electric radiators 800°C (MEDIUM WAVE)
Ceramic resistance. Wave length 2.3 – 3.0 microns

• Gas radiators 400- 700° C

• Catalytic no flame anti deflagration and anti detonation with regulation of temperature emission, variable and relative to the adjustable wave length of 3.0 – 8.0 microns.