The IR radiation

The Infrared (IR) radiation is an electromagnetic field with a wavelength ranging, conventionally, from 300 µm to the edge of visible red light (approx. 700 nm). These wavelengths correspond to a frequency range of approx. 1 to 400 THz.
Infrared radiation is popularly known as "heat" or "thermal radiation". Unlike heat transmitted by conduction or convection, thermal radiation can propagate through vacuum.

Infrared radiation can be used as a deliberate heating source and its use has become quite widespread in several application fields, from ambient heating to cooking, from health-care applications to industrial processing.

Due to the high IR energy absorption rate of many substrates, thermal radiation cannot penetrate them deeply and is therefore an ideal method for surface heating applications (coating, laminating, paint drying, etc.).

Typical advantages of the IR heating method are:

- fast and easily adjustable heating rate
- quick pre-heating of the heat source
- low thermal inertia
- accurate process control
- partial / localised heating is possible- high energy efficiency (one-stage heat transfer from the source to the product)
- no need for contact with solid surfaces or hot fluids (no-contact heating)
- environmentally friendly (no fumes, no noise released by the heat source)
- flexible and modular system

Microscopically, IR waves are typically emitted or absorbed by molecules when they change their vibrational-rotational status. Emission and absorption of infrared radiation by the matter occurs across a spectrum of wavelengths, but in most cases only a limited region of the spectrum is of practical interest, depending on the specific purpose of the IR application (industrial, scientific, diagnostic, etc.).

Various sub-division schemes of the IR spectrum have been elaborated according to convenience, and that of practical use in the industry with reference to thermal processes is the following:

- Short-wave Infrared (SWIR): emission peak in the frequency range 1-2 µm
- Medium-wave Infrared (MWIR): emission peak in the frequency range 2-4 µm
- Long-wave Infrared (LWIR): emission peak in the frequency range 4-10 µm

The higher is the temperature of the IR source, the lower is the wavelength of the emission peak and the higher is the total amount of energy emitted.

A large variety of IR sources (emitters) operating at temperatures up to 1,200°C and radiated power values up to 150 kW/m2 are available in the market, that can be conveniently selected according to the specific application required.

The Long Wave IR (LWIR) technology

Some heating processes require, or can be carried out at, high or relatively high temperatures: in this case, short or medium wave IR emitters (quartz lamps and tubes with tungsten or carbon emitters, filled or not with halogen gas) can be conveniently used and several tens kW/m2 of radiant energy can be applied.

In other cases, however, such drastic process conditions are not acceptable, and the process can be carried out more conveniently at lower temperature and radiant power values, ie. by using long wave IR (LWIR) emitters.

STALAM specialises in the LWIR heat processing technology, having developed and patented innovative electrical radiating panels, which offer all the advantages of the IR technique while eliminating the problems associated with long and medium wave radiations, typically product surface defects such as colour changes, chemical degradation, bubbles, fissures, etc.

Additional benefits of the LWIR technology are:

- higher penetration depth
- lower specific power (gentle heat treatment)
- higher energy efficiency transfer
- lower temperature gradients within the product
- perfectly even energy distribution on large surfaces
- longer life of the emitter