July 2007
In This Issue...
Resources
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Infrared Application of the Month #1:
IR Booster to Preheat Powdercoated Compressors
A compressor manufacturer's process required preheating of the compressors. Their previous means of doing this -- a tunnel oven -- was effective, but higher efficiency was desired. Heraeus Noblelight supplied a solution in the form of fast mediumwave heaters. The new system allows semiautomatic power control via potentiometers. Compressors are detected at the entrance of the oven, so the heaters turn on only when compressors are present. The quick on/off characteristics of the fast mediumwave heaters makes this possible, increasing efficiency and line speed.
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Infrared Application of the Month #2:
Drying Waterbased Varnish on Linoleum
A manufacturer of linoleum flooring replaced their hot air system for drying lacquers with a carbon twin-tube infrared heating system from Heraeus Noblelight. The new system facilitated in-line drying, greatly increasing production speed.
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Tech Center Spotlight:
Shortwave Twintube Heaters
Shortwave IR heaters from Heraeus are suitable for all applications in which the attainment of high temperatures in the shortest possible time is what counts. Their emission maximum is between 0.9 and 1.6 micron. Among their advantages are high radiation density in the most compact space, and low space requirements.
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Special Designs:
Watercooled Heater
Heraeus designed a special twin tube lamp heater with one water cooled channel. This heater type transfers a large amount of energy (more than a million watts per square meter) in a very short time. Temperatures of more than 1000°C on the surface of the product can be achieved within seconds. Popular applications include coil coating, edge coating on wood, and surface sealing.
For more on watercooled heaters, click HERE.
A wide assortment of other special design heaters is available from Heraeus. Click HERE for details.
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Engineering Aspects of Radiation Theory
Technical Learning: What is Infrared Heating?
All bodies above zero temperature (-273°C) emit infrared radiation in the form of waves which pass through space and are
partly absorbed by bodies they strike. This radiation forms a part of the electromagnetic spectrum and has the strongest
heating effect of all. The nature of the radiation is the same in essence as that of x -rays, ultraviolet, visible light and radio
waves.
It has been known since the mid nineteenth century that infrared radiation, or group of rays, behave in a similar manner to
visible light as far as transmission, reflection and absorbtion are concerned. The concept of radiation is not easy to define,
as both corpuscular and oscillatory aspects are involved.
The electromagnetic energy that is emitted from the surface of a heated body is called thermal radiation, and consists of a
continuous spectrum of frequencies extending over a wide range. The spectral distribution and the amount of energy
radiated depend chiefly on the temperature of the heating surface.
Careful measurements show that for a given temperature there is a definite frequency at which the radiated power is
maximum. Furthermore the frequency of the maximum is found to vary in direct proportion to the absolute temperature. At
room temperature, for example, the maximum occurs in the far infrared region of the spectrum and there is no perceptible
visible radiation emitted. But at higher temperatures the maximum power is radiated at correspondingly higher
frequencies, and at about 500°C a body begins to glow visibly. The rate at which energy is radiated by a hot body is also
found to be dependent on temperature.
Electromagnetic radiation is created by oscillatory electric charges, and the frequency of oscillation determines the kind of
radiation emitted. Radio waves and microwaves exist at the lower frequencies and x -rays and gamma rays exist at the
higher frequencies. In between these is a range of frequencies known as the optical spectrum, with infrared, visible light
and ultraviolet light.
The optical spectrum is characterized by the fact that the radiation can be directed, focused and controlled by mirrors and
lenses and that prisms and gratings can be used for dispensing it into a spectrum.
Ordinary sources of radiation in the optical spectrum, such as tungsten filament lamps, fluorescent lamps and flames
consist of a very great number of molecules which have electric charges that oscillate independently of each other,
producing a range of frequencies.
Unlike these sources, excited individual atoms and molecules give out radiation at various discrete frequencies, which are
characteristic of the particular kinds of atom or molecules involved. The optical spectra of most atoms are quite complex,
but a few elements such as the hydrogen and the alkali metals have relatively simple spectra.
The most simple of all is the hydrogen atom which consists of an electron and a proton. The electron may be considered
as being able to inhabit only certain levels about the proton and to move from one level to another it needs to gain or lose
an amount of energy, called a quantum.
Small quantities of energy are measured in electron -volts (eV), and for radio waves a quantum is about 0.000004 eV, for
infrared a quantum is about 0.004 eV, and for x -rays and gamma rays it is about 40,000 eV.
When an electron moves to a lower energy level a discrete amount of energy in the form of a photon is emitted from the
atom. This photon takes the form of electromagnetic radiation. Movement between the lowest levels produces a photon of
far ultraviolet, movement between the next lowest levels produces visible light and near ultraviolet; movement between
the middle levels produces infrared.
A photon may be considered as having a cross sectional area, like that of a ball; the larger the ball the greater the chance
of it hitting something. Similarly, atoms and molecules can be considered as having a cross sectional area and materials
made of larger atoms and molecules are likely to absorb photons more quickly than materials made of small ones.
However, materials absorb infrared selectively. Virtually all transparent solids show broad absorption bands that extend
into the visible frequencies.
This article will be continued in our next issue.
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That's it for this month's issue of Application Notes for IR Heating. Feel free to encourage your colleagues to subscribe. Just click HERE to send them an invitation to subscribe. It's quick, easy, FREE, and no-obligation.
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