February 2009
In This Issue...
Resources
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Infrared Application of the Month #1:
Bacteria Reduction on Pies
A food processor required a means to reduce bacteria on the top of a Pastiera Napoletana (a confection of whole wheat and cheese popular during the Easter season). Because part of the pie is wet and part is dry, targeted lamps of different intensity were required to produce a homogeneous end product.
Heraeus Noblelight provided carbon twin tube infrared heaters, chosen for their proven and superior ability to provide targeted heat.
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Infrared Application of the Month #2:
Drying Resin on Wiring
A manufacturer of copper wiring for electrical and electronics applications sought a method for drying the resin jackets of the wiring. They called on Heraeus Noblelight's team of application engineers for assistance. The Heraeus team was tasked with developing a solution to a challenging problem: because of the thickness of the coating, the drying method had to apply heat in a way that would allow even drying at all coating depths, form the surface all the way down to adjacent to the copper wire itself. Hot air had been tried previously, but the results were unacceptable. Short wave heating technology from Heraeus -- along with a new resin designed to allow even drying -- solved the customer's challenge.
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Tech Center Spotlight:
Carbon Mediumwave Heaters
High heating efficiency and rapid cool down make the mediumwave carbon heater from Heraeus the only medium-wave heater to offer you shortwave response times. Suitable for all medium-wave applications, this heater also offers the capability to match temperatures to the optimum absorption wavelength for each application. Together, these features eliminate overheating and contamination of sensitive substrates.
A particular large portion of medium wave radiation is absorbed in water, solvents and plastics and converted into heat. This allows significant benefits: carbon heaters dry printing inks, with less stress for the paper because the radiation acts more intensively on the ink. The high power heater increases print drying speed and reduces drying time. It also heats plastics in a targeted manner, with less heating of the surrounding environment.
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Special Designs:
Ring Heater
Designed for horizontal use, this shortwave ring heater, internally focused for intense rapid heat-up of rods, stakes etc. is made of quartz glass, has a diameter of 8 mm, a two-sided connection, and is available with or without the Heraeus gold reflector.
A wide assortment of ring heaters are in stock at Heraeus. Click HERE to 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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