August 2007
In This Issue...
Resources
|
Infrared Application of the Month #1:
Test Oven for Heating PBV Foil between Glass Plates
A manufacturer of PVB foil sought a method to heat the foil between glass plates. Heraeus Noblelight provided a system that included carbon infrared modules mounted on a conveyor system. The system provided double-sided heating; the conveyor featured speed control. Infrared power is controlled via two potentiometers, and temperatures are measured by two pyrometers. Adherence between PVB and glass can be tested in the laboratory so that the process parameters of the production machine can be changed at any time.
Click for more IR applications... [ Back to Top ]
Infrared Application of the Month #2:
Pre-gelling of MDF Panels
A manufacturer of MDF panels sought a method to preheat powdercoating prior to curing. Heraerus Noblelight furnished a system unsing mediumwave infrared heaters. IR technology prevents delamination of product and prevents color contamination. The process also provides a superior surface finish.
Click for more IR applications... [ Back to Top ]
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.
Read more about Carbon Heaters... [ Back to Top ]
Special Designs:
Mediumwave Small Area Heater
For applications requiring precision heating of a specific, small area, Heraeus Noblelight offers the Mediumwave small area heater. Approximate heated area of the example shown here is 2" x 2" and the power output is 400W.
A wide assortment of other special design heaters is available from Heraeus. Click HERE for details.
[ Back to Top ]
Engineering Aspects of Radiation Theory
continued from last month's issue
Reflection, Absorption and Color
Solids have atoms that are fixed in position relative to each other, and each atom has electrons that are tightly bound to it.
These are known as polarization ions.
A low frequency electromagnetic field falling on the surface of a solid would cause the electrons near the surface to
become more energetic and to oscillate at the applied frequency. After a time of perhaps less than a second the energy is
given off as a photon.
The solid does not absorb energy unless the frequency of the electromagnetic field is close to the resonant frequency of
the electrons. At this frequency the magnitude of the electrons' oscillation is sufficiently large for them to "bump" into one
another electrons, so the solid gains energy.
An electromagnetic wave always transports the same amount of energy per second. When the wave enters a solid the
increase in the electrons' oscillations causes the energy density to increase, so the wave travels more slowly. An electric
field is set up by the oscillating electrons and this causes a part of the electromagnetic field to be reflected.
Materials made only of atoms with only tightly bound electrons absorb very little energy. They are good insulators.
In many solids some of the electrons are not tightly bound, and some solids contain electrons that can move freely. These
are called conduction electrons. An electromagnetic wave causes conduction electrons to oscillate in anti-phase with it,
and this decreases the wave's energy density. The wave cannot increase its velocity so energy must be reflected. The
electrons screen the solid, and it takes only a few conduction electrons to reflect the wave totally.
The polarization electrons resonate at frequencies in the infrared and visible radiation bands and energy from infrared
and visible electromagnetic waves is absorbed by solids at these frequencies.
At higher frequencies the conduction electrons undergo smaller and smaller oscillations, so the wave penetrates more
deeply.
As the frequency increases through the visible range and the penetration increases the overall absorption before the
wave is completely reflected stays roughly the same. This is why most metal looks grey and not blue or red. The higher
conductivity of a solid the more light it reflects and the whiter it appears.
Very white surfaces are usually prepared from very transparent materials powdered into small particles. The light entering
the particles is reflected by the randomly oriented surfaces.
A solid appears a certain color because IR reflects one part of the optical spectrum preferentially to another part. A paint
achieves its color by mixing a fine transparent powder with other particles which absorb particular frequencies in the
visible spectrum. To make colored films the transparent powder is omitted.
To assess the reflection and absorption properties of paints, coatings and nonmetallic solids in the infrared spectral region
it will always be necessary to rely on empirical measurements. Properties vary not only with chemical composition but
also with fine structure, surface roughness and temperature. Where objects are heated with short wave infrared lamps as
much as 20% of the radiation can be in the red end of the visible spectrum. This inevitably leads to blue paints absorbing
more radiant energy than red paints.
This article will be continued in our next issue.
View more technical bulletins... [ Back to Top ]
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.
|
