December 2005
In This Issue...
Resources
|
Infrared Application of the Month #1:
Drying Water-based Paint on MDF Panels
A manufacturer of decorative wood panels uses Heraeus Fast Mediumwave IR technology to control process and save energy.
Seamless integration of the infrared module into the production machine allows IR power to be constantly switched on and off, conserving energy. The process is controlled by limiting temperature rise of the wooden panels to between 20°C and 50°C.
This efficient system now processes 10m of decorative wood per minute.
Click for more IR applications... [ Back to Top ]
Infrared Application of the Month #2:
Manufacture of Automobile Airbags
A carbon infrared heating system helps improve the manufacture of side impact airbags and has significantly reduced scrap levels on the manufacturer's coating line.
Typical of all textile factories, the environmental humidity is quite high and, as the airbags' nylon fabric is hydroscopic, its moisture content can be as much as 3-5% when the relative humidity rises above 38%. This was causing a problem at the coating stage for the heavier cloth used for inflatable curtains. Heraeus IR technology lowered moisture content to 2% to ensure the correct adhesion, drying and surface finish of the silicon coating and to reduce scrap levels.
Click for more IR applications... [ Back to Top ]
Tech Center Spotlight:
Fast Response Mediumwave Heaters
Stable and Efficient
Fast response medium wave heaters can transfer high power over long lengths. The high absorption by surface layers and films makes them particularly applicable to thin materials, while the fact that they also have a penetrative effect fits them for use in plastics processing. The heaters can be switched on and off in seconds and are consequently best suited for processes with short cycle times.
Because infrared heaters can be individually matched to a particular application, heating and drying processes can be seamlessly integrated within finishing operations – and with minimum disruption to existing manufacturing lines.
Read more about Fast Response Mediumwave Heaters... [ Back to Top ]
Special Designs:
Watercooled Heater
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.
Click HERE to download a brochure on Heraeus shortwave watercooled heaters.
[ 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.
|
