Infrared Application of the Month:
Thermoforming of Bioplastics
Because they are produced from renewable raw materials, are biodegradable and are not petroleum-based, environmentally-friendly bioplastics are an increasingly popular packaging material. A manufacturer of a vegetable-based bioplastic forms trays, blister packs and sorting inserts for food packaging.
Because bioplastics are sensitive to long heat-up times, a heat source for the thermoforming phase was required that provided nearly instant heat-up. The manufacturer chose a modular infrared heat system from Heraeus Noblelight. The IR system heats up in less than two seconds, minimizing water loss, and the modular system provides homogeneous temperature distribution across the product for consistent quality.
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Infrared Application of the Month:
Cutting Laminated Glass
A laminated glass manufacturer sought a heat source to aid in the glass cutting stage of production. The manufacturer already understood the advantages of IR in the glass lamination phases, and turned to the application experts at Heraeus Noblelight for a solution to this new challenge.
A method currently used is to score the glass, break it and then separate the foils. The foils can be separated particularly well with the aid of infrared radiation. A Heraeus Noblelight fast response medium wave infrared lamp (with a gold reflector) heats the foil only in the small crack resulting from scoring. The foils can then be easily separated by pulling them apart or with cutting tools. Because Heraeus IR lamps can be custom-manufactured in specific lengths, the manufacturer was able to apply the heat process to large sheets, cutting production time.
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Tech Center Spotlight:
Shortwave Heaters
Fast and Intensive
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.
Performance advantages include high radiation density in the most compact space; near-instant heating-up and cooling down times; optimized reflection; much more.
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Special Designs:
Spiral Heaters
With heaters in spiral form discs, tubes or rods made of plastics, metal or glass can be heated homogeneously. Compared with conventional heating methods, spiral heaters can provide savings in energy, time and costs. Heraeus offers a wide range of heaters for special applications.
Click HERE to download a brochure on Heraeus spiral heaters.
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
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.
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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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