Infrared Application of the Month:
Heating of Polished Tool Carrier
The finishing process for a higly polished metal tool carrier required heat to be applied prior to final cleaning. The manufacturer selected Heraeus Noblelight's shortwave infrared technology for its high efficiency. In this application -- as with many others in industry and processing -- infrared is superior to convection, induction and thermal contact heating methods.
Click for more examples of IR for industry... [ 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: Slot Heater
Infrared heater with a slot in one of the tubes, working like a drying channel for fibers or ropes. Twin tube made of quartz glass, gold coating around the whole heater. Fast response medium wave heater. The special slot design makes drying very intensive and efficient.
A wide assortment of special design heaters are available from Heraeus. Click HERE to for details.
[ Back to Top ]
Technical Learning: Workpiece Characteristics and Their Effects, Part 1
In modern industry, infrared equipment is being used to heat a vast range of products, varying in size and complexity. Each different product or material will respond in a different way to infrared heat depending on such factors as mass, surface area, geometrical shape, surface condition, color and conductivity.
Probably the easiest product to heat with infrared is a flat metal sheet with a matt black surface because for a given mass it has a large surface area compared with its thickness. Moreover, it can be placed very close to an infrared panel to receive uniformly the vast majority of the heat available. Its ability to absorb heat is very considerable as a matt black surface has a high emissivity value near to unity, The direction of the projected radiation would be normal to the receiving surface, thus any losses due to the Cosine Law would be eliminated. The simple conditions for rapid and very efficient heating are therefore all easily met. However, in the real world infra- red systems have to be designed to cope with products and situations which can be far more complex than this ideal example, and the aim of this chapter is to give an insight into the behavior of a representative sample of materials and products.
Heating trials with each new product or material remain a prudent step as the results provide a basis for the specification of an efficient and correctly sized oven.
Effect of wavelength
Plastic film An industrial application that illustrates the effect of heater wavelength is the use of infrared to heat shrink-wrap film. In trials two such films of the same thickness, one virtually clear the other aluminum colored were exposed to different heater panels. Aluminum colored film shrank rapidly with all wavelengths, but because of the lack of pigment in the clear film, the long wave heaters took three times longer to achieve the same shrinkage, the medium wave heaters took four times as long while the short wave types were the least effective.
Powder coatings and absorptivity
The curing of coatings on metal substrates has great relevance to the choice of wavelength for corridor ovens. For powder coating with thermosetting epoxy and polyester materials heat transfer does not need to take account of solvent release.
One might expect a fine white powder covering the surface of a metal to have an insulating effect on radiant heat transfer. However, polished metals, exemplified in trials by brass billets, absorb infrared heat very much faster with such a covering than without. This result applies equally before fusion of the powder and at the higher temperatures after fusion.
Long and medium wave infrared unlike short wave are almost blind to color difference.
Metallic powders are an exception to this rule, just as bright metals are more reflective to the longer Wavelengths than to the short. Prior to fusion of the metallic powders, heat absorption occurs at the level of the other coatings. However, a step change in the heating rate occurs at the point of fusion. The eight remaining powders indicate that little if any adjustment would be needed to allow for a change of color or texture in a medium or long wave oven.
Continued in our next issue...
View a variety of 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.
|
