| Technology (History) |
Heating and drying processes as well as the thermal treatment of materials require increasingly more efficient technological solutions in many industrial processes in order to enable a profitable production and manufacturing. If you take a look at many of these industrial applications in detail, it is no wonder that the transfer of energy through electromagnetic radiation in the field of infrared waves is used more and more frequently for drying processes, thermal treatment of plastic materials and metal, soldering or gluing. It is in particular the spectrum of the short-wave infrared waves (0.76 µm to 2 µm) that has got more to offer than is normally known, like for example the use of UV drying systems has proven successful in the coating technology for cross-linking silicone systems or in label printing and flexographic printing for specific product segments and applications for the practical use of the *KIR technology. Starting with various areas of application in offset printing to package printing and the drying and melting-on of coating powders and coatings or also the drying of paintwork in the automotive sector. In addition, there are innumerable thermal processes ranging from adhesiving on bodywork parts to thermoforming processes in the plastics industry. In several areas of application, infrared heating and drying systems have been a familiar sight in a variety of processes for years, without, however, the users being able to specify them in more detail. Other areas still have to make do without them today despite the existence of considerable economical advantages of the use of IR radiation, and here in particular of the *KIR technology.
If you take a look at the electromagnetic spectrum, you see the division into different ranges and definitions of types of radiation, ranging from gamma rays, X-rays (also known as Roentgen rays), UV rays, visible light, IR rays to radio waves. Here we look at the range of the infrared rays. Infrared rays are divided into the ranges IR-A, IR-B and IR-C, to be physically correct. However, the familiar designations are not admissible for the customary classification and division of the rays per se into short-wave, medium-wave and long-wave as every solid body radiator emits a continuum and covers at least two ranges. IRK radiators emit rays in all 3 ranges. Here we intend to describe in particular the spectrum in the IR-A range between 0.76 µm and 2 µm in order to underline its enormous advantages for a profitable use. Over 20 years ago, the company MICOR®-Lichtstrahltechnik GmbH, emerged from Hoechst AG and still based in Kronberg/Ts. at that time, today based in Idstein, advertised using the slogan "All infrared rays are not equal". A technological development designated as MELTING by INFRARED CONCENTRATED RADIATION and developed by the department "New products" of the company Messer Griesheim, a subsidiary of the former Hoechst AG, at the end of the Sixties and used for example for joining techniques in the beginning, has consistently been refined for many industrial sectors until today. The life-cycle of so-called radiant emitter systems (near infrared, up to 3,200 K) have been increased from approx. 50 hours at that time to partly over 30,000 hours today, they have been taken over from lighting engineering and developed and made available for industrial applications. Many world-wide patents are witness to this long period of research and development, from which the users of today can profit. Close to visible light and using the highest intensity, short-wave infrared radiation is produced by the coiled filament of quartz lamps. The colour temperature is up to 3200 K (halogen lamps), but the range of up to 2400 K colour temperature is more important. The advantages of short-wave infrared radiation are hidden here. Taking the law of the physicists Stefan and Bolzmann
| A = | surface of the emitter (Take into consideration here that a *KIR emitter radiates with the surface of its entire reflector system) |
| T1 = | temperature of the coiled filament [K] |
| T2 = | ambient temperature [K] |
The higher temperature of the coiled filament of the short-wave emitters has the most significant influence here as this factor comes into the considerations with the value of the fourth power.
Long-wave IR-C radiators
In the case of long-wave IR flat panel radiators with approx. 1000 K, 50% of the radiation go into the direction of the object and 50% of the radiation go into the direction of the back, like for example the furnace walls. Reflector systems are of little use here because the radiator itself with its considerable mass forms a shadow for a possible radiation reflected by a reflector.
Medium-wave IR-B radiators
The same also applies to medium-wave IR radiators of up to approx. 1300 K and carbon radiators of up to approx. 1200 K that are equipped with very strong coiled filaments.
Here the coiled filament itself forms a shadow for the radiation reflected by the vapour-deposited gold plating. In addition, the vapour-plated coating comes undone as it is situated on the quartz cladding and therefore close to the coiled filament, at a temperature of approx. 700°C and thus also reduces the efficiency factor.
Short-wave IR-A radiators
A short-wave infrared radiator with its radiation maximum of 1.2 µm has a very thin coiled filament producing only a very slight shadow and is therefore an ideal prerequisite for a high-quality reflector system. The energy that is produced is transmitted contact-free by way of the radiation (approx. 6-7 % of it is the amount of light) that is transformed into heat only when it is absorbed in and/or on the material to be heated/dried. On the irradiated material, three important factors are decisive for the degree of heating, drying or cross-linking of materials or substrates. These factors are absorption, reflection and transmission.
If all factors were always clearly determinable and absolute, the widespread theory stating that it is possible to find a source of radiation that exactly corresponds to the absorption spectrum of a material or substrate would be correct. As for example a printing ink or coating never only consists of one material, this theory does not work. In addition, the transmission of the radiation is another important factor. It guarantees that the radiation penetrates into deeper layers and thus also absorption in the inside of a layer and not only on the surface. The result is an ideal mass and heat transfer in the material. In that way, paint on a watery basis, for example, can be dried extremely well using short-wave infrared radiation because a sufficient number of paint pigments, binders, resins, etc., absorb short-wave infrared radiation.
The total efficiency of a heating and drying system is much more decisive for a profitable use; a high-quality reflector system in combination with an efficient source of radiation guarantees the user a maximum of profit. Another important economical factor is the combination of *KIR radiation dryers on the basis of laminar air-flow. Contrary to medium-wave and long-wave infrared radiation, the medium air does not serve as a heat-carrier in the case of short-wave infrared radiation. There is no loss of energy in transmission, so that short-wave infrared radiation can be combined with convective drying in an ideal way; heated air only plays a secondary role for the thermal flow QAir because the heat transfer is effected by way of the absorption described above in the first place. MICOR *KIR DRYING SYSTEMS, for example, combine the two technologies in such a way that laminar air flows in the area of the *KIR dryer are transformed in turbulent ones. In that way, boundary layers that impede above all the mass transfer (expulsion of the solvent into the dryer air) are broken up, and the process of drying is accelerated.
In the meantime, the complete range of infrared radiation sources is produced in all types of designs by many companies and is distributed by even more dealers. This also includes standard elements for the preparation of complete heating and drying zones on the part of the customer as well as components for the electrical actuation of infrared radiators.
But people too often forget that applications engineering and process engineering know-how is as important as a special performance of the entire system for a successful use of the *KIR technology. This includes for example high-capacity reflector systems, process controls that are ideally adapted to the relevant production plant, as well as the complete layout of the drying processes with the relevant air engineering considerations in order to achieve a maximum of economy (costs, installed capacity, output), performance reliability and life-cycle.
*KIR heating systems as complete process systems with a maximum efficiency can also be used for realising and optimising thermal processes like for example heating of paper and cardboard webs as well as plastic foils for conditioning and embossing heating.