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Dr. Guido Link
Head of Material process technology with microwaves
Institute for Pulsed Power and Microwave Technology (IHM)

Phone: +49 721 608-22275

Fax: +49 721 608-26595

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Material process technology with microwaves

Nowadays the use of microwaves for heating is familiar to anyone due to the domestic microwaves operating at 2.45 GHz. It is advantageous that the heat is generated inside the material volume, so the heating is quick, direct, and energy efficient. In particular, materials characterized by low thermal conductivity such as plastics, glass, ceramics and powders can be heated much faster. In the technical material process technology these advantages are opposed by problems also known from domestic microwaves: Heat distribution may be inhomogeneous, and the microwave penetration of some materials is insufficient, while others are more transparent to microwaves and hardly can be heated.

   

At the IHM solutions to such problems were investigated for both the industrial microwave frequency 2.45 GHz and in the millimeter wave range. This includes the determination of process parameters and product quality in comparison to conventional heating. Thus, microwave heating proves to be faster, more energy efficient and sometime allows for a reduction of the process temperature. Hence, in many cases the properties of the microwave processed materials can be improved, as it was shown, for example, for carbon fiber reinforced plastics (CFRP) and various ceramics.
 

HEPHAISTOS Experimental Center (HEC)

 

Our goal is the development of novel energy-efficient industrial microwave processes.

The modular microwave product line HEPHAISTOS represents a radical innovation in the field of heating and process systems for material treatment. These chamber systems provide an excellent homogeneous field distribution. The generation of uniform and homogeneous fields at 2.45 GHz over a wide area has been a key problem of industrial microwave technology. For many industrial applications and processes this is an essential prerequisite. There are several HEPHAISTOS microwave systems (walkable up to 7500l in volume) available for industrial process development. By use of this new energy-efficient and fast production processes can be developed for tailor-made industrial applications. This technology is licensed to our partner Vötsch Industrietechnik, Reiskirchen. 

       

Field of microwave systems and processes

Using common software tools such as CST Microwave Studio and COMSOL Multiphysics new microwave applicators are optimized for product specific processes. Based on this, new microwave systems are designed, built, and tested. For large-scale industrial applications inside large applicators which are difficult to simulate with commercial simulation tools new software concepts are developed. Unlike thermal ovens where the control response is substantially determined by the thermal mass of the furnace walls, in the case of microwave heating, the control behavior is determined only by the product itself. This places Special demands on flexibility of control concepts used in microwave Systems. With innovative, self-learning and model-predictive control algorithms one can minimize costly series of experiments for process optimization. Based on LabWindows CVI and LabView, process-specific Software tools for process control and Monitoring with appropriate data acquisition and storage are developed.   

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Field of materials characterization

The basis for for process and system developments is a fundamental understanding of the dielectric properties of the materials involved. For appropriate characterization different measurement methods are used and continuously developed and expanded with new measurement methods. Currently, various test stands are available:  
  • Coaxial probe for measurements of lossy materials
    (0.5 to 20 GHz frequency range, temperature range up to 150°C)
  • Transmission / reflection measurement method inside WR340 waveguide
    (2.45 GHz, temperature range up to 200°C)
  • Resonator method for low-loss materials
    (2.45 GHz, temperature range up to 1200°C)

    Current Research and development topics

    There exists extensive experience in the following fields of high-temperature process:
    • Keramik:  
      • Sintern
      • Entbindern
      • Calcination 
    • Glass:      
      • Heat Treatment 
      • Recrystallization 
      • Glass soldering 
      • Glass melting 
      • Melting of quartz sand
    • Phyllosilicates:
      • Dehydroxylation
      • Intercalation
      • Reduction of layer charges
    • Metals:        
      • Sintering 
      • Melting 
      • Smelting
    • Glass and carbon fiber reinforced plastics 

    Besides the optimization of the process parameters, the challenge is to work out the microwave specific advantages compared to conventional processes. Thus, the investigations are generally accompanied by a corresponding material characterization and microstructure analysis.
    Besides all these materials science applications, it is always a new challenge to investigate the potential of this innovative technology in terms of productivity and quality in industrial processes in collaboration with industry.