A focal point of the Fraunhofer-Center HTL is the optimization of the heat treatment processes used in manufacturing ceramics, metals and metal-ceramic composites. Eligible processes are drying, debinding, pyrolysis, sintering, melt infiltration, but also various methods from the area of melting metallurgy. Potential of improvement often exists in the temperature time cycles, the furnace atmosphere or the set-up of the charge in the industrial furnace. The optimization goal is to receive high and reproducible product quality with optimized material-, energy- and cost efficiency of thermal processes (see Project EnerTHERM). Both the furnace perspective as well as the perspective of the charge are equally considered.
In-situ High Temperature Measurement Method
Fraunhofer-Center HTL develops ThermoOptical measurement devices (TOM), in which the industrial heating process is imitated in the laboratory. At 15 different TOM devices, all relevant industrial atmospheres can be provided: gas burner atmosphere, air, inert gases, forming gas, hydrogen, vacuum, overpressure etc. The devices are equipped with detectors monitoring material changes with high accuracy during the heat treatment. In addition, a thermophysical characterization of materials can be performed. Some TOM devices are specially designed for relatively low temperatures to be able to imitate the industrial conditions for the processes debinding/pyrolysis (see Ziebold, H.; Raether, F.; Seifert, G.: Radical Time Reduction of Debinding Processes by Combined in-situ Measurements and Simulation) and drying as accurately as possible, while for sintering (see Raether, F.; Seifert, G.; Ziebold, H.: Simulation of Sintering across Scales) and melt infiltration (see Hofbauer, P. J.; Rädlein, E.; Raether, F.: Fundamental Mechanisms With Reactive Infiltration of Silicon Melt Into Carbon Capillaries) high-temperature measurement furnaces are available. In-situ measuring quantities are amongst others thermal expansion, sintering shrinkage, warpage, thermal conductivity, emissivity, heat capacity, heat of reaction, weight change, gas emission, sound emission, wetting, creep, viscosity and thermal shock resistance. In contrast to conventional methods for thermal analysis, the TOM-systems use a sample volume of about 10 to 100 cm³. With this, properties of small components, composite materials or heterogeneous materials are reproducibly measurable during heat treatment.
Simulation of Heat Treatment Processes
For process optimization, the measured data are parameterized. In particular, the kinetics of thermally activated reactions are described with robust models – and then used in FE simulations to optimize the heat treatment on the computer. In the FE models the interaction between the industrial furnace and the charge is taken into account so that the laboratory results can be transferred to the production scale. In addition, Fraunhofer-Center HTL offers methods for investigating temperature distribution, furnace atmosphere and energy balance of production furnaces (see industry furnace analysis). These data can also be transferred to the FE models and used for process optimization with respect to product quality and energy efficiency.