Thermal processes play a significant role in the production of metallic raw materials as well as in the processing of semi-finished metallic products. Metals such as steel, aluminum or copper are subjected to various heating processes before the finished component is manufactured. Even during the processing of the ores, reduction and sinter processes must be performed at high temperatures in order to extract the raw metals. In the liquid melt state, refining and alloy processes are needed before it is possible to commence with the mold casting process. In the solid state, further thermal processes, such as annealing, tempering and hardening, are undertaken. Mechanical properties, such as the modulus of elasticity, hardness, elongation at break and strength, largely depend on these thermal processes. In addition, the temperature control, the furnace atmosphere and the interactions with refractory materials are crucial for a successful process. The manufacturing costs and the CO2 balance are heavily dependent on the thermal processes.
The Fraunhofer-Center HTL contributes in various ways for a purposeful improvement of metal manufacturing processes:
- The high-temperature properties of the metals and the associated refractory materials are determined using special HTL-developed ThermoOptical measurement systems (TOM). With these TOM systems, for example, the thermal conductivity, the emissivity, the creep behavior or the elastic response can be measured in controlled atmospheres at temperatures relevant for metal manufacturing. For the viscosity measurement of the melt, special measurement procedures have also been developed. The wetting properties of metallic melts compared to refractory materials are measured directly at high temperatures. Likewise, corrosion or erosion of metals in gases, vapors or in particle flows at high temperatures can be examined. Changes to the metals during the heat treatment can be measured in situ in the TOM systems. Thus, dimensional changes, e.g. during annealing can be determined with a very high level of precision and reproducibility using optical dilatometry on two directions in space. Changes to the viscoelastic properties during the heat treatment are measured in situ by natural frequency analysis as well as by dynamic-mechanical analysis.
- The high-temperature measured data is used for the computer simulation of the heat treatment processes during the manufacture of metals. The HTL has commercial finite element (FE) programs available for this purpose. The HTL has also developed FE models at varying size scales to design the heat management in industrial furnaces. Thus, heat distribution in the interior of the components can also be calculated as is the case with the stacking or usable volume of the furnace. The thermomechanical loads, which result from the temperature changes on the metallic components and the refractory materials, are also calculated using thermal-mechanical-coupled FE models. Using the FE simulations, process parameters of the heat treatment are optimized and transferred to the industrial furnace.
- The HTL has also developed a mobile furnace measuring system that can be used to make measurements on site with the industrial furnaces used for metal manufacture. The furnace measuring system enables the quantitative determination of heat flows on the outer shell of the furnace and the measurement of temperature fields in the interior of the furnace. It delivers analysis of the gas flow and the gas composition in the furnace or the furnace exhaust. Cooling water requirement and electrical power can be measured without interruption. The HTL has also developed special high-temperature sensors used in industrial furnaces.
- The HTL develops thermal shock resistant auxiliary equipment for the heat treatment of metals. In particular, fiber-reinforced ceramics (CMC) are used. The CMC can – depending on the application – consist of oxide and non-oxide ceramics. Fiber-reinforcement provides a high resistance to damage as well as a high thermal shock resistance and resistance to changes in temperature. CMC materials can, for example, be used in charge frames loaded with metal components in tempering processes that need to be cooled extremely rapidly. CMCs also perform diverse tasks as auxiliary equipment with metal casting, e.g., as molds, protective pipes or casting runners.