Fraunhofer ISC, Center for High Temperature Materials and Design HTL, Bayreuth
Very different types of furnaces are used for industrial heat treatment, e.g. pusher plate furnaces, tunnel furnaces, belt furnaces, roller furnaces, ring furnaces or chamber furnaces. The mode of operation (continuous / batch), the required furnace atmosphere, the maximum temperature, the throughput, the charging as well as the holding and transport of the material to be heated in the furnace are decisive for the selection of the furnace type. Depending on the requirements of the furnace user, furnace systems must be planned very flexibly for different products and production quantities or for constant high throughput of large series.
With the finite element (FE), fluid dynamics (CFD) and kinetics models available at the Fraunhofer-Center HTL, thermal processes can be thermally designed and optimised. These include drying, debinding, pyrolysis, sintering, recrystallisation or crystal growth and diffusion processes. A special feature is the possibility to simulate the heating process from the point of view of the material to be heated (cf. thermal processes), which ensures high product quality. At the same time, the energy efficiency of the processes is optimised.
Heat management
For a successful heat management, exact input data for the FE simulation are required. These are insufficiently known for many refractory materials. The application properties of the furnace materials are determined under operating conditions with the ThermoOptic Measuring (TOM) systems developed at the Fraunhofer Centre HTL (cf. high-temperature characterisation). FE simulation can then be used, for example, to dimension the frequently multi-layered structure of a furnace insulation (app for heat transfer calculation) and to select the best material in terms of price and performance. Heat management in the useful volume can also be significantly facilitated by FE and CFD methods (cf. furnace simulation). Thus, setting plans can be optimised with regard to minimum temperature gradients. If required, mechanical or thermomechanical material properties of the furnace materials are also measured at the Fraunhofer-Center HTL and taken into account in the design. For large furnace components, specific tests are developed at the Fraunhofer Centre HTL with which the component behaviour can be tested under operating conditions. At the customer's request, the HTL carries out firing tests on a total of 40 of its own furnace systems.
Industrial furnaces that have already been installed can be examined directly on site with the mobile furnace measuring stand developed at the Fraunhofer Centre HTL (cf. Furnace analysis) as well as with autonomous sensor modules. Furnace operation does not have to be interrupted for this purpose.
Development of furnace components
The Fraunhofer-Center HTL develops furnace components. These can be moving components such as fans (cf. heat exchangers), hot gas flaps or lift gates (publication: Oxide Ceramic Matrix Composites) or parts that are exposed to particularly high temperature gradients, thermal shocks or corrosive loads, e.g. burner components (publication: High-Temperature and Corrosion-Resistant Perforated Boards), heat exchangers or sensors. Furthermore, foam ceramics (publication: Cost-Efficient Directly Foamed Ceramics) are developed as high-temperature thermal insulation. In addition to material selection, HTL also carries out component design and its optimisation by means of simulation of the application behaviour. Monolithic ceramics, ceramic protective coatings or fibre composite ceramics (CMC) are used as high-temperature materials.