Continuous Materials Processing

Abstract

Continuous materials processing, as contrasted with batch processing, is discussed. There is growing interest in continuous processes because of higher production rates and lower costs. A wide range of processes can be considered for continuous processing. These include hot and cold rolling, extrusion, wire and fiber drawing, heat treatment of moving materials, and deposition on continuously moving surfaces. The problem is time dependent at the start of the process, but generally approaches steady-state conditions as time elapses. Both situations are of practical interest. Fluctuations and instabilities can also lead to time dependence. Of particular interest is the thermal field in the moving material, since the resulting thermal stress and microstructure are determined by the temperature distribution. The temperature rise or decay with distance is also critical in designing the system to maintain temperatures above certain values, such as the recrystallization temperature for hot rolling. Though a convective heat transfer coefficient, obtained from empirical data and correlations, may be employed at the surface, the problem is actually a conjugate one and both the fluid flow and the thermal field in the solid have to be considered. Though boundary-layer assumptions are valid in some cases, solution of the full elliptic equations is generally needed for a realistic simulation. Buoyancy effects are important in many circumstances and an additional forced flow, in an extensive environment or in a channel, may be employed to enhance the heat transfer. Experiments are used to validate the analytical and numerical models, to provide physical insight into the basic mechanisms, and to provide realistic and practical operating conditions. The basic formulation, solution strategies, and typical results are presented on this materials processing technique. The relevance of such results in the operation, control, design, and optimization of practical continuous manufacturing processes is discussed.