Analysis of in-line systems for rapid annealing

Abstract

The thermal cycle for the continuous electrical resistance annealing process has been modelled, based on classical thermodynamics and heat transfer theory, and by using the material properties and process parameters and variables. Transient and steady state, steady flow solutions are presented. Sensitivity analyses based on the process/material variables show that accurate control of the thermal cycle during the process relies heavily on the wire product quality and the electrical current. Conduction and radiation losses have been shown to be minimal for this process. Convective losses during the heating portion of the process are only significant during 'slow' line speed operation. The sensitivity of the process on quenching heat transfer is relatively small under ‘ideal’ conditions. The effects of electrical current on the process have also been addressed.

An annealing response model, which is based on the Arrhenius relationship, has been established for virtually any thermal cycle, isothermal and non-isothermal. The model requires knowledge of the activation energy for recrystallization and the annealing curve in order to project material properties. These annealing data are presented for both ETP copper and EC aluminum. Effects of cold work on the annealing behavior of ETP copper have also been investigated.

Continuous thermal processing of metals is a widespread practice that is often implemented in tandem with other manufacturing operations to improve productivity. These processes are generally characterized by poorly defined non-isothermal cycles, yet past research has dealt primarily with the isothermal spectrum. This research presents the development of comprehensive process theory for continuous annealing of wire by electrical resistance heating. The material used in this work was electrolytic tough pitch (ETP) copper and electrical conductor (EC) grade aluminum.