NUMERICAL INVESTIGATION OF A METHOD TO REDUCE THE REHEATING TIME OF STEEL BARS

Reduction of reheating time saves on energy input and increases the pr oduction rate in the steer-making process. Reductions can be achieved by allowing the centre temperature of a steel bar to be lower than the surface temperature by a small margin, before starting with the hot r olling process. This can only be done if the temperature difference do es not adversely affect the quality of the final product or the rollin g equipment. The paper presents numerical simulations to investigate t he savings that can be obtained for various temperature differences be tween surface and centre temperatures to evaluate the feasibility of t he concept. The results presented include the cross-sectional temperat ure distribution in a typical steel bar during reheating at hourly int ervals as well as the effect of various differences between centre and surface temperatures on reheating time. The reheating time predicted for various steel bar sizes as well as for various differences between surface and centre temperatures are then compared against measured re heating times. To indicate the practical applicability of the concept to the hot rolling process the detailed temperature distribution in a typical steel bar, with an initial temperature difference between the surface and centre of the bar, was simulated numerically. This was com pared to a similar simulation for a well soaked steer bar for which ex perimental measurements are also available. The numerical method used to obtain the simulations is also presented. Boundary conditions accou nt for radiation, convection and conduction inside the steel bar. It i s concluded that the concept of allowing differences between surface a nd centre temperatures of a steel bar during reheating herds great pot ential for energy savings in the steel-making process.