Model and scheduling of a continuous galvanizing line

In this paper, we introduce a continuous galvanizing line in a steel plant which is one of the biggest iron and steel enterprises of the world. The continuous galvanizing line we research produces principally two kinds of coils, inner coils and outer coils. Due to the technical constraint, outer coils can not be produced continuously more than a specified number. So the inner coils must be inserted between outer coils. The difficulty of solving the problem is the interrelation of sequencing these two kinds of coils. No model and algorithm about such a scheduling problem has been published. We propose an integer programming model to describe the scheduling problem. To solve the problem, a heuristic based on tabu search is developed. Due to the model of the scheduling problem is an integer programming model, problems with less than 100 coils can be solved by CPLEX 11.0 MIP optimizer to obtain the optimal solution or a lower bound of the problem. By comparing our heuristic schedule and the CPLEX schedule, the tabu search heuristic is proven to be effective.