An effective heuristic algorithm to minimise stack shuffles in selecting steel slabs from the slab yard for heating and
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An effective heuristic algorithm to minimise stack shuffles in selecting steel slabs from the slab yard for heating and rolling L Tang1, J Liu2*, A Rong2 and Z Yang1 1
Northeastern University, Shenyang, China and 2The Hong Kong University of Science and Technology, Kowloon, Hong Kong, China Steel production is a multi-stage process. A slab yard serves as a buffer between the continuous casting stage and the steel rolling stage. Steel slabs are stored in stacks in the yard. Shuffling is needed when picking up a slab for heating and rolling, if it is not in the top position of a stack. This paper studies the problem of selecting appropriate slabs in the yard for a given rolling schedule so as to minimise the total shuffling cost. The study uses the hot strip rolling mill in Shanghai Baoshan Iron and Steel Complex as an application background. We propose a new heuristic algorithm to solve the problem. This is a two-phase algorithm that first generates an initial feasible solution and then improves it using local search. The new algorithm is compared with the algorithm in use on randomly generated test problems and on real data. Experimental results show that the proposed algorithm yields significant better solutions. The average improvement over the old algorithm is 15%. Keywords: iron and steel industry; material handling; slab stack shuffling; heuristics
Introduction Iron and steel production can be divided into four major stages: iron-making, steel-making, continuous casting and hot rolling. In some steel production systems, slabbing= blooming is used, instead of continuous casting, to produce slabs for hot rolling. In the cold charge process, a slab yard is situated between the continuous casting (or slabbing= blooming) stage and the hot rolling stage, serving as a storage buffer (see Figure 1). Slabs from continuous casting (or slabbing=blooming) are stored in stacks in the yard. When needed for rolling, they are picked up and charged to the reheating furnace for heating and then rolling. In the last couple of decades a number of new technologies have been developed and applied to connect continuous casting and hot rolling more directly. These include hot charge (hot slabs from continuous casting are directly charged to the reheating furnace with at most a short delay in a heat preservation pit) and direct rolling (continuous cast slabs at very high temperature are moved directly for rolling after quick heating on the edges). Although these new technologies can significantly save energy and slab handling cost, they involve investment and require a wellsynchronised production at different stages. Therefore the cold charge process is still widely used in many places and *Correspondence: J Liu, Department of Industrial Engineering and Engineering Management, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong. E-mail: [email protected]
the slab yard is still playing an impo
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