A successful black box design : digital regulation of deposited zinc in hot-dip galvanizing at Sollac Florange

The paper is focused on the design and implementation of the main control loops : regulation of the deposited zinc, at the new hot-dip galvanizing line of Sollac Florange. The main difficulties for implementing a high-performance feedback control come from the presence of a large and variable time-delay (depending on the steel strip speed) and from the nonlinear character of the plant model. The regulation scheme is implemented on a PC connected to the process through an industrial network. It uses a digital controller designed on the basis of an identified discrete-time black box model. The scheme is open-loop adaptive in the sense that the sampling frequency is related to the steel strip speed, and that the parameters of the controllers for various regions of operation are stored on a table. The results obtained on the site conclude the paper. An improvement of the product quality and a reduction of the zinc consumption have been achieved