Computer Control of Coating Weight on Galvanizing and Tinning Lines

Abstract

Coating weight gauging and control have developed rapidly in zinc galvanizing processes. Development has been somewhat slower in control of tin electroplating processes. This paper discusses the surprisingly large number of similarities between these two steel coating processes. The basic mathematical models for each process are developed and the automatic control strategies are analyzed. A linear model is used which over a limited range provides accuracy equal to the more complex non-linear models. There are many factors that affect coating weight which are essentially unmonitored. A method is presented for continuous adaptive learning that will adequately compensate for the unmonitored parameters. Control methods of feedforward and feedback control are explored. It is shown that the Dahlin algorithm reduces to a “pulse and wait” philosophy in both processes. The economies of gauging and control of coating weight are also discussed.