Successful closed loop control of coating weight on hot-dip galvanizing lines is a challenging control problem. The biggest technical challenges arise from the fact that coating weight is a complex nonlinear function of many variables. The interactions among the principal control variables: line speed, knife pressure, and knife distance, are so strong as to render simple feedback control approaches helpless. Yet many other variables enter the relationship to make it even more complex. Furthermore, while a given coating weight can be achieved by many combinations of these variables, some combinations will yield much better uniformity and product quality than others.
Add to this the complexities of a scanning measurement, variations across and on both sides of the sheet, and the lengthy delay between knives and measurement, and you have a control problem that can only be addressed by the most experienced engineers.

The interactions among line speed, knife pressure, and knife distance are so strong as to render simple feedback control approaches helpless.

Heart of the
galvanizing process.