The evolution of coating control systems as the need for new coated products expands

Abstract

Hatch has been developing and deploying a model-based coating control system for over 25 years. The resultant physics-based gas wiping process model has been adapted to a wide variety of equipment and coatings now being produced by the major steel producers. As the coating control technology has matured and the processing ability of PLCs has increased, the process model and control system have been migrated from computers to industrially robust PLCs.

The coated product market is moving from traditional zinc and zinc/aluminium coatings and carbon steel substrates, to more advanced products with a wide range of coating and substrate properties. At the same time, the relentless demand to lower production costs and increase product quality needs to be met. The Hatch process model, through the addition of techniques such as the parameterisation of the air wiping process, has matured over time to meet these demands. Strip stabilisation and flattening at the wiping zone have become commonplace and can be attained using Electromagnetic Stabilisation (EMS) or Air Floatation Stabilisation (AFS).

Tighter requirements, both in the processing of magnesium-dosed coatings and the introduction of Advanced High Strength Steels (AHSS) and other 3rd Generation steels, require the implementation of even more advanced control strategies. Coating process control is now moving into the realm of managing strip shape effects. Hatch’s model-based coating control system can now include passline tracking using laser measurement techniques and is being further developed to include active crossbow control.

This paper presents the current state of coating control systems and the progress towards the next evolutionary step, which is the use of crossbow modelling and active crossbow correction to manage the strip shape prior to the gas wiping.