Applying Distributed Computer Control to Modernize Steel Strip Rolling Mills

Abstract

Very few new strip mills are being built, or considered. However, there is worldwide interest in modernizing the many existing mills to provide the high quality flat rolled products demanded by today's users while keeping to a minimum scrap and production losses.Islands of Automation, a concept introduced in the sixties with the early application of digital computers to process control, still provides the most cost effective approach to modernizing and upgrading the control of both discrete and continuous manufacturing processes.Distributed Computer Control Systems (DCCS) technology used in Islands of Automation permits step-by-step implementation to modernize and upgrade many existing strip rolling mills. Carefully planned programs can optimize the use of limited capital resources, and provide early benefits to fund the next step. And, the step-by-step approach provides an efficient method for training, and technology transfer for projects in developing countries.The Factory of the Future, and The Factory for the Future, in most cases, remain unrealized visions for the foreseeable future, even in developed countries. Millions of dollars have been spent to promote appealing ''blue sky" concepts to sell hardware and software. Billions of dollars have been spent by technically unsophisticated users to install equipment to automate factories too worn out to ever operate automatically, let alone even operate satisfactorily without continuous human operator observation and intervention. Automation is not an easy Fix-It for fundamental problems.This paper is intended to provide basic guide-lines for the selection of potentially viable projects, to discuss project hazards frequently overlooked, and to present a basic system architecture utilizing today's technology, yet suitable for the future. The examples are from U.S. installations. Process examples are the steel hot strip rolling mill, and the tandem cold reduction mill. The outcomes and experiences could be repeated elsewhere, in both developed and developing countries.Even a thirty year-old hot strip mill has high investment and high throughput values. Daily throughput is more than (U.S.) $1/day per tonne per year, more than $l,000,000/day. A 1% improvement in yield returns $10,000 per day, easily achievable by adding computer mill setup and control.On cold reduction mills, automatic gage control using both feed forward and feedback techniques can produce high quality strip from relatively poor hot bands. Flatness or shape control can help adapt the cold mill to the incoming hot band cross-sectional shape.On both mills the digital computer can provide an accurate mill setup for every coil rolled. Steel strip can be produced to tighter dimensional and metallurgical specifications. Mill production can be increased, and scrap losses reduced.