Plant-wide automation at Elgiloy Specialty Metals. Background of project. Process utilization and efficiency. Production scheduling and monitoring, страница 2

The long-range business plan incorporated a vision of capturing increased market share with the development of superior gauge tolerances, as well as the ability to provide extremely thin gauges. Additionally, it was envisioned that it would be possible to expand the customer base to indude numerous other consumers of specialty cold rolled strip. To summarize, the expansion objectives were: expanded production capacity, expanded product line of new alloys, superior product quality, enhanced corporate profitability -and expanded customer base.

Scope of project

As noted above, industry demands have swiftly developed toward requiring suppliers to produce strip with extremely tight gauge tolerances. In addition, the industrial business sector supplied by Elgiloy requires the strictest surface conditions, extremely flat product, and a narrow range of physical properties. Consequently, in order to meet industry demand for this material, ESM made engineering studies onthe necessary mechanical, electrical and control components needed to achieve the planned objectives.

To facilitate these objectives, it was decided that the new plant would incorporate several processes, which have characteristics consistent with the market demands. These processes included a rolling mill, vertical annealing furnace, horizontal annealing furnace, coil preparation line, tension leveler and slitting line.

Since the principal characteristics of the strip are largely formed in the rolling mill, special attention was paid to selecting this process. Issues regarding the minimum gauge attainable, gauge control response and flatness were considered before choosing a 20-hi reversing mill featuring four independent columns with individual hydraulic positioning. The rolling mill was designed to load coils onto a payoff reel and finish on either the left or the right tension reel. Each coil position has independent coil cars for loading or unloading coils (see rolling mill automation section). Top speed of the mill was chosen to be consistent with the production capacity target of 30,000 tonnes per year.

To support product processing at the new facility, two annealing furnaces were also constructed. These two lines allow annealing of material in two gauge ranges. One annealing furnace operates horizontally in a batch mode processing one coil at a time. Another annealing furnace operates vertically with a tower, and in a continuous mode with strip storage at the entry and exit sections. The horizontal furnace was constructed to produce the most stringent alloy requirements in smaller lot size quantities, while the vertical furnace was installed to supply material at lowest possible cost and in larger lot size quantities. Additionally, a tension leveler, coil preparation line and slitting line complete the complement o: processes needed to produce the targeted products.

With regard to automation of the various processes, it was decided that the annealing furnaces, tension leveler, coil preparation line and slitter would be controlled using basic process controllers such as PLCs. This hardware platform was chosen due to the fact that these processes are largely controlled by sequences and advanced digital interlocking. Predefined programs for different product types are entered by the operator and then executed by PLC logic during coil processing.

Rolling mill automation is far more demanding because it requires sequencing, fast digital regulation loops and a mathematical model for proper control. In addition, intelligent sensor subsystems are necessary for the efficient operation of a rolling mill. As previously mentioned, product quality and physical characteristics are exclusively determined by the processing in the rolling mill. Therefore, it was necessary to select a more sophisticated control structure in this area. Consequently, a layered control system consisting of supervisory process computers (MMI and process control), PLCs, fast real-time control processors and smart sensors, was chosen. It is organized into a two-level control hierarchy and will be described later under rolling mill automation.