Rockwell Automation Drive Systems

Shanghai No. 2 Steel Company Modernizes a
Two-Strand Rod Mill to Improve Quality and
Increase Production Capacity

System Overview

The Rod making process begins by heating billets to a yellow hot state in a reheat furnace, the metal is then sent through multiple roughing, intermediate, and prefinishing mill stands where the metal is elongated and rolled into bar. The final reductions are rolled in the Morgan high speed No Twist Finishing mills. The rod exits the finishing mills, is cooled in the water boxes and then coiled onto the Stelmor cooling conveyor by the inclined laying head. The rod proceeds down the Stelmor conveyor where the cooling rate is controlled to provide the required metallurgical characteristics. The rod spirals are poured in to the reforming tubs, transferred to the C-hook conveyor system for final cooling, compacted, banded and transferred to storage. Crop and cobble shears are located after stand 8 and crop and divide shears are located before the No Twist Mill to provide head crops and divide cut the rod to required lengths.

To achieve Shanghai No. 2 Steel's production goal of 550,000 tons/year, the billet size would have to increase from 100x100mm to 140x 140mm. To roll the larger billets to the diameter required for entry into the prefinishers, the motor horsepower and the number of mill stands in the roughing and intermediate sections needed to be increased.

The first challenge was to add the additional drives and increase the horsepower, yet keep the project within both time and cost budgets. Re-using the existing thyristor power modules on drive sections over 100 Hp was the most cost effective approach. These power modules were supplied in the mid-80's and were in good shape with parts readily available. AutoMax DPS allows for direct digital firing of these existing power modules. The cost of new thyristor power modules and their associated magnetics was saved, while obtaining the advanced digital control needed for this project. "The AutoMax family of controls was selected because it offered the most flexibility for the systems being considered" explained Mr. T.C. Shen, Control Systems Manager for Shanghai NO. 2 Steel. "In addition, Rockwell Automation has a long time presence in China and could provide local Services and Support."

The second challenge facing Shanghai No. 2 Steel was the need for better control and higher accuracy than the new machine speeds demanded. "The key to the control system was the AutoMax DPS. It allowed for high speed control loops necessary for the system and solved communication problems with control logic" said Mr. Shen. Two areas where Shanghai has seen the most dramatic improvement are in the laying head and shear applications. The Laying Head Pinchroll and Laying Head drives performance had to be improved to avoid frequent cobbles. AutoMax DPS provides the high performance required to achieve this goal. A significant reduction in scrap rod was achieved by improving the accuracy of the #8 Crop and Cobble Shear and #16 Crop and Divide Shears, positioning control in AutoMax provided this performance.

Any control modernization project undertaken today must simplify the operation and improve the maintainability of the resulting system. The Rockwell Automation SIGMA Rod mill control and management system was chosen. "SIGMA software provided dynamic process information to the operator and minimized the programming time" said Mr. Shen. SIGMA provided state-of-art MMI's graphic displays with stations in the Main Mill and Finishing Mill Pulpits. The SIGMA Rod Mill package provides Recipe management, Rod Outlet Management, Roll Shop Management and a Production Management. A Computer room SIGMA is used by maintenance and engineering to monitor the mill. Through the use of pre-designed screens, operators select production schedules, setup data, and monitor the mill permissives, loads, speeds and other process variables. The finish mill operator can adjust the control parameters to help eliminate defects. Most of the operator screens are displayed in either Chinese or English.

Improving Production and Reducing Cost

Shanghai Ergang No. 2 Steel selected Rockwell Automation Drive Systems for a number of reasons:

• The speed and accuracy of the AutoMax DPS controls and drives.
• The Flexibility of the AutoMax DPS to interface with existing Power Modules.
• SIGMA Rod Mill Management System uses non-proprietary hardware and Windows' based software with real time data acquisition capability.
• Rockwell Automation's established presence in China and the Metals industry.

"By using refurbished machinery along with new control software, digital drive and automation systems, the project was able to be delivered in less than 3 months, from stop to full production, and at a 30% cost savings. The change over was fast and start up was extremely smooth. We are pleased wit the final product - a very modem, high-speed and well-controlled two strand rod mill."

Mr. Lu Bao Xing
Vice General Engineer, Shanghai Ergang Works

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