Adapting existing rolling mills to present day market requirements has become imperative for present day aluminium producers. Modernization of old rolling mills has made Aluminum rolled product plants more profitable and competitive in both domestic and export market. Automation helps in increasing uptime and productivity, reduces mill breakdowns by over 35% and product rejection rate by over 40%. Latest generation rolling mills with lower power demand and higher productivity can produce at a low cost with the help of newer technologies.

Background 

One of India’s major aluminum producers, operating for over last six decades, upgraded their cold mills in 2005 with the then state of the art automation and till date, they have been enjoying the leading status in producing high value – sophisticated rolled products for domestic and export markets.

The sheet rolling plant had two cold strip rolling mills e.g. one intermediate and one thin gauge finishing, which were in operation over two decades.

Challenge 

In early 2000, the Company decided to completely modernize the controls of these two mills to become more quality competitive on both the domestic and export market and realize their vision of becoming the industry leader. The management felt that the mill electrics had become obsolete and was not delivering the desired results leading to high downtime, inconsistent product quality, and fluctuation of operating cost, customer dissatisfaction, and loss in market share.

The Company approached different electrical & automation giants through the original mill builders, who had good working relationship with them and finally chose a “mill upgrader” to retrofit as well as modernize both mills with new control systems and automation solutions. Key objectives for the project included improving product quality to meet international standards, reducing the cost of production through improved productivity, increasing the consistency of quality through automation and reducing waste, customer rejection and rework. Improving productivity required optimizing rolling speed, reducing coil turnaround and roll changeover time, and increasing yield per pass.

The upgrade required a complete and clear understanding of mill operations and desired future enhancements to plan the appropriate migration path. While the task was relatively simple for the intermediate mill, it posed a major challenge for the finishing mill, since most of the technical data for the mill had been destroyed in a recent major mill fire and the mill was under shutdown at that time to make it ready after the fire.

To acquire the information the mill upgrader had to interview plant engineers and the original mill builder, to acquire more details about its old electrics and control system.

The interviews revealed that frequent breakdown of old electrics and controls were resulting in long periods of downtime. The breakdowns were associated with lengthy startup procedures due to multiple operating stations employing an outdated hard-wired relay-logic system , which needed regular maintenance. With limited documentation and diagnostics, troubleshooting was extremely difficult. Moreover, obsolete spare parts were scarce and expensive to procure.

To minimize downtime and huge daily loss due to the mill shutdown, caused by the fire, the Company required that a solution comprising hardware, software integration, startup, and commissioning is implemented within 110 days.

Solution  

Like others, the Company also used a variety of branded equipment/components in their mills. The mill upgrader’s solutions, therefore, were designed to be integrated in exactly this type of environment.

They proposed a control system that would precisely interface with the OEM’s equipment. The system is designed around OEM’s Distributed Power System (DPS) drives and provided a specially engineered PLC system with very special type of chosen I/Os. This modular system delivers power to the motor and signals to the customer’s existing sub-systems, including OEM’s Automatic Gauge Control (AGC) and Automatic Flatness Control (AFC) systems.

The Power Module Interface provides digital regulation for the main mill, coiler, and pay off. It communicates with the Universal Drive controller on the main PLC rack through a fiber optic network, which is capable of interfacing with different brands of power modules. The ‘Panel View’ .provided the human machine interface (HMI) for process monitoring. An Ethernet (TCP/IP) network interfaces with the auto shape controller.

The system is connected to the mill management system. Data can be shared with mill operators to control recipes for optimum rolling.

 Results 

The entire project was completed ten days before time, significantly reducing losses accrued due to shut down. The Company was able to start operating both the mills at desired rolling speeds within just 30 days of commissioning of each mill.

The Electrical supplier was able to resurrect and completely modernize the aging mills. Integration between the distributed power system and controls such as AGC and shape control had been seamless. Digital regulation has meant improved mill performance and simplified startup. PLC-based logic and sequencing, complete documentation, and detailed diagnostics through Sigma and PanelView made maintenance much easier.

The upgrade had increased productivity and improved product quality, while reducing waste and downtime. The upgrade increased the reliability of the intermediate mill by 12% and of the finishing mill by 22%. The breakdown hours for the intermediate mill reduced by 37% and that for the finishing mill by 39%. The rejection rate due to quality issues was reduced by 41%, while recovery of the highest contribution product improved by 33% compared to what it was before the upgrade. Intermediate mill roll change time was also reduced by 50%, increasing uptime and productivity.

In the words of Company’s spokesman “The automation solution has made us more competitive in the export market,” and “The project helped us to improve operational efficiencies and product quality. It has resulted in increased production and an excellent return on investment.”

(The author is a Chartered Mechanical Engineer with over 38 years of working experience in downstream sectors of leading Aluminium Industries in India and abroad. Executed Greenfield projects both in India and abroad to set up new Aluminium downstream facilities and also led various brownfield developments at different Aluminium manufacturing locations in India.)