Alcoa Exit Coiler Upgrade
Alcoa Yennora produces aluminium sheet by a rolling process. Aluminium billets are progressively rolled and coiled through pressure rollers until the correct thickness of the aluminium sheet is obtained. In this way a continuous sheet of aluminum approximately 1,000m in length and around than 1mm thick can be obtained from an original aluminium block measuring approximately three metres in length by 250mm high.
Critical to the process is the precise and consistent tension control between the coiler and uncoiler units. The coiler units are powered by very large Direct Current motors rated at 2250 Kilowatts. The motors are finely controlled by DC thyristor drives (rated at 1,900 ampere) with independent DC field controllers (rated 100Ampere).
Alcoa was having problems with a product variation resulting in ‘out of spec’ aluminium sheet due to the difficulty in setting up the main DC drive control. Because of the age of the equipment, it was proving difficult to maintain, as spares were no longer readily-obtainable. After investigation by Alcoa it was decided to re-engineer the coiler motor controls and DC drives in an attempt to improve the product.
This presented a number of serious challenges as the project was not a simple new installation. It would potentially mean extensive downtime with consequent loss of production for the plant while the changeover was taking place. Also, the complex calculations for tension and diameter control were done on unsupportable legacy control and communication equipment which had to be re-engineered and interfaced with the existing line. The new control and communication system would have to be intensively tested and proven before it could be placed into operation.
In consultation with Alcoa production staff, I S Systems developed a changeover strategy for replacement of the DC drives and the re-engineering of the control system. This ensured that changeover could be undertaken without any loss of production. Drive hardware was pre-manufactured and sited close to existing drive components to enable quick changeover and connection when the time came. The controls and calculations for the line, tension and diameter control had to be developed from scratch as existing legacy control equipment was no longer supportable. Redundant communication protocol had to be decoded and interfaced with the new network.