It is a simple fact that plants which have performed faithfully for decades nearly always benefit from a new control system. Generally such a retrofit will be initiated by the fact that the spare parts supply for the control system is not guaranteed anymore and that the customer cannot guard against loss of production should problems occur.
If the rolling mill can be shut down for a particular period – generally during the annual maintanence period or the Christmas season – and the supplier is able to finish the retrofit successfully so that the production can restart on schedule all involved parties will be satisfied. Bühler-Würz received a request from the Austrian Mint AG to upgrade their old reversing mill. The cold rolling process of the precious metal strips largely determines the weight of the finished coins. Each 1/1000 gram saved off the blank reduces reworking and scrap. As for the weight of the blank the tolerance of thickness of the rolled strip is essental.
The Austrian Mint wanted to get from Bühler-Würz an improvement of the thickness tolerance up to ± 5µ. Karl Zant, project manager for the Austrian Mint, is pleased to report that they have now reached, on 95% of the finished strip, ± 2µ.
This has been achieved by the electronic experts from Bühler-Würz through the application of a control circuit which connects the precontrol and trend control with the mass flow-control.
In consequence of the continous visualization it is possible to see at any time how changes in input parameters become noticeable. Mr. Zant said that they have already found out a few influencing variables from the preceeding casting process.
Bühler-Würz is continuing to apply these advances in technology. At present a large reversing mill being built for the Royal Canadian Mint will be equipped with the same automatic control technique.
Even across the Atlantic the successful improvement realized at the Austrian Mint is already known. Mr. Xianyao Li, Director Corporate Engineering, of the Royal Canadian Mint said that if they can achieve comparable results the investment in the new mill will be redeemed even faster than they had hoped. For Stefan Nixdorf, Managing Director of Bühler-Würz, it is a matter of strategic direction that with the consistent application of the measurement and feedback control systems the quality and efficiency of our customers rolling mills will be increased therefore justifying the upgrading of older mills with new control systems.