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In 1998, Hydro Aluminium installed a batch process to remove alkaline metals from its potroom metal. The Hycast RAM System is based on Aluminium Fluoride injection and offers to reduce costs and improve working environments. By Per Gunnar Strand
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Hydro Aluminium Hycast's Removal of Alkaline Metals (RAM) System removes impurities from potroom metal before it is transferee! into the casting furnace, thereby improving the overall metal quality, HSE and reducing costs in the casthouse.
The actual refining process takes place in a crucible, in which aluminium fluoride (A1F3) and inert gas are added beneath the metal surface by a specially designed and patented rotor system.
The RAM System is environmentand operator friendly, fully automated, has low operating costs, low gas consumption and can be supplied in various models to comply with customer requirements.
Extensive full-scale industrial experiments have been performed at two plants in Norway, with crucible sizes of 1.8 and 3.7t respectively.
In 1998 five systems were put in full operation at Hydro Aluminium's Sunndal plant in Norway, treating the full capacity of potroom metal. One unit is in full operation in the USA for lithium removal.
In addition to a rapid reduction in alkaline content (Na, Ca and Li) in the metal during this process, a substantial decrease in inclusion content is observed.
BACKGROUND
Due to ever-increasing market demands concerning the content of alkaline impurities in certain aluminium products, the need for a process that could remove these impurities in an effective way grew stronger.
Starting off with a crucible fluxing process involving chlorine as the active element, we soon realised that this was not the way to do it. Both from an environmental point of view, and also due to the fact that this process was temperature sensitive, we had to look for a better solution.
A batch process where A1F3 is introduced into the melt through a spinning rotor head seemed promising, and efforts were put into the construction of the first experimental equipment1.
Over the years since 1991, the equipment has been improved until the first full-scale pilot fluxing campaign was performed in 1994. A further development of the equipment led to a second full-scale industrial test campaign in 1996.
In addition to the...