It is usual practice in pre-bake aluminium smelters to coat anode stubs with a thin layer of graphite prior to sealing them into the carbon anode with molten cast iron.
This graphite film reduces the risk of the cast iron fusing into the stub surface, which can prevent easy removal of the cast iron ‘thimble’ when the spent anode rod is recycled.
In the past, rodding plants often used an organic solvent and graphite mixture which quickly dried at ambient temperatures. Environmental considerations have largely eliminated this practice and today most smelters use an aqueous graphite suspension.
The use of water as the diluent means that careful drying is necessary to eliminate the risk of dangerous steam explosions during the anode sealing process.
VHE‘s Anode Stub Graphite Coating Systems comprise a graphite coating tank and a drying system.
The coating tank contains an aqueous graphite suspension and is elevated to the anode rod by hydraulic or pneumatic rams such that the anode stubs are partially immersed in the graphite mixture. The graphite is kept in suspension by continuous agitation of the tank contents.
The drying module may be one of several options, including gas burners, high intensity radiant electric heaters, or induction pre-heating, where residual heat in the stubs dries the graphite film.