Aluminum circle are circular discs cut from aluminum strips or sheets used in the manufacture of aluminum utensils, pressure cookers, containers, bottle caps, meter dials, etc. The most common thickness of these circles in commerce is 18 to 22 SWG. For making pressure cookers aluminum circles of much higher thickness are used. These diameters of the circle depend upon the type and size of utensil for which it is required.
In the manufacture of aluminum circles, aluminum scrap along with ingots is melted in a pit type furnace and casted into slabs of desired thickness and width. The slabs are then rerolled in hot or cold rolling mill into sheets of 18 to 22 SWG. These sheets are then sheared into squares. Circles are cut from these squares on circle cutting machines and finally annealed in the annealing furnace to get soft temper for spinning and deep drawing into utensils.
As mentioned above, the melting unit is an oil fired pit type furnace which is fire brick lined from inside. Before melting, the aluminum scrap is washed with water to remove adhering dust and sheared to a desirable size, suitable for feeding the furnace, on a shearing machine. The furnace is fired by burning oil and its temperature is allowed to rise to about 700oC before loading. Lost of aluminum scarp and aluminum ingots in the ratio 1:1 are weighed and piled separately for charging into the furnace. When it is melted, ingots are introduced one by one into the molten metal to facilitate easy melting. Now flux is added to purity the scrap. Degasser tablet (1/4 to ½) is also dipped to remove the gases entrapped in the molten metal. The dross formed over the melt is removed by skimming. This dross ca be melted again after removing the unclaimable portion by proper screening.
When all metal in pit furnace is melted and all impurities along with all entrapped are removed, the molten metal is taken out from the crucible with ladles and poured into cast iron molders, also called die blocks. The molds are allowed to cool and finally slabs are taken out by opening or titling the molded boxes.