Ingot, Billet

Ingot and billet play an integral part in the production of many aluminum products. Plate, sheet, foil, wire, rod, and bar products are all produced by pressing or rolling ingot and billet.

Ingot and billet are cast from molten aluminum. In the cast house, crucibles of molten aluminum empty their silvery liquid either directly into molds or into a holding furnace where the metal is kept molten at temperatures between 1,200 and 1,500 degrees Fahrenheit. Alloying elements are then added.

Before the alloyed metal can be cast, it must be purified by forcing mixtures of gases through the hot metal. Impurities (dross) come to the surface and are skimmed off.

Most metal is cast by the direct-chill (DC) process, which produces huge sheet ingot for rolling mills, round log like billet for extrusion presses, or square billet for production of wire, rod, and bar.

In DC casting, alloyed aluminum flows from the furnace through troughs to the casting station and into molds. For sheet ingot, weighing several thousand pounds each, three or four molds or a dozen or so billet molds may be poured simultaneously. The mold itself is only a few inches deep and forms the cross-sectional shape of the ingot. In the mold, sprays of cool water rapidly solidify the metal, which is gradually lowered into the casting pit. The process continues until the desired length is achieved. The process can be done either vertically or horizontally.