Furnace used for smelting , refining, or melting in which the fuel is not in direct contact with the contents but heats it by a flame blown over it from another chamber.
Such furnaces are used in copper , tin , and nickel production, in the production of certain cements , and in {{link=aluminum">aluminum recycling. In steelmaking, this process (now largely obsolete) is called the open-hearth process . The heat passes over the hearth and then radiates back (reverberates) onto the contents. The roof is arched, with the highest point over the firebox. It slopes downward toward a bridge of flues that deflects the flame so that it reverberates.