TABLE OF CONTENTS Now much less common due to environmental factors, this method utilizes a furnace in stack form as shown in Fig. 1A1. Fuel and metal to be melted are in direct contact. The stack is lined with refractory material and alternate layers of coke and metal are placed in it. Some minerals, primarily limestone (CaCO 3), are included with the metals to be melted. Air is blown through the stack from the bottom through openings called tuyeres. The bottom layer of coke is ignited initially. Heat from the burning coke melts the metal, which flows to the bottom of the cupola from where it can be removed by opening a tap hole. Slag is also removed from the bottom, from an exit hole just above the one used to remove molten metal. As the coke is consumed and the metal charge melts, the burning gradually proceeds upward. The upper layers are preheated by the flow of hot gases. Additional metal, coke, and limestone can be added from a charging door in the upper part of the stack as the operation proceeds. Metal charges may consist of steel scrap, cast iron scrap or pig iron, or, more commonly, a combination of them. The molten metal absorbs car-bon from the coke, so cupola melting is generally restricted to cast, malleable, and ductile iron (though the electric arc method is preferred for the latter).
