The use of cupola furnaces is one of the oldest process for making cast iron and is still among the dominant technologies in the world. In Queensland, most of the larger foundries have replaced their cupola furnaces with more efficient electric furnaces. Some of these foundries still maintain a cupola furnace for specific melts or for reserve capacity.

A typical cupola melting furnace consists of a water-cooled vertical cylinder which is lined with refractory material. The process is as follows:

The charge, consisting of metal, alloying ingredients, limestone, and coal coke for fuel and carbonisation (8-16% of the metal charge), is fed in alternating layers through an opening in the cylinder. Air enters the bottom through tuyeres extending a short distance into the interior of the cylinder. The air inflow often contains enhanced oxygen levels. Coke is consumed. The hot exhaust gases rise up through the charge, preheating it. This increases the energy efficiency of the furnace. The charge drops and is melted. Although air is fed into the furnace, the environment is a reducing one. Burning of coke under reducing conditions raises the carbon content of the metal charge to the casting specifications. As the material is consumed, additional charges can be added to the furnace. A continuous flow of iron emerges from the bottom of the furnace. Depending on the size of the furnace, the flow rate can be as high as 100 tonnes per hour. At the metal melts it is refined to some extent, which removes contaminants. This makes this process more suitable than electric furnaces for dirty charges. A hole higher than the tap allows slag to be drawn off. The exhaust gases emerge from the top of the cupola. Emission control technology is used to treat the emissions to meet environmental standards. Hinged doors at the bottom allow the furnace to be emptied when not in use.

The cupola furnace has received a lot of negative publicity in recent years. However, the system does have a number of inherent advantages over electric furnaces:

• It is simple and economical to operate.
• A cupola is capable of accepting a wide range of materials without reducing melt quality. Dirty, oily scrap can be melted as well as a wide range of steel and iron. They therefore play an important role in the metal recycling industry
• Cupolas can refine the metal charge, removing impurities out of the slag.
• From a life-cycle perspective, cupolas are more efficient and less harmful to the environment than electric furnaces. This is because they derive energy directly from coke rather than from electricity that first has to be generated.
• The continuous rather than batch process suits the demands of a repetition foundry.
• Cupolas can be used to reuse foundry by-products and to destroy other pollutants such as VOC from the core-making area.