Process of Combustion for a Cupola Furnace

Materials

• The furnace is made from long-lasting steel and ceramic materials designed to resist temperatures that would easily melt other metals. Inside the shaft, the furnace is lined with refractory surfaces that encourage heat energy to stay inside the furnace, concentrating the heat even more. Refractory materials are often made of brick, and the entire system rests on a plate or foundation.

Combustion

• Most of the heat in the cupola furnace comes from the wide base, where a bed of coals combusts and produces heat, which is funneled into the shaft. From the top of the flue, metals such as iron are pushed in. The rising combustion gases meet the falling metals. The metals melt as the gases escape. Flux materials are added to the iron or other metals to precipitate impurities as the metal melts. This forms a floating coating that prevents rapid oxidation, which might otherwise ruin the liquid metal. Once fully melted, the metal is drained through a tap hole down near the hearth section, where slag materials are removed through openings at higher levels.

Fuel

• Cupolas started off as coke furnaces, using basic coal and char products to create heat. During the Industrial Revolution, these fuels were common and easy to use. But as decades passed the high number of particulate emissions produced became a problem. Modern cupola furnaces use wet scrubbers or large fabric filters to remove fly ash and other particles. Some cupola furnaces keep the design but use alternative methods of heat, such as gas.

Uses

• The most common use for cupola furnaces is cast iron melting. Cast iron is made to be molded into a variety of shapes. The cupola furnace can quickly melt the iron and prepare it for extruding into a mold. This helps reclaim old cast iron or scrap iron and re-use it for other purposes.