For many years, the cupola was the primary method of melting used in iron foundries. The cupola furnace has several unique characteristics which are responsible for its widespread use as a melting unit for cast iron.
- The cupolas is one of the only methods of melting which is continuous in its operation
- High melt rates
- Relatively low operating costs
- Ease of operation
In more recent times, the use of the cupola has declined in favour of electric induction melting, which offers more precise control of melt chemistry and temperature, and much lower levels of emissions.
The construction of a conventional cupola consists of a vertical steel shell which is lined with a refractory brick. The charge is introduced into the furnace body by means of an opening approximately half way up the vertical shaft. The charge consists of alternate layers of the metal to be melted, coke fuel and limestone flux. The fuel is burnt in air which is introduced through tuyeres positioned above the hearth. The hot gases generated in the lower part of the shaft ascend and preheat the descending charge.
Most cupolas are of the drop bottom type with hinged doors under the hearth, which allows the bottom to drop away at the end of melting to aid cleaning and repairds. At the bottom front is a taphole for the molten iron at the rear, positioned above the taphole is a slaghole. The top of the stack is capped with a spark/fume arrester hood.