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Home > Tips and Facts > Foundry Melting Furnaces > Cupola Furnace

The Cupola Furnace

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.

  1. The cupolas is one of the only methods of melting which is continuous in its operation
  2. High melt rates
  3. Relatively low operating costs
  4. 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.

Typical internal diameters of cupolas are 450 mm to 2000 mm diameter wich can be operated on different fuel to metal ratios, giving melt rates of approximately 1 to 30 tonnes per hour.

A typical operation cycle for a cupola would consist of closing and propping the bottom hinged doors and preparing a hearth bottom. The bottom is usually made from low strength moulding sand and slopes towards a tapping hole. A fire is started in the hearth using light weight timber, coke is charged on top of the fire and is burnt by increasing the air draught from the tuyeres. Once the coke bed is ignited and of the required height, alternate layers of metal, flux and coke are added until the level reaches the charged doors. The metal charge would typically consist of pig iron, scrap steel and domestic returns.

An air blast is introduced through the wind box and tuyeres located near the bottom of the cupola. The air reacts chemically with the carbonaceous fuel thus producing heat of combustion. Soon after the blast is turned on, molten metal collects on the hearth bottom where it is eventually tapped out into a waiting ladle or receiver. As the metal is melted and fuel consumed, additional charges are added to maintain a level at the charging door and provide a continuous supply of molten iron.

At the end of the melting campaign, charging is stopped but the air blast is maintained until all of the metal is melted and tapped off. The air is then turned off and the bottom doors opened allowing the residual charge material to be dumped.

Next: Induction Furnaces >>
Previous: << Crucible Furnaces

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Atlas Foundry Company, Inc.
601 N. Henderson Avenue
Marion, IN 46952-3348
Telephone: (765) 662-2525 • Fax: (765) 662-2902
Email: Atlas Foundry • Sales: Email Sales

Call Atlas Foundry today at 765-662-2525
Basics of Foundry Melting Furnaces
  1. Introduction
  2. Crucible Furnaces
  3. The Cupola Furnace
  4. Induction Furnaces
  5. Electric Arc Furnaces

Article by Jeff Meredith, foundry consultant with Casting Solutions Pty Ltd.
Reprinted with permission