A cupola furnace is a vertical shaft furnace that melts cast iron by burning coke. It has been used for more than a century and remains one of the cheapest ways to produce large, continuous tonnages of liquid iron. In Turkey, most foundries have moved to induction because of emission rules and analysis control.
How it works
The furnace is a steel shell with a refractory lining. Coke, pig iron, scrap, steel scrap and limestone are charged from the top in layers. Air is blown through tuyeres at the bottom, the coke burns and the heat melts the metal. Liquid iron collects at the bottom and is tapped continuously or in batches. Limestone forms slag, which is removed through a separate hole.
Cold blast and hot blast
A cold blast cupola blows ambient air. It is simple and cheap to build. Coke consumption is roughly 10–15% of the metal charge.
A hot blast cupola preheats the air to 400–600 °C using flue gas heat. Coke consumption falls, metal temperature rises and more steel scrap can be used. Investment and maintenance cost more; it pays back at high tonnage.
Gas-fired cupolas also exist but are rare in Turkey.
Advantages
- Continuous, high-tonnage melting: 5–20 t/h and above.
- No large electrical supply needed, which can make it the only option where grid capacity is limited.
- Tolerates cheap and rusty scrap.
Disadvantages
- High flue gas and dust emissions; without filtration and gas treatment, permits are very hard to get today.
- Chemistry is harder to hold than in induction. Coke adds sulphur, so ductile iron needs desulphurisation.
- Inefficient for short runs or low tonnage; once lit, it must run for long periods.
- Slow alloy changes.
Cupola or induction
It comes down to three questions:
- How many tonnes and hours a day do you pour? At two shifts and more than 10 t/h continuous, the cupola is still competitive. For smaller or interrupted production, induction wins.
- What are your power capacity and price? Induction uses 550–650 kWh per tonne. Can your grid connection be upgraded, and how long will it take?
- What do you cast? For ductile and alloyed iron, induction's analysis control is a major advantage.
A duplex layout is also possible: melt in the cupola, hold and alloy in an induction furnace.
Switching from cupola to induction
Items most often missed when switching:
- Transformer, MV switchgear and a grid capacity upgrade
- Closed-circuit cooling
- Charge preparation: induction needs different size and cleanliness of charge material
- Operator training: lining sintering and furnace operation
ZENES works out the power calculation, furnace selection, transformer and cooling plan together. A used induction furnace can cut the investment roughly in half; see the melting group on our Used Machinery page.
FAQ
How much coke does a cupola use per tonne?
About 10–15% of the metal charge in a cold blast cupola; less in hot blast.
Are cupola furnaces still used in Turkey?
Yes, in some high-tonnage grey iron foundries. Most new investments are induction.
Does a cupola need an emission permit?
Yes. Dust and flue gas limits require filtration and measurement. Plan the permit process from the start.
