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Casting Iron in a Cupola Furnace — Re-Melting Pig Iron into Finished Castings

أنشأه

Piett

25. يونيو 2026

Casting Iron in a Cupola Furnace — Re-Melting Pig Iron into Finished Castings

The blast furnace makes pig iron by the tonne, but pig iron in bars is not yet a useful object. To turn it into pots, pipes, stoves, and machine frames, a foundry re-melts it and pours it into moulds — and the workhorse that does the re-melting is the cupola furnace.

A cupola is a tall iron chimney lined with firebrick, charged from the top with alternating layers of coke, pig iron, and limestone, and blown with air near its base. Unlike the blast furnace it does not smelt ore; it simply melts iron that is already made, quickly and cheaply, keeping a steady stream of molten metal ready to tap. The melting iron picks up a little carbon from the coke and runs out of the tap hole as grey cast iron.

Poured into sand moulds shaped from wooden patterns, that iron sets into castings of almost any form. Cast iron is brittle but immensely strong in compression and cheap to pour into complex shapes, which made the cupola the beating heart of Victorian industry — casting everything from cooking pots and drainpipes to the columns and machines of the factories themselves.

متقدم

A full day; the cupola runs for hours once lit

التعليمات

Understand the cupola

A cupola re-melts solid pig iron and scrap into molten cast iron for pouring into moulds. It does not smelt ore like a blast furnace — it is a fast, cheap melting furnace that keeps a foundry supplied with liquid iron on demand.

Build and line the cupola

Build a tall cylindrical steel shell lined with firebrick. Set a ring of tuyeres for the air blast near the bottom, a tap hole at the base of the well for iron, a slag hole just above it, and a charging door near the top.

المواد لهذه الخطوة:

Firebrick100 قطع

الأدوات المطلوبة:

Trowel

Light the coke bed

Fill the bottom of the cupola with coke and light it, building a deep, glowing bed above the tuyeres. This bed both melts the iron and holds up the charge above it, so it must be well established before any iron goes in.

المواد لهذه الخطوة:

Metallurgical Coke60 كغ

Start the blast

Turn on the air blast through the tuyeres to drive the coke to melting heat. A cupola depends on a strong, steady blast — the harder it blows, within limits, the faster it melts iron.

الأدوات المطلوبة:

Air Blower

Charge in layers

Charge the cupola from the top in repeating layers: coke, then pig iron and clean scrap, then limestone flux, then coke again. Keep topping it up as the charge sinks so the furnace runs continuously.

المواد لهذه الخطوة:

Pig Iron Ingots80 كغ

Limestone6 كغ

Melt the iron

As the charge descends into the hot zone the iron melts and trickles down through the coke into the well at the bottom, picking up a little carbon on the way so it stays as cast iron. Molten metal gathers ready to tap.

Flux off the slag

The limestone becomes lime and combines with coke ash and dirt into a slag that floats on the molten iron. Periodically open the slag hole to run it off, keeping the iron in the well clean.

الأدوات المطلوبة:

Tapping Bar

Prepare the sand moulds

While the cupola melts, make moulds in moulding sand. Pack damp sand around a wooden pattern in a two-part flask, remove the pattern, and cut channels for the iron to flow in and the air to escape. Have the moulds ready before you tap.

المواد لهذه الخطوة:

Casting Sand60 كغ

الأدوات المطلوبة:

Moulding Flask

Tap the molten iron

Open the tap hole and run the molten cast iron into a preheated ladle. This is liquid metal near 1300 degrees Celsius — keep the path clear, work behind protection, and make sure the ladle and moulds are bone dry to avoid steam explosions.

الأدوات المطلوبة:

Foundry Ladle

Pour the castings

Carry the ladle to the moulds and pour in one steady stream until each mould is full and the iron shows at the riser. A smooth, unbroken pour avoids trapping gas and gives a sound casting.

Shake out and clean

Once the iron has solidified and cooled, break the sand away and lift out the casting. Cut off the runners and risers, knock off adhering sand, and grind the surfaces smooth. The waste iron and sand are recycled into the next melt.

الأدوات المطلوبة:

Angle Grinder

Identify cast iron

Grey cast iron is hard and brittle but immensely strong in compression and cheap to pour into intricate shapes — it cannot be forged, only cast and machined. From cooking pots and drainpipes to columns and machine beds, the cupola's castings built the fabric of industrial life.