A foundry furnace, specifically a cupola furnace, works by melting metal, typically iron, using a combination of fuel (coke), metal stock, and flux (limestone) under intense heat generated by a forced air blast.
Here's a breakdown of the process:
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Loading the Furnace: The cupola furnace is charged with alternating layers of:
- Metal Stock: This is the iron (or other metal) being melted.
- Coke: Coke, a carbon-rich fuel derived from coal, provides the necessary heat source when burned.
- Limestone: Limestone acts as a flux, binding with impurities in the metal and coke to form slag.
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The Air Blast: A powerful blast of air, often preheated, is forced into the furnace through tuyeres (nozzles) located near the bottom. This air blast fuels the combustion of the coke.
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Combustion and Melting: The coke burns intensely due to the air blast, generating extremely high temperatures. This heat melts the metal stock as it descends through the furnace.
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Chemical Reactions: The high temperatures facilitate chemical reactions within the furnace. The coke reduces any iron oxides present, and the limestone reacts with impurities to form slag.
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Slag Formation: The impurities, now bound to the limestone, form a molten slag that floats on top of the molten metal.
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Tapping the Furnace: The molten metal is tapped (drained) from the bottom of the furnace. The slag, being less dense, is tapped separately from a higher port.
Here's a table summarizing the components and their roles:
| Component | Role |
|---|---|
| Metal Stock | The material being melted (e.g., iron). |
| Coke | Fuel source for generating heat. |
| Limestone | Flux; removes impurities as slag. |
| Air Blast | Provides oxygen for coke combustion. |
Simplified Process Summary:
- The furnace is loaded with layers of metal, coke, and limestone.
- A strong blast of air is forced into the furnace, igniting the coke.
- The burning coke generates intense heat, melting the metal.
- Limestone binds with impurities to form slag.
- Molten metal and slag are tapped from the furnace.
