Melting furnaces

There are different types of melting furnaces used to obtain liquid cast iron for casting inside a mould. The following can be mentioned:

Cupola furnace

The cupola furnace, where melting takes place through the combustion of carbon coke, is a vertical furnace consisting essentially of a vertical metal tube called a shaft, internally lined with refractory material.

The carbon burns in direct contact with the material to be melted, which consists of crushed solid cast iron ingots and scrap cast iron. The slag produced made up of soil, ash and foreign bodies, considerably lighter than molten cast iron – floats to the surface and is easily removed. The liquid cast iron is poured directly into the ladles or into a crucible placed under the casting hole. This is the “historical” cast iron melting system, which is still used to some extent. In some types of cupola furnaces, the molten metal is not poured directly into the ladles, but into a crucible placed under the casting hole (fore hearth), where elements with corrective and purifying functions (de-sulphurising, deoxidising and scorifying) are added to improve the chemical and technological characteristics of the cast irons.

Electric induction furnaces

In electric induction furnaces, the molten metal acts like a closed short-circuited secondary, while the primary is constituted by a winding connected to an alternate current power supply. The Joule effect, by way of the eddy and conduction currents, is used to heat the mass to be treated. When the charge material is molten, the interaction of the magnetic field and the electric currents flowing through the induction coil produces agitation inside the molten metal, the extent of which depends on the power and frequency applied, as well as the dimensions and shape of the coil and the density and viscosity of the molten metal. This agitation inside the bath is important as it helps with the mixing of the alloys and melting of the turnings, as well as the uniformity of the temperature throughout the furnace.

Excessive agitation may increase refractory wear and alloy oxidation.  

This is a very popular type of furnace able to satisfy the need of cast iron foundries in terms of flexibility and speed.

Reverberatory furnace

The operating principle of the reverberatory furnace is based on air and combustible gas, which penetrate inside through two channels; when the air and gas meet inside the chamber, they enter into contact and burn, lapping a metal charge that can reach a temperature of up to 1800°C. The fumes produced are diverted to another section, where they heat the refractory bricks, thus restarting the cycle. Inside the main chamber, the cast iron is continuously stirred by a special rod to encourage the deposit of waste matter on the floor.

Rotary furnaces

Rotary furnaces, which have a cylindrical shape, are generally rested on rollers. The heat is typically provided by burners located at the ends of the cylinder. The ends of the cylinder can also be opened to introduce the material for melting, even in several steps.

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