Melting means of cast-irons - Cupola furnaces

Since the 2000s, the melting equipment used by foundries has undergone major changes:

• reduction in the number of cold-wind cupola furnaces and in the share of liquid pig iron tonnage supplied by this means,

• decrease in the number of hot-air cupolas, but tonnage virtually unchanged,

• the number of induction furnaces and their share of tonnage virtually unchanged.

One of the main reasons for this development is the tightening of environmental regulations. Faced with the need to control waste, smelters have preferred to invest in electric smelting when renewing their smelting equipment. The advantages and disadvantages of the different melting methods, and their respective fields of excellence, are well known to foundrymen:

• the cupola is a single-use machine that is only justified for high tonnages (6 to 12 tonnes per hour), in the case of cold-wind cupolas, and this mainly in lamellar graphite cast iron. Above 10 to 12 tons per hour, a hot-air cupola is preferred;

• the [M 765][M 766][M 767] medium-frequency induction furnace is best suited to foundries producing several grades of cast iron, including spheroidal graphite cast iron and alloyed cast iron. On the other hand, its metallurgical operation is more delicate than that of the cupola furnace, particularly when it comes to carbonizing lamellar graphite cast irons.

The cost of producing liquid cast iron depends on the materials used, the nature and relative proportions of which are linked to the melting process.

This article describes the technology and operation of the various cupola furnaces. The various developments studied by foundries, with the aim of reducing production costs, show that this means of melting can be a tool that contributes to sustainable development.