The main smelting unit in the steel industry is the open-hearth furnace. It is intended for smelting steel of a given chemical composition and with certain physical and mechanical characteristics. The open-hearth furnace, which has survived several industrial and technological revolutions, allows smelting the most complex steel grades , including alloyed ones.
The open-hearth-type melting furnace is a flaming reflective unit of the regenerative principle of operation, consisting of the following structural elements:
- Workspace, including the back and front walls and the arch.
- Heads with vertical channels through which the supply of fuel and air mixture to the working chamber and the removal of combustion products from it.
- Gas and air slag, designed to collect and accumulate large fractions of melting dust.
- Regenerators to ensure a constant temperature regime by heating the gas fuel and air mixture with heat from the residual combustion products that exit the working chamber.
- The system of flip reversing control valves, designed to change the direction of supply of gas fuel and air mixture into the working space, as well as to remove combustion products from it.
- Heat recovery boiler.
- Chimney.
The open-hearth furnace is a symmetrical unit, which implies the same design of its right and left parts relative to the vertical axis. Loading of raw materials is carried out through special openings - filling windows, closed by valves, which are thick steel plates. An outlet is located on the rear wall of the unit through which the finished steel is drained into a ladle. During melting, the outlet is clogged with low-caking refractory clay, which is knocked out when the finished melt is discharged.
The open-hearth furnace allows producing almost all types of carbon steels and many grades of alloy steel. But the use of various charge materials necessary for the open-hearth process saturates the molten metal with a significant amount of harmful impurities. Even a tiny fraction of such additives as sulfur, phosphorus, arsenic and some other elements contribute to a sharp deterioration in the physicochemical properties of steel, reduce the plastic properties of the metal, and give it excessive brittleness.
An electric arc furnace is intended for the smelting of high-quality grades of steel. The whole history of the development of mechanical engineering and metallurgy boils down to the struggle for the qualitative characteristics of metals, the improvement of their mechanical, physical and chemical properties. And the secret of the highest quality of the metal lies in its chemical purity. Electrometallurgy helps to obtain chemically pure, which means high-quality metals and alloys. The bulk of alloyed high-quality steels is smelted in electric arc furnaces.