In the most promising form of this process an acid converter and a basic open-hearth furnace are used.
The slag is then poured and skimmed, the blast turned on and converter retilted.
Looking at the duplex process in another way, the preliminary desilicidizing in the Bessemer converter should certainly be an advantage; but whether it is more profitable to give this treatment in the converter than in the mixer remains to be seen.
Whatever be the form into which the steel is to be rolled, it must in general first be poured from the Bessemer converter in which it is made into a large clay-lined ladle, and thence cast in vertical pyramidal ingots.
The other items of cost are labour, the quantity of which depends on the mechanical appliances provided for handling the converter shells and inserting the lining; and the blast, which in barrel-shaped converters is low and in vertical converters is high, and which varies therefore from 3 to is lb to the square inch.
Though all this is elementary to-day, not only was it unknown, indeed unguessed, at the time of the invention of the Bessemer process, but even when, nearly a quarter of a century later, a young English metallurgical chemist, Sidney Gilchrist Thomas (1850-1885), offered to the British Iron and Steel Institute a paper describing his success in dephosphoriz ing by the Bessemer process with a basic-lined converter and a basic slag, that body rejected it.
Why the molten metal can be freed from mechanically suspended slag more perfectly in them than in the Bessemer converter or the open-hearth furnace.
In either case such a lining is expensive, and has but a short life, in few works more than 200 charges, and in some only loo, though the silicious lining of the acid converter lasts thousands of charges.
When the converter is full the pressure is raised somewhat, and the heating continued until the conversion is complete.
Electric furnaces are at an advantage over others as regards the removal of sulphur and of iron oxide from the molten steel, because their atmosphere is free from the sulphur always present in the flame of coal-fired furnaces, and almost free from oxygen, because this element is quickly absorbed by the carbon and silicon of the steel, and in the case of arc furnaces by the carbon of the electrodes themselves, and is replaced only very slowly by leakage, whereas through the Bessemer converter and the open-hearth furnace a torrent of air is always rushing.