The essentials of operating an acid converter are here given. The operation for the basic method is but slightly different.

After the converter has been emptied of a charge, the vessel is revolved another quarter of a turn until it is upside down. In this position it rests for a moment to drain out the excess of slag, and another quarter revolution places the vessel horizontally. In this position it receives a new charge. Ten tons or more of metal are brought over from the mixer in a large ladle and poured into the converter. Cranes * and other lifting appliances handle the ladle and other movable equipment, and all the movements of the converter are managed by mechanical appliances, handled by an operator on a high platform at a safe distance from its heat. Metal poured into the mixer is always hot enough to remain fluid for an hour or more and it needs no re-heating when conveyed to the converter.

The converter, with its new charge, is now revolved to an upright position, and the air blast is turned on just as soon as the metal begins to reach the tuyeres, to prevent it flowing into the blast box. The air pressure is about 20 or 25 lbs. per square inch, sufficient to push through the molten metal.

The chemical part of the operation at once begins when the air enters the molten metal, and a yellow flame of burning impurities, accompanied by a profuse shower of sparks of burning iron, issues from the mouth of the converter. Silicon and iron are first attacked by the oxygen, and these form, when oxidized, a slag which tends to rise, but is kept more or less agitated and mixed with the charge. After the silicon is burned out, the carbon is next attacked, and the formation of carbonic oxide causes a violent bubbling of the charge, a stage known as the boil. The small quantity of manganese usually present is now oxidized, and passes into the slag.

After about 20 minutes, the flame from the mouth of the converter has about died out, indicating the complete oxidation of carbon, silicon and manganese. A continuation of the blast would ruin the charge of metal by filling it with iron oxide. The blow is then stopped, but just before doing this, the converter is turned horizontal to prevent metal entering the tuyeres. Little, if any, of the sulphur and phosphorus originally in the iron are removed, because in the presence of the silicious lining these impurities cannot remain oxidized.

* Figs. 25 and 27 show cranes and appliances for handling large ladles. Each of these views shows a ladle suspended from the crane.

After the blow the charge consists of molten iron without carbon silicon or manganese, but it contains phosphorus, sulphur and iron oxide. Enough carbon must now be supplied to produce the kind of steel desired, also the iron oxide and gases mixed with the charge as a result of the blow must be removed, so far as can be done. These are accomplished by adding to the charge about 10% of ferro-manganese. This is melted in a small cupola near the converter, or may be thrown cold into the converter in small quantities. The quantity and composition of the ferro-manganese must be so adjusted that the carbon therein will give the converter contents just the needed amount, and the quantity of manganese must be sufficient to reduce the iron oxide and also consume the free oxygen absorbed in the charge, the oxide of manganese so formed rising into the slag. The slight agitation caused by these reactions helps to expel inert gases from the charge.

The stopping of the blow allows the charge to become quiet, and most of the slag and gases rise to the surface. After the ferro-manganese has been stirred in thoroughly (which must be done promptly, as the metal must not become chilled) the process is completed by tilting the converter and pouring its contents into a large ladle, previously heated inside by a charcoal fire or an oil flame. The greater part of the slag flows from the converter into the ladle and floats on the surface of the metal, affording it protection against oxidation and rapid cooling. Some slag sticks to the converter lining. This protects the lining, assists in the converter reactions of the next charge, and retains much heat.