In Bessemer's early days, it was arranged that he should attend a meeting of ironmasters at Birmingham to explain his new process. On the morning of his lecture two eminent ironmasters were breakfasting together in a Birmingham hotel when one exclaimed to the other, "What do you think, there is a fellow coming here to-day to tell us how to make steel without fuel." To this eminent South Wales ironmaster the proposal seemed preposterous but it was true all the same.
Although vast quantities of steel are made by the Bessemer process there is another one of equal importance known as the Siemens-Martin Open-hearth process. In this the molten metal is kept in a huge
bath practically boiling until the carbon has been reduced to the required amount. Perhaps the most interesting feature about it is the way in which fuel is saved by what is called the "regenerative" method due to that versatile genius Sir William Siemens.
The open-hearth, as it is termed, is a huge rectangular chamber of firebrick with a firebrick roof, and doors along one side just under the roof through which the process can be watched and new materials be added from time to time.
The fire is some way away and not underneath as one might perhaps expect. Now if a deep coke fire is fed with insufficient air it does not give off carbonic acid such as usually arises from a fire, and which as everyone knows will not burn, but a gas called carbon monoxide which will burn very well. So the fire-place for these furnaces is constructed in such a manner as to produce carbon monoxide, which then passes through a huge flue to one end of the open-hearth. Here it meets air coming through another flue and the two combining burst into flame over the metal.
The hot gases resulting from this burning pass out through a flue at the other end of the hearth to a tall chimney which causes the necessary draught, but on their way they pass through a chamber loosely filled with bricks. Consequently the hot gases only reach the open air after having given up much of their heat to these bricks.
After that operation has been going on for a time certain valves are operated and the gas and air then
come in at the other end of the hearth, travelling through it in the opposite direction. And the air comes through the chamber which has the hot bricks in it, bringing back into the furnace a large quantity of that heat which otherwise would have gone up the chimney but which the bricks intercepted. Thus all day long does this reversal take place at intervals, the fresh air all the time picking up and bringing back some of the heat which just previously had escaped towards but not into the chimney. This arrangement enables the process to compete, so far as economy is concerned, with the Bessemer process.
At intervals the steel is tapped off from the furnace and run into ingot-moulds, the same as with the other process. On the whole it is regarded as producing a slightly better steel, the operation being under slightly better control.
However the steel is made the ingots are reheated and either hammered under a powerful steam hammer or pressed in an enormous hydraulic press. This greatly improves the quality.