Early Iron Rolls
While Cort did not originate the idea, it was he who first made the rolling process successful, and, therefore, he is given credit for the invention.
But Cort did not stop here. He saw the desirability of a quicker and more economical method of reducing the “blooms” or balls of iron into bars or other finished shapes than the hammering process up to that time used. He accomplished this by the use of power driven rolls, such as those shown in the cut.
These two inventions of Cort’s were epoch making, though of the two the more important one was the invention of the rolls from which has developed the modern rolling mill.
There remains to be described in a little more detail the making of wrought iron as practiced to-day. The puddling furnace used has a grate upon which is built the coal fire. The long flame passes over the fire wall and is deflected by the roof down upon the charge of pig iron piled upon the “fettling” or lining of iron oxide (iron ore or mill scale) over the air or water cooled iron plates which form the bottom and the sides of the hearth.
With a long iron bar the “puddler” (the expert attendant) turns the pigs until they have melted down into the bath of slag or cinder charged and continually being formed by the chemical union of iron from the ore or pig and some of the sand and other impurities present. This cinder, which is largely a silicate of iron, is a protection for the bath of molten iron and its use prevents excessive oxidation and loss of metal.
During the melting of the charge the heat is kept as high as possible and the molten iron is “puddled,” i. e., stirred, by the “puddler” or his helper with a “rabbler” or iron bar. In order to take out the phosphorus and sulphur, which for best results should be removed before the carbon is eliminated, the heat of the furnace is lowered somewhat as soon as all of the pig has melted, and some iron oxide is mixed into the “bath” of molten iron and cinder. Most of the phosphorus and sulphur are chemically acted upon and pass into the cinder which covers the iron. Soon the mass begins to boil or seethe and small blue flames break through the cinder covering. This indicates that the carbon is being oxidized by the oxygen of the iron ore which was added, the oxygen, as in the blast furnace, having a greater “affinity” for carbon than it has for the iron.
This “pig boiling” goes on for twenty or thirty minutes, the “puddler” meanwhile “rabbling” the charge in order to hurry the reactions and to make sure that all parts of the bath of molten metal are uniformly exposed to the oxidizing conditions.
The Making of Wrought Iron To-day. Charging the Pig Iron
Soon the metal begins to “come to nature” and little lumps of pure iron here and there through the bath stiffen up into little pasty balls. Some may be seen sticking out through the cinder covering of the bath and others must be torn loose from the bottom with the rabbler. This “balling” period lasts from fifteen to twenty minutes, during which time all of the iron has “come to nature.”