The process immediately following the puddling or boiling is called " shingling," and consists in hammering the puddled balls with either the helve or steam-hammer, or in passing them through a squeezer till they are sufficiently consolidated, and the greater part of the cinders forced out. For a description of the steam-hammer, which is much used for heavy forgings as well as for shingling, see that head. Piddled balls which have undergone shingling are called slabs or blooms. These are next passed through heavy rollers termed "forge" or "puddle-bar rolls," and reduced to the form of a fiat bar. For all the better kinds of iron the bars thus treated are cut into short lengths, piled together, reheated in a furnace, and again passed through the forge rolls. Once more the iron is cut, piled, and heated, and then passed through the " con of what are termed the " bolting" or " rough rolls," and finally through the •' finishing rolls." Both these sets of rolls in the case of plates and sheets are plain, but in the case of bars are grooved, so as to form them into the required shape, such as fiat, square, round, octagonal, or T-shaped iron.
There is still another important variety of iron, viz., steel, the manufacture of which remains to be described. Steel differs from malleable iron in containing a varying pro portion of carbon, usually from .5,to 1.8 per cent. When rich in carbon, it closely e resembles cast-iron in composition, except that it is more free from impurities. Steel can be made by adding carbon during the direct reduction of a pure iron ore in a furnace or crucible. but the results of this method are scarcely ever uniform. The finer kinds of steel are still made by the old cementation process—that is, by the roundabout plan of first converting cast into malleable iron, by depriving the former of its carbon, and then adding carbon again by heating the iron with charcoal 4see BLISTER STEEL). In making any kind of steel, however, the getting rid of silicon, phosphorus, and sulphur is as important, and a matter of more difficulty than the securing of any required pro portion of carbon.
As blistered steel is full of cavities, it is necessary to render it dense and uniform, especially for the finer purposes to which steel is applied. By one method it is con. verted into what is called "shear steel." This is done by breaking the bars of blister steel into short lengths, heating them in bundles, and partially with a forge hammer. The rod so formed is heated again, and now brought under the action of the tilt-hammer. Here, by a succession of blows, it is formed into bars, which are much more compact and malleable than blister steel, and consequently better fitted for edge tools and the like. If the single-shear steel is doubled upon itself, and again welded and drawn into bars, it is called double-shear steel. By another method, viz., that of melt ing the blister steel in fire-clay crucibles, and casting it into ingots, " cast-steel " (q.v.) is made. This is the best kind of steel, being finely granular, homogeneous, dense, and well adapted for the finest cutting instruments.
Steel is now largely made directly from pig-iron by puddling, much it the same way as that process is applied to the production of malleable iron (see STEEL). By another plan (1.7chatius's process), pig-iron is granulated and heated in a crucible with the oxides of iron and manganese, and fire-clay, the result being cast-steel. This process has succeeded well in Sweden. The Siemens-Martin process consists in melting pig-iron along with malleable iron and Bessemer steel scrap, about 7 per cunt of spiegcleisen being added towards the end of the process. The operation is ccultk led in the Siemens regenerative furnace, and the product in this case is also cast-steel.
There are also several modes of manufacturing steel direct from the ore, such as by the old way in the Catalau forge, and by Chenot's process, in which hydrocarbons are used.
Bessemer's method of producing malleable iron directly from pig-iron is altogether a failure. Steel, howeVer, is successfully and largely made by his process. which consists in blowing air through molten pig-iron till the whole of the carbon and silicon is removed by oxidation, and then iqtroducing into the melted iron a given quantity of spiegelcisen (a peculiar kind of casAron), containing a known percentage of carbon (see I.:ESSE:UE.1G PROCESS).
It would appear from the results of recent experiments made on the large scale at Middlesborough, that Messrs. Thomas & Gilchrist have succeeded, by a comparatively simple device, in practically eliminating the phosphorus from Cleveland pig-iron during the conversion of the latter into steel in the Bessemer converter. The great importance of this discovery will be at once understood when we state that the Cleveland iron is the cheapest in Great Britain, and that the Cleveland ore yields one-fourth of all time iron made in the country. Hitherto it has not been remunerative to make steel from this. pig-iron on account of the exceptionally high percentage of phosphorus it contains, and the difficulty there has been of removing an ingredient so deleterious to steel. Success, however, has at length been achieved by obtaining, through the use of lime and oxide of iron, a basic slag in the converter, and by listing this vessel with bricks made chiefly of magnesian limestone fired at a very high heat. A basic lining is thus given to the con verter instead of the ordinary siliceous one, which is acid, and so a base is furnished with which the phosphoric acid can combine without the certainty of the lining being eaten away by the basic slag, as would be the case when this lining is siliceous. It is only as respects the nature of the sh* in the converter, and the kind of lining used for this vessel, that Thomas & Gilchrist's mode of making steel, as far as it has yet been tried, differs from Bessemer's; except that for the latter a high-priced pig-iron is required. Of course steel can be made by the new process from other low-priced irons besides Cleveland.