STEEL.— Crucible.
a more solid steel. It is true that the quantity ofsilicon found in the steel is very small, but this maybe no measure of the quantity which may have beenreduced, as a double reaction may go on as follows:—
Si0 2 -t C ~ C0 2 + Si.
Si + 2CO = Si0 2 + 20.
In this way the carbonic oxide, which is known to beoccluded in large volume in the steel and is almost
certainly the cause of unsoundness, may be got ridof, and hence when dead melted the metal will con-tain no gas and will run solid. This question willbe touched upon again further on.
The metal having been “ dead melted ” has nextto be teemed. This is a delicate operation, andrequires a good deal of skill. The moulds areusually made of cast iron in halves, which arebound together by a hoop and wedges, after theinner surfaces have been well coated with alayer of soot from burning tar. They are placedslightly inclined in a small pit in the floor. Thesteel melter, having enveloped his legs in severallayers of sackcloth well steeped in water, standsstraddle legged across the furnace, and with thetongs, a (Fig. 11 ), grasps the crucible securely, liftsit quickly from the furnace, and deposits it into the“ teeming hole ” close behind him. The bottom of thisis covered with coke dust, to prevent the cooling ofthe crucible. The lid is then removed, and theclinker which may have gathered round the crucibleis cut away with a long chisel-shaped bar. Themelter then grasps the pot around the middle withthe teeming tongs, b (Fig. 11), and gradually poursthe steel down the centre of the mould, while anVOL. II.
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assistant keeps back any scoria that may be floatingon the surface with a “ flux stick,” which is simplyan iron rod on the end of which a lump of tenacioushot slag has been accumulated. When the pot hasbeen emptied the lid is put on, and it is returned tothe furnace preparatory to receiving another charge;one melter takes charge of six holes or twelve pots.The second charge is made lighter than the first,so as to lower the slagging line in the pot, for itis found that the pots eat away most along the levelof the fluid steel, owing to the corrosive action ofthe floating slag. With good pots a third chargecan be obtained, but they sometimes give out atthis point, and the steel is lost by running throughthe fire into the ash pit. It is very remarkable thatsteel which has thus run through the coke fire, called“slag” or “ runnings ” by the workmen, is found tohave taken up so much sulphur as to render it unfitfor the finer purposes, and it has therefore to beutilized for common steel castings, &c. The steelsets almost instantly in the small moulds used forcutlery and tool-steel ingots, which are about 3 inchessquare. The hoops are, therefore, knocked off atonce, the ingots removed and taken out into theopen air to cool. The tops are then broken offdown to the bottom of the piping, and if the steelhas been dead melted it is found to show a peculiarradiated structure, the lines of crystallization runningat right angles to the cooling surfaces.
If heavy ingots or castings are to be made, thecontents of a number of pots have to be pouredinto one mould. Sometimes this is done direct—that is, without the use of an intermediate receiver;and in this case the men have to be very expert,so as to keep up a continuous stream of metal froma great number of pots. The pots are broughtup in rapid succession, two men carrying a potbetween them in a pair of two-handled tongs;generally, however, where large castings are tobe made, an iron receiver, lined with loam, isplaced over the mould. This has a hole in thebottom, stopped by a fire-clay plug on the end of aloamed-up iron rod, which is lifted when the metalis to be poured. The rude valve above describedis kept closed till the contents of several potshave been run in. The valve is then lifted, andas the metal runs out, crucible after crucible isteemed into the receiver, which is never allowedto get empty till the mould is full. If the castingis large, the metal will continue to sink in the mouldfor some time, and fresh steel is added to make upfor the shrinkages.
Although David Mushet had patented “themelting of malleable iron in the form of bar orscrap, or iron ore, when sufficiently rich and pure,in crucibles, with a proper per cent, of carbonaceousmatter ,” in the year 1800, and had well describedthe process in his celebrated treatise on iron andsteel—thus clearly showing, what indeed was wellknown from the Indian process of making wootz,that at a high heat iron in the fluid state was capableof taking up carbon—yet most of the steel made incrucibles was produced from cemented bar before108