Engineering Wonders of the World
Volume III

REMARKABLE MACHINERY. 261 The operator travels with the trolley, the motions of which he governs by means of mag- netic controllers, and always has a clear view of what is being done. The automatic buckets for this class of machines hold up to seven tons of ore, which can be dumped upon the top of the stock pile or into the railway trucks as required. These bridges are designed for quick operation, and are able to shift 1,500 tons each in ten hours—an achievement which necessitates the trolley travelling at a speed of 800 feet per minute along the girders. Their use is not confined to ore handling, for when fitted with lighter buckets they are employed to shift coal and limestone. From the transportation and loading we pass to the next process in steel-making— namely, the introduction of the ore into the blast furnace which extracts Blast from the ore the iron from ■ "it rn m which the steel is manufac- tured. A blast furnace consists of a huge column of brickwork inside a metal casing, shaped like a chimney, from 75 to 100 feet high, and about 20 feet in diameter at the largest part. At the top it is contracted and fitted with a bell to keep the gases from escaping. From the widest part, about 18 feet from the ground, the furnace tapers downward sharply to about 8 feet in diameter at the bottom. This lower tapered part is called the bosh. At several points round the bosh the air of the blast enters through water- cooled pipes called tuyeres. The contents of a blast furnace are, to put it briefly, a column of alternate layers of coke, ore, and limestone, varying in temperature from a white heat at the tuyeres to a black heat at the bell. The chemical reactions that take place provide the heat necessary to separate the metal from the refuse. For the full details of the process we must refer the reader to a good book on metallurgy.* The interesting feature of a * A simple explanation of the mechanical and chemical processes of iron and steel manufacture is given on pp. 207- 262 of How It Is Made. SECTION OF BLAST FURNACE. The air blast passes from the pipe P P into ths furnace through the tuyeres T T. Slag is drawn off at S, and the liquid iron at I. Ore, etc., is fed in past the conical trap C. blast furnace from a mechanical point of view is the method adopted in the United States and on the Continent for charging. A blast furnace producing 400 tons of iron per day of twenty-four hours requires three times that amount of material (1,200 tons) to be poured into it during that period. The charging installation consists of an inclined lattice girder reaching from the ground-level to the top of the blast furnace. The girder is fitted with two sets of rails, parallel to one another for the whole of their length up to