But the romantic period of the hand-fed furnace and the gloriously beautiful pig beds at casting time are rapidly passing; in fact, are almost past. Modern “skip-hoists” carrying automatically dumped buckets or cars charge the furnace more economically than even low-waged laborers can do it. The two charging cars alternate, one filling at the bottom in the stock house while the other is dumping through the double bell at the top of the furnace. Furnaces are now tapped by power driven drills which make quick work of a formerly difficult operation. Instead of running it into the sand bed, the molten iron from the furnace is nowadays run into ladles alongside the cast house as is the cinder which was described above. If the metal is to be made into pigs it goes to the pig casting machine, where the traveling iron molds very quickly convert the entire cast into “chilled cast” pigs. At the top of the incline these pigs which have been cooling under sprays of water fall from the traveling molds into railroad cars below which deliver them to the consumer.
How Pig Iron Is Now Cast into Traveling Molds
Upper End of Casting Machine Where Pigs Are Dumped from Traveling Molds into Railway Cars
In large steel works the greater part of the molten iron is not cast into pigs at all but while yet molten is directly charged into the open-hearth or Bessemer furnaces which convert it at once into steel of which the greater part is made into plate, rails, or other shapes before being allowed to cool. Even the gas is recovered nowadays. Its journey through the “dust arrester” rids it of most of its dust, after which filters and washers clean it thoroughly. That not required for the heating of the stoves is used for firing the steam boilers about the plant and as fuel for batteries of huge gas engines which in large plants have been installed to generate low-priced electric current.
It should be noted that in modern practice iron is mined, loaded, transported to the furnaces, unloaded, charged and made into pigs or converted into steel and even into the finished products with practically no hand labor, all operations being performed by machinery.
Though a “direct” process for converting the ore into wrought iron or steel has been long sought, a method has never been found, except that used in the very small way followed by the old iron-workers with their crude furnaces. It has always proved commercially advantageous to make pig iron in the blast furnace as an intermediate step and then by a second step convert it into wrought iron, steel, etc. So the ore is brought from the mines to the furnace, the coke and limestone arrive from another region, and batteries of huge blast furnaces through the country make from them the pig iron.
| Blast Furnace Data and Annual Pig Iron Production | ||||||
|---|---|---|---|---|---|---|
| Year | Average Height[[1]] of Blast Furnace | Average Cu. Ft. Capacity of Blast Furnace | Average Daily Output in Tons Each | Tons Pig Iron Produced During Year | ||
| United States | Great Britain | Germany and Luxemberg | ||||
| 1850 | 30′ | 2000 | 29 | 565,000 | ||
| 1860 | 920,000 | |||||
| 1870 | 1,865,000 | 5,963,000 | 1,391,000 | |||
| 1880 | 70′ | 8200 | 117 | 3,835,000 | 7,749,000 | 2,729,000 |
| 1890 | 90′ | 18200 | 360 | 9,000,000 | 7,904,000 | 4,658,000 |
| 1900 | 100′ | 24000 | 600 | 13,790,000 | 9,003,000 | 7,550,000 |
| 1905 | 90 to 100′ | 24000 | 600 | 23,000,000 | 9,746,000 | 10,988,000 |
| 1910 | 90 to 100′ | 24000 | 600 | 27,300,000 | 10,380,000 | 14,495,000 |
| 1912 | 90 to 100′ | 24000 | 600 | 30,000,000 | 9,037,000 | 17,869,000 |
| 1913 | 90 to 100′ | 24000 | 600 | 31,000,000 | 10,654,000 | 19,292,000 |
[1]. No advantage has been found in furnaces having a height of over 110 feet.