IRON IN ANCIENT DAYS
The first use of iron in the service of man dates far back into the ages. An iron tool was found in the pyramid of Kephron which must have been used 3,500 years before Christ. However, because of the difficulty of working it, iron was not extensively employed except for swords and cutlery. The conversion of iron into steel and the tempering of steel blades grew to be an art which gave Damascus and Toledo a world-wide reputation that dates back over a thousand years.
The ancients used to smelt their iron ore in what was known as a Catalan forge because of its extensive use in Catalonia, Spain. Whether the forge was invented there or not we cannot say. Similar forges have been found in India and other widely remote places. They comprised an inclined tray leading to a pot which formed the furnace and in which a charcoal fire was kindled. The ore and charcoal were placed on the tray and from time to time were raked down into the furnace and air was forced into the bottom of the furnace by means of bellows. In an improved form of the Catalan forge air was furnished by means of an air compressor operated by a stream of water. This has already been referred to and illustrated on page 90. Limestone served as a flux to melt the earthy matter. The iron obtained from these primitive furnaces was not heated sufficiently to flow as a stream, but was merely reduced to a pasty mass which was then hammered into shape by the blacksmith. Ten or twelve pounds of metal per day was considered a fair output for one of these forges.
DISCOVERY OF COKE
It was not until the middle of the 14th Century that a blast furnace, crudely similar to those we have to-day, was first built and with it a temperature was obtained that was high enough to turn the metal into a liquid which could be cast in molds. Charcoal continued to be the fuel used until about four centuries later, when Abraham Darby discovered that by baking coal to remove its free gases, he could produce a new fuel known as coke which was a good substitute for charcoal. This gave a wonderful impetus to the iron industry in England where there were ample deposits of coal adjacent to the iron mines. Shortly after that, Mr. Henry Cort of Gasport, England, invented the processes of puddling and rolling the product of the blast furnace, thus converting the iron into a tough, malleable metal.
ALLOYS OF CARBON AND IRON
We must pause here to learn the difference between cast iron, wrought iron and steel. Iron, as we know, has a high affinity for oxygen. When exposed to air and moisture it oxidizes, rusts very quickly. The iron we find in nature is largely oxidized. In other words, it is rusty. It is also found in combination with other elements as well. The object of putting iron ore through a furnace is to rid it of oxygen and this is most readily accomplished by melting it in a carbon fire. The highly heated carbon combines with the oxygen and passes off as carbon dioxide and carbon monoxide gas. But a certain amount of carbon unites with the iron and it is this alloy of carbon and iron that makes cast iron so stiff and brittle. The less carbon present the softer is the metal and pure iron is very ductile.
It was to rid cast iron of its carbon content that Cort invented the puddling process. As the metal came out of the blast furnace it ran into a “reverberatory” furnace where, without coming in contact with coke or other carbon fuel, it was exposed to flames from an adjoining furnace which burned out the carbon, and then the carbon-free iron was cast into large pieces known as blooms which were hammered to rid them of slag. The final product was known as wrought iron. Wrought iron then differs from cast iron in having no carbon. Steel, on the other hand, stands half way between wrought iron and cast iron in having a small percentage of carbon. How steel is made will be described later.
MECHANICAL HANDLING OF ORE
Of course machinery plays a large part in the modern iron industry. It would be an endless task even to load one of the big blast furnaces by hand and then the enormous output of molten metal—40 tons for every pound produced by the old Catalan furnaces—could not be handled without ponderous machines whose huge arms and fingers are not scorched and blistered by the intense heat. Along the Great Lakes vast loading machines fill the holds of ore vessels and at the plant there are enormous unloading machines that travel on rails. These have long bridgelike arms that reach out over the ore boat and drop huge clam-shell buckets into their holds. The buckets quickly unload the boats and dump the ore on shore where other buckets pick up the ore, carry it back and pile it up in big heaps that look like mounds of reddish earth.