Chemistry

How to Make Iron



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Making Iron

The simplest way of making iron is with the so-called Catalan forge named after the Catalan district in Spain Although the basics of the process has been known for thousands of years. In this method the iron ore, an oxide of iron, was mixed with charcoal and some sort of fluxing agent rich in calcium. Limestone is usually best, but other rocks rich in calcium have been used when limestone is not available. The commonest one is basalt it is hard to make iron using basalt, but at least it works. It was then exposed to a blast of air from a bellows that made the fire burn hotter until a ball of molten iron was formed from the ore and flux. This ball of iron contained much slag that had to be removed by beating the mass that weighed upwards of 100 pounds with a large hammer driving out the slag as droplets.

A Catalan forge has a hearth that was slightly concave to hold a charge that could weigh upwards of 300 pounds of raw ore, charcoal and flux. The hearth of the forge was covered with a layer of charcoal powder, and then the forge was charged with the above mixture. The bellows were arranged so that a continuous blast of air could be directed at the charge by the use of two bellows, and a box between them to equalize the air. This process was called a "bloomery" and made iron by the direct method of refining. In this process the finished product was wrought iron.

This method of making iron is within the grasp of any blacksmith, and is still used today in many parts of the world. Some artisans in the United States use this method for making specialized iron for their wares.

A more complex method of making iron in the form of cast iron pigs was with the blast furnace. Here a large pear shaped chamber was erected from firebrick or firestone that was a schistose variety of quartzite. This chamber that was called the bosh could be more then twenty feet high, and over nine feet in diameter. It was surrounded by a layer of sand that acted as insulation. Finally the covering of the furnace was made from cut building stones. The covering had as many as four arches build into its base. One of the arches was so that the furnace could be tapped of its fiery iron when required. The other arches were for the great pipes called tuyeres. These were used to admit compressed air from the bellows into the lower part of the furnace to supply the blast. A furnace could remain in blast for months closing down only in the winter when the waterpower used to supply the air blast or to operate the helving hammer froze. Sometimes this also happened during severe droughts.

The iron ore, limestone and charcoal was introduced to the furnace from the top next to the furnace stack. A covered bridge was run to the top of the furnace from what was called the charging bridge that was at the same level as the top of the furnace. This level of the charge remained pretty constant while it was smelting iron ore. As the charge burned away in lower levels of the furnace more charge was added at the top.

When a sufficient amount of iron had collected in the crucible at the very bottom of the furnace the ironmaster tapped the crucible so that the white hot iron flowed out of the furnace into molds made of sand that produced the desired pig iron. He also tapped regularly the tap hole further up the side of the crucible allowing the slag to run out onto the sand floor of the furnace house. The workers would break it up, and dispose of it on the slag heap somewhere away from the furnace.

The last thing done with the iron if it wasn't used for casting was to send the pigs to a "Finery" where it was converted into wrought iron the same way it was done in one of the earlier bloomery forges.

This was how iron was made in the 19th century.

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