On the side of the vessel, the blast furnace, or other container designed for making steel are two or more plugs that stop-up holes in the thick walls. They are often huge, thick, and unwieldly, as they must sustain temperatures that can reach over 3,000 degrees, and the plugs must be stuck into the hole in a way that keeps the molten liquid inside. Have you ever wondered what the plugs are for?
In order to make steel, the coal used as the necessary carbon must be almost free of impurities. Huge ovens burn the coal in extreme temperatures so that the levels of the different metal contaminates drop to less than 5 percent. This new mixture is called coke and is then used in the huge blast furnaces or pouring vessels with the coke oven door plugs on the side.
The iron is heated to such a high temperature the layers form in the various impurities, iron, and coke. Once the metals are sufficiently heated to make those layers, the top plug is opened, and the impurities are poured off the mixture. The liquid metal is heated again, and scraps of iron are added to make the heat spread more evenly through the molten liquid. In some methods, oxygen is used to burn the few remaining impurities from the liquid, and all the remaining carbon. A contained amount of carbon is added to the mixture to make the desired type of steel.
Once the creation of the steel is complete, the bottom plug is removed, and the perfect mixture of carbon and iron is poured out to be used in items you use every day. The steel can be tempered, made into sheets, or shaped into designs.
Steel is an amazing metal that has been around for centuries. Someone long ago created the two-plug system in the vast containers that hold the hot metal mixtures – and we still use those plugs today.
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