Steel Making Process
Steel is an iron alloy that has specific additives that give it increased strength, resistant to corrosion and other properties (depending on the metals added in it).
Steel gives a better life and more durability and has replaced nearly all kinds of iron works. An ancient art, steel manufacturing goes back to ancient Rome, China and even India.
Steel production, however, was done on a limited basis as the process of refining iron ore and the tight quality control required was difficult.
This changed with the Bessemer process, where concentrated oxygen (99% purity) replaced normal air. Since air is nearly 78% nitrogen and is chemically neutral in the process, it would take a lot of time and effort to refine the ore.
Introduction of pure oxygen through the Bessemer process largely increased the efficiency and reduced the time required, making steel a commercial viability. Overtime, other processes have been introduced, which are much more efficient.
Steel Mini Mill & Electric Arc Furnace
Once a secondary process, minimills mostly consists of recycling scrap metal to create steel. Modern steel making industry has changed this, with many industries using it exclusively.
The most common method of steel making in minimills is using and Electric Arc Furnace (EAF). EAFs consist of a large vat known as the furnace, which is lined with corrosion resistant chemicals.
Scrap iron placed inside the furnace in a layered fashion (bottom layer of small pieces, middle of large and then the top of smaller scrap pieces).
How Graphite Electrodes are used
Three thick graphite rods are lowered into the furnace and are electrically charged. When the graphite cores touch the metal, they create an electric arc which heats the scrap.
As the top scrap melts, the graphite rods are lowered and the electric potential increased. After a certain depth, the rods are slightly raised, allowing the liquid metal to pool around it and conduct the heat and electricity more efficiently.
The process is highly controlled and to decrease the time for smelting, the furnace can be with heated through a gas/fuel fire or even charged with pre melted material from the last batch.
Once the scrap is melted and impurities float on top, the furnace is tilted and tapped, allowing for the metal to flow down into a ladle furnace, where further chemicals can be added according to customer requirements.
Since the electric arc furnace is a batch process that can be started up or shut down with ease, it has become a very popular choice as it allows steel manufacturers to follow the market demand and cut down on production without incurring process losses.
http://www.cim.mcgill.ca/ (link below)