An electric arc furnace is a high-temperature furnace that uses high-voltage electric arcs to make steel. Electric arc furnaces are a feature of the so-called minimills that recycle iron and steel scrap into new steel products. The electric arc furnace was invented in France in 1907 and adopted in the United States soon afterward. As of 2010, roughly half the steel produced in the United States was made in electric arc furnaces.
How It Works
An electric arc furnace is essentially a giant kettle lined with heat-resistant ceramic refractory material. The furnace has a water-cooled lid that lifts off for loading with scrap. The lid also holds the three graphite electrodes that create the electric arc to melt the scrap into new steel. Large electric lines lead to the furnace. The lid tilts up for loading. When the furnace is loaded, the lid is lowered and clamped tight, and the electrodes are lowered into the scrap. When power is fed to the furnace, the electricity jumps into the steel from the two energized electrodes and travels through the steel to the neutral electrode connected to ground. The direct and radiant heat from the electric arcs melts the steel scrap.
To obtain additional heat, steelmakers inject pulverized coal and oxygen to supplement the electrical heat. Roughly 35 percent of the heat produced in electric arc furnaces comes from injection of fuel and oxygen. The additional energy is precisely controlled to ensure that the carbon content of the finished steel is at the level required for the products to be made from it.
Throughout the melting process, the steelmaker monitors the furnace temperature and takes samples of the melt to check the progress. When the steel is done, the molten metal is drained from the furnace into a vessel called a "teeming ladle" that carries the melted steel to a nearby mill, where it will be cast or forged into products. An electric arc furnace works fast. It can melt a load of steel in as little as an hour.
Pluses and Minuses
Electric arc furnaces have several advantages for steelmaking. They provide precise control of temperature and internal atmosphere. Because they start with scrap metal, electric arc furnaces are economical compared to other steelmaking processes. They can cost-effectively make batches of steel as small as 1 ton. On the minus side, electric arc furnaces can't be put just anywhere. The process is noisy. It also requires access to lots of cheap electricity, road or rail access to bring in a steady supply of scrap metal, and room to site a steel mill to process the furnace's output.