How Iron is Extracted and Turned into Steel
Banded iron formations are sedimentary rock, which is mined in every continent except Antarctica. Crude iron ore, which is obtained by grinding the rock (commonly called taconite in North America) into powder and separating the ore with powerful magnets. The ore is then heated and formed into marble-sized pellets, that will later be converted into iron, and eventually turned into sheet metal
Coke is formed from bituminous coal and used to fuel the iron-making furnaces. The coke is sealed in airtight ovens and baked for 12 – 16 hours, it’s then removed from the oven as solid carbon fuel.
The fuel and iron pellets now come together in the blast furnace, where limestone is added to remove impurities. From below the blast furnace; a continuous blast of super-heated air combusts the coke, intensifying the heat and changing raw materials into molten iron. Sometimes more than 9000 tons a day are created by just one furnace, reaching temperatures of almost 15000°c. At regular intervals the molten iron is tapped from the brew into giant submarine ladles, these are transported on rails to the basic oxygen charge where iron is turned into steel.
The steelmaking process begins by dumping recycled steel scrap into the BOF vessel (Basic Oxygen Furnace vessel) and adding hot iron. High purity oxygen is blown into the mix at supersonic speeds and molten iron becomes molten steel. In this fast-paced sequence, up to 250 tons of steel can be made to order in less than 45 minutes.
How Molten Steel Is Transformed into Sheet Metal
Molten steel is tapped from the BOF vessel into a ladle, a large portion of it is then transported into a vacuum de-gasser, where it is made highly formable. The focus then shifts to forming and finishing, which determine even more of the steel’s characteristics. The first step in this sequence is to position the ladle above a massive tundish, or funnel, that feeds a continuous caster containing moulds that shape the steel. The molten steel (now at 1600°c) is channelled from the ladle to the tundish and then to the caster. Inside the caster, the molten steel cools and becomes a red hot solid.
The shape of the mould determines the shape of the semi-finished products that come out of the caster, and because most steel plants make sheet metal products; most of the casters output slabs. The steel slabs are typically 8-9 inches thick and 3-5 feet wide. As they exit the caster, the steel slabs are cut into sections up to 40 feet long and stacked to await further processing.
Next, it’s on to the hot strip mill. This is where the huge steel slabs are transformed into steel sheet metal. The slabs are reheated to 1300°c and descaled before running through a series of roughing stands which make them thinner and longer. They then cycle through finishing stands where they’re rolled even thinner. Once cooled, the sheet metal is rolled into coils that may be 1000’s of feet long, but only a fraction of an inch thick.
Treating the Newly Formed Sheet Metal
The sheet metal rolls are moved to the pickling line; this is where coils move through an acid bath that cleans the surface of the metal. Some of the emerging coils are then shipped directly to customers as ‘hot-band’, others are destined for applications that require special finishing.
Sheet metal rolls that require further finishing are ‘cold rolled’ to make them even thinner. Again, coils may be shipped at this point or go on to one or more additional finishing processes such as;
- Coating, to make the steel resistant to make corrosion.
- Tinning, to further reduce the gauge and add the tin coat we commonly see on canned goods.
- Annealing, to make steel that is easier to bend and form.
- Tempering, that uses special rollers to add hardness and create surface textures.
Where Does the Steel Sheet Metal Go from There?
Out of the finishing facility, the steel sheet metal will then be shipped to metal fabrication companies across the world. There the sheet metal is cut, bent, punched, welded, polished and more. What started off as taconite now becomes the products we see in our homes, high-rises, highways and every other part of our daily lives.
Amazingly, the journey doesn't end there for most steel products. As the world progresses to become more eco-friendly; recycling is becoming more common. Here you can watch a video which follows the recycling process of steel in the United States.
The entre process; from rock in the ground to steel sheet metal, is completely untouched by human hands. The process is instead controlled by operators using state of the art, fully automated equipment from pulpits that overlook the action.
Sheet metal rolls leave the finishing facility as the industries newest superstars; lighter, stronger, highly engineered formable steels that were unheard of less than 200 years ago.
Radshape is a metal fabrication company based in the heart of Birmingham. If you’re interested in the metal fabrication processes offered by Radshape, you can check them out here. Alternatively, you can call our friendly team on +44 (0) 121 242 3323 or email us at email@example.com if you require professional metal fabrication services.