Today most molten iron goes into steel. Elements such as chromium, nickel, and manganese are added to the iron. The material is then tempered—heated and cooled to make it hard and tough. Forged—hammered or squeezed—steel is strong and dense. To produce iron and steel in traditional, integrated mills, the iron is first melted in huge blast furnaces, often more than 10 stories tall. These furnaces are water-cooled steel cylinders heated by blasts from other, dome-topped cylinders that heat air for melting ore.
Skip operators fill railroad cars with raw materials, such as iron ore, coke, and limestone, work controls that hoist the cars up to the top of the furnace, and dump the contents in layers into the furnace. Stove tenders heat air in the domed cylinders (or stoves) until it is the correct temperature and open valves to blast the heated air into the furnace. At temperatures exceeding 3000 degrees Fahrenheit, the materials burn and melt. The limestone purifies the iron, and pure molten iron collects at the bottom of the furnace, while the limestone and impurities float on the top as slag.
Blast furnace keepers and helpers then tap the furnace to remove the molten metal. They drill tapholes in the furnace's fire-brick lining and allow the slag to run out of the furnace. The liquid iron flows through a taphole that is drilled lower into torpedo or bottle cars that keep the iron heated. Keepers and helpers then shoot clay into the tapholes to plug them. One furnace can make as many as 8,000 tons of molten iron per day.
Pure molten iron may be cast into molded forms called "pigs," which are used to make engine blocks and other items. Pig-machine operators and their helpers run machines that position molds under ladles holding the molten iron. By moving controls, they tilt the ladles and allow the iron to flow into the molds. Workers spray the molds with lime to keep iron from sticking.
Most iron is made into steel in one of three kinds of furnaces: the basic oxygen furnace, the open-hearth furnace, and the electric furnace. To make steel, kiln operators heat minerals such as lime, chromium, or manganese before they are mixed with iron. Mixer operators transfer molten iron from bottle cars to mixers and mix the iron and other elements together. Furnace operators regulate the temperature and flow of coolant in furnaces into which charging-machine operators dump loads of iron and other elements. Using controls that move mechanical arms to pick up boxes of materials and rotate them, the operators spill the contents into the furnace.
When the steel is ready, the furnace is tilted or tapped to allow the molten metal to run into ladles. Next the steel is formed by pouring it into molds to make ingots. Hot-metal crane operators control cranes that pick up the ladles and hold them above molds. Steel pourers and their helpers assemble the stoppers used to plug these ladles. Other workers maintain the molds. Hot-top liners and helpers line the mold covers with firebrick and mortar. Mold workers remove the ingots from the molds and clean and coat the molds for the next casting.
The steel ingots then go to soaking pits for further processing. In the soaking pits, the ingots are reheated so that they may be rolled. Charger operators and helpers move steel through soaking-pit furnaces, where it stays heated at temperatures of up to 2450 degrees Fahrenheit for as long as 14 hours. The ingots are then ready for rolling or shaping into billets, blooms, and slabs. Bottom makers reline the bottom of the soaking pits with coke dust to keep oxide scale from forming on ingots. The soaking pits are then ready for more ingots.
Rail-tractor operators transport hot ingots and slabs from soaking pits to conveyors that take them to rolling mills. There, massive steel rollers squeeze the hot ingots into specified shapes. In five minutes, a 25" x 27" ingot can be rolled into a bloom with a 9" x 9" cross section or into a 4" billet. Roll builders and mill utility workers set up rollers for steel to pass through. Guide setters adjust rollers according to the type of shape required. Mill recorders control the scheduling of rolling ingots and record production data. Manipulators operate mechanisms that guide the ingots into the rolling mills. Primary mill rollers and rolling attendants operate machines that perform the first rolling operations. Roll-tube setters adjust machines that roll ingots into shapes for pipes and tubing.
Some rolled steel goes to foundries to be made into tools, heavy equipment, and machine gears. Most, however, goes to finishing mills to be made into sheet steel, piping, wire, and other types of steel. Hot-mill tin rollers run machines that roll slabs into sheets and strips. Roller-leveler operators run machines that remove wrinkles from sheets. Roughers, rougher operators, speed operators, screwdown operators, and table operators set up and operate mills that reduce billets, blooms, and slabs to various shapes, depending on requirements. Some finishing operators make seamless tubing by piercing steel billets lengthwise and rolling them into tubing. Reeling-machine operators then round out and burnish the inner and outer surfaces of these tubes. As steel strips are made, coiler operators wind them into coils, checking for defects and cutting them into specified lengths. Tubing-machine operators roll metal ribbon into tubes and solder the seams to form conduit. Finishers roll strips, sheets, and bars to specified gauges, shapes, and finishes.
Most rods and tubes and other solid and hollow objects are formed through extruding and drawing hot metal through a die. Draw-bench operators and their helpers adjust dies to specified dimensions and draw hot metal rods through them to give them a specified shape and diameter. Tube drawers do the same in forming steel tubes.
Other workers process metal that is recovered in powder form from other iron and steel making processes. Much of this powder comes from dust in furnace flues. Batch makers tend equipment that recovers powdered metal and separates it from impurities. Mixers blend batches of powdered metal, and sinter workers make sinter cake, a mass of powdered metal formed without melting. This powder is processed by press setters and operators to make bearings, gears, filters, and rings.
The introduction of technology into the manufacturing process has increased productivity, but reduced the number of workers needed to operate certain types of machinery in steel manufacturing plants. Computer-controlled machine tool operators oversee computer-controlled machines or robots during the steel manufacturing process. Computer numerically controlled machine tool programmers design software programs that control the machining or processing of steel.
Steel production is recorded by workers to assure that procedures are carried out correctly. Inspectors and assorters check steel products to make sure they meet customers' specifications. Other workers test samples of metal to measure their strength, hardness, or ductility.
The industry also employs various mechanics and construction workers, including bricklayers who line furnaces with firebrick and refractory tile and repair cracked or broken linings. Millwrights install and maintain equipment and machinery. Electricians install and repair computer controls for machine tools and other equipment. Industrial engineers determine the most efficient and cost-effective methods for production. Mechanical engineers often work in management positions to solve mechanical issues on the production line. Environmental engineers design, build, and maintain systems to control air and water pollution. Metallurgical engineers try to improve or alter the properties of steel, as well as find new uses for the metal. General laborers are employed to feed, unload, and clean machines; to move supplies and raw materials; to hoist materials for processing; and to perform a variety of other unskilled tasks. Other workers bale scrap metal or strap coils.
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