Text d Finishing Processes

Steel is marketed in a wide variety of sizes and shapes, such as rods, pipes, railroad rails, tees, channels, and I-beams. These shapes are produced at steel mills by rolling and otherwise forming heated ingots to the required shape. The working of steel also improves the quality of the steel by refining its crystalline structure and making the metal tougher.

The basic process of working steel is known as hot rolling. In hot rolling the cast ingot is first heated to bright-red heat in a furnace called a soaking pit and is then passed between a series of pairs of metal rollers that squeeze it to the desired size and shape. The distance between the rollers diminishes for each successive pair as the steel is elongated and reduced in thickness.

The first pair of rollers through which the ingot passes is commonly called the blooming mill, and the square billets of steel that the ingot produces are known as blooms. From the blooming mill, the steel is passed on to roughing mills and finally to finishing mills that reduce it to the correct cross section. The rollers of mills used to produce railroad rails and such structural shapes as I-beams, H-beams, and angles are grooved to give the required shape.

Modern manufacturing requires a large amount of thin sheet steel. Continuous mills roll steel strips and sheets in widths of up to 2.4 m. Such mills process thin sheet steel rapidly, before it cools and becomes unworkable. A slab of hot steel over 11 cm thick is fed through a series of rollers which reduce it progressively in thickness to 0.127 cm and increase its length from 4 m to 370 m. Continuous mills are equipped with a number of accessory devices including edging rollers, descaling devices, and devices for coiling the sheet automatically when it reaches the end of the mill. The edging rollers are sets of vertical rolls set opposite each other at either side of the sheet to ensure that the width of the sheet is maintained. Descaling apparatus removes the scale that forms on the surface of the sheet by knocking it off mechanically, loosening it by means of an air blast, or bending the sheet sharply at some point in its travel. The completed coils of sheet are dropped on a conveyor and carried away to be annealed and cut into individual sheets. A more efficient way to produce thin sheet steel is to feed thinner slabs through the rollers. Using conventional casting methods, ingots must still be passed through a blooming mill in order to produce slabs thin enough to enter a continuous mill.

By devising a continuous casting system that produces an endless steel slab less than 5 cm thick, German engineers have eliminated any need for blooming and roughing mills. In 1989, a steel mill in Indiana became the first outside Europe to adopt this new system.

Words and expressions

tee - тавровая балка; тройник; Т-образный

элемент

channel - швеллер

I-beam - двутавровая балка

ingot - слиток

soaking pit - томильный, нагревательный колодец

blooming mill - прокатный стан блюминг

continuous mill - непрерывный стан

to anneal - отжигать, обжигать

Exercise 1

Ответьте на следующие вопросы:

1. In what main shapes steel is generally marketed?

2. What are the main methods of steel shapes production at steel mills?

3. Does the working of steel improve the quality of steel and how?

4. What process of working of steel is considered to be the basic?

5. What is passed between a series of pairs of metal rollers during the hot rolling process?

6. How do we call the first pair of rollers through which the ingot passes in hot rolling process?

7. What structural shapes are rolled through specially grooved rollers?

8. What type of steel product is widely required by modern manufacturing enterprises?

9. What is the main equipment of modern rolling mills?

10. Who were to eliminate any need for blooming and roughing mills?

Exercise 2

Соответствуют ли данные предложения содержанию текста:

1. Pig Iron is marketed in a wide variety of sizes and shapes, such as rods, pipes, railroad rails, tees, channels, and I-beams.

2. Steel shapes are produced at Blast furnaces by rolling and otherwise forming heated ingots to the required shape.

3. The working of steel improves the quality of the steel.

4. The basic process of working steel is known as cold rolling.

5. In hot rolling the steel is elongated and reduced in thickness.

6. The first pair of rollers through which the ingot passes is commonly called the section mill.

7. From the blooming mill, the steel goes to roughing mills and finally to finishing mills.

8. The rollers of sheet mills are grooved to give the required shape.

9. Modern manufacturing requires a large amount of thin sheet steel.

10. A more efficient way to produce thin sheet steel is to feed thicker slabs through the rollers.

11. A continuous casting system produces an endless steel slab less than 5 cm thick.

Exercise 3

Заполните пропуски недостающими по смыслу словами, используя текст:

1. Such steel shapes as rods, pipes, railroad rails, tees, channels, and I-beams are produced at … … .

2. The basic process of working steel is known as … rolling.

3. In hot rolling the cast ingot is first heated in a furnace called a … pit.

4. The first pair of rollers through which the ingot passes is called the … mill.

5. The rollers of mills used to structural shapes as I-beams, H-beams, and angles are … to give the required shape.

6. Continuous mills roll steel strips … before it cools and becomes unworkable.

7. A more efficient way to produce thin sheet steel is to feed … slabs through the rollers.

8. A continuous casting system eliminated any need for … and … mills.

Exercise 4

Используя текст, составьте высказывания с данными словами и выражениями:

Sizes and shapes – required shape - working of steel - hot rolling - cast ingot - desired size - pair of rollers - correct cross section – to be grooved - to become unworkable – to be equipped with - accessory device – to cut into individual sheets- conventional casting methods – to eliminate any need for - to adopt a new system.

Exercise 5

Кратко передайте содержание каждого абзаца.

Exercise 6

Выделите пять основных идей текста.

Exercise 7

Составьте предложения, используя данные выражения:

• Ingot (слиток; болванка); bled ingot (вытекающий слиток, слиток с пустотами); burnt ingot (перегретый слиток); capped ingot (успокоенный в изложнице слиток); forging ingot (поковочный, кузнечный слиток); rimming ingot (слиток кипящей стали); slab ingot (листовой слиток); ingoted (разлитый с литки).

• Shape (профиль, форма); first shape (первоначальная форма); intricate shape (сложный или фигурный профиль); rolled shape (катаный профиль); special shape (специальный шаблон, специальный профиль).

• Mill (прокатный стан); roughing mill (обжимной стан, черновая клеть); billet mill (заготовочный стан); blooming mill (обжимной стан, блюминг); cold rolling mill (стан холодной прокатки); cold-strip mill (листовой стан холодной прокатки); continuous rolling mill (непрерывный прокатный стан); edging mill (стан с валками для обжатия кромок); finishing mill (чистовой, отделочный прокатный стан); heavy-plate rolling mill (толстолистовой прокатный стан); merchant mill (среднесортный прокатный стан); pipe mill (трубопрокатный стан); plate mill (толстолистовой стан); rod mill (проволочнопрокатный стан); sheet mill (тонколистовой прокатный стан); slab mill (слябинг, стан для прокатки слябов); universal mill (универсальный прокатный стан);

• Air blast (воздушное дутье); enriched blast (обогащенное дутье); high temperature blast (высокотемпературное дутье); hot blast (горячее дутье); oxygen-enriched blast (дутье, обогащенное кислородом); oxygen-steam blast (парокислородное дутье); sand-blast (струя воздуха с песком).

Exercise 8

Переведите на русский язык следующие предложения:

1. Shapes are long products with irregular cross sections, such as beams, channels, angles, and rails.

2. The blooms are received, either cold or hot, directly from the blooming mill or continuous caster.

3. There are usually three to five stands arranged in various ways, each taking one to five passes.

4. Only one pass is made through the finishing stand, which controls the final dimension and surface.

5. Mills that produce medium and small shapes often have stands in tandem arrangement.

6. Rolling temperatures are carefully controlled for metallurgical reasons.

7. Heavy-walled, wide-flange I-beams are sometimes heat-treated in-line by computer-controlled water quenching and by tempering with their own retained heat.

8. The heads of rails are often heat-treated in-line to improve wear and impact resistance.

9. Rails are also slow-cooled under an insulated cover, directly after rolling, for at least 10 hours to diffuse hydrogen out of the steel.

10. After rolling, a hot saw cuts the shapes into lengths that can be handled by the cooling bed.

11. Each shop conducts large-size finishing operations such as straightening, cold-cutting to ordered length, marking, and inspection.

12. Tubular products are manufactured according to two basic technologies. One is the welding of tubes from strip, and the other is the production of seamless tube from rounds or blooms.

Exercise 9

Переведите на английский язык:

1. Металлургические заводы производят сталь в широком разнообразии размеров и профилей.

2. Наша компания успешно торгует на рынке такими продуктами как: арматура, трубы, ж/д рельсы, тавровые балки, швеллеры, и двутавровые балки.

3. Обработка стали на прокатных станах улучшает ее качество, очищает ее кристаллическую структуру и делает метал более жестким.

4. В горячем прокатном производстве литой слиток в горячем виде подается на блюминг.

5. Расстояние между валами на прокатном стане уменьшается для каждой последовательной клети.

6. Первая пара валов, через которые проходит слиток называется блюмингом.

7. От блюминга, сталь передается на обжимной стан и наконец на чистовой прокатный стан.

8. Непрерывные станы прокатывают стальные полосы и листы в ширину до 2.4 м.

9. Непрерывные прокатные станы оборудованы большим количеством дополнительного оборудования.

10. Для удаления окалины с поверхности листа используется специальный аппарат удаления окалины.

11. Применение системы непрерывной разливки исключило использование блюмингов.

Exercise 10

Текст на самостоятельный перевод:

Pipe

Cheaper grades of pipe are shaped by bending a flat strip, or skelp, of hot steel into cylindrical form and welding the edges to complete the pipe. For the smaller sizes of pipe, the edges of the skelp are usually overlapped and passed between a pair of rollers curved to correspond with the outside diameter of the pipe. The pressure on the rollers is great enough to weld the edges together. Seamless pipe or tubing is made from solid rods by passing them between a pair of inclined rollers that have a pointed metal bar, or mandrel, set between them in such a way that it pierces the rods and forms the inside diameter of the pipe at the same time that the rollers are forming the outside diameter.

Tin Plate

By far the most important coated product of the steel mill is tin plate for the manufacture of containers. The “tin” can is actually more than 99 percent steel. In some mills steel sheets that have been hot-rolled and then cold-rolled are coated by passing them through a bath of molten tin. The most common method of coating is by the electrolytic process. Sheet steel is slowly unrolled from its coil and passed through a chemical solution. Meanwhile, a current of electricity is passing through a piece of pure tin into the same solution, causing the tin to dissolve slowly and to be deposited on the steel. In electrolytic processing, less than half a kilogram of tin will coat more than 18.6 sq m (more than 200 sq ft) of steel. For the product known as thin tin, sheet and strip are given a second cold rolling before being coated with tin, a treatment that makes the steel plate extra tough as well as extra thin. Cans made of thin tin are about as strong as ordinary tin cans, yet they contain less steel, with a resultant saving in weight and cost. Lightweight packaging containers are also being made of tin-plated steel foil that has been laminated to paper or cardboard.

Wrought Iron

The process of making the tough, malleable alloy known as wrought iron differs markedly from other forms of steel making. Because this process, known as puddling, required a great deal of hand labor, production of wrought iron in tonnage quantities was impossible. The development of new processes using Bessemer converters and open-hearth furnaces allowed the production of larger quantities of wrought iron.

Wrought iron is no longer produced commercially, however, because it can be effectively replaced in nearly all applications by low-carbon steel, which is less expensive to produce and is typically of more uniform quality than wrought iron.

The puddling furnace used in the older process has a low, arched roof and a depressed hearth on which the crude metal lies, separated by a wall from the combustion chamber in which bituminous coal is burned. The flame in the combustion chamber surmounts the wall, strikes the arched roof, and “reverberates” upon the contents of the hearth. After the furnace is lit and has become moderately heated, the puddler, or furnace operator, “fettles” it by plastering the hearth and walls with a paste of iron oxide, usually hematite ore. The furnace is then charged with about 270 kg of pig iron and the door is closed. After about 30 min the iron is melted and the puddler adds more iron oxide or mill scale to the charge, working the oxide into the iron with a bent iron bar called a raddle. The silicon and most of the manganese in the iron are oxidized and some sulfur and phosphorus are eliminated. The temperature of the furnace is then raised slightly, and the carbon starts to burn out as carbon-oxide gases. As the gas is evolved the slag puffs up and the level of the charge rises. As the carbon is burned away the melting temperature of the alloy increases and the charge becomes more and more pasty, and finally the bath drops to its former level. As the iron increases in purity, the puddler stirs the charge with the raddle to ensure uniform composition and proper cohesion of the particles. The resulting pasty, spongelike mass is separated into lumps, called balls, of about 80 to 90 kg each. The balls are withdrawn from the furnace with tongs and are placed directly in a squeezer, a machine in which the greater part of the intermingled siliceous slag is expelled from the ball and the grains of pure iron are thoroughly welded together. The iron is then cut into flat pieces that are piled on one another, heated to welding temperature, and then rolled into a single piece. This rolling process is sometimes repeated to improve the quality of the product.

The modern technique of making wrought iron uses molten iron from a Bessemer converter and molten slag, which is usually prepared by melting iron ore, mill scale, and sand in an open-hearth furnace. The molten slag is maintained in a ladle at a temperature several hundred degrees below the temperature of the molten iron. When the molten iron, which carries a large amount of gas in solution, is poured into the ladle containing the molten slag, the metal solidifies almost instantly, releasing the dissolved gas. The force exerted by the gas shatters the metal into minute particles that are heavier than the slag and that accumulate in the bottom of the ladle, agglomerating into a spongy mass similar to the balls produced in a puddling furnace. After the slag has been poured off the top of the ladle, the ball of iron is removed and squeezed and rolled like the product of the puddling furnace.

Classifications of Steel

Steels are grouped into five main classifications.

Carbon Steels

More than 90 percent of all steels are carbon steels. They contain varying amounts of carbon and not more than 1.65 percent manganese, 0.60 percent silicon, and 0.60 percent copper. Machines, automobile bodies, most structural steel for buildings, ship hulls, bedsprings, and bobby pins are among the products made of carbon steels.

Alloy Steels

These steels have a specified composition, containing certain percentages of vanadium, molybdenum, or other elements, as well as larger amounts of manganese, silicon, and copper than do the regular carbon steels. Automobile gears and axles, roller skates, and carving knives are some of the many things that are made of alloy steels.

High-Strength Low-Alloy Steels

Called HSLA steels, they are the newest of the five chief families of steels. They cost less than the regular alloy steels because they contain only small amounts of the expensive alloying elements. They have been specially processed, however, to have much more strength than carbon steels of the same weight. For example, freight cars made of HSLA steels can carry larger loads because their walls are thinner than would be necessary with carbon steel of equal strength; also, because an HSLA freight car is lighter in weight than the ordinary car, it is less of a load for the locomotive to pull. Numerous buildings are now being constructed with frameworks of HSLA steels. Girders can be made thinner without sacrificing their strength, and additional space is left for offices and apartments.

Stainless Steels

Stainless steels contain chromium, nickel, and other alloying elements that keep them bright and rust resistant in spite of moisture or the action of corrosive acids and gases. Some stainless steels are very hard; some have unusual strength and will retain that strength for long periods at extremely high and low temperatures. Because of their shining surfaces architects often use them for decorative purposes. Stainless steels are used for the pipes and tanks of petroleum refineries and chemical plants, for jet planes, and for space capsules. Surgical instruments and equipment are made from these steels, and they are also used to patch or replace broken bones because the steels can withstand the action of body fluids. In kitchens and in plants where food is prepared, handling equipment is often made of stainless steel because it does not taint the food and can be easily cleaned.

Tool Steels

These steels are fabricated into many types of tools or into the cutting and shaping parts of power-driven machinery for various manufacturing operations. They contain tungsten, molybdenum, and other alloying elements that give them extra strength, hardness, and resistance to wear.

Structure of Steel

The physical properties of various types of steel and of any given steel alloy at varying temperatures depend primarily on the amount of carbon present and on how it is distributed in the iron. Before heat treatment most steels are a mixture of three substances: ferrite, pearlite, and cementite. Ferrite is iron containing small amounts of carbon and other elements in solution and is soft and ductile. Cementite, a compound of iron containing about 7 percent carbon, is extremely brittle and hard. Pearlite is an intimate mixture of ferrite and cementite having a specific composition and characteristic structure, and physical characteristics intermediate between its two constituents. The toughness and hardness of a steel that is not heat treated depend on the proportions of these three ingredients. As the carbon content of a steel increases, the amount of ferrite present decreases and the amount of pearlite increases until, when the steel has 0.8 percent of carbon, it is entirely composed of pearlite. Steel with still more carbon is a mixture of pearlite and cementite. Raising the temperature of steel changes ferrite and pearlite to an allotropic form of iron-carbon alloy known as austenite, which has the property of dissolving all the free carbon present in the metal. If the steel is cooled slowly the austenite reverts to ferrite and pearlite, but if cooling is sudden, the austenite is “frozen” or changes to martensite, which is an extremely hard allotropic modification that resembles ferrite but contains carbon in solid solution.

Heat Treatment of Steel

The basic process of hardening steel by heat treatment consists of heating the metal to a temperature at which austenite is formed, usually about 760° to 870° C and then cooling, or quenching, it rapidly in water or oil. Such hardening treatments, which form martensite, set up large internal strains in the metal, and these are relieved by tempering, or annealing, which consists of reheating the steel to a lower temperature. Tempering results in a decrease in hardness and strength and an increase in ductility and toughness.

The primary purpose of the heat-treating process is to control the amount, size, shape, and distribution of the cementite particles in the ferrite, which in turn determines the physical properties of the steel.

Many variations of the basic process are practiced. Metallurgists have discovered that the change from austenite to martensite occurs during the latter part of the cooling period and that this change is accompanied by a change in volume that may crack the metal if the cooling is too swift. Three comparatively new processes have been developed to avoid cracking. In time-quenching the steel is withdrawn from the quenching bath when it has reached the temperature at which the martensite begins to form, and is then cooled slowly in air. In martempering the steel is withdrawn from the quench at the same point, and is then placed in a constant-temperature bath until it attains a uniform temperature throughout its cross section. The steel is then allowed to cool in air through the temperature range of martensite formation, which for most steels is the range from about 288° C to room temperature. In austempering the steel is quenched in a bath of metal or salt maintained at the constant temperature at which the desired structural change occurs and is held in this bath until the change is complete before being subjected to the final cooling.

Other methods of heat treating steel to harden it are used. In case hardening, a finished piece of steel is given an extremely hard surface by heating it with carbon or nitrogen compounds. These compounds react with the steel, either raising the carbon content or forming nitrides in its surface layer. In carburizing, the piece is heated in charcoal or coke, or in carbonaceous gases such as methane or carbon monoxide. Cyaniding consists of hardening in a bath of molten cyanide salt to form both carbides and nitrides. In nitriding, steels of special composition are hardened by heating them in ammonia gas to form alloy nitrides.