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English for Special Purpose

By Alfred Reyes,2014-05-20 21:06
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English for Special Purpose

    English for Special Purpose

    ?? Materials Science & Engineering

    Chongqing University

    2003-8-25

    CONTENTS

    UNIT 1 HOW STEEL IS MANUFACTURED ............................................................................. 1 UNIT 2 THE MAKING OF STEEL ............................................................................................. 3 UNIT 3 WHAT IS WELDING? ................................................................................................... 6 UNIT 4 CASTING ....................................................................................................................... 8 UNIT 5 METALS AND FERROUS METALS ........................................................................... 12 UNIT 6 MECHANICAL PROPERTIES OF METALS ............................................................... 15 UNIT 7 CRYSTAL STRUCTURE ............................................................................................. 17 UNIT 8 PHASES IN METALS .................................................................................................. 19 UNIT 9 HARDENING OF PLAIN CARBON STEELS.............................................................. 21 UNIT 10 CARBON IN STEEL .................................................................................................. 23 UNIT 11 HEAT TREATMENT ................................................................................................. 25 UNIT 12 EFFECTS OF MECHANICAL WORK ON METALS ...................................... 28 UNIT 13 STRENGTH OF MATERIALS ? BASIC ASSUMPTIONS ..................................... 30 UNIT 14 HOT WORKING OF METALS .................................................................................. 32 UNIT 15 COLD WORKING OF METALS ................................................................................ 34 UNIT 16 CLASSIFICATION OF FORMING PROCESSES ...................................................... 35 UNIT 17 ROLLING OF METALS ............................................................................................. 37 UNIT 18 ROLLING MILLS ...................................................................................................... 39 UNIT 19 HOT ROLLING .......................................................................................................... 41 UNIT 20 COLD ROLLING ....................................................................................................... 43 UNIT 21 FORGING .................................................................................................................. 45 UNIT 22 FORGING EQUIPMENT............................................................................................ 48 UNIT 23 EXTRUSION .............................................................................................................. 51 UNIT 24 EXTRUSION EQUIPMENT ....................................................................................... 53 UNIT 25 SHEET METAL FORMING ....................................................................................... 55 UNIT 26 MACHINING OF METALS ....................................................................................... 57 UNIT 27 MATERIALS AND ENGINEERING .......................................................................... 59 UNIT 28 SINGLE COMPONENT METALS ............................................................................. 61 UNIT 29 IMPURE METALS ..................................................................................................... 65 UNIT 30 ALLOYS OF METALS (I) .......................................................................................... 69 UNIT 31 ALLOYS OF METALS (II) ........................................................................................ 74 UNIT 32 ATOMIC CRYSTALS ................................................................................................ 78 UNIT 33 TRANSITIONS IN MATERIALS ............................................................................... 82 UNIT 34 GLASSES ................................................................................................................... 86 UNIT 35 CONDUCTORS AND INSULATORS ........................................................................ 91 UNIT 36 SEMICONDUCTORS ................................................................................................ 94

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    UNIT 1 HOW STEEL IS MANUFACTURED

    Steel production is one of the largest and most important industries. The iron ore used to make steel comes from openpit and underground mines. It is moved by boat and rail to steelmaking centres, where the iron ore is transformed into a variety of kinds and grades of steel.

    Blast furnace. The blast furnace is basically a huge steel shell, lined with firebrick. Some are almost as high as a ten story building.

    Ore processing begins in the blast furnace. A mixture of iron ore, coke, and limestone is first brought to the top of the furnace and dumped into it .This mixture is called the charge. Air that has been dried and heated to about 1250?F is then blown into the furnace near its base. As the coke burns in this air, it generates heat and gases which melt the charge. Impurities in the charge are absorbed by the limestone and form a substance known as slag. The temperature at the base of the furnace rises to approximately 3500?F and the iron and slag in this area become liquified. Since molten slag is lighter than the molten iron, it floats on top of the iron.

    Tapping or removing the molten iron from the furnace is done every 4 or 5 hours. From 150 to 300 tons of pig iron (the type of iron produced in the blast furnace) can be drawn off at a time. It is interesting to note that it takes almost 2 tons of ore, 1 ton of coke, nearly 1/2 ton of limestone, and a little less than 4 tons of air to make just 1 ton of pig iron.

    The molten pig iron that is tapped from the blast furnace still contains some impurities. To change pig iron into steel, these impurities must be removed. This is done in one of three kinds of furnaces: open hearth, basic oxygen, or electric.

    Open hearth Furnace. This furnace is used to convert molten pig iron, iron ore, and scrap iron into steel. Between 8 and 12 hours of intense heat are required before purified molten steel can be run from the furnace into a ladle.

    Basic oxygen Furnace. In this furnace, 80 tons of scrap and molten iron are

    changed into steel in just 40 to 60 minutes. The furnace is first tipped on its side and charged with molten iron and iron scrap. It is then rotated into an upright position. Oxygen, blown into the furnace at high speed, burns out the impurities. Limestone, converted into burnt lime, is also added at the same time as the oxygen.

    Electric Furnace. This furnace is used to produce high grade carbon and alloy steels. Powerful electric currents are sent through three large rods (electrodes) that pass through the top of the furnace. When sparks from these electrodes strike the iron charge, they generate an intense heat. This heat is sufficient to melt the charge and burn out any impurities.

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    The ladle of freshly made steel is held by a crane above a row of ingot moulds. A valve in the bottom of the ladle is opened and steel flows into each mould, filling it to the top.

    After the liquid steel has solidified, the moulds are lifted or stripped off. The first solid form of steel is called an ingot. The ingots are placed in pits and soaked in heat until brought to a uniform rolling temperature. White hot steel is fairly soft and can be squeezed into various shapes by passing it through a rolling mill. The mill contains powerful steel rolls. Ingots first go to a semifinishing mill where they are rolled into blooms, slabs, and billets. These three semifinished shapes then go to finishing mills where they are formed into plate, sheet, strip, rails, rods, bars, and other shapes.

Comprehension:

    1. What is the function of a blast furnace?

    2. How and where is the iron ore transformed into iron?

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    UNIT 2 THE MAKING OF STEEL

    The principal function of a steel furnace is to control the amount of impurities and ingredients in the steel. The delivered hot metal contains more than 4% carbon, which the steel melting furnace will reduce to less than 1% by burning it out at a temperature of about 3000?F. At the same time, any required alloying ingredients will be added to the molten steel, such as small percentages of nickel, chromium, and manganese. Certain alloying elements have the disappointing habit of disappearing into the slag instead of dissolving in the metal, but these will be added to the molten steel after it is poured from the furnace into a ladle.

    Almost all steels are made in one of the following steel refining furnaces:

    1. The open hearth furnace

    2. The oxygen converter, sometimes called the L-D converter

    3. The electric arc furnace

    The open hearth furnace is about 100 years old. To some degree, it is being replaced, by the oxygen converter. Both the open hearth furnace and the oxygen converter can produce steel in large tonnages. For the specialty steels, which are made in smaller amounts, the electric arc furnace is used. The electric furnace began to come into use about 60 years ago. For still smaller quantities of steel, the electric induction melting furnace is used.

    All three types of melting furnaces may be charged with either hot metal or steel scrap, but each has its specialties. Hot metal from the blast furnace is not usually charged into an electric furnace, and the oxygen converter is not well adapted to the melting of steel scrap.

    The open hearth furnace can melt 300 to 500 tons of steel at a time but may take 8 to 10 hours to melt and refine its charge. A large gas burner throws a flame over the bath of steel, which is melted under a lime slag. Compared with the slow performance of the open hearth, the oxygen converter is remarkably fast. It can refine steel before the laboratory can analyze it and pronounce it ready to pour and will melt 150 tons or more in less than an hour. A deep pot lined with firebrick, the converter, after receiving the hot metal charge, is tilted back to vertical position and an oxygen lance, water cooled, is lowered to the molten steel in the furnace. Pure oxygen at high pressure issues from the lance at high velocity and in minutes burns down the carbon to the required low percentage. Indeed, the converter works so furiously at the job of making steel that it burns out its firebrick lining in about a week, when it is then shut down for repairs.

    Specialty steels, such as the stainless steels, are prepared in electric arc melting

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    furnaces. These furnaces do not operate on hot metal but instead use scrap steel. Steel mills that do not have access to blast furnace hot metal must also melt from scrap in electric furnaces. Such furnaces are large scale arc welders using three graphite electrodes 12 in. or more in diameter. Three electrodes are used instead of one as in arc welding because the electric furnace uses three phase alternating current. The large currents travel through the scrap metal and melt it by resistance heating. The voltage used is almost 200 V for meltdown, being reduced to about 120 during the subsequent refining stage.

    The most important function of a steel melting furnace is to control the carbon content of the steel. If the carbon is too high, it is burned down to the proper level by the sustained heat of the furnace. If the carbon is too low, coke, graphite or pig iron is charged into the furnace. Other melting operations include control of impurities in the metal by means of suitable slagging practice and the addition of alloying metals. When the laboratory has checked the analysis of the steel as satisfactory, the molten steel is tapped out of the furnace into a large ladle and transported by overhead crane to the pouring floor for casting into ingots.

    Plain carbon steels are made in three grades: rimmed, semikilled, and killed steel. A killed steel is deoxidized by ladle additions of silicon or aluminum. These two metals are strong oxide formers and remove the dissolved oxygen in the steel as silicon or aluminum oxide. Since gases are not released when the molten steel cools in the ingot mold, such steels are quiet, that is, killed. A semikilled steel is partially deoxidized. A rimmed steel does not receive this treatment and is named from the characteristic crystals that grow around the rim of the ingot. Killed steels have better notch toughness at low temperatures than rimmed steels do. Rimmed steels are more suitable for drawing and forming.

    The killing process of course removes only oxygen from the steel. The oxygen remains as nonmetallic inclusions in the steel only visible under the microscope. For some steels these inclusions are harmful, one of their effects being a reduction in the endurance limit (fatigue life) of the steel. Where inclusions cannot be tolerated and where other dissolved gases such as hydrogen must be removed also, the steel is degassed under vacuum conditions. The improvement in quality gained by vacuum degassing is considerable.

    The steel, rimmed, killed, or degassed, lies in the ingot mold until it freezes. After freezing, the molds are stripped from the ingots, and the ingots are then reheated in soaking pits until they are at a uniform temperature throughout for hot rolling into final shape. The original hot metal has too much carbon, more than 4%, for hot rolling; it is actually a cast iron without ductility. The final refined steel containing less carbon

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    may be readily rolled or forged. During hot rolling the coarse grains produced by the slowly cooling ingot are broken up to make a fine grained steel product.

    In the rolling mill, the ingot is passed through a succession of rolls until it is reduced to the shape and size required. The final shape may be reinforcing rod, rod or bar, structural shape, rail, skelp (plate for welding into pipe), plate, or sheet. A larger tonnage of steel is rolled into sheet than into any other form, and sheet may be obtained either hot or cold rolled. Hot rolled sheet is cheaper and commoner and can be recognized by its black coat of mill scale. Cold rolled steel has a bright finish and is less ductile than hot rolled steel. Cold rolled steel is rolled at a somewhat lower temperature for the final pass than hot rolled steel is. The smaller gauges of steel sheet are produced only in the cold rolled condition.

    As a result of rolling, steel becomes anisotropic, that is, its mechanical characteristics are not the same in all three directions. The tensile strength and notch toughness are greatest in the direction of rolling and not quite so favorable in the other two directions. If an isotropic metal is desired, with uniform characteristics in three directions, it may have to be forged, cast, or sintered from metal powders.

Comprehension:

    1. What is the function of a steel furnace?

    2. Where are almost all steels made?

    3. What is the main process of making steel?

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    UNIT 3 WHAT IS WELDING?

    Welding techniques have become so versatile that it is difficult nowadays to define "welding." Formerly welding was "the joining of metals by fusion," that is, by melting, but this definition will no longer do. Even though fusion methods are still the most common, they are not always used. Welding was next defined as the "joining of metals by heat," but this is no longer a proper definition either. Not only metals can be welded, so can many of the plastics. Furthermore, several welding methods do not require heat. Every machinist is familiar with heatless welding. When the chip slides over the cutting tool on a lathe, it often leaves a built up edge of chip material welded to the top of the cutter bit. This is cold pressure welding, which under other circumstances is a proper production welding method. Besides pressure welding, we can weld with sound and even with light from the famous laser. Faced with a diversity of welding methods that increase year by year, we must here adopt the following definition of welding: "Welding is the joining of metals and plastics by methods that do not employ fastening devices."

    The joining of metals by methods that do not employ fastening devices is an art as old as blacksmithing. Nevertheless welding as a manufacturing process must be considered a development of the twentieth century. In the 1880's carbon arc lamps were used for street lighting. At that time it was noted that the carbon arc lamp, like all lamps, produced more heat than light, and the first attempts were made to use this heat for welding metals. Thus the first welding method of those still in use was carbon arc welding, perfected about the turn of the century. Stick electrodes and oxyacetylene welding also appeared about 1900. Welding was generally used only for repair and maintenance until the 1920's. X-ray examination of welds came soon afterward and did much to develop confidence in welded joints. The middle of the 20th century saw great development in welding as well as in other techniques. It also gave us, among other things, inert gas welding. Since then welding has progressed at a tremendous rate. It helps develop science and technology, including the electronic technique. At the same time, the technology of welding embraces a wide area. Many electronic circuits are required to control the more intricate welding machines. Even radio frequencies have their applications in welding, in induction brazing and the ultrasonic testing of welds. Photography is also drawn into the scope of welding for X-ray and -ray photography is used in the examination of welded joints. Welding has made important contributions to the modernization of our national defence industry, such as the making of nuclear reactors and man made earth satellites, for both are weldments. On the other side of the coin, those products of the nuclear reactors, radioisotopes, are

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    familiar around welding shops in their function of weld testing. All these and other developments show that welding is no longer what it was in time past, the simple matter of running a bead with a gas flame or a stick electrode.

    The operator of the modern automatic welder wears neither welding helmet nor goggles when welding the heavy walled pressure vessel. But depositing weld metal is about fifteen times faster than by manual methods. His welding rods are the two large coils of wire at the top of the welding machine, and these are automatically fed into the weld. The arc is not visible in this method of welding, and so no helmet is required. The welding controls are grouped on the control panel to the immediate right of the operator. This is union melt submerged arc welding, a commonly used welding method that can in an hour deposit weld metal equal in weight to that of the operator himself. At the opposite extreme is microwelding, in which the operator may need a microscope to see what he has welded. Between these two extremes in size and welding capacity are perhaps five dozen other welding methods.

Comprehension:

    1. What is the most proper definition of welding?

    2. How did the carbon arc welding come on?

    3. Give some welding products used in our life.

    4. What did the author think about the typical welding procedure in time past?

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    UNIT 4 CASTING

    1. This method of shaping metal consists of melting it and pouring it into shaped moulds. Other methods of shaping metals are by cutting or machining them or by pressing or squeezing them when solid.

    Common examples of cast iron are frames and bedplates for machinery. There is an enormous number of different steel castings, varying from alloy steel components weighing an ounce or two for aeroengines and aircraft, to frames for locomotives, liners, and warships, some of which weigh over 100 tons.

    Castings are made in foundries. There are three main groups of castings: cast iron, steel, and nonferrous metals, in which aluminium, copper, zinc, and so on are used.

    There are four parts to a founder's task: making the mould, melting the metal, pouring the metal, then removing the mould from the solidified metal. The general principle of melting is the same for all metals, though the details vary with the composition of each.

    In making cast iron, solid lumps of pig iron are melted in a device known as a cupola, a metal tube 15 to 20 feet high and about 4 feet in diameter, lined with firebrick to retain heat. It is like a small blast furnace and is heated by coke. Pig iron, together with scrap iron, is charged into the cupola through a door near the top; at the foot, air is blown through nozzles to keep the coke burning furiously. As the iron melts, it trickles down and collects at the bottom of the cupola, to be poured out through a tap hole into large buckets called ladles. In the past the top of the cupola was usually open, and the glow and flames from it were a common and impressive sight in most industrial towns. Today, to avoid atmospheric pollution, various types of equipment are used to collect dust and fumes. The process is fast, the iron passing through a cupola in an hour or less. The output from a normal cupola is about 8 tons an hour.

    Steel for casting is made either by refining pig iron by the open hearth process, in a Bessemer or similar converter, or by melting steel scrap in electric furnaces. As the steel founder generally wants only small quantities of molten steel at a time, he uses small, fast furnaces.

    2. MOULDS. The commonest method is to make a mould by packing stiff, damp sand round a wooden 'pattern', which has the shape of the finished casting. The pattern is then removed, leaving its impression on the sand, and the molten metal is poured into this impression.

    Moulds are made in moulding boxes which are in two halves. The procedure is

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