Ex. 13. Make up the dialogue:
You are a student of the 2 course and you have a task to write down a report on the subject Welding and its using You are going to visit a plant and have a meeting with a fitter of the shop. Ask questions in order to get the information about:
- The most common types of welding;
- The necessity to protect hot metal;
- Two main ways to shield an arc welding.
- Some kinds of welding not using an electric arc.
- Ways of protection during welding.
VI. Reading and comprehension
Ex. 14. Read and translate the text without a dictionary for 5 minutes and answer the questions after the text:
Text B
Arc welding
Any kind of welding that uses an electric arc is a kind of arc welding. There are different kinds of arc welding too shielded metal arc welding (SMAW) is a common type. Sometimes SMAW is called stick welding. Another common one is gas metal arc welding (GMAW). It is sometimes called wire welding or metal inert gas welding (MIG welding). Another type of arc welding that is less common is gas tungsten arc welding (also known as tungsten inert gas welding or TIG welding). Before there were many kinds of arc welding, SMAW was called just 'arc welding'. Sometimes it is still called that today, but it's better to call it by it's real name instead. Arc welding heats metals by making an electric arc between the piece of metal and something called an electrode. An electrode is the part of the welder that the arc touches.
Sometimes the electrode is used up by the welding, sometimes it is not. In SMAW, GMAW, and some other kinds, the electrode is used up. The electrode is made of the same kind of metal that is being welded, and melts into the weld and becomes part of it. Because it is used up, it must constantly be fed into the weld. In SMAW, the electrode is a rod of metal with flux on it. There is more information on flux further down. The person doing the weld feeds the rod into the weld. In GMAW, the electrode is a thin wire that might be as thin as 0.635 millimeters. Really big welds might use a 4 millimeter electrode, but the biggest common electrode size is around 2 millimeters. The welding machine has a motor in it that pushes this wire into the weld.
1. What can be called a kind of arc welding?
2. What is stick welding?
3. What is an electrode?
4. What do you know about welding machine?
Supplementary reading.
Texts for written translation with a dictionary
Read the texts and translate them in writing. Use a dictionary
Other kinds of welding
Spot welding - forge welding
Some kinds of welding do not use an electric arc. They might use a flame, electricity without an arc, an energy beam, or physical force. The most common type of welding that does not use an arc is called gas welding. In gas welding, a flammable (meaning it will burn) gas and oxygen are combined and burn at the end of a torch. Gas welding does not need any special shielding because a flame which is adjusted right has no extra oxygen in it. It is still important to make sure the metal is clean. The flame heats up the metal so much that it melts. When both the pieces of metal are melted at the edge, the liquid metal becomes one piece.
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The other kind of welding that does not use an arc still uses electricity. It is called resistance welding. With this kind, two pieces of thin metal are pinched together and then electricity is made to go through them. This makes the metal get really hot and melt where it is pinched together. The two pieces melt together at that place. Sometimes this is called spot welding because the welding can only happen at one small place(or spot) at a time.
Forge welding is the very first kind of welding that ever was used. Forge welding needs the two pieces of metal to so hot that they almost melt. Then they are beat together with hammers until they are one piece.
The other kinds of welding that do not use an arc are hard to do, and usually new. They are expensive too. Most of these kinds of welding are only done where specially needed. They might use an electron beam, laser, or ultrasonic sound waves.
Types of Welding
Non consumable Electrode Arc welding
As a non consumable electrodes tungsten or carbon electrodes can be used. In gas-tungsten arc welding a tungsten electrode is used in place of the metal electrode used in shielded metal-arc welding. A chemically inert gas, such as argon, helium, or carbon dioxide is used to shield the metal from oxidation. The
heat from the arc formed between the electrode and the metal melts the edges of the metal. Metal for the weld may be added by placing a bare wire in the arc or the point of the weld. This process can be used with nearly all metals and produces a high quality weld. However, the rate of welding is considerably slower than in other processes.
Shielded Metal Arc weldingIn shielded metal-arc welding, a metallic electrode, which conducts electricity, is coated with flux and connected to a source of electric current. The metal to be welded is connected to the other end of the same source of current. An electric arc is formed by touching the tip of the electrode to the metal and then drawing it away. The intense heat of the arc melts both parts to be welded and the point of the metal electrode, which supplies filler metal for the weld. This process is used mainly for welding steels.
Gas metal Arc weldingIn gas-metal welding, a bare electrode is shielded from the air by surrounding it with argon or carbon dioxide gas and sometimes by coating the electrode with flux. The electrode is fed into the electric arc, and melts off in droplets that enter the liquid metal of the weld seam. Most metals can be joined by this process.
Submerged Arc Welding
Submerged-arc welding is similar to gas- metal arc welding, but in this process no gas is used to shield the weld. Instead of that, the arc and tip of the wire are submerged beneath a layer of granular, fusible material that covers the weld seam. This process is also called electroslag welding. It is efficient but can be used only with steels.
Building Materials
The mortars used in bricklayers work consist of an admixture of lime, or Portland cement, and sand. A knowledge of the properties of these materials is very necessary t the craftsman, if he is to obtain the best results from his labours.
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Lime is manufactured by the calcination, or burning, of a carbonate of calcium, of which chalk is the commonest example. During calcination, decomposition occurs, and carbonic acid and water are driven off, an oxide of calcium (quicklime) remaining. If water be addedd to lumps of quicklime, rapid combination ensues, great heat and volumes of steam being generated. The lumps disintegrate with a series of small explosions, and are eventually reduced to a very fine powder. This process is termed slaking; and when making mortar it is highly necessary that it should be thoroughly carried out, as any unslaked particles subsequently expand and seriously damage the work. Limes may be divided into three distinct classes - Rich limes.
2. Poor limes.
3. Hydraulic limes.
Rich limes contain not more than 6 percent of impurities, slake very rapidly, and are entirely dependent on the external agents for setting power. They are chiefly used for interior plasters work. Poor limes contain from 15 percent to 30 percent of useless impurities, and possess the general properties of rich limes, only to a lesser decree. They are only fit for unimportant work. Hydraulic limes contain certain proportions of impurities, which, during calcination, combine with the lime, and endow it with the valuable property of setting under water, or without external agents. The proportions of these impurities determine whether a lime is eminently, moderately, or only feebly hydraulic. The principal limes used in making mortar for constructional work are of the Greystone variety. These have hydraulic properties, and will take a large proportion of sand, without weakening their setting powers. The usual proportions are from two to four parts of sand to one lime. The setting of lime depends largely upon its absorption of carbonic acid from the atmosphere. The particles return to their original form of a carbonate, and crystallize. The crystals have a tendency to adhere to anything rough, such as sand or the surfaces of a brick. Pure lime mortars built into thick walls never harden in the interior. The crystallization of the exterior of the joint when set prevents access of carbon dioxide to the inside of the wall. For this reason, pure lime mortars should not be used for constructional work, only those which are not entirely dependent on external agents. For more important work, where great strength is required, Portland cement is used instead of lime. Portland Cement is an artificial cement, manufactured by calcining chalk and clay, or river mud containing certain chemical constituents in definite proportions. The chalk and clay are ground and mixed into a slurry, which after being strained through very fine sieves, is pumped into an orifice in the top of an inclined revolving cylinder. A blast of intense flame is directed through this cylinder, which is lined with firebrick. As the slurry drops through the flame, it is burned into small clinkers, which are afterwards ground exceedingly fine in specially constructed mills, and then passed through sieves, having as many as 35,000 meshes to the square inch. The powder is aerated by being spread on wooden floors, with an occasional turning, to ensure the thorough slaking and cooling of all particles. It is then put up in sacks ready to use.
This process of aeration has now been superseded in many cement works by the addition of small quantity of gypsum (plaster of Paris), which retards the otherwise rapid setting tendency of a freshly ground cement. Sand. When used for mortar, sand should be angular in grain, free from clay or dirt, and moderately coarse. If too fine, the proportion of lime or cement will have to be considerably increased. Mixing. This should be carried out on a close boarded platform, or stage, and the heap opened out into the form of a ring. The correct proportion of lime is measured into the ring, clean water being added to start the slaking, and more as the process advanced. When the generation of steam ceases, the mass should be stirred with a long handled, hoe shaped tool called a larry, until a thick, cream like consistency is obtained. The sand may then be gradually drawn into and thoroughly mixed with the lime by means of the same tool. The mortar should be allowed to stand for some days before use and again well beaten up with larry and shovel.
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For cement mortar, the sand is measured and heaped on the stage, and bottomless box of definite capacity is placed on the top of the sand. This box is filled with cement, and then removed. The dry heap is turned over at least twice and opened out into a ring. Clean water is added in sufficient quantity to wet the whole mass, which is then thoroughly mixed in the same manner as lime mortar. Cement mortar should be used directly after being made, and should not be subjected to the further mixing after setting has commenced. If this is done, the cement rapidly loses its strength, and further repetition would render it practically inert. The proportions of sand and cement or lime, are from two to four parts of sand to one part of either, according to the class of work for which the mortar is required. Another mortar mix which is becoming popular, and which some engineers have proved to be stronger for some classes of work such as reinforced brickwork, is 4 parts of sand to 1 part of Portland cement and 1/8th part of lime. On large works, mixing is usually performed in a mortar mill, which consists of a pair of a pair of heavy millstones and a pan, or container into which the measured ingredients are fed. The mill, by reason of its large and rapid output, has a distinct advantage over hand mixing. It also has many disadvantages unless operated by a reliable man. Grinding may be carried on to such a stage that the sand is ground so fine as to render the original quantity of lime or cement inadequate. Cement mortars may be also ground long after the initial setting has commenced, and thus rendered useless for the required purpose.
Notes:
admixture -
cement
lime
oxide
lump
to ensure ,
to slake ()
hydraulic
impurity
constituent
sieve ,
exceedingly-
to supersede
to retard
consistency
to reinforce -
UNIT 5
MY FUTURE SPECIALITY
I. Language
Exercise 1. Remember the following words and word combinations:
| Technological equipment Automated control system Industrial electronics Electrical engineering Engineering Mechanical engineering Machine-tool manufacture Instrument-making Processing engineer Output Measuring and control instruments Strength of materials Machine parts Design bureau Design office Term paper Graduation thesis Research work Theoretical investigation Skilled Sophisticated devices Production process to enable To mailer Flexible To combine Opportunity Senior engineer foreman | , - - , |
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II. Reading
Exercise 2. Read the text A and translate it:
Text A:
My future speciality.
I am a second year student of Kherson National Technical University. I study at the department of Mechanical Engineering. My future speciality is the processing engineer. The students of our department are specializing in mechanics, automation of technological processes and automated control systems, industrial electronics, electrical engineering. Mechanical engineering is called a key industry due to its importance to all sectors of the national economy including mechanization, automation, chemical engineering, etc. Engineering is a complex consisting of inter-linked industries.
Machine-tool manufacture is the material and technical base of engineering. Mechanical engineering is rapidly changing. Instrument-making plays an increasingly important part. This branch of engineering produces automation equipment, quality control devices, computers, etc.
The development of automation is closely linked with progress in instrument-making and output of up-to-date measuring and control instruments and devices. Mechanical engineers deal with the design and construction of engineering structures, machines. They design engineering equipment and use these equipment in different production processes. As future engineers we get thorough knowledge of physics, mathematics, technical drawing, electrical engineering, strength of materials and machine parts, automation and automated control systems, computing, etc.
The course of study lasts 5 years. The academic activities for subjects fall into such types: lectures, seminars, practical classes, laboratories, tutorials, credits, examinations.
The department offers four year courses leading to the degree of Bachelor of Engineering and five year courses leading to the degree of Master of Engineering.
We are taught by a highly-qualified staff of professors, assistant professors and teachers. Our practical training and laboratory works are done in the laboratories equipped with modern installations, apparatuses and devices. Theoretical training is combined with scientific work at the scientific centers and students design bureaus. As a rule, students write their term-papers and graduation theses on the problems connected with their scientific work.
They operate experimental and industrial installations, conduct research work, read scientific literature which deals with their speciality. It is also combined with practical training at the advanced enterprises. All these help to turn a student into a highly-skilled engineer, ready for independent work.
Graduates from our University can work as an engineers, foremen, shop managers or directors of the plant.
III. Language.
