Методичка МТ-7 Шевченко Сварка (Методичка по сварке), страница 5

Why shouldn’t the electrodes be filed by an operator?4. What is used to join members in large structures?5. When is it difficult to make multiple welds?V. Translate the following sentences from Russian into English.1. Сваривать два куска металла значит соединить их подвоздействием (under the influence) тепла, обеспечивая со29единение как можно более однородным (as homogeneous aspossible).2. Точечная сварка обычно используется при сварке определенных типов тонколистового металла.3.

Вскоре за дуговой и газовой сваркой последоваласварка сопротивлением.4. Томсон первый усовершенствовал (to perfect) процессконтактной сварки и разработал его до практического применения.5. Образование усадочной раковины (shrinkage) можетвызывать остаточные напряжения (residual stresses) как врадиальном (radial), так и в окружном (rotational) направлениях.VI.

Read and translate the text.Text 5B. Projection WeldingProjection welding is the use of a projection on one or bothpieces to be welded, which forms a spot weld. More than oneprojection weld can be made at a time, as the area and locationof the spot weld and contact pressures can be controlled. Thecurrent will be distributed uniformly between the multiple spotsand good welds will result. Spot- and projection-welded joints,like riveted joints, are not liquid- or gas-tight; therefore, seamwelding was developed to make a continuous joint.In all projection welding, it is necessary to have point or linecontact in order to start a weld. When joining dissimilar sections, the projection should be placed on the heavier part. Heavysections lend to joining by projection welding.

The AmericanWelding Society’s “Recommended Practices for ResistanceWelding” include recommended projections for sheet and platesections up to 0.50 in. It should be remembered that as sections30increase in thickness, the diameter and height of projections areincreased to develop greater strength.Only clean, scale-free surfaces should be used in projectionwelding. A dirty surface will cause considerable variation in theresistance between the parts being joined, with resulting variation in current flow and weld strength.Line projection welds are recommended over point weldswhen sections are subject to heavy static or dynamic loads.VII.

Answer the following questions.1. What is projection welding?2. Is it necessary to have a point or line contact in order tostart a weld?3. When should the projection be placed on the heavier parts?4. What surfaces should be used in projection welding?5.

When is projection welding recommended?VIII. Translate the text in written form without a dictionary(time – 10 min).Percussion welding is similar to flash, stud1, and spot welding in that a very high current is passed instantaneously throughthe surfaces to be joined, and the parts are joined immediatelythereafter. The parts are moved toward one another rapidly. Justprior to contact the current is passed through the two conductorsbeing joined. This is usually accomplished by the discharge of acondenser.

Dissimilar metals are welded with very little penetration of the heat within the parts.Stored energy welding2 involves an electrical means of storing and releasing large amounts of energy. Spot or percussionwelding utilizes a condenser or a transformer circuit, or a combination of the two. Thus, less capacity is required in feeder31lines and transformers. Stored energy systems are used frequently for welding aluminum.Notes:1stud welding – приварка шпилек или шиповstored energy welding – сварка накопленной энергией,импульсная сварка232UNIT 6I. Learn the words below:abutting – стыкуемый; примыкающий; смежный; упирающийся торцомto blast – 1) взрывать; 2) дуть; продуватьbutt – 1) стык; соединение встык; 2) конец; торецcabinet – корпус; ящик; шкаф; отделение; секцияto converge – 1) сходиться, сливаться; сводить в одну точку;2) зд. сближать(ся)movable die – 1) подвижная половина формы; 2) подвижнаяматрицаend face – торецflashing – 1) вспыхивание; блеск; сверкание; искрение;2) оплавлениеupset force – усилие усадкиinterface – поверхность контакта; граница разделаintermittent – прерывистый (о шве)overlapping – перекрытиеlap-joint seam – шов соединения внахлесткуseam weld – сварной шовflash butt resistance welding – стыковая контактная сваркаоплавлениемupset butt welding – стыковая сварка сопротивлениемupset welding – стыковая сварка с осадкой (методом сопротивления)II.

Read and translate the text.Text 6A. Flash Butt WeldingFlash welding is a resistance welding process where joiningis produced simultaneously over the entire area of abutting surfaces.33The flash butt welding process produces a homogeneousweld between two sheets, wires, or bars, without overlappingand without the addition of any materials. Dissimilar materialsmay be flash- and butt-welded. Flash welding is limited only bythe amount of current available to heat the surfaces and the pressure available for forging the parts together. Flash welding joinssheets together in fabricating the typical automobile body.

It isnecessary that welding small sheets into a large sheet fromwhich a car top is made be economical.Flash butt resistance welding, in its turn, is divided into continuous flash welding and flash welding with preheating.By continuous flash welding voltage is supplied from thewelding transformer to upset welding dies and workpieces, respectively, and the workpieces start converging at an initialcomparatively low speed. Convergence of workpieces is performed due to movement of the movable die ensured by theflashing drive. When the workpieces contact each other, separate contact connectors are formed between their end faces, getmelted down with current, blast and escape from the butt in theform of sparks. Further convergence of workpieces results information of new contacts and their meltdown to take place continuously within the flashing process, which leads to heating ofthe end faces and formation on them of a molten metal layer.

Atthe end of the flashing process, fast convergence of the endfaces is performed with a strong upset force, with the moltenlayer and oxide films being pressed out of the butt and theheated end faces undergo plastic deformation.By flash welding with preheating workpieces are generallypreheated with current before flashing, end faces being periodically clamped with a little force and released. In this case, heating during clamping of the workpieces is similar to that of during upset butt resistance welding. The welding process is furtherperformed similarly to continuous flash welding.34III.

Give the corresponding English equivalents from the text:в производстве обычного автомобильного корпуса; предварительный нагрев; расплавление; заклепка; цилиндрические цистерны (баки); консервная банка для напитков; всвою очередь; привод для оплавления; подвергаются пластической деформации; сближение; за один прием, за одинраз.IV. Answer the following questions.1. What is flash welding?2.

What does the flash butt welding process produce?3. Where is flash butt welding used?4. What is flash butt resistance welding divided into?5. What takes place during continuous flash welding?6. What occurs during flash welding with preheating?V. Translate the word groups in Russian by their Englishequivalents using the Infinitive.1. Уместно (wise) проанализировать each design application carefully before deciding which production method is superior.2. Most machine tool bases are cast if they are complex and ifthere are more than a few, которые нужно построить.3. The parts are held together while they cool sufficiently,чтобы получить (gain) механическую прочность.4.

Portable spot welders are used для соединения элементов(members) in large structures.VI. Give a summary of Text 6A.35VII. Read and translate the text.Text 6B. Seam WeldingА seam weld is а joint being continuously welded bу the resistance welding process. The electrodes are disks which аrеdriven аs the two pieces to bе welded pass between them.

Pressure and current are applied to the joint, аs in spot welding.When seam оr continuous welding was first developed, the current was continuous, but the heat was difficult to control. It wassoon discovered that overlapping spot welds was more successful. By making а series of spot welds in rapid succession, theoperator finds slight variations in contact pressure, surface conditions, and electrode contact resistance to result in а betterweld. Representative seam welds are 12 spots per inch оn stock0.01 in. thick аt а speed of 100 in./min, and 5 spots per inch for1/8 in.