Методичка МТ-7 Шевченко Сварка (Методичка по сварке), страница 4

Give the following English equivalents from the text:в значительной степени; требовать; соединение, выполненное кузнечной сваркой; пропорционально сопротивлению металла; электрическое распределительное устройство;предъявляет огромные требования; вызывает искажение;смежный; публика, общественность.IV. Answer the following questions.1. What is resistance welding?2.

What forms of resistance welding do we know?3. What does the amount of heat depend on?4. What does the amount of current depend on?5. What are contact resistances significantly affected by?V. Translate the sentences paying attention to the functions ofthe Infinitive.1. First, mechanical devices were developed to apply properpressure and control the length of time the current was applied.2. Sometimes the parts do not have proper contact at the jointof the weld and considerable pressure is required to force thetwo surfaces together and make a weld at the place desired.3.

In all projection welding, it is necessary to have point orline contact in order to start a weld.4. The initial pressure should be great enough to obtain contact and then provide a forging action.245. As outlined under the general principles of resistancewelding, the greatest resistance should be between the two partsto be joined.6. The important factor to control the metal properties is thetime at those temperatures.VI. Discuss three factors that affect the total resistance or impedance of the welding and welding equipment’s circuit.VII. Read and translate the text.Text 4B.

Resistance Welding (Part II)One should understand that in resistance welding high resistivity materials necessitate greater consideration of base materialresistances, while low resistivity materials such as aluminumcall for more consideration of contact resistances. Successfulapplication of resistance welding to designs depends upon consistency of material composition, surface, pressure and currentapplied, and time of their application. Low carbon steel isknown to be the most common material welded bу resistancewelding.Resistance welding is usually performed with alternating current. The greatest advance in the use of various forms of resistance welding came in the early 1920s when engineers realizedthat consistency in each of the related factors would assure goodwelds.

First, mechanical devices were developed to apply properpressure and control the length of time the current was applied.Recently, with air and hydraulic systems for applying pressureat the correct time and in the right amount through electroniccontrols, resistance welding has been advanced. The length oftime for applying current can bе controlled from one-half cycleto as many cycles as desired. А shot of high current for а shorttime produces the best weld, since the heat is concentrated at the25joint and does not have time to spread, cause distortion, or affectthe material adjacent to the joint. Resistance welds in automobiles, airplanes, passenger cars, and all forms of sheet metalequipment аrе accepted without question оn the part of the public and in many cases have replaced arc welding and riveting.Equipment designed for resistance welding (such as electricalswitch gear) has reduced scrap, weight, and labor, and has increased the use of standard parts.

In general, resistance weldingmethods are efficient and cause little pollution, but their applications are limited to relatively thin materials and the equipmentcost can be high.VIII. Answer the following questions.1. What do high resistivity materials necessitate?2. What do low resistivity materials such as aluminum callfor?3. What does successful application of resistance welding todesigns depend on?4. What is the most common material welded by resistancewelding?5.

What current is applied in resistance welding?6. What advantages does equipment designed for resistancewelding offer?IX. Give a summary to Text 4B.26UNIT 5I. Learn the words below:assembling – сборка, монтажto file – опиливать; зачищать напильникомguide – (техн.) справочник; руководство; инструкция (поэксплуатации)to machine – обрабатывать на станкеto mushroom – расплющивать (расклепывать) в виде шляпкигриба (об электроде)positioning – размещение; расположениеto regain – восстановить; получить обратноsoftening – размягчениеsqueezing – сжатие; сдавливание; обжатие; обжимshear strength – предел прочности при сдвигеtensile strength – предел прочности на растяжениеgas-tight – газонепроницаемый; герметичныйliquid-tight – непроницаемый для жидкости; герметичныйportable welder – 1) дуговой сварочный полуавтомат; 2) переносная (сварочная) машина для точечной сваркиprojection weld – соединение, полученное при рельефнойсваркеII.

Read and translate the text. Retell the text.Text 5A. Spot WeldingSpot welding, the most common form of resistance welding,consists of joining two pieces of material by placing them between two electrodes and passing a current to heat the materialsufficiently at the joint to cause plastic flow and the union of thetwo parts. The parts are held together while they cool sufficiently to regain mechanical strength. As outlined under thegeneral principles of resistance welding, the greatest resistance27should be between the two parts to be joined. The initial pressure should be great enough to obtain contact and then provide aforging action. The current must be controlled to give sufficientheat yet not melt or burn the material.The diameter of the electrode end must remain the same andnot mushroom and increase the area of contact. When this happens, the current density is reduced.

The area increases in proportion to the square of the diameter, and the heat generated isreduced in proportion to the square of the current (I 2R); therefore, the electrodes should be machined to size and should notbe filed by an operator. The contact surface should meet the material surface evenly. The electrodes are usually water-cooled toprevent softening. Electrodes of special alloys are stronger, buthave more electrical resistance. Copper is known to be the bestelectrode material for general application.Spot welds, unlike rivets, require no holes or riveting, heading, or squeezing operations. The spot can be placed easily because the operator can see the work as the weld is made.

It isrequired that the time for assembling and positioning the parts inthe spot welder be greater than a few seconds necessary formaking a spot weld; therefore, it is common practice to makemultiple spot welds. Strength equivalent to that of riveted jointscan be obtained by an equivalent spot welded structure. Sincethere is no movement of joints, squeaks are avoided.

Shear andtensile strength are close to that of the material welded. Thestrength of spot welds should be determined by experiment, using material and equipment suppliers’ data as a guide. Portablespot welders are used to join members in large structures. Theypermit the same flexibility that is obtained with riveting airhammers.Sometimes the parts do not have proper contact at the joint ofthe weld and considerable pressure is required to force the twosurfaces together and make a weld at the place desired.

This28condition may cause a poor weld. Multiple welds made withelectrodes in series or parallel are difficult to make unless allfactors are controlled. For this reason, projection welding hascome into general use.The advantages of spot welding include efficient energy use,limited workpiece deformation, high production rates, easyautomation, and no required filler materials. Weld strength issignificantly lower than with other welding methods, making theprocess suitable for only certain applications.

It is extensivelyused in the automotive industry – ordinary cars can have severalthousand spot welds.III. Give the corresponding English equivalents from the text:согласно общим принципам; вошла в общее использование; множественные швы, сделанные электродами последовательно и параллельно; пневматический молот; рельеф(рельефной сварки); самая распространенная форма контактной сварки; высадка (головок); пропорционально квадрату диаметра; позволяют ту же гибкость; пластическая деформация; присадочные материалы; без окалины.IV. Answer the following questions.1. What does spot welding consist of?2. When is the current density reduced?3.