Гричин С.В., Ульянова О.В. - Английский язык для инженеров сварочного производства, страница 7

Millions of IBM cards werethen sent to every fabricator. These cards gave fabricators the width, length,thickness and grade of steel of every plate and section in all of the columnsand panels. "In addition," he said, "the fabricators are given all of therequirements of every weld needed to make up the columns and panels.Many of these cards are used as equable to the production of drawings. Theyare sent directly from the designer to the fabricators. Draftsmen neverbecome involved."Vocabularywar effortbrittle fracturenotchcrack propagationfield weldingtoughnessplaneloadX-ray inspectioninduction heatingstructural steelrolled steelfillet weldcontact faceвоенная экономикахрупкий изломзубец, вырез, паз, пропил, прорезразвитие трещинсварка в полевых условиях, сварка при монтажетвердостьполная загрузка самолетарентгенодефектоскопияиндукционный нагревконструкционная стальстальной прокатугловой сварной шовповерхность контакта38Speaking19Use the information in the table as a plan and speak about theachievement you have read about to the class.RevisionName:Ø a method to protect welds from the effects of oxygen and nitrogen inthe atmosphereØ the inventions in welding attributed to Russian scientistsØ the code providing safety for construction of pressure-related itemsØ some recently developed types of welding39PART 3.

WELDING PROCESSES & EQUIPMENTLead-in1There are processes similar to welding which a welder should knowabout. Read the definitions of metal joining processes (1-6) and supply themwith Russian equivalents from the list (a-f).a) резкаb) пайка мягким (легкоплавким) припоемc) свинцеваниеd) клепкаe) лужениеf) пайка твердым припоем резка1. Soldering: Bonding by melting a soft metal to the surface of pieces to bejoined. Low temperature. Good for joining dissimilar materials. Mostcommon solders are lead-tin alloys.2.

Tinning: A soldering process, where the surface of a metal is coated withsolder.3. Leading: A form of soldering, solder is used to fill in the surface of metal.4. Brazing: Similar to soldering, but uses a higher temperature to fuse thefiller metal to the work pieces. Stronger bond.

(Includes "Silver Soldering")Work heated to pre-melt temperatures.5. Cutting: Work is heated to melting point and beyond, and "cut" byoxidizing metal. (Literally burning it away).6. Riveting: A process of fastening with a rivet which is a heavy pin having ahead at one end and the other end being hammered flat after being passedthrough holes in the pieces that are fastened together.2Remember the definition of welding and say what the main differencebetween welding and related metal joining processes is.Reading 13You will read the text Basic Principles of Welding.Before you read list all the ways of generating heat for welding.Ways of Generating Heat for Welding1.

Electric arc……404Read the text and answer the questions.1. What is a weld?2. How can the heat be supplied for welding?3. Is pressure employed in solid-phase processes?4. What does an arc column consist of?5. How is heat applied during welding?6. What is the role of inert atmospheres?7. What can make a joint brittle while welding?8. What does the weld metal comprise in arc welding?9. What is the base metal influenced by?10. How can residual stress in welded structures be controlled?Basic Principles of WeldingA weld can be defined as a coalescence of metals produced by heatingto a suitable temperature with or without the application of pressure, and withor without the use of a filler material.In fusion welding a heat source generates sufficient heat to create andmaintain a molten pool of metal of the required size. The heat may besupplied by electricity or by a gas flame.

Electric resistance welding can beconsidered fusion welding because some molten metal is formed.Solid-phase processes produce welds without melting the basematerial and without the addition of a filler metal. Pressure is alwaysemployed, and generally some heat is provided. Frictional heat is developedin ultrasonic and friction joining, and furnace heating is usually employedin diffusion bonding.The electric arc used in welding is a high-current, low-voltagedischarge generally in the range 10–2,000 amperes at 10–50 volts.

An arccolumn is complex but, broadly speaking, consists of a cathode that emitselectrons, a gas plasma for current conduction, and an anode region thatbecomes comparatively hotter than the cathode due to electron bombardment.Therefore, the electrode, if consumable, is made positive and, ifnonconsumable, is made negative. A direct current (dc) arc is usually used,but alternating current (ac) arcs can be employed.Total energy input in all welding processes exceeds that which isrequired to produce a joint, because not all the heat generated can beeffectively utilized. Efficiencies vary from 60 to 90 percent, depending on theprocess; some special processes deviate widely from this figure.

Heat is lostby conduction through the base metal and by radiation to the surroundings.41Most metals, when heated, react with the atmosphere or other nearbymetals. These reactions can be extremely detrimental to the properties of awelded joint. Most metals, for example, rapidly oxidize when molten. Alayer of oxide can prevent proper bonding of the metal. Molten-metaldroplets coated with oxide become entrapped in the weld and make the jointbrittle. Some valuable materials added for specific properties react so quicklyon exposure to the air that the metal deposited does not have the samecomposition as it had initially. These problems have led to the use of fluxesand inert atmospheres.In fusion welding the flux has a protective role in facilitating acontrolled reaction of the metal and then preventing oxidation by forming ablanket over the molten material.

Fluxes can be active and help in the processor inactive and simply protect the surfaces during joining.Inert atmospheres play a protective role similar to that of fluxes. Ingas-shielded metal-arc and gas-shielded tungsten-arc welding an inert gas —usually argon—flows from an annulus surrounding the torch in a continuousstream, displacing the air from around the arc.

The gas does not chemicallyreact with the metal but simply protects it from contact with the oxygen in theair.The metallurgy of metal joining is important to the functionalcapabilities of the joint. The arc weld illustrates all the basic features of ajoint. Three zones result from the passage of a welding arc: (1) the weldmetal, or fusion zone, (2) the heat-affected zone, and (3) the unaffected zone.The weld metal is that portion of the joint that has been melted duringwelding. The heat-affected zone is a region adjacent to the weld metal thathas not been welded but has undergone a change in microstructure ormechanical properties due to the heat of welding. The unaffected material isthat which was not heated sufficiently to alter its properties.Weld-metal composition and the conditions under which it freezes(solidifies) significantly affect the ability of the joint to meet servicerequirements. In arc welding, the weld metal comprises filler material plusthe base metal that has melted.

After the arc passes, rapid cooling of theweld metal occurs. A one-pass weld has a cast structure with columnargrains extending from the edge of the molten pool to the centre of the weld.In a multipass weld, this cast structure may be modified, depending on theparticular metal that is being welded.The base metal adjacent to the weld, or the heat-affected zone, issubjected to a range of temperature cycles, and its change in structure isdirectly related to the peak temperature at any given point, the time ofexposure, and the cooling rates.

The types of base metal are too numerous todiscuss here, but they can be grouped in three classes: (1) materials42unaffected by welding heat, (2) materials hardened by structural change, (3)materials hardened by precipitation processes.Welding produces stresses in materials. These forces are induced bycontraction of the weld metal and by expansion and then contraction of theheat-affected zone. The unheated metal imposes a restraint on the above, andas contraction predominates, the weld metal cannot contract freely, and astress is built up in the joint.

This is generally known as residual stress, andfor some critical applications must be removed by heat treatment of thewhole fabrication. Residual stress is unavoidable in all welded structures, andif it is not controlled bowing or distortion of the weldment will take place.Control is exercised by welding technique, jigs and fixtures, fabricationprocedures, and final heat treatment.Vocabularycoalescencemolten poolgas flamesolid-phaseultrasonicfrictionfurnacediffusionhigh-currentlow-voltagedischargearc columndirect current (dc)alternating currentlayermolten-metaldropletinert atmosphereannulustorchbase metalgrainprecipitationresidual stressсоединение, слипание, сращениеванна расплавленного металла, сварочная ваннагазовое пламятвёрдая фазаультразвуковойтрениепечь1) рассеивание 2) диффузиясильноточныйнизковольтный, низкого напряженияразрядстолб дугипостоянный ток(ac)переменный токслой, пласт, рядкапля жидкого металлаинертная средатех.