Гричин С.В., Ульянова О.В. - Английский язык для инженеров сварочного производства (1044906), страница 11
Текст из файла (страница 11)
Compared to other processes, a large amount of moltenmetal is present during welding, and this poses an additional safety and firehazard. Since the process is often performed at great heights, the work andequipment must be properly secured, and the operator should wear a safetyharness to prevent injury in the event of a fall. EGW uses a constant voltage,direct current welding power supply, and the electrode has positive polarity.A wire feeder is used to supply the electrode, which is selected based on thematerial being welded.
The electrode can be flux-cored to provide the weldwith protection from atmospheric contamination, or a shielding gas can beused with a solid wire electrode. The welding head is attached to an apparatusthat elevates during the welding process. Also attached to the apparatus arebacking shoes which restrain the weld to the width of the workpieces. Toprevent them from melting, they are made of copper and are water-cooled.They must be fit tightly against the joint to prevent leaks.Stud welding is a form of spot welding where a bolt or specially formed nutis welded on to another metal part. The bolts may be automatically fed intothe spot welder. Weld nuts generally have a flange with small nubs that meltto form the weld.
Studs have a necked down, unthreaded area for the samepurpose.10Write a brief summary to the text in the previous activity.11Say if the following is true or false. Correct the false sentences.1. Electrogas welding is less hazardous than electroslag welding.2. Electroslag welding is more frequently used to weld in a horizontalorientation.3. Carbon Arc Welding is broadly used in industry in the present time.4.
Filler metal is always necessary in Atomic Hydrogen Welding.5. Quenched and tempered steels are not welded using Electrogas welding.6. Carbon Arc Welding is the newest arc welding process.12Answer the following questions.1. What kind of electrodes are used in Electrogas and Atomic HydrogenWelding processes?2. What structures can be welded by Electrogas welding?3. Can thick workpieces be easily welded by Electroslag welding?604. Why is Electrogas welding relatively unsafe and hazardous?5. What is the difference between Electrogas and Electroslag welding?6. Why does the operator have to wear protective clothes?13Complete the following sentences.1.
To ensure safety while using arc welding processed operators have towear… .2. Electroslag welding is no more used to weld… .3. In Electrogas welding the weld area is protected from atmosphericcontamination … .4. In Atomic Hydrogen Welding the work itself becomes… .5. Since Electrogas welding is performed at great heigh… .Writing14Write a short report about arc welding. Include the items below.Ø Types (SMAW, MMA, GMAW, MIG, FCAW, SAW, GTAW, TIG,electroslag welding, stud arc welding, EGW)Ø Types of filler material used (consumable/none-consumable,covered/bare electrode/wire)Ø Type of current used (direct/alternating)Ø Type of shielding gas used (helium, argon, CO2)Ø Major application areasSpeaking15Discuss the following questions in the group.1.
What is the difference in methods of gas cutting and gas welding?2. Is there any difference in equipment used for gas welding and gas cutting?3. What might be the advantages and disadvantages of gas cutting comparedto other methods of cutting metals?4. Do you remember what appeared before: arc or gas welding?5. What type of cutting (arc or gas) is :a) more expensiveb) more operator skills demandingc) safere) faster61f) more precise?6. Do you know what metals (steels) are better cut using gas welding?16Look at the picture of Oxygas Cutting Equipment (Fig. 3) and tellabout its design.
The phrases below will help you.The oxygas cutting equipment consists of …The main parts of the equipment are …It also has …… are installed on (at) …Fig. 2 Oxygas cutting outfit62Reading 317Read about welding gases and fill in the table.AcetyleneMapp GasChemical compositionFlame temperatureColour and odorStability (temperature)Cylinder packingDangerous effects onhealthAcetyleneFig. 3Portable welding outfitAcetylene is a flammable fuel gascomposed of carbon and hydrogen having thechemical formula C2H2.When burned withoxygen, acetylene produces a hot flame,having a temperature between 5700°F and6300°F.
Acetylene is a colorless gas, having adisagreeable odor that is readily detected evenwhen the gas is highly diluted with air. Whena portable welding outfit, similar to the oneshown in figure 4 is used, acetylene isobtained directly from the cylinder. In the caseof stationary equipment, similar to theacetylene cylinder bank shown in figure atright, the acetylene can be piped to a numberof individual cutting stations.Hazards: Pure acetylene is selfexplosive if stored in the free state under apressure of 29.4 pounds per square inch (psi).A slight shock is likely to cause it to explode.WARNING: Acetylene becomes extremelydangerous if used above 15 pounds pressure.63Cylinder DesignAcetylene can besafely compressed up to 275psi when dissolved inacetone and stored inspecially designed cylindersfilled with porous material,suchasbalsawood,charcoal, finely shreddedasbestos, corn pith, portlandcement, or infusorial earth.These porous filler materialsaid in the prevention of highpressure gas pockets formingin the cylinder.Fig.
4Acetylene cylinderAcetone is a liquid chemical that dissolves large portions of acetyleneunder pressure without changing the nature of the gas. Being a liquid, acetonecan be drawn from an acetylene cylinder when it is not upright. You shouldnot store acetylene cylinders on their side, but if they are, you must let thecylinder stand upright for a minimum of 2 hours before using. This allows theacetone to settle to the bottom of the cylinder.An example of an acetylene cylinder is shown in figure 5. Thesecylinders are equipped with fusible plugs that relieve excess pressure if thecylinder is exposed to undo heat. A common standard acetylene cylindercontains 225 cubic feet of acetylene and weighs about 250 pounds.
Theacetylene cylinder is yellow, and all compressed-gas cylinders are colorcoded for identification.MAPP GasMAPP (methylacetylene-propadiene) is an all-purpose industrial fuelhaving the high-flame temperature of acetylene but has the handlingcharacteristics of propane. Being a liquid, MAPP is sold by the pound, ratherthan by the cubic foot, as with acetylene. One cylinder containing 70 poundsof MAPP gas can accomplish the work of more than six and one-half 225cubic-foot acetylene cylinders; therefore, 70 pounds of MAPP gas is equal to1,500 cubic feet of acetylene.64Because of its superior heat transfercharacteristics, MAPP produces a flametemperature of 5300°F when burned withoxygen.
MAPP equals, or exceeds, theperformance of acetylene for cutting, heating,and brazing. MAPP is not sensitive to shock andis nonflammable in the absence of oxygen. Thereis no chance of an explosion if a cylinder isbumped, jarred, or dropped. You can store ortransport the cylinders in any position with nodanger of forming an explosive gas pocket. TheFig. 5 Compressed gascharacteristic odor, while harmless, givescylinders containingoxygen oxygen and MAPP warnings of fuel leaks in the equipment longbefore a dangerous condition can occur. MAPPgasgas is not restricted to a maximum workingpressure of 15 psig, as is acetylene. In jobs requiring higher pressures and gasflows, MAPP can be used safely at the full-cylinder pressure of 95 psig at 70°F.
Because of this, MAPP is an excellent gas for underwater work.Cylinder DesignTotal weight for a MAPP cylinder, which has the same physical size asa 225-cubic-foot acetylene cylinder, is 120 pounds (70 pounds which isMAPP gas). MAPP cylinders contain only liquid fuel. There is no cylinderpacking or acetone to impair fuel withdrawal; therefore, the entire contents ofa MAPP cylinder can be used.
For heavy-use situations, a MAPP cylinderdelivers more than twice as much gas as an acetylene cylinder for the sametime period.Speaking18Discuss in the group advantages and disadvantages of using Acetyleneand map gas. Say which gas you would prefer to use for gas welding andwhy.Reading 419Skim the two texts Regulators and Cutting Torches and writeannotations.65RegulatorsYou must be able to reduce the high-pressure gas in a cylinder to aworking pressure before you can use it. This pressure reduction is done by aregulator or reducing valve.
The one basic job of all regulators is to take thehigh-pressure gas from the cylinder and reduce it to a level that can be safelyused. Not only do they control the pressure but they also control the flow(volume of gas per hour).Regulators come in all sizes and types. Some are designed for highpressure oxygen cylinders (2,200 psig), while others are designed for lowpressure gases, such as natural gas (5 psig).
Some gases like nitrous oxide orcarbon dioxide freeze when their pressure is reduced so they requireelectrically heated regulators.Most regulators have two gauges: one indicates the cylinder pressurewhen the valve is opened and the other indicates the pressure of the gascoming out of the regulator. You must open the regulator before you get areading on the second gauge. This is the delivery pressure of the gas, and youmust set the pressure that you need for your particular job.The pressures that you read on regulator gauges is called gaugepressure.
If you are using pounds per square inch, it should be written as psig(this acronym means pounds per square inch gauge). When the gauge on acylinder reads zero, this does not mean that the cylinder is empty. Inactuality, the cylinder is still full of gas, but the pressure is equal to thesurrounding atmospheric pressure. Remember: no gas cylinder is emptyunless it has been pumped out by a vacuum pump.Problems And SafetyRegulators are precise and complicated pieces of equipment.Carelessness can do more to ruin a regulator than any other gas-usingequipment.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
