11 - 1 Shielded Metal Arc Welding (SMAW) Arc welding –Heat for welding generated by electric arc established between flux-covered consumable metal rod.
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Shielded Metal Arc Welding(SMAW)Arc weldingHeat for welding generated by electric arc established between flux-covered consumable metal rod (electrode) and workCalled stick electrode weldingCombustion and decomposition of electrode creases gaseous shield (Gases given off)Protects electrode tip, weld puddle, arc, and highly heated work from atmospheric contaminationAdditional shielding provided by covering of molten slag (flux)Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.SMAWAmerican Welding SocietyCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.SMAW AdvantagesEquipment less complex, more portable and less costlyCan be done indoors or outdoors, in any location and any positionElectrodes available to match properties and strength of most base metalsNot used for welding softer metalsSMAW Operating PrinciplesSets up electric circuitIncludes welding machine, work, electric cables, electrode holder and electrodes, and a work clampHeat of electric arc brings work to be welded and consumable electrode to molten stateHeat intense: as high at 9,000F at centerCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.SMAW Operating PrincipleAmerican Welding SocietyCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Welding Power SourcesEach type of power source has fundamental electrical differences that best suit particular processesWelding machineMust meet changing arc load and environmental conditions instantlyMust deliver exact amount of electric current precisely at right time to welding arcAvailable in wide variety of types and sizesFour Types of Power SourceEngine-driven generatorsPowered by gas or diesel combustion engineCan be found with a.c. or d.c. electric motor No longer being manufactured and rarely foundInvertersIncreases frequency of incoming primary powerConstant current, constant voltage, or bothProduce a.c. or d.c. welding currentFour Types of Power SourceA.C. transformersUsed to step down a.c. line power voltage to a.c. welding voltageTransformer-rectifiersUse basic electrical transformer to step down a.c. line power voltage to a.c. welding voltageWelding voltage then passed through rectifier to convert a.c. output to d.c. welding currentMay be either d.c. or a.c.-d.c. machines Bridge RectifierOutput SlopeTwo basic typesConstant currentConstant voltageCurrent ControlsAmperageQuantity of current (flow)Determines amount of heat produced at weldVoltageMeasure of force of current (push)Determines ability to strike an arc and maintain its consistencyConstant Current Welding MachinesUsed for shielded metal arc welding and gas tungsten arc weldingAvailable in both d.c. and a.c. welding current Current remains fairly constant regardless of changes in arc lengthTotal Wattage stays the sameVoltage drops as amps increase (dropping arc voltage (DAV) machine)Enables welder to control welding current in specific range by changing length of arcOpen Circuit and Arc VoltageOpen circuit voltage runs between 50-100 volts (no welding being done, volts high, no amps)Drops to arc voltage when arc struckArc voltages (Voltage generated between electrode and work during welding, voltage lower, amps higher)Range: 36 volts (long arc) to 18 volts (short arc)Determined by arc length held by welder and type of electrode usedArc lengthened, arc voltage increases and current decreasesPolarityElectrode negative and electrode positive used in d.c. weldingDCEN (d.c. electrode negative)Electrode connected to negative terminal of power source and work connected to positive terminal (current flows from neg to pos) flow from electrode to work = more electrode consumption.DCEP (d.c. electrode positive)Electrode connected to positive terminal of power source and work connected to negative terminalD.C. Transformer-Rectifier Welding MachinesHave many designs and purposesFlexibility one reason for wide acceptanceDeliver either DCEN or DCEPMay be used for:Stick electrode weldingGas tungsten arc weldingSubmerged arc weldingMulti-operator systemsStud weldingCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Transformer-Rectifier MachinesHave two basic partsTransformer for producing and regulating alternating current that enters machinerectifier that converts a.c. to d.c.Third important part is ventilating fanKeeps rectifier from overheatingDesign improves arc stability and makes it easy to hold short arc which is soft and steadyNo major rotating parts so consume little powerA.C. Transformer Welding MachinesMost popular a.c. welding machineFunction of transformerStep down high voltage of input current to high amperage, low voltage current required for weldingEspecially suited for heavy workCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Advantages of a.c. Power SourcesReduces tendency to arc blowCan use larger electrodesResulting in faster speeds on heavy materialsLower costDecreased power consumptionHigh overall electrical efficiencyNoiseless operationReduced maintenanceD.C. and A.C.-D.C. Inverter Welding MachinesPortable, lightweight, and versatileMay be either constant current, constant voltage or bothCan perform several different processesCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Duty CyclePercentage of any given 10-minute period that machine can operate at rated current without overheating or breaking downRating of 100% means machine can be used at rated amperage on continuous basisRequired by continuous, automatic machine weldingRating of 60% means machine can be used at its capacity 6 out of every 10 minutes without damageSatisfactory for heavy SMAW and GTAWTwin Carbon Electrode HolderCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.The Lincoln Electric Co.Two leads are required because the arc is created between the two electrodes.Metal shield to protect welder's hand from intense heat.Larger than the metal electrode holderHolder is water cooledAtomic-Hydrogen Arc WeldingProcess in which electric arc surrounded by atmosphere of hydrogenGas shields molten metal from oxidation and contamination from the airTransfers heat from electrode to workArc formed between two electrodesTemperature produced by arc: 7,500FCurrent supplied by a.c. welding transformerHydrogen supplied in cylindersAtomic-Hydrogen Electrode HolderCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.General Electric Co.Atomic-Hydrogen Arc WeldingMetal of same analysis as being welded can be depositedWelds may be heat treatedUnusually smooth, ductile, nonporous and free from impuritiesSurface free from scaleMay weld hard-to-weld metalsAdvantages: increased production, low operating cost, and low maintenance cost
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