2DefinitionShield Metal Arc Welding is an arc welding process that uses a consumable electrode to initiate the arc and provide the filler material.
3Arc Welding SafetyWhat are the principle hazards associated with SMAW?What can be done to manage the hazards associated with SMAW?Hot metal.Harmful raysFireBurnsExplosiontripping/falling_______Use appropriate PPEInspect equipmentPliersshaded lenswelding apparel
4What’s the purpose of slag? SMAW ProcessThe arc temperature over 9,000 oF melts the base metal, the wire core and the coating on the electrode.The high temperature causes some of the ingredients in the flux to form a gaseous shield.The electric energy is provided by a power source.As the weld cools slag forms on top of the weld puddle.The slag contains the impurities that were in the weld pool and it retards the cooling rate.What’s the purpose of slag?
5Equipment Polarity switch Power cord Electrode holder Electrode Base metalGround clampElectrode leadGround leadAmperage scaleAmperage adjustmentOn/Off switchWelder case
6Six (6) Common SMAW Power Supplies What welding current is available from each of these power supplies?TypeCurrentTransformerTransformer with rectifierGeneratorAlternatorAlternator with rectifierInverterTransformer AcTransformer-rectifier AC & DCGenerator DCAlternator ACAlternator-rectifier AC and DCInverter AC and DC
7Initiating The Arc List the six (6) steps for initiating the arc. Select the best electrodeSet the welder currentTurn on welderWarn bystandersLower helmetStart arc (two methods)BrushingTapping
8Brushing MethodHold end of electrode about 1/4 - 1/2 inch above the surface.Lower helmetGently brush surface of the metal with the end of the electrode.When arc starts, lift electrode 1/8 inch.If electrode sticks, twist it back and forth. If it does not break loose, release electrode from electrode holder.Do not shut off the welder with the electrode stuck to the metal.Burn out the switchWhy?
9Tapping Method Set up welder Hold the electrode at the travel angle and 1/4 - 1/2 inch above the metal.Quickly lower the electrode until it touches the metal and then lift it 1/8 inch.Recommended method for E7018 electrode because the flux must be broken off before the arc will start.
10Five (5) Factors Controlling the Quality of SMAW Welds HeatElectrodeElectrode angleArc lengthSpeed of travel
11Five (5) Factors 1. HeatThe arc welder must produce sufficient heat (BTU’s) to melt the electrode and the base metal to the desired depth.How is the amount of heat at the weld controlled?What factors determine the amount of heat required for a weld?Adjusting the amperageThickness of the metalType of joint,Electrode typeElectrode diameterWeld position
12Five (5) Factors 1. Heat – cont. What are the characteristics of excessive heat when completing a SMAW joint?What are the characteristics of insufficient heat when completing a SMAW weld?Electrode easier to startExcessive penetration (burn through)Excessive bead widthExcessive splatterElectrode overheatingHard to startReduced penetrationNarrow beadCoarse ripples
13Five (5) Factors 2. Electrodes What are the two (2) primary requirements for an SMAW electrode?What metals can be welding with the SMAW process?How are SMAW electrodes classified?Must be compatible with base metalMust be correct size.Carbon steelsLow alloy steelsCorrosion resisting steelsCast ironsAluminum and alloysCopper and alloysNickel and alloysAmerican Welding Society system and grouping
14American Welding Society (AWS) Classification System The AWS system designates:tensile strength,weld positioncoating (flux)current.The primary difference in the performance of electrodes is the flux.Manufactures may and do use their own numbering system and sell electrodes that do not use the AWS system.
15Arc Welding Electrode Flux Flux: A material used during arc welding, brazing or braze welding to clean the surfaces of the joint chemically, to prevent atmospheric oxidation and to reduce impurities and/or float them to the surface. (British Standard 499)SMAW fluxes are naturally occurring minerals.The quality, and cost, of the flux is directly related to the amount of resources the manufacture invests purifying the minerals for the flux.
16Seven (7) Classifications of Flux constituents calcium, manganese, calcium fluoride and celluloseProtection from atmospheric contamination & slag formersFluxing agentsArc initiators and stabilizersDeoxidizesPhysical properties of the fluxFillers and metallic additionsBinders and flux strength improverscalcium carbonates, rutile, silica, talcnickel and iron powders, sodium, feldspar, clay, talcferroalloys, ferrosilicon, iron powdermanganese, iron, rutile, alumina, silica, calcium fluoridewaterglass, mica organic bindersferrow alloys, iron and nickel powders
17Electrode Performance Groups Fast-freezeMild steelQuick solidification of weld poolDeep penetratingRecommended for out of position weldsDeep penetrating arcFast-fillHighest deposition rateStable arcThick fluxFlat position and horizontal laps onlyFill-freezeGeneral purpose electrodesCharacteristics of fast-freeze and fast-fillLow hydrogenWelding characteristics of fill-freezeDesigned for medium carbon and alloy steels
18Selecting Electrode Size What factors determine the optimum diameter of electrode that should be used?Is it permissible to use more than one diameter of electrode to complete a joint?YesExplain!thickness of the base metal,welding positioncapacity of the welding power supplySmall diameter for route pass—larger for filler passes.ROT: the diameter of the electrode should not exceed the thickness of the metal.
19Electrode StorageElectrodes are damaged by rough treatment, temperature extremes and moisture.The should be kept in their original container until used.They should be stored in a heated cabinet that maintains them at a constant temperature.The storage of low hydrogen electrodes is very critical.Designed to reduce underbead cracking in alloy and medium carbon steels by reducing the the amount of hydrogen in the weld pool.The flux is hydroscopic--Moisture in the flux also causes excessive gasses to develop in the weld pool and causes a defect in the weld called worm holes.What is the primary source of hydrogen in the weld pool?What does that mean?Waterattracts moisture (H2O).
20Five (5) Factors 3. Electrode Angle Two angles are important:TravelWorkThe travel angle is the angle of the electrode parallel to the joint.The correct travel angle must be used for each joint.Beads = 15o from vertical or 75o from the work.Butt joint = 15o from vertical or 75o from the work.Lap joint = 45o.T joint = 45o.Corner = 15o from vertical or 75o from the work.Excessive—poor puddle geometryInsufficient—reduced penetration, tall narrow beadWhat is the effect of incorrect travel angle?
21Five (5) Factors Electrode Angle-cont. The work angle is the angle of the electrode perpendicular to the joint.The appropriate angle must be used for each joint.Beads = 90oButt joint = 90oLap joint = 45oT joint = 45oCorner = 90oCan you think of a situation where the travel angle should be modified?When completing a joint with metal of different thickness.
22Five (5) Factors 4. Arc Length The arc length is the distance from the metal part of the electrode to the weld puddle.The best arc length is not a fixed distance, but should be approximately equal to the diameter of the electrode.What are the characteristics of a weld completed with excessive arc length?Excessive lengthExcessive spatterReduced penetrationPoor quality weldElectrode sticksNarrow weldWhat are the characteristics of a weld completed with insufficient arc length?
23Five (5) Factors 5. Speed of Travel The speed of travel is measured in inches per minute.What factors determine the best speed of travel?The size of the joint,The type of electrodeThe size of the electrodeThe current setting on the machineDeposition rate of the electrode (cubic inches per minute)
24Five (5) Factors 5. Speed-cont. The ideal speed can be calculated using the volume of the joint and the deposition rate of the electrode.Step one: determine the area of the weld. (Assuming 1/16 inch penetration.)Step Two: knowing the deposition rate of the electrode, determine the welding speed. (Deposition rate = 2.5 in3/min.)
25Five (5) Factors 5. Speed-cont. The correct welding speed is indicated by the shape of the ripples.Too slow = excessive width, excessive penetrationToo fast = narrower width, elongated ripple pattern, shallow penetration.Recommended = width 2-3 times diameter of electrode, uniform ripple pattern, full penetration.
27Square GrooveA butt joint can be completed with a groove welded on metal up to 1/8 inch thick with a single pass on one side, with no root opening.Electrode manipulation should only be used to prevent burning through.
28Square Groove Thicker Metal A groove weld on metal up to 1/4 inch thick can be welded with a single pass on one side but, if possible, it should be completed with a single pass on both sides.Metal this thick requires a root opening to achieve adequate penetration.Electrode manipulation will reduce penetration.
29Single V Groove WeldButt joints on metal greater than 1/4 inch thick require joint preparation.Note that the groove does not extend all the way. A short distance, called the root face, is left undisturbed.Several different combinations of passes can be used to complete this joint.What determines that amount of joint preparation that must be done before welding?The purpose of the joint preparation is to compensate for not having sufficient amperage and electrode diameter.Note: this is the principle use of pattern beads.
31InformationIn a T-joint the two welding surfaces are at an angle close to 90 degrees from each other.The welding side and number of passes uses depends on the thickness of the metal, the welding access and capacity of the power supply.Common joints include.Plane TT with joint gapSingle preparationDouble preparation
32Plane T-Joint The plane T joint is very useful for thin metal. Can be completed at angles other than 90 degrees.Can be completed with metal of different thickness.The work angle must be changed to direct more heat to the thicker piece.
33T-joint--Thicker Metal When the metal thickness exceeds 1/8 inch the recommendation is to gap the joint.Improves penetrationMay not be necessary if larger diameter electrode is used and sufficient amperage is available.The need for a joint gap varies with the type of electrode, but should not exceed 1/8 inch.
34T-joint Single Single Bevel As with other joints, thicker metal must have joint preparation to achieve full penetration with smaller diameter electrodes.Several different preparations can be used. A popular one is the bevel.A bevel can be completed by grinding or cutting.The bevel joint can be completed with electrode manipulation or no electrode manipulation.When when electrode manipulation is used to fill the joint, the first pass should be a straight bead with no manipulation.
35T-joint Double BevelThe double bevel T-joint is recommended for metal 1/2 inch thick and thicker.The root passes should be with not manipulation, but the filler passes can be completed with either straight beads or patterns beads.Alternating sides reduces distortion.
37Common SMAW Defects Hot cracks Undercutting Slag inclusions Porosity Caused by excessive contraction of the metal as it cools.Excessive bead sizeMay also be found at the root of the weld.Slag inclusionsLong arcIncomplete removal of slag on multipass welds.Undercuttingimproper welding parameters; particularly the travel speed and arc voltage.PorosityAtmospheric contamination or excess gas in the weld pool.
38SMAW Weld Defects-cont. Incomplete fusionToe cracksMicrocracksUnderbead cracksToe CracksExcessive heat and rapid cooling.Underbead cracksExcessive hydrogen in weld poolMicrocracksCaused by stresses as weld cools.Incomplete fusionIncorrect welding parameters or welding techniques.