Presentation on theme: "Selecting the Electrode"— Presentation transcript:
1 Selecting the Electrode Shielded Metal-Arc WeldingChapter 6
2 ElectrodesClassified into 5 main groupsMild steelMajority of weldingHigh-carbon steelSpecial-alloy steelCast ironNon-ferrousEx. Aluminum, Copper, & BrassElectrode – a coated metal wire having approximately the same composition as the base metal.Standards set forth by AWS (American Welding Society) & ASTM (American Society for Testing Materials)
3 Two kinds of mild steel electrodes Bare & ShieldedBare electrodes are still covered with little covering, this limits their use in the welding field.Shielded electrodes have a heavy coating on the outside of them (flux)Purpose of flux- prevents corrosion from taking placeAct as a cleaner and deoxidizesRelease an inert gas to protect from oxygen, nitrogen, & hydrogen in the atmosphere. These elements will weaken the weld if they were to come in contact with the molten metal.Form slag to protect the cooling metal & allows metal to cool at a slower rate protecting the metal properties.Provide easier starting arc, stabilizer, reduce splatter.Permit better penetration & X-ray quality.
4 FluxAs the electrode burns the flux produces a gaseous shield around the weld.This prevents harmful contaminants from hurting the weld.3 harmful elements present in the atmosphereHydrogenOxygenNitrogen
6 Consider the following when selecting an electrode: The weld groove designTensile strength of the required weldBase metal compositionElectrode diameter 1/8, 3/32, 5/32 (never use a rod with a diameter larger than the thickness of the base metal)Electrode size means the size of the wire, not overall size of the rodAmp setting: simple way divide the rod thickness 1/8= 125ampsThe position of the weld jointThe rate at which you want to deposit the weld metalThe shape of the deposited bead (filler) is caused by oscillationThe type of current usedPenetration requiredMetal thicknessThe experience of the welderThe specifications of the weld to be madeQUIZ
8 Identifying Electrodes Standards set up by AWS (American Welding Society) & ASTM (American Society of Testing Materials)Prefix E stands for electric arc (E-6010)The first two digits stand for tensile strength in thousands psi (60,000)The third digit represents welding position (1,2,3)1= any position2= horizontal & flat position3= flat position onlyThe fourth digit represents a manufacturers special characteristicThe numbers 0 – 8 may used
10 Conserving & Storing Electrodes Electrodes are very expensive so use them up to 1 ½” to 2” in length. (do not burn them into the stinger handle)Always store electrodes in a dry place at normal room temp“Moisture will cause the flux tocrack & disintegrate”Please burn electrodes to this length!!!Fast freeze electrodesDeep penetrating arc & fast-freezing deposits (commonly called reverse polarity electrodes)
11 Fill-freeze electrodes Moderately forceful arc & deposition rateCommonly called straight polarity rodsGeneral purpose electrodeCan be used in all positionsPreferred in vertical & overhead weldingFast-fill electrodesHeavy coated iron powder electrodes with soft arc & fast deposit rateHeavy slag & exceptionally smooth beadsGenerally used for flat welding (production work)
12 Characteristics of Common SMAW Electrodes Covering/Flux: cellulose-sodium & 0-10% iron powderPosition: All Current: DCRP Penetration: deepArc: Digging Freeze: fast Fill: medium slowSlag: light, easy to remove (wire brush is better)Bead Appearance: flat, rough & much spatter.Quality of fit-up for successful weld: poor to goodAverage amperage: 1/8” rod = amps* E-6010 is only for reverse polarity, so it is sometimes used to check polarity. It will give a strong hissing arc if the incorrect polarity is being used. Try it in your booth & become familiar with it.E-6010
13 E-6011 Covering/Flux: cellulose-potassium & 0-10% iron powder Position: All Current: AC or DCRP Penetration: deepArc: digging Freeze: fastFill: medium-slow Slag: light, easy to removeBead Appearance: flat, rough & much spatterQuality of fit-up for successful weld: poor to goodAverage Amperage: 1/8” rod 70 – 110 amps
14 E-7018 Covering: low-hydrogen & 25-40% iron powder. Position: All Current: DCRP Penetration: mediumArc: medium Freeze: medium Fill: fastSlag: heavy & hard to removeBead Appearance: medium smooth with some spatter.Quality of fit-up for successful weld: goodAverage Amperage: 1/8” rod 100 – 150 ampsE-7018
22 Tie-Ins Always remove slag from previous weld Chipping hammer or wire brush
23 AWS Pipe Welding Positions 5G – Pipe is horizontal & the joint is verticalMay be welded uphill or downhillUphill welding – starting the weld at the bottom or 6 o’clock position and moving upward to the top of the joint or 12 o’clock position.Uphill welding usually produces:Better penetrationFewer passes are requiredUsed on thicker-walled pipeUsed on high-pressure pipe welds
24 Root pass – 1st pass on pipe Downhill welding – starting the weld at the 12 o’clock position and is welded downward towards the 6 o’clock position.The welds must move more rapidly to prevent molten slag from rolling into the weld pool.Penetration is better when welding uphill.Downhill is used on pipe with wall thickness thinner than ½”Pipe welding PassesRoot pass – 1st pass on pipeRemove slag after root passUsually performed with E-6010 or E –7010The root pass is usually ground out partially to remove any crown in the 1st pass.Penetration is essential in the root pass, therefore GTAW is sometimes preferred for this pass for the highest quality.
25 Hot pass – 2nd pass on pipe Hot pass uses more current than the rootIt must fuse well with the root pass & pipe wallsIt must melt any slag left from the root passThe hot pass should be welded within five minutes after the root pass is completed.Filler passesUsed to fill the weld joint – several are performedMay be stringer beads or slight weavesEach pass must fuse the previous pass & into the pipe wallsTo prevent slag inclusions, each pass must be cleaned prior to welding the next pass
26 Cover pass – final pass Used to cover the weld joint Weaving motion is used to produce a wide beadHot, filler, & cover passes are made with E-6010 or E-7010, & E-7018 electrodes.E-6010, E-7010 are used with downhill welding.E-7018 are used with uphill weldingWhen a backup ring is used E-7018 can be used for the root pass.
28 2G – Horizontal Pipe Welding Similar to horizontal welding on plateBefore attempting to weld in the 5G position, a person must be able to weld satisfactorily in the flat, vertical, & overhead positions.1G – Rotated Flat Pipe WeldingSame as 5G, but pipe is rotated mechanically
29 6G – Multiple passPipe is angled with multiple passes, but it is not rotated.Backing ring for pipe butt joints. This device helps control penetration & aligns the pipe. Used with E-7018
30 AWS Welding Positions for Groove Welds: Plate 1G Flat Position:2G Horizontal Position3G Vertical Position4G Overhead Position
31 AWS Welding Positions for Fillet Welds: Plate 1F Flat Position:2F Horizontal Position3F Vertical Position4F Overhead Position