Selecting the Electrode Shielded MetalArc Welding Chapter 6

Selecting the Electrode Shielded Metal-Arc Welding Chapter 6

• Electrodes – Classified into 5 main groups • Mild steel – Majority of welding • • High-carbon steel Special-alloy steel Cast iron Non-ferrous – Ex. Aluminum, Copper, & Brass • Electrode – 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)

• Two kinds of mild steel electrodes – Bare & Shielded • Bare 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 place – Act as a cleaner and deoxidizes – Release 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.

• Flux – As 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 atmosphere • Hydrogen • Oxygen • Nitrogen

• Consider the following when selecting an electrode: – – The weld groove design Tensile strength of the required weld Base metal composition Electrode 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 rod – Amp setting: simple way divide the rod thickness 1/8= 125 amps – The position of the weld joint – The rate at which you want to deposit the weld metal • The shape of the deposited bead (filler) is caused by oscillation – – – The type of current used Penetration required Metal thickness The experience of the welder The specifications of the weld to be made QUIZ

• 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 position – 2= horizontal & flat position – 3= flat position only • The fourth digit represents a manufacturers special characteristic – The numbers 0 – 8 may used

• 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 to crack & disintegrate” Please burn electrodes to this length!!! • Fast freeze electrodes – Deep penetrating arc & fast-freezing deposits (commonly called reverse polarity electrodes)

• Fill-freeze electrodes – – – Moderately forceful arc & deposition rate Commonly called straight polarity rods General purpose electrode Can be used in all positions Preferred in vertical & overhead welding • Fast-fill electrodes – Heavy coated iron powder electrodes with soft arc & fast deposit rate – Heavy slag & exceptionally smooth beads – Generally used for flat welding (production work)

• Characteristics of Common SMAW Electrodes – E-6010 • • Covering/Flux: cellulose-sodium & 0 -10% iron powder Position: All Current: DCRP Penetration: deep Arc: Digging Freeze: fast Fill: medium slow Slag: light, easy to remove (wire brush is better) Bead Appearance: flat, rough & much spatter. Quality of fit-up for successful weld: poor to good Average amperage: 1/8” rod = 70 -100 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

– E-6011 • • Covering/Flux: cellulose-potassium & 0 -10% iron powder Position: All Current: AC or DCRP Penetration: deep Arc: digging Freeze: fast Fill: medium-slow Slag: light, easy to remove Bead Appearance: flat, rough & much spatter Quality of fit-up for successful weld: poor to good Average Amperage: 1/8” rod 70 – 110 amps

– E-7018 • • Covering: low-hydrogen & 25 -40% iron powder. Position: All Current: DCRP Penetration: medium Arc: medium Freeze: medium Fill: fast Slag: heavy & hard to remove Bead Appearance: medium smooth with some spatter. Quality of fit-up for successful weld: good Average Amperage: 1/8” rod 100 – 150 amps E-7018

Next E-6010 E-6011 video

Back to E 6013 outline

Cont. E-7018 video

Cont. Notes

A = correct current, arc length & travel speed B= Amperage too low C = Amperage too high D = Too short an arc length E = Arc length too long F = travel speed too slow G = Travel speed too fast

Striking an Arc 2 methods Stringer Bead Weave

• Tie-Ins – Always remove slag from previous weld – Chipping hammer or wire brush

AWS Pipe Welding Positions • 5 G – Pipe is horizontal & the joint is vertical – May be welded uphill or downhill • Uphill 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 penetration Fewer passes are required Used on thicker-walled pipe Used on high-pressure pipe welds

• 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 Passes • Root pass – 1 st pass on pipe – Remove slag after root pass – Usually performed with E-6010 or E – 7010 – The root pass is usually ground out partially to remove any crown in the 1 st pass. • Penetration is essential in the root pass, therefore GTAW is sometimes preferred for this pass for the highest quality.

• Hot pass – 2 nd pass on pipe – Hot pass uses more current than the root – It must fuse well with the root pass & pipe walls – It must melt any slag left from the root pass – The hot pass should be welded within five minutes after the root pass is completed. • Filler passes – Used to fill the weld joint – several are performed – May be stringer beads or slight weaves – Each pass must fuse the previous pass & into the pipe walls – To prevent slag inclusions, each pass must be cleaned prior to welding the next pass

• Cover pass – final pass – Used to cover the weld joint – Weaving motion is used to produce a wide bead • Hot, 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 welding • When a backup ring is used E-7018 can be used for the root pass.

Two pipe welders welding in the 5 G position

• 2 G – Horizontal Pipe Welding – Similar to horizontal welding on plate – Before attempting to weld in the 5 G position, a person must be able to weld satisfactorily in the flat, vertical, & overhead positions. • 1 G – Rotated Flat Pipe Welding – Same as 5 G, but pipe is rotated mechanically

• 6 G – Multiple pass – Pipe 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

AWS Welding Positions for Groove Welds: Plate • 1 G Flat Position: • 2 G Horizontal Position • 3 G Vertical Position • 4 G Overhead Position

AWS Welding Positions for Fillet Welds: Plate • 1 F Flat Position: • 3 F Vertical Position • 2 F Horizontal Position • 4 F Overhead Position