Selecting the Electrode

1. Selecting the Electrode Shielded Metal-Arc Welding Chapter 6

2. 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)

3. 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.

4. 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

6. 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= 125amps • 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

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 position • 2= horizontal & flat position • 3= flat position only • The fourth digit represents a manufacturers special characteristic • The 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 to crack & disintegrate” Please burn electrodes to this length!!! • Fast freeze electrodes • Deep penetrating arc & fast-freezing deposits (commonly called reverse polarity electrodes)

11. 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)

12. 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

13. 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

14. 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

15. Next E-6010-E-6011 video

16. Back to E-6013 outline

17. Cont. E-7018 video

18. Cont. Notes

19. 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

20. Striking an Arc • 2 methods Stringer Bead Weave

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 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

24. 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 – 1st 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 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 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

26. 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.

27. Two pipe welders welding in the 5G position

28. 2G – Horizontal Pipe Welding • Similar to horizontal welding on plate • Before 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 Welding • Same as 5G, but pipe is rotated mechanically

29. 6G – 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

30. 4G Overhead Position AWS Welding Positions for Groove Welds: Plate • 1G Flat Position: • 2G Horizontal Position • 3G Vertical Position

31. 3F Vertical Position AWS Welding Positions for Fillet Welds: Plate • 1F Flat Position: • 2F Horizontal Position • 4F Overhead Position