Selecting the ElectrodeShielded 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= 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

• 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• 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

• 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.

• 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

• 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 5G position

• 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

• 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

AWS Welding Positions for Groove Welds: Plate• 1G Flat Position:

• 2G Horizontal Position

• 3G Vertical Position

• 4G Overhead Position

AWS Welding Positions for Fillet Welds: Plate• 1F Flat Position:

• 2F Horizontal Position

• 3F Vertical Position

• 4F Overhead Position