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= 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 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

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 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