Smaw Intro 2

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SMAW WeldingSection 8

Unit 26



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Arc Welding Safety

1. Recognize that arc welding produces a lot of heat.2. Use equipment according to manufacturers

recommendations.

3. Insure fire extinguishers are available

4. Provide a first aid kit

5. Use water filled containers to receive hot metal from

cutting operations.

6. Practice good housekeeping

7. Use appropriate PPE



3

Arc Welding Safety-cont.

7. Insure all wiring is correctly installed and

maintained.

8. Remove or shield all combustible materials in work

area.

9. Do not use gloves or clothing which contain

flammable substances

10. Protect others from arc flash.

11. Protect equipment from hot sparks.

12. Use a fume collector.

13. Never work in damp or wet area.

14. Shutoff power source before making repairs oradjustments, including changing electrode.

15. Don’t overload the welding cables or use cables with

damaged insulation.



4

Arc Welding PPE

Helmet Shade 10 or darker

Face protection

Always wear safety glasses underneath

Auto helmet recommended

Clothing Long sleeves

Button up shirt

Work shoes

Protective apron, sleeves, jackets or pants if available. (Fig 26-6)



5

SMAW Process

•

The arc temperature over 9,000o

F melts the basemetal, the wire core and the coating on the

electrode.

• The high temperature causes some of the

ingredients in the flux to form a gaseous shield.

• The electric energy is provided by a special power

source.

• As the weld cools slag forms on top of the weld

puddle.



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SMAW Power Supplies

SMAW requires a constant current (CC) of either DC orAC.

Some power supplies will supply both DC and AC.

Power supply capacity determines the maximum diameter

of electrode that can be used.



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Equipment

Power Supply Polarity Switch

Electrode

Base Metal

(work Piece)

Ground ClampGround Cable

Amperage

Scale

Power Switch

Amperage

Adjustment

Electrode Cable

Electrode Holder

Power

Cord



8

Open Circuit Voltage (OCV)

Open circuit voltage is the potential between the welding

electrode and the base metal when the machine is on, butthere is no arc.

The higher the OCV a machine has, the easier it will be tostrike an arc.

Only adjustable of dual control machines.



9

Arc Voltage

Arc voltage is the potential between the electrode andthe base metal when the arc is present.

Arc voltage is less than OCV.

Adjustable on dual control machines.



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Polarity

The polarity of an object is its physical alignment ofatoms.

The term is often used to describe the positive and

negative ends of batteries and magnets.

The negative end has an excess of electrons

The positive end has a deficiency of electrons.



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Five (5) Common Power

Supplies

Transformer AC only

Rectifier

DC only

Transformer/rectifier

AC or DC

Generator

DC and/or AC

Inverter

AC and DC



12

Striking The Arc

Select the best electrode Set the welder (Fig 26-8)

Turn on welder

Warn bystanders

Lower helmet

Start arc (two methods)

Brushing

Tapping



13

Brushing Method

Hold end of electrode about 1/4 -

1/2 inch above the surface. Lower helmet

Gently brush surface of the metal

with the end of the electrode.

When arc starts, lift electrode 1/8

inch.

If electrode sticks, twist it back and forth. If it does not break loose,

release electrode from electrode holder.

Do not shut off the welder with the electrode stuck to the metal.

Recommended method for beginning weldors.



14

Tapping Method

Set up welder

Hold the electrode at thetravel angle and 1/4 -1/2 inch above the metal.

Quickly lower theelectrode until it touches

the metal and then lift it1/8 inch.

More difficult method to learn



15

Arc Welding Bead Nomenclature

Flux Electrode

Electrode

metal

PenetrationMolten

puddleBeadBase metal

Slag

Gas

shield



16

Running Beads

Practice running stringer beads

No weaving or pattern.

Remember the electrode burns off as the weld is made.

Speed used should result in a bead 2-3 times wider than

the diameter of the electrode.

Cool metal between beads.

Practice holding a long arc for a couple of seconds after

striking the arc.

Preheats the weld

Practice filling in the crater.



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Five (5) Factors of Arc Welding

1. Heat

2. Electrode

3. Electrode angle

4. Arc length

5. Speed of travel



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Five (5) Factors

1. Heat

The arc welder must produce sufficient heat (electric arc) to meltthe electrode and the base metal to the desired depth.

The amount of heat produced is determined by the amperage.

Amperage is limited by the diameter of the electrode and the capacity of thewelder.

The amount of heat needed to complete the weld is determined

by several factors:

Excessive heat.

Electrode easier tostart

Excessive penetration(burn through)

Excessive bead width

Excessive splatter

Electrode overheating

Insufficient heat.

Hard to start

Reduced

penetration

Narrow bead

Coarse ripples

Thickness of themetal

Type of joint,

Electrode type

Electrodediameter

Weld position



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Five (5) Factors

2. Electrodes

The SMAW process usesa consumable electrode.

Electrode must becompatible with basemetal.

Electrodes are availablefor different metals.

Carbon steels

Low alloy steels

Corrosion resisting steels

Cast irons

Aluminum and alloys

Copper and alloys

Nickel and alloys

Another useful group ofelectrodes is

hardsurfacing.

NEMA color coding

System of of colors on the

end or dots on the barewire indicating the class ofelectrode.

Not very common today.

AWS numerical coding

Most popular method.



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American Welding Society (AWS)

Classification System

The AWS systemdistinguishes the tensile

strength, weld position and,

coating and current.

Manufactures may and do

use there own numbering

system and produce

electrodes that do not fit in

the AWS system.



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Welding Currents

Not all electrodes are designed to work with all currents. Common SMAW currents.

Alternating Current (AC)

Direct Current straight polarity (DCSP) or (DCEN)

Direct Current Reverse polarity (DCR P) or (DCEP)



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Arc Welding Electrode Flux

Flux: A material used during arc welding, brazing or brazewelding to clean the surfaces of the joint chemically, toprevent atmospheric oxidation and to reduce impurities and/or float them to the surface. (British Standard 499)

Seven (7) Classifications of Flux constituents

1. Protection from atmospheric contamination2. Fluxing agents

3. Arc initiators and stabilizers

4. Deoxidizes

5. Physical properties of the flux

6. Fillers and metallic additions7. Binders and flux strength improvers



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Electrode Grouping Electrodes are also grouped

according to there performancecharacteristics.

Fast-freeze• Mild steel

• Quick solidification of weld

pool

• Deep penetrating

• Recommended for out of

position welds• Deep penetrating arc

Fast-fill• Highest deposition rate

• Stable arc

• Thick flux

• Flat position and horizontallaps only

- Fill-freeze• General purpose

electrodes

• Characteristics of

fast-freeze and fast-

fill

Low hydrogen• Welding

characteristics of

fill-freeze

• Designed for medium

carbon and alloy

steels



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Selecting Electrode Size

The optimum electrodediameter is determined

by the thickness of thebase metal, the weldingposition and the capacityof the welding powersupply.

A diameter of 3/32 or 1/8

inch can be used on metalsup to 1/4 inches thick

without joint preparation.

ROT: the diameter of the

electrode should not

exceed the thickness of themetal.

A smaller diameter isusually recommended for

out of position welding.

When completing root

passes in V-joints, a

smaller diameter maybeused and then a largerdiameter is used for the

filler passes.



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Electrode Storage

Electrodes are damaged by rough treatment, temperature

extremes and moisture. The should be kept in their original container until used.

They should be stored in a heated cabinet that maintains

them at a constant temperature.

The storage of low hydrogen electrodes is very critical. Designed to reduce underbead cracking in alloy and medium

carbon steels by reducing the the amount of hydrogen in the weld

pool.

The flux is hydroscopic--attracts moisture (H2O).

Moisture in the flux also causes excessive gasses to develop in theweld pool and causes a defect in the weld caused worm holes.



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Five (5) Factors

3. Electrode Angle

The electrode angle influences the

placement of the heat.

Two angles are important:

Travel

Work

The travel angle is the angle of theelectrode parallel to the joint.

The correct travel angle must be used for each joint.

Beads = 15o from vertical or 75o from the work.

Butt joint = 15o from vertical or 75o from the work.

Lap joint = 45o.

T joint = 45o.

Corner = 15o from vertical or 75o from the work.



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Five (5) Factors

Electrode Angle-cont.

The work angle is the angle of the

electrode perpendicular to the joint.

Beads = 90o Butt joint = 90o

Lap joint = 45o

T joint = 45o

Corner = 90o

The appropriate angle must be used for

each joint.

The work angle may need to bemodified for some situations. For example, a butt joint with two

different thickness of metal.



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Five (5) Factors

4. Arc Length

The arc length is the distance from the metal part of theelectrode to the weld puddle.

The best arc length is not a fixed distance, but should be

approximately equal to the diameter of the electrode.

Arc length can be adjusted slightly to

change the welding process. Excessive length

Excessive spatter

Reduced penetration

Poor quality weld

Insufficient length Electrode sticks

Narrow weld

Poor quality weld



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Five (5) Factors

5. Speed of Travel

The speed of travel (inches per minute) is an importantfactor when arc welding.

The best speed of travel (welding speed) is determined by

several factors:

The size of the joint,

The type of electrode The size of the electrode

The amperage setting on the machine

Deposition rate of the electrode (cubic inches per minute)

The deposition rate of an electrode will change with the

welding amperage.



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Five (5) Factors

5. Speed-cont.

The ideal speed can be calculatedusing the volume of the joint and

the deposition rate of the electrode.

Area =1

2bh =

0.25 in x 0.25 in

2= 0.0625 in

2

Step one: determine the area of

the weld. (Assuming 1/16 inch

penetration.)

Step Two: knowing the deposition rate of the electrode,

determine the welding speed. (Deposition rate = 2.5

in3/min.)

in

min=2.5 in

3

min x

1

0.0625 in2= 40

in

min



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Five (5) Factors

5. Speed-cont.

The correct welding speed is indicated by the shape of the

ripples.

Too fast = narrower width,elongated ripple pattern,

shallow penetration.

Recommended = width 2-3

times diameter of electrode,

uniform ripple pattern, fullpenetration.

Too slow = excessive width,

excessive penetration



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SMAW Joints



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Square Groove

A butt joint can be completed with a groove welded on

metal up to 1/8 inch thick with a single pass on one side,with no root opening.

Electrode manipulation should only be used to prevent

burning through.



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Square Groove Thicker Metal

A groove weld on metal up to 1/4 inch thick can be

welded with a single pass on one side but, if possible, itshould be completed with a single pass on both sides.

Metal this thick requires a root opening to achieve

adequate penetration.

Electrode manipulation will reduce penetration.



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Single V Groove Weld

Butt joints on metal greater than 1/4 inch thick require joint preparation.

Note that the groove does not extend all the way. A shortdistance, called the root face, is left undisturbed.

The amount of joint preparation is dependent on thediameter of the electrode and the amperage capacity ofthe power supply.

Several different combinations of passes can be used tocomplete this joint.

Note: this is the principle use of pattern beads.



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T-Joints



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Information

In a T-joint the two welding surfaces are at an angle closeto 90 degrees from each other.

The welding side and number of passes uses depends on

the thickness of the metal, the welding access and

capacity of the power supply.

Common joints include. Plane T

T with joint gap

Single preparation

Double preparation



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Plane T-Joint

The plane T joint is very useful for thin metal.

Can be completed at angles other than 90 degrees.

Can be completed with metal of different thickness.

The work angle must be changed to direct more heat to the thickerpiece.



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T-joint--Thicker Metal

When the metal thickness exceeds 1/8 inch the

recommendation is to gap the joint. Improves penetration

May not be necessary if larger diameter electrode is used and sufficientamperage is available.

The need for a joint gap varies with the type of electrode, butshould not exceed 1/8 inch.



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T-joint Single Single Bevel

As with other joints, thickermetal must have joint preparation toachieve fullpenetration withsmaller diameter

electrodes. Several different preparations can be used. A popular one is

the bevel.

A bevel can be completed by grinding or cutting.

The bevel joint can be completed with electrode manipulation

or no electrode manipulation. When when electrode manipulation is used to fill the joint,

the first pass should be a straight bead with no

manipulation.



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T-joint Double Bevel

The double bevel T-joint is recommended for metal 1/2inch thick and thicker.

The root passes should be with not manipulation, but thefiller passes can be completed with either straight beads orpatterns beads.

Alternating sides reduces distortion.



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Weld Defects



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Common SMAW Defects

Undercutting

improper weldingparameters; particularly thetravel speed and arc voltage.

Porosity

Atmospheric contaminationor excess gas in the weldpool.

Hot cracks

Caused by excessive contractionof the metal as it cools.

Excessive bead size

May also be found at the root ofthe weld.

Slag inclusions

Long arc

Incomplete removal of slag onmultipass welds.

Under Cutting

Hot Cracks

Slag Inclusions

Porosity



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SMAW Weld Defects-cont.

Toe Cracks

Excessive heat and rapid cooling.

Underbead cracks

Excessive hydrogen in weld pool

Microcracks

Caused by stresses as weld cools.

Incomplete fusion

Incorrect welding parameters or welding techniques.

Toe cracks

Underbead cracks

Microcracks

Incomplete fusion



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