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
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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.
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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)
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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
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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.
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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
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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
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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.
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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
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Arc Welding Bead Nomenclature
Flux Electrode
Electrode
metal
PenetrationMolten
puddleBeadBase metal
Slag
Gas
shield
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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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Questions