Transcript File

TSM 233: Unit 5
Shielded Metal Arc
Welding
What is SMAW?
The SMAW process
is accomplished
by producing an
electric arc
between the base
metal and a
consumable fluxcovered
electrode.
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What are the basic components of the
SMAW process?
Welder
Leads
Electrode
holder
Ground clamp
Electrode
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What are some specific safety
precautions for SMAW?
Produces intense ultra-violet rays.
Need to use number 10 or 12 shade lens.
U-V rays burn the outer layers of the
skin/eyes.
Electrical shock.
Toxic fumes/smoke.
Heat exposure.
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How does the SMAW process
produce heat?
Volt –electrical pressure
Amperage – amount of electricity
Resistance – produces heat.
Welder works at a lower voltage,
pushes large amounts of
electricity, across a gap.
Voltage drops, amperage increases
as the arc length decreases.
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What are the key variables when
SMAW?
Type of metal, thickness, weld-ability.
Type of weld, characteristics, position.
Types of electrodes.
Types of electrical current, amperage
range.
Welder (person) characteristics, speed,
skill, electrode angles.
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What are the different types of SMAW
welders?
Two basic types:
Constant
current – preset the
amperage, used mostly for SMAW and
GTAW (TIG)
Constant
potential (voltage), preset the
voltage, GMAW (MIG) and FCAW (Flux
Core)
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What are the characteristics of the different
types of electrical current used for SMAW?
AC –alternating current
DC – direct current
 DCEN
– electrode negative, straight polarity, greater
deposit of metal and thinner metal. (electricity flows
from the (-) negative pole to the positive (+) pole
 DCEP
– reverse polarity, electrode positive, heat is
greater at the metal, deeper penetration.
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How are different types of electricity
produced by the welders?
AC is easier to get from electrical service,
DC is easier to produce from a generator.
Generators – produces the electricity, need an alternator to
produce AC. To get DC from an alternator, convert the AC
to DC.
Static Converted power
 Transformer – very common, most lighter duty welders,
changes the voltage/amperage.
 Rectifier – converts AC to DC.
 Inverter – converts the 60 mHz to High Frequency, 1000 –
50,000mHz., actually….
AC to DC to HFAC to Transformer to DC
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Factors to consider when selecting
SMAW welders.
Input Voltage.
Whether need AC and/or DC.
Duty Cycle: the ratio of welding time to total time.
Whether planning to also use the welder for GTAW.
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How are welders classified?
Welders are classified by their duty cycles for the
rated output.
Class I: 60%, 80% and 100% duty cycles.
Class II: 30%, 40%, and 50% duty cycles.
Class III: 20% duty cycle
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What types of metals can we SMAW?
Most all common metals, except Magnesium.
Aluminum and Copper alloys are very difficult
SMAW is still the most common, widely used
type of welding process.
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What to consider when selecting
electrodes?
 type
of base metal
 weld groove design
 required tensile
strength
 position of the weld
joint
 the rate of desired
weld deposit
 the type of electrical
current available
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How do we identify the different types
of electrodes?
E
– Electrode
 60
– tensile strength
in 1,000#
1
– position (1=all,
2=flat/horizontal
only)
1
– special
characteristics, flux,
current.
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What are some of the different types
of electrodes?
Low-Alloy Steel Covered Electrodes
Low Hydrogen Electrodes
Stainless Steel Electrodes
Cast Iron Electrodes
High Tensile Strength Electrodes
Aluminum Electrodes
Copper and Copper Alloy Electrodes
Hard-facing/surfacing Electrodes
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Low-Alloy Steel Covered Electrodes
 E6010
 E6011
 E6012
 E6013
 E7014
 E7024

High cellulose, sodium
High cellulose, potassium
DCEP
AC/DCEP
High titania, sodium
High titania, potassium
AC/DCEN
AC/DC
Iron powder, titania
Iron powder, titania
AC/DC
AC/DC
Suffixes: A,B…G.
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Low Hydrogen Electrodes

E7015
Low hydrogen, sodium
DCEP

E7016
Low hydrogen, potassium
AC/DCEP

E7018
Low hydrogen, potassium, iron powder AC/DCEP

E7028
Low hydrogen, potassium, iron powder AC/DCEP
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Why use “stringer” type beads and
“weave” type bead?
 Stringer
Beads, welded with little side to side motion
 Weave beads use a deliberate side to side motion.
 Stringer beads:
 easier to perform
 generally a smoother finish.
 Less metal mass, therefore less potential distortion
 generally less penetration, less overall strength
 Weave beads:
 generally greater strength.
 More metal deposited
 Potentially deeper penetration.
 A “back and forth” forward motion is also often used to increase
penetration and to help “freeze” the weld puddle
 An “in and out” motion is used to help freeze puddle, used for out-ofposition welds, called a “whip” motion.
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When should we groove the metal for
welding?
 Grooving
is used to help insure deeper weld
penetration.
 Recommended when the base metals are equal to, or
greater than twice the thickness of the electrode core
wire diameter.
 Generally a 60 degree angle, not less than 45
degrees.
 Do not groove to a sharp point, leave a “root face”
equal to the diameter of the electrode core wire.
 Use multiple passes:


first pass is the “root pass”
the last pass is a “wash pass” which uses a wide
weave pattern to cover the pervious passes.
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How do we store electrodes?
 Moisture
and extreme temperature changes can
harm/destroy electrodes.
 Store in a dry, air-tight environment.
 Commercial electrode storage cabinets are available,
provide a warm, low humidity environment.
 Low hydrogen electrodes are very sensitive to
moisture, and must be stored in a continuous dry
environment.
 Heating electrodes in an oven above 212 degrees
can help “dry” and restore electrodes.
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What is “arc blow” and what can we do
to reduce it?
Arc Blow is caused by a distorted magnetic attraction
of the electric arc to the base metal.
The arc “curves” to one side.
Or “jumps” from side to side in an inconsistent
pattern.
Generally a problem when using DC welding current
Causes metal to be deposited to one side of the weld.
How to control?
Switch to AC.
Move the ground clamp
Use intermittent welds
Use a weave pattern.
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What is a weld “undercut” and what
can we do to reduce it?
Undercut is when the weld has a depressed area
between the bead and base metal.
Can be caused by:





electrode side angle
too high amperage
poor weave pattern
wrong type of electrode, too “hot”
base metals are too dissimilar
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Weld Heat Affected Zone
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Types of Groove Welds
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Welding Positions
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