Transcript Ohm’s Law - Westlake FFA

Shielded Metal Arc Welding
Safe practices when Arc Welding
Don’t stand in water
 Discard frayed cords and wires
 Keep flammable liquids away from heat
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Don’t look at the arc with out a number 10
lens.
Dress Code
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Wear properly fitted clothes.
When welding, sleeves should be buttoned and
gloves should be worn.
Wear boots or high top; Tightly laced shoes.
Do not wear loose clothing, shirt tails, and
unbuttoned sleeves around power equipment.
Do not wear clothes that you do not want to get
dirty.
The Arc
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When electrons jump through the air
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When the pressure overcomes resistance
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V=A X R
Parts of the Arc
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Arc stream
 Vaporized metal
 Appears yellow
 Liquid metal
 Appears green
Arc flame
 Natural gases surrounding arc stream
 Pale red
Arc Control
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Length
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Angle
Reverse Polarity
(DCEP)
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Electrode positive
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Better penetrated welds
Straight Polarity
(DCEN)
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Electrode Negative
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Used when a high rate of filler metal is
required.
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EXX2X Electrodes
Alternating Current
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Stops and starts
 Must have enough voltage restart arc
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Good penetration
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Less expensive
Classification of Steel Electrodes
Electrode designated by “E” followed by a
4- or 5- digit number
 First two or three digits - minimum tensile
strength as-welded deposited weld metal
expressed in thousands of pounds per
square inch (1000psi)
 E-60xx - 60,000psi TS
 E-120xx - 120,000 psi TS
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Classification of Steel Electrodes
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Third or fourth digit refers to the welding
position.
 E-xx1x - all positions
 E-xx2x - flat and horizontal fillet
positions
 E-xx3x - flat position only
Classification cont.
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The fourth or fifth and last digit indicates the type
of welding current and the type of flux covering
 E-xx10 - DC reverse polarity (electrode
positive) only (cellulose sodium).
 E-xx11 - AC or DC reverse polarity (cellulose
potassium ) Fast freeze, cutting
 E-xx13 - AC or DC straight polarity (titania
potassium)
Factors of Electrode Selection
Type of metal to be welded
 Thickness of metal
 Position of weld
 Type of power (DC or AC)
 Cleanliness of metal
 Weld bead appearance desired
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Flux
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Improves the performance in handling, storage
and operation of the electrode
Floats out impurities
Directs arc stream (stabilizer)
Insulator
Prevents oxidation (slag or gas)
Holds in heat
Iron-powder improves striking ability and
increases metal deposition rate
Striking the Arc
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Pecking
 Touching electrode to
the base metal and
moving away to proper
arc distance. Moving
electrode in a vertical
motion.
 Can start precisely
where the weld is to
be.
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Scratching
 Moving electrode
across base metal
then moving
electrode away to
the proper arc
distance.
 Dose not work
good in tight places
Common Striking Problems

Sticking
 Lift electrode and
metal
 Break electrode
from metal
 Remove electrode
from clamp
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Arc is extinguished
 The electrode is
moved to far away
from the base metal
after the arc is
struck.
Arc Length
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Longer arc
 Increases
Resistance
 Increases Voltage
 Decreases Current
 Decreases filler
consumption
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Shorter arc
 Decreases
Resistance
 Decreases Voltage
 Increases Current
 Increases filler
consumption
Arc Length
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Should be no more then ¼ inch
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The sound of the arc should sound like eggs
frying
Bead Width
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Stringer bead
 Only motion is in the
direction of travel
 About 3 times the
width of the electrode
 With 1/8 inch electrode
should be 3/8 inch
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Weaving bead
 Motion side to side
as well as forward
 About 6 times the
width of the
electrode
 With 1/8 inch
electrode should be
3/4 inch
Stringer Bead
Weaving Bead
Electrode Angle
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Should be 15° to 20° tipped forward in the
direction of travel
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Stringer bead should be at 90° from the base
metal
Travel Speed
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Bead width
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Bullet-nose-shaped ripples
Restarting
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Strike ark 3/8 inch in front of previous weld
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Move back to crater
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Move forward to finish weld
Restarting