Transcript FLUX CORED ARC WELDING

FLUX CORED ARC WELDING
TWI Training & Examination
Services
EWF/IIW Diploma Course
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Flux cored arc welding
FCAW
methods
With gas
shielding “Outershield”
Without gas
shielding “Innershield”
(114)
With active
gas shielding
(136)
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With metal
powder “Metal core”
With inert
gas shielding
(137)
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“Outershield” process
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“Innershield” process
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Structure of the cored wires
Functions of metallic
sheath:
• provide form
stability to the wire
• serves as current
transfer during
welding
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Function of the filling
powder:
• stabilise the arc
• add alloy elements
• produce gaseous
shield
• produce slag
• add iron powder
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Core elements and their function
• Aluminium - deoxidize & denitrify
• Calcium - provide shielding & form slag
• Carbon - increase hardness & strength
• Manganese - deoxidize & increase strength
• Molybdenum - increase hardness & strength
• Nickel - improve hardness, strength, toughness
& corrosion resistance
• Potassium - stabilize the arc & form slag
• Silicon - deoxidize & form slag
• Sodium - stabilize arc & form slag
• Titanium - deoxidize, denitrify & form slag
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Types of cored wire
Seamless
cored wire
• not sensitive to
moisture pick-up
• can be copper coated 
better current transfer
• thick sheath  good
form stability  2 roll
drive feeding possible
• difficult to manufacture
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Butt joint
cored wire
Overlapping
cored wire
• good resistance
to moisture
pick-up
• can be copper
coated
• thick sheath
• difficult to seal
the sheath
• sensitive to
moisture
pick-up
• cannot be
copper coated
• thin sheath
• easy to
manufacture
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Cored wire manufacturing process
Forming
rollers
Draw die
Thin sheet
metal
Closing
rollers
Flux input
Strip reel
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FCAW wire designation
Wire designation acc. BS EN 758:
Diffusible hydrogen content (optional)
Shielding gas
Light alloy additions
Tensile properties
Standard number
EN 758 - T 46 3 1Ni B M 4 H5
Tubular cored electrode
Impact properties
Type of electrode core
Welding position (optional)
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FCAW wire designation
Wire designation acc. AWS A-5.20:
27J at -40°C requirement (optional)
Electrode usability (polarity, shielding
and KV); can range from 1 to 14
Welding position (0 - F/H only; 1- all
positions)
Designates an electrode
E 71
71 T-6 M J H8
Minimum UTS of weld metal (ksi x 10)
Flux cored electrode
Shielding gas for classification
Diffusible hydrogen content
(optional); can be 4, 8 or 16
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FCAW - differences from MIG/MAG
• usually operates in
DCEP but some
“Innershield” wires
operates in DCEN
• power sources need to
be more powerful due
to the higher currents
• doesn't work in deep
transfer mode
• require knurled feed
rolls
• “Innershield” wires
use a different type
of welding gun
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FCAW - differences from MIG/MAG
350 Amps self shielded welding gun
Close wound stainless
steel spring wire liner
(inside welding gun cable)
24V insulated
switch lead
Handle
Conductor
tube
Trigger
Welding
gun cable
Thread protector
Hand shield
Contact tip
Courtesy of Lincoln Electric
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FCAW - differences from MIG/MAG
Self shielded
electrode nozzle
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Travel Angle
75°
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90°
75°
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Backhand (“drag”) technique
Advantages
•
•
•
•
preferred method for flat or horizontal position
slower progression of the weld
deeper penetration
weld stays hot longer  easy to remove dissolved
gasses
Disadvantages
• produce a higher weld profile
• difficult to follow the weld joint
• can lead to burn-through on thin sheet plates
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Forehand (“push”) technique
Advantages
• preferred method for vertical up or overhead
position
• arc is directed towards the unwelded joint 
preheat effect
• easy to follow the weld joint and control the
penetration
Disadvantages
• produce a low weld profile, with coarser ripples
• fast weld progression  shallower depth of
penetration
• the amount of spatter can increase
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FCAW advantages
•
•
•
•
•
•
•
less sensitive to lack of fusion
requires smaller included angle compared to MMA
high productivity
all positional
smooth bead surface, less danger of undercut
basic types produce excellent toughness properties
good control of the weld pool in positional welding
especially with rutile wires
• seamless wires have no torsional strain  twist
free
• ease of varying the alloying constituents
• no need for shielding gas
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FCAW advantages
Deposition rate for carbon steel welding
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FCAW disadvantages
• limited to steels and Ni-base alloys
• slag covering must be removed
• FCAW wire is more expensive on a weight
basis than solid wires (exception: some high
alloy steels)
• for gas shielded process, the gaseous shield
may be affected by winds and drafts
• more smoke and fumes are generated
compared with MIG/MAG
• in case of Innershield wires, it might be
necessary to break the wire for restart (due to
the high amount of insulating slag formed at
the tip of the wire)
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