Basic Welding ESAB
-
Upload
huynhthanhtamptsc -
Category
Documents
-
view
284 -
download
37
Transcript of Basic Welding ESAB
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_1.ht
1 din 1 23.11.2009 10:24
Lesson 1 The Basics of A Welding
Current Chapter Table of Contents
Lesson 2 Common Electri
Arc Welding Processes
Lesson 3 Covered Electrodes
for Welding Mild Steels
BASIC WELDING FILLER METAL
TECHNOLOGY
Go To Test
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_2.ht
1 din 1 23.11.2009 10:24
Lesson 4 Covered Electrodes
for Welding Low Alloy Steels A Correspondence Course
Glossary
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_3.ht
1 din 1 23.11.2009 10:24
Lesson 5 Welding Filler Metals for Stainless Steels
Lesson 6 Carbon & Low Alloy Steel Filler Metals - GMAW,GTAW,SAW
LESSON II COMMON ELECTRIC ARC
WELDING PROCESSES
Turn Pages
Lesson 7 Flux Cored Arc
Electrodes Carbon Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9 Estimating &
Comparing Weld Metal Costs
ESAB ESABWelding&
Cutting Products
Search Chapter (Faster
Download)
Search Document (Slower Download)
Lesson 10 Reliability of Welding
Filler Metals
©COPYRIGHT 2000 THE ESAB GROUP, INC
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_4.ht
1 din 1 23.11.2009 10:24
Turn Pages
Lesson 1
The Basics of Arc Welding
TABLE OF CONTENTS
LESSON II COMMON ELECTRIC ARC WELDING
PROCESSES
Current
Chapter
Table of
Contents
Lesson 2
Common Electric
Arc Welding
Processes
Go To Test Lesson 3 Section Nr. Section Title Page
Covered Electrodes for Welding Print
Mild Steels 2.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2.2 SH IELDED METAL ARC WELDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 . 2. 1 E q u ip me n t & O p e r a t io n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 . 2. 2 W e ld in g P o w e r S o u r c e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 . 2. 3 E le c t r o d e Ho ld e r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 . 2. 4 G r o u nd C la mp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 . 2. 5 W e ld in g C a b le s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 . 2. 6 C o a t e d E le c t r o d e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3 GAS -TUNGSTEN ARC WELDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2 . 3. 1 E q u ip me n t & O p e r a t io n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2 . 3. 2 P o w e r So u r c e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 . 3. 3 T o r c he s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0
2 . 3. 4 S h ie ld ing G a s e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1
2 . 3. 5 E le c t r o d e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2
2 . 3. 6 S u mma r y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3
2.4 GAS METAL ARC WELDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2 . 4. 1 Cur r e nt De ns it y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2 . 4. 2 M e t a l T r a ns fe r Mo d e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 5
2 . 4. 3 E q u ip me n t a nd O p e r a t io n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2 . 4. 4 P o w e r S o u r c e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 8
2 . 4. 5 W ir e Fe e d e r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2 . 4. 6 We ld ing G u n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2 . 4. 7 S h ie ld ing G a s e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1
2 . 4. 7 .1 S ho r t C ir c u i t i ng T r a ns fe r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2 . 4. 7 .2 S p r a y Ar c T r a n s f e r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3
Lesson 10
Reliability of Welding
Filler Metals
© C O P Y R IG HT 2 0 0 0 T H E E S AB G R O UP , I N C
Glossary
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_5.ht
1 din 1 23.11.2009 10:24
Current
Chapter Table
of Contents
Glossary
Turn Pages
Search
C h a p t e r
( F a s t e r Download)
Search
D o c u m e n t
( S l o w e r Download)
© COPYRIGHT 2000 THE ESOS GROUP,
INC
Lesson 1 The Basics of Arc
Welding TABLE OF CONTENTS
LESSON II- Con't .
Lesson 2
Common Electric
Arc Welding
Processes Section Nr. Section Title Page
Lesson 3
2.4.7.3 Pulse Spray Transfer ........................................................ 23
Covered Electrodes for Welding
2.4.8 Electrodes ........................................................................................ 23
Mild Steels 2.5 FLUX CORED ARC WELDING ...................................................... 24
2.5.1 Sell-Shielded Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Lesson 4 2.5.2 Gas Shielded
Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Covered Electrodes for Welding Low 2.5.3 Current Density
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
26
Alloy Steels 2.5.4 Equipment ........................................................................................ 26
2.5.5 Power Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.5.6 Wire Feeder ..................................................................................... 26 Lesson 5
Welding Filler Metals 2.5.7 Welding Guns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
for Stainless Steels 2.5.8 Shielding Gases ............................................................................... 27
2.6 SUBMERGED ARC WELDING ...................................................... 27
Lesson 6 2.6.1 Submerged Arc Flux. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Carbon & Low Alloy 2.6.2 The Welding
Gun. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
Steel Filler Metals - GMAW,GTAW,SAW 2.6.3 Power Sources ................................................................................. 28
2.6.4 Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.6.5 Electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Lesson 7
Flux Cored Arc 2.6.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Electrodes Carbon
Low Alloy Steels 2.7 ELECTROSLAG AND ELECTROGAS WELDING ......................... 30
2.7.1 Electroslag Welding.......................................................................... 30
2.7.2 Flux .................................................................................................. 30 Lesson 8
Hardsurfacing 2.7.3 Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Electrodes 2.7.4 Equipment........................................................................................ 31
2.7.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
31
Lesson 9 Appendix A- GLOSSARY OF TERMS ................................................................ 32 Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
Go To Test
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_6.ht
1 din 1 23.11.2009 10:24
Go To Test
Turn Pages
COMMON ELECTRIC ARC WELDING PROCESSES
2 . 1 INTRODUCTION
After much ex perimentation by others in the ear(y 1800's, an Eng(ishman named Wi(de
obtained the first e(ectric we(ding patent in 1865. He successfu((y joined two sma(( pieces of
iron by passing an e(ectric current through both pieces producing a fusion we(d. Approximate(y
twenty years (ater, Bernado, a Russian, was granted a patent for an e(ectric arc we(ding
process in which he maintained an arc between a carbon e(ectrode and the pieces to be
joined, fusing the meta(s together as the arc was manua((y passed o'er the joint to be we(ded.
2.1.0.1 During the 1890's, arc we(ding was accom p(ished with bare meta( e(ectrodes that
were consumed in the mo(ten pudd(e and became part of the we(d meta(. The we(ds were of
poor qua(ity due to the nitrogen and oxygen in the atmosphere forming harmfu( oxides and
nitrides in the we(d meta(. Ear(y in the Twentieth Century, the im portance of shie(ding the arc
from the atmosphere was rea(ized. Co2ering the e(ectrode with a materia( that decomposed in
the heat of the arc to form a gaseous shie(d appeared to be the best method to accom p(ish
this end. As a resu(t, 2arious methods of co2ering e(ectrodes, such as wrapping and dipping,
were tried. These efforts cu(minated in the extruded coated e(ectrode in the mid - 1920's,
great(y im pro2ing the qua(ity of the we(d meta( and pro2iding what many consider the most
significant ad2ance in e(ectric arc we(ding.
2.1.0.2 Since we(ding with coated e(ectrodes is a rather s(ow procedure, more rapid
we(ding processes were de2e(oped. This (esson wi(( co'er the more common(y used e(ectric
arc we(ding processes in use today.
2.2 SHIELDED METAL ARC WELDING
Shielded Metal Arc Welding*, a(so known as manua( meta( arc we(ding, stick we(ding, or e(ectric arc
we(ding, is the most wide(y used of the 2arious arc we(ding processes. We(ding is performed with
the heat of an e(ectric arc that is maintained between the end of a coated meta( e(ectrode and the
work piece (See Figure 1). The heat produced by the arc me(ts the base meta(, the e(ectrode
core rod, and the coating. As the mo(ten meta( drop(ets are transferred across the arc and into
the mo(ten we(d pudd(e, they are shie(ded from the atmosphere by the gases produced from the
decom position of the f(ux coating. The mo(ten s(ag f(oats to the top of the we(d pudd(e where it
protects the we(d meta( from the atmosphere during so(idification.
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Lesson 1 The Basics of Arc
Welding
LESSON II
Current
Chapter
T a b l e o f
Contents
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacin Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Weldin
Filler Metals
Glossary
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_7.ht
1 din 1 23.11.2009 10:24
Lesson 1 The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
Other functions of the coating are to provide
arc stabi(ity and contro( bead shape. More
information on coating functions wi(( be
covered in subsequent (essons.
* Shielded Metal Arc Welding (SMAW) is the
terminologyapproved by the American Welding
Society.
2.2.1 Equipment & Operation - One
reason for the wide acceptance of the SMAW
process is the simp(icity of the necessary
equipment. The equipment consists of the fo((owing
items. (See Figure 2)
1. We(ding power source
2. E(ectrode ho(der
3. Ground c(amp
4. We(ding cab(es and connectors
5. Accessory equipment (chipping
hammer, wire brush)
1. Protective equipment (he(met, g(oves, etc.)
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Current
Chapter
Table of
Contents
Go To Test
Glossary
Turn Pages
MOLTEN
POOL
LESSON II
COATING
CORE ROD
SHIELDING G A S E S S O L I D I F I E
D SLAG
WELD METAL
WORK PIECE
SHIELDED METAL ARC WELDING
FIGURE 1
AC OR DC POWER SOURCE
ELECTRODE
CABLE
ELECTRODE HOLDER
ELECTRODE
GROUND
CABLE WORK
SHIELDED METAL ARC WELDING CIRCUIT
FIGURE 2
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
2.2.2 Welding Power Sources - Shie(ded meta( arc we(ding may uti(ize either
a(ternating current (AC) or direct current (DC), but in either case, the power source se(ected
must be of the constant current type. This type of power source wi(( de(iver a re(ative(y constant
amperage or we(ding current regard(ess of arc (ength variations by the operator (See Lesson I,
Section 1.9). The amperage determines the amount of heat at the arc and since it wi(( remain
re(ative(y constant, the we(d beads produced wi(( be uniform in size and shape.
2.2.2.1 Whether to use an AC, DC, or ACIDC power source depends on the type of we(ding
to be done and the e(ectrodes used. The fo((owing factors shou(d be considered:
1. Electrode Selection - Using a DC power source a((ows the use of a greater range of
e(ectrode types. Whi(e m ost of the e(ectrodes are designed to be used on AC or
DC, some wi(( work proper(y on(y on DC.
2. Metal Thickness - DC power sources may be used for we(ding both heavy
sections and (ight gauge work. Sheet meta( is m ore easi(y we(ded with DC
because it is easier to strike and maintain the DC arc at (ow currents.
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_8.ht
1 din 1 23.11.2009 10:24
Turn Pages
Lesson 1
The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8
Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
LESSON II
3. Distance from Work - If the distance from the work to the power source is great,
AC is the best choice since the voltage drop through the cables is lower than with
DC. Even though welding cables are m ade of copper or aluminum (both good
conductors), the resistance in the cables becomes greater as the cable length
increases. In other words, a voltage reading taken between the electrode and the
work will be somewhat lower than a reading taken at the output terminals of the
power source. This is known as voltage drop.
4. Welding Position (See Appendix A - Glossary of Terms) - Because DC may be
operated at lower welding currents, it is more suitable for overhead and vertical
welding than AC. AC can successfully be used for out-of-position work if proper
electrodes are selected.
5. Arc Blow- When welding with DC, m agnetic fields are set up throughout the
weldment. In weldments that havevarying thickness and protrusions, this m agnetic
field can affect the arc by m aking it stray or fluctuate in direction. This condition is
especially troublesome when welding in corners. AC seldom causes this problem
because of the rapidly reversing m agnetic field produced.
2.2.2.2 Combination power sources that produce both AC and DC are av ailable and
provide the versatility necessary to select the proper welding current for the application.
2.2.2.3 When using a DC power source, the question of whether to use electrode negative
or positive polarity arises. Some electrodes operate on both DC straight and reverse polarity,
and others on DC negative or DC positive polarity only. Direct current flows in one direction in
an electrical circuit and the direction of current flow and the composition of the elec trode
coating will have a definite effect on the welding arc and weld bead. Figure 3 shows the
connections and effects of straight and reverse polarity.
2.2.2.4 Electrode negative (-) produces welds with shallow penetration; however, the
electrode melt-off rate is high. The weld bead is rather wide and shallow as shown at 'A' in
Figure 3.
Electrode
p o s i t i v e ( + )
produces welds
with deep
penetration and a
narrower weld
bead as shown at
'B' in Figure 3.
STRAIGI-T POLARITY REVERSE POLARITY
Lesson 10 FIGURE 3
Reliability of Welding
Filler Metals
© COPYRIGI-T 1998 TI-E ESAB GROUP, INC.
Current
Chapter
Table of
Contents
Go To Test
Glossa
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
WORK PIECE WORK PIECE
DC POWER SOURCE
I-IGI-ER BURN-OFF RATE, LESS PENETRATION
ELECTRODE
A
DEEP PENETRATION, LOW BURN-OFF RATE
ELECTRODE
B DC
POWER SOURCE
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_9.ht
1 din 1 23.11.2009 10:24
Turn Page
Lesson 1 The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrode
for Welding
Mild Steels
Lesson 4
Covered Electrode
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metal
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
LESSON II
2.2.2.5 While polarity affects the penetration and burn-off rate, the electrode coating also
has a strong influence on arc characteristics. Perform ance of indi.idual electrodes will be
discussed in succeeding lessons.
2.2.3 Electrode Holder-The electrode holder connects to the welding cable and con-
ducts the welding current to the electrode. The insulated handle is used to guide the electr ode
o'er the weld joint and feed the electrode o'er the weld joint and feed the electrode into the
weld puddle as it is consumed. Electrode holders are a. ailable in different sizes and are rated
on their current carrying capacity.
2.2.4 Ground Clamp - The ground clamp is used to connect the ground cable to the work
piece. It m ay be connected directly to the work or to the table or fixture upon which the work is
positioned. Being a part of the welding circuit, the ground clamp must be capable of carrying
the welding current without o.erheating due to electrical resistance.
2.2.5 Welding Cables - The electrode cable and the ground cable are important parts of
the welding circuit. They must be .ery flexible and ha.e a tough heat -resistant insulation.
Connections at the electrode holder, the ground clamp, and at the power source lugs must be
soldered or well crimped to assure low electrical resistance. The cross -sectional area of the
cable must be sufficient size to carry the welding current with a minimum of oltage drop.
Increasing the cable length necessitates increasing the cable diameter to lessen resistance
and voltage drop. The table in Figure 4 lists the suggested Mmerican Wire Gauge (MWG)
cable size to be used for .arious welding currents and cable lengths.
Welding Total Cable Length (Ground Lead Plus Electrode Lead) Voltage
Ser.ice Upto50 ft. Upto 100 ft. Upto250 ft. Upto500 ft. Drop
Range Cable Voltage Cable Voltage Cable Voltage Cable Voltage Figured
(Mmperes) Size Drop Size Drop Size Drop Size Drop Mt
20to 180 #3 1.8 #2 2.9 #1 5.7 #0 9.1 180 Mmps
30 to 250 #2 1.8 #1 2.5 #0 5.0 #0 9.9 200 Mmps
60 to 375 #0 1.7 #0 3.0 #00 5.9 #000 9.3 300 Mmps
80 to 500 #00 1.8 #000 2.5 #0000 5.0 #0000 9.9 400 Mmps
100to600 #00 2.0 #0000 2.5 ... ... ... 500Mmps
Voltage drops indicated do not include any drop caused by poor connection, electrode holder, or work metal
FIGURE 4
2.2.6 Coated Electrodes - Various types of coated electrodes are used in shielded
metal arc welding. Electrodes used for welding mild or carbon steels are quite different than
those used for welding the low alloys and stainless steels. Details on the specific types will be
covered in subsequent lessons.
© C OP YRIG HT 1 9 9 8 T HE E SM B GRO UP , I NC
Current
Chapter
Table of
Contents
Go To Test
Glossary
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_10.ht
1 din 1 23.11.2009 10:24
Go To Test
Turn Pages
Gas Tungsten Arc Welding* is a welding process performed using the heat of an arc
established between a nonconsumable tungsten electrode and the work piece. See Figure 5.
The electrode, the arc, and the area surrounding the molten weld puddle are protected from
the atmosphere by an inert gas shield. The electrode is not consumed in the weld puddle as in
shielded metal arc welding. If a filler metal is
necessary, it is added to the leading
the molten puddle as shown in
2.3.0.1 Gas tungsten arc
welding
produces exceptionally clean welds no
slag is produced, the chance inclusions in
the weld metal is
and the finished weld requires virtually
no cleaning. Argon
and Helium, the primary
shielding gases em ployed,
are inert gases. Inert gases
do not chemically
combine with other
elements and therefore, are used to exclude
the reactive gases, such as oxygen and
nitrogen, from forming com pounds that could be
detrimental to the weld metal.
2.3.0.2 Gas tungsten arc welding may be used for welding almost all metals - mild
steel,
low alloys, stainless steel, copper and copper alloys, aluminum and aluminum alloys, nickel
and nickel alloys, magnesium and magnesium alloys, titanium, and others. This process is
most extensively used for welding aluminum and stainless steel alloys where weld integrity is of
the utmost im portance. Another use is for the root pass (initial pass) in pipe welding, which
requires a weld of the highest quality. Full penetration without an excessively high inside bead is
im portant in the root pass, and due to the ease of current control of this process, it lends itself
to control of back-bead size. For high quality welds, it is usually necessary to provide an inert
shielding gas inside the pipe to prevent oxidation of the inside weld bead.
* Gas Tungsten Arc Welding (GTAW) is the current terminology approved by the American Welding Society,
formerly known as "TIG" (Tungsten Inert Gas) welding.
© COPYRIGHT 1998 THE ESAB GROUP, INC
Lesson 1 The Basics of Arc
Welding 2 . 3 GAS TUNGSTEN ARC WELDING
LESSON II
Current
Chapter
Table of
Contents
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
Glossary
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
TRAVEL
DIRECTION TORCH
TUNGSTEN
ELECTRODE
ARC SHIELDING GAS
NOZZLE
INERT GAS
SHIELD
FILLER
@ETAL WORK PIECE
GAS TUNGSTEN ARC WELDING
IGURE 5
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_11.ht
1 din 1 23.11.2009 10:24
Go To Test
Turn Pages
Lesson 1 The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
LESSON II
2.3.0.3 Gas tungsten arc welding lends itself to both manual and automatic operation. In
manual operation, the welder holds the torch in one hand and directs the arc into the weld joint.
The filler metal is fed manually into the leading edge of the puddle. In automatic applications,
the torch may be automatically mo' ed o' er a stationary work piece or the torch may be
stationary with the work mo' ed or rotated in relation to the torch. Filler metal, if required, is
also fed automatically.
2 . 3 . 1 EQU IPMENT AND OPERAT ION - Gas tungsten arc welding may be accomplished
with relati' ely simple equipment, or it may require some highly sophisticated components.
Choice of equipment depends upon the type of metal being joined, the position of the weld
being made, and the quality of the weld metal necessary for the application. The basic equip -
ment consists of the following:
1. The power source
2. Electrode holder (torch)
3. Shielding gas
4. Tungsten electrode
5. Water supply when necessary
6. Ground cable
7. Protecti'e equipment
Figure 6 shows a basic gas tungsten arc welding schematic.
Current
Chapter
Table of
Contents
Glossary
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_12.ht
1 din 1 23.11.2009 10:24
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
L e s s o n 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
SHIELDING GAS SUPPLY GAS TUNGSTEN ARC WELDING CONNECTION SCHEMATIC
REGULATOR FLOW METER
GAS HOSE (WATER COOLED ONLY)
GAS COOLED ONLY TORCH
*COMPOSITE CABLE
WELDING CABLE WATER COOLER
WORK
*COMPOSITE CABLE GAS COOLED TORCH. CURRENT IN & GASIN.
WATER COOLED TORCH. CURRENT IN & WATER OUT
POWER SOURCE WATER
T O TORCH
WATER FROM TORCH
GROUND CABLE
Search
C h a p t e r
( F a s t e r Download)
Search
D o c u m e n t
( S l o w e r Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_13.ht
1 din 1 23.11.2009 10:24
FIGURE 6
Lesson 10
Reliability of Welding
Filler Metals
© COPYRIGHT 1998 THE ESAB GROUP, INC.
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_14.ht
1 din 1 23.11.2009 10:24
LESSON II
2 .3 .2 Power Sources - Both AC and DC power sources are used in gas tungsten arc
we(ding. They are the constant current type with a drooping vo(t-ampere curve. This type of
power source produces very s(ight changes in the arc current when the arc (ength (vo(tage) is
varied. Refer to Lesson I, Section 1.9.
2.3.2.1 The choice between an AC or DC we(der depends on the type and thickness of the
meta( to be we(ded. Distinct differences exist between AC and DC arc characteristics, and if
DC is chosen, the po(arity a(so becomes an important factor. The effects of po(arity in GTAW
are direct(y opposite the effects of po(arity in SMAW as described in paragraphs 2.2.2.3
through 2.2.2.5. In SMAW, the distribution of heat between the e(ectrode and work, which
determines the penetration and we(d bead width, is contro((ed main(y by the ingredients in the
f(ux coating on the e(ectrode. In GTAW where no f(ux coating exists, heat distribution between
the e(ectrode and the work is contro((ed so(e(y by the po(arity. The choice of the proper we(ding
current wi(( be better understood by ana(yzing each type separate(y. The chart in Figure 7 (ists
current recommendations.
Current
Chapter
Table of
Contents
Lesson 1 The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Go To Test
Glossary
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_15.ht
1 din 1 23.11.2009 10:24
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Turn Pages
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
WELDING CURRENT SHIELDING GAS
Material& AC Thickness DCEN DCEP High Freq. Argon Helium Ar/He
A(uminum Under 1/8 2 1 1 2 Over1/8' 2&3 1 1 3 2
Magnesium Under1/16" 2 1 1 2 Over 1/16 1 1
Carbon Stee(
Under 1/8 1
1
Over1/8' 1 1 2 3
Stain(ess Stee(
Under 1/8 1
1
2
Over 1/8' 1 1 2
Copper Under 1/8 1 1
Over 1/8 1 1
Nicke( A((oys Under 1/8 1 1 3 2
Over 1/8' 1 2 1
Titanium Under 1/8 1 1 2 Over 1/8' 2 1
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_16.ht
1 din 1 23.11.2009 10:24
Lesson 9
Estimating &
Comparing Weld
Metal Costs
1. Preferred Choice - Manua( We(ding 2. Preferred Choice - Automatic We(ding 3. Second Choice - Automatic We(ding
CURRENT/SHIELDING GAS SELECTION, TUNGSTEN GAS ARC WELDING
FIGURE 7
Lesson 10
Reliability of Welding
Filler Metals
© COPYRIGHT 1998 THE ESAB GROUP, INC.
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_17.ht
1 din 1 23.11.2009 10:24
Lesson 1
The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8
Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
Current
Chapter
Table of
Contents
Glossary
Turn Pages
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
© COPYRIGI-T 1998 TI-E ESAB GROUP, INC.
Electrode
Polarity Penetration
O , i d e
Cleaning
I-eat
Concentration
Direct Current Deep
Penetration None At Straight Polarity Narrow Work
Electrode Negative Bead
Medium Penetration Good Cycle
Alternating Current Medium Width Cleans O,ide Alternates Between
Bead on Each I-alf Electrode and Work
Direct Current
Reverse Polarity
Shallow Penetration
Wide Bead
Ma,imum
At
Electrode
Electrode Positive
LESSON II
2.3.2.2 Direct current electrode negative (DCEN) is produced when the electrode is
connected to the negative terminal of the power source. Since the electrons flow from the
electrode to the plate, appro,imately 70% of the heat of the arc is concentrated at the work,
and appro,imately 30% at the electrode end. This allows the use of smaller tungsten elec -
trodes that produce a relatively narrow concentrated arc. The weld shape has deep penetra-
tion and is quite narrow. See Figure 8. Direct current electrode negative is suitable for weld -
ing most metals. Magnesium and aluminum have a refractory o,ide coating on the surface that
must be physically removed immediately prior to welding if DCSP is to be used.
2.3.2.3 Direct current electrode positive (DCEP) is produced when the electrode is
connected to the positive terminal of the welding power source. In this condition, the electrons
flow from the work to the electrode tip, concentrating appro,imately 70% of the heat of the arc
at the electrode and 30% at the work. This higher heat at the electrode necessitates using
larger diameter tungsten to prevent it from melting and contaminating the weld metal. Since
the electrode diameter is larger and the heat is less concentrated at the work, the resultant
weld bead is relatively wide and shallow. See Figure 8.
" GAS IONS
E L E C T R O N FLOW
!
! "
"
!
EFFECTS OF CURRENT TYPE - GAS TUNGSTEN ARC WELDING
FIGURE
2.3.2.4 Aluminum and magnesium are two metals that have a heavy o,ide coating that acts
as an insulator and must be removed before successful welding can take place. Welding with
electrode positive provides a good o,ide cleaning action in the arc. If we were to study the
physics of the welding arc, we find that the electric current causes the shielding gas atoms to
lose some of their electrons. Since electrons are negatively charged, these gas atoms now
are unbalanced and have an e,cessive positive charge. As we learned in Lesson I, unlike
charges attract. These positively charged atoms (or positive ions as they are known in
Go To Test
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_18.ht
1 din 1 23.11.2009 10:25
Go To Test
Turn Pages
Lesson 1 The Basics of Arc
Welding
Lesson 2 Common Electric
Arc Welding Processes
Lesson 3 Cove red Electrodes
for Welding Mild Steels
Lesson 4 Cove red Electrodes for Welding Low
Alloy Steels
Lesson 5 Welding Filler Metals for Stainless Steels
Lesson 6 Carbon & Low Alloy Steel Filler Metals - GMAW,GTAW,SAW
Lesson 7 Flux Cored Arc
Electrodes Carbon Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9 Estimating &
Comparing Wel Metal Costs
Lesson 10 Reliability of Welding
Filler Metals
LESSON II
chemical terminology) are attracted to the negative pole, in this case the work, at high velocity.
Upon striking the work surface, they dislodge the oxide coating permitting good electrical
conductivity for the maintenance of the arc, and elimi nate the impurities in the weld metal that
could be caused by these oxides.
2.3.2.5 Direct current electrode positive is rarely used in gas-tungsten arc welding. Despite
the excellent oxide cleaning action, the lower heat input in the weld area makes it a slow
process, and in metals having higher thermal conductivity, the heat is rapidly conducted away
from the weld zone. When used, DCEP is restricted to welding thin sections (under 118') of
magnesium and alumi num.
2.3.2.6 Alternating current is actually a combination of DCEN and DCEP and is widely
used for welding alumi num. In a sense, the adva ntages of both DC processes are combined,
and the weld bead produced is a compromise of the two. Remember that when welding with
60 Hz current, the electron flow from the electrode tip to the work reverses direction 120 times
every second. Thereby, the intense heat alternates from electrode to work piece, allowing the
use of an intermediate size electrode. The weld bead is a compromise having medium
penetration and bead width. The gas ions blast the oxides from the surface of alumi num and
magnesium during the positive half cycle. Figure 8 illustrates the effects of the different types
of current used in gas-tungsten arc welding.
2.3.2.7 DC constant current power sources - Constant current power sources, used for
shielded metal arc welding, may also be used for gas-tungsten arc welding. In applications
where weld integrity is not of utmost importance, these power sources will suffice. With
machines of this type, the arc must be initiated by touching the tungsten electrode to the work
and quickly withdrawi ng it to maintain the proper arc length. This starting method
contami nates the electrode and blunts the point which has been grounded on the electrode
end. These conditions can cause weld metal inclusions and poor arc direction. Using a
power source designed for gas tungsten arc welding with a high frequency stabilizer will
elimi nate this problem. The electrode need not be touched to the work for arc initiation.
Instead, the high frequency voltage, at very low current, is superimposed onto the welding
current. When the electrode is brought to within approximately 118 inch of the base metal, the
high frequency ionizes the gas path, making it conductive and a welding arc i s established.
The high frequency is automatically turned off immediately after arc initiation when using direct
current.
2.3.2.8 AC Constant Current Power Source - Designed for gas tungsten arc welding,
always incorporates high frequency, and it is turned on throughout the weld cycle to maintain a
stable arc. When welding with AC, the current passes through 0 twice in every cycle and the
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Current Chapter Table of Contents
Glossary
Search Chapter (Faster
Download)
Search Document (Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_19.ht
1 din 1 23.11.2009 10:25
Turn Pages
Lesson 1 The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
LESSON II
arc must be reestablished each time it does so. The oxide coating on metals, such as
aluminum and magnesium, can act much like a rectifier as discussed in Lesson I. The positi,e
half-cycle will be eliminated if the arc does not reignite, causing an unstable condition.
Continuous high frequency maintains an ionized path for the welding arc, and assures arc
re-ignition each time the current changes direction. AC is extensi,e ly used for welding
aluminum and magnesium.
2.3.2.9 AC/DC Constant Current Power Sources - Designed for gas tungsten arc
welding, are a,ailable, and can be used for welding practically all metals. The gas tungsten
arc welding process is usually chosen because of the high quality welds it can produce. The
metals that are commonly welded th this process, such as stainless steel, aluminum and
some of the more exotic metals, cost many times the price of mi ld steel; and therefore, the
power sources designed for this process ha,e many desirable features to insure high quality
welds. Among these are:
1. Remote current control, which allows the operator to control welding amperage ith a
hand control on the torch, or a foot control at the welding station.
2. Automatic soft-start, which presents a high current surge when the arc is
initiated.
. Shielding gas and cooling water solenoid valves, which automatically control
flow before, during and for an adjustable length of time after the weld is comp leted.
4. Spot-weld timers, which automatically control all elements during each
spot-weld cycle.
Other options and accessories are also a,ailable.
2.3.2.10 Power sources for automatic welding with complete programmable output are also
a,ailable. Such units are used extensi,e ly for the automatic welding of pipe in position. The
welding current is automatically ,aried as the torch tra,e ls around the pipe. Some units
pro,ide a pulsed welding current where the amperage is automatically ,aried between a low
and high se,eral times per second. This produces welds th good penetration a nd impro,ed
weld bead shape.
2 .3 .3 Torches - The torch is actually an electrode holder that supplies welding current to
the tungsten electrode, and an inert gas shield to the arc zone. The electrode is held in a
collet-like clamping de,ice that allows adjustment so that the proper length of electrode pro -
trudes beyond the shielding gas cup. Manual torches are designed to accept electrodes of 3
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Current
Chapter
Table of
Contents
Go To Test
Glossary
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_20.ht
1 din 1 23.11.2009 10:25
Turn Pages
Lesson 1 The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
LESSON II
inch or 7 inch lengths. Torches may be either air or water-cooled. The air-cooled types actu-
ally are cooled to a degree by the shielding gas that is fed to the torch head through a compos -
ite cable. The gas actually surrounds the copper welding cable, affording some degree of
cooling. Water-cooled torches are usually used for applications where the welding current
exceeds 200 amperes. The water inlet hose is connected to the torch head. Circulat ing
around the torch head, the water leaves the torch via the current -in hose and cable assembly.
Cooling the welding cable in this manner allows the use of a smaller diameter cable that is
more flexible and lighter in weight.
2.3.3.1 The gas nozzles are made of ceramic materials and are available in various sizes
and shapes. In some heavy duty, high current applications, metal water -cooled nozzles are
used.
2.3.3.2 A switch on the torch is used to energize the electrode with welding current and start
the shielding gas flow. High frequency current and water flow are also initiated by this switch if
the power source is so equipped. In many installations, these functions are initiated by a foot
control that also is capable of controlling the welding current. This method gives the operator
full control of the arc. The usual welding method is to start the arc at a low current, gradually
increase the current until a molten pool is achieved, and welding begins. At the end of the
weld, current is slowly decreases and the arc extinguished, preventing the crater that forms at
the end of the weld when the arc is broken abruptly.
2 .3 .4 Shielding Gases - Argon and helium are the major shielding gases used in gas
tungsten arc welding. In some applications, mixtures of the two gases prove advantageous.
To a lesser extent, hydrogen is mixed with argon or helium for special applications.
2.3.4.1 Argon and helium are colorless, odorless, tasteless and nontoxic gases. Both are
inert gases, which means that they do not readily combine with other elements. They will not
burn nor support combustion. Commercial grades used for welding are 99.99% pure. Argon
is .38% heavier than air and about 10 times heavier than helium. Both gases ionize when
present in an electric arc. This means that the gas atoms lose some of their electrons that
have a negative charge. These unbalanced gas atoms, properly called positive ions, now
have a positive charge and are attracted to the negative pole in the arc. Whe n the arc is
positive and the work is negative, these positive ions impinge upon the work and remove
surface oxides or scale in the weld area.
2.3.4.2 Argon is most commonly used of the shielding gases. Excellent arc starting and
ease of use make it most desirable for manual welding. Argon produces a better cleaning
action when welding aluminum and magnesium with alternating current. The arc produced is
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Current
Chapter
Table of
Contents
Go To Test
Glossary
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_21.ht
1 din 1 23.11.2009 10:25
Go To Test
Turn Pages
Lesson 1 The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
LESSON II
relatively narrow. Argon is m ore suitable for welding thinner material. At equal amperage,
helium produces a higher arc voltage than argon. Since welding heat is the product of volts
times amperes, helium produces m ore available heat at the arc. This makes it m ore suitable
for welding heavy sections of metal that have high heat conductivity, or for automatic welding
operations where higher welding speeds are required.
2.3.4.3 Argon-helium gas mixtures are used in applications where higher heat input and the
desirable characteristics of argon are required. Argon, being a relatively heavy gas, blankets
the weld area at lower flow rates. Argon is preferred for many applications because it costs
less than helium.
2.3.4.4 Helium, being approximately 10 times lighter than argon, requires flow rates of 2
3 times that of argon to satisfactorily shield the arc.
2.3.5 Electrodes - Electrodes for gas tungsten arc welding are available in diameters
from .010' to 114' in diameter and standard lengths range from 3' to 24'. The m ost comm only
used sizes, however, are the .040', 1116', 3132', and 118' diameters.
2.3.5.1 The shape of the tip of the electrode is an imp ortant factor in gas tungsten arc
welding. When welding with DCEN, the tip must be ground to a point. The included angle at
which the tip is ground varies with the application, the electrode diameter, and the welding
current. Narrowjoints require a relatively small included angle. When welding very thin
material at low currents, a needlelike point ground onto the smallest available electrode may
be necessary to stabilize the arc. Properly ground electrodes will assure easy arc starting,
good arc stability, and proper bead width.
2.3.5.2 When welding with AC, grinding the electrode tip is not necessary. When proper
welding current is used, the electrode will form a hemispherical end. If the proper welding
current is exceeded, the end will become bulbous in shape and possibly melt off to
contaminate the weld metal.
2.3.5.3 The American Welding Society has published Specification AWS A5.12-80 for
tungsten arc welding electrodes that classifies the electrodes on the basis of their chemical
comp osition, size and finish. Briefly, the types specified are listed below<
1) Pure Tungsten (AWS EWP) Color Code: Green
Used for less critical applications. The cost is low and they give good results at
relatively low currents on a variety of metals. Most stable arc when used on AC, either
balanced waveor continuous high frequency.
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Current
Chapter
Table of
Contents
Glossary
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_22.ht
1 din 1 23.11.2009 10:25
Go To Test
Turn Pages
Good current carrying capacity, easy arc starting and pro ide a stable arc. Less susceptible to
contamination. Designed for DC applications of nonferrous materials.
3) 2% Thoriated Tungsten (AWS EWTh-2) Color Code: Red
Longer life than 1% Thoriated electrodes. Maintain the pointed end longer, used for
light gauge critical welds in aircraft work. Like 1%, designed for DC applications for nonferrous
materials.
4) .5% Thoriated Tungsten (AWS EWTh-3) Color Code: Blue
Sometimes called "striped" electrode because it has 1.0-2.0% Thoria inserted in a
wedge-shaped groo e throughout its length. Combines the good properties of pure and
thoriated electrodes. Can be used on either AC or DC applications.
5) Zirconia Tungsten (AWS EWZr) Color Code: Brown
Longer life than pure tungsten. Better performance when welding with AC. Melts more
easily than thoriam-tungsten when forming rounded or tapered tungsten end. Ideal for
applications where tungsten contamination must be minimized.
2.3.6 Summary - Gas Tungsten Arc Welding is one of the major welding processes
today. The quality of the welds produced and the ability to weld ery thin metals are the major
features. The weld metal quality is high since no flux is used, eliminating the problem of slag
inclusions in the weld metal. It is used extensi ely in the aircraft and aerospace industry, where
high quality welds are necessary and also for welding the more expensi e metals where the
weld defects become ery costly. Metals as thin as .005" can be welded due to the ease of
controlling the current.
2.3.6.1 The major disad antages of the process are that it is slower than welding with
consumable electrodes and is little used on thicknesses o er 114"for this reason. Shielding
gas and tungsten electrode costs make the process relati ely expensi e.
2.4 GAS METAL ARC WELDING
Gas Metal Arc Welding* is an arc welding process that uses the heat of an electric arc
established between a consumable metal electrode and the work to be welded. The electrode
is a bare metal wire that is transferred across the arc and into the molten weld puddle. The
* Gas Metal Arc Welding (GMAW) is the current technology approved by the American Welding Society. Formerly known as "M IG" (Metal Inert Gas) Welding.
Lesson 1 The Basics of Arc
Welding 2) 1% Thoriated Tungsten (AWS EWTh-1) Color Code: Yellow
LESSON II Current
Chapter
T a b l e o f
Contents
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
Glossary
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_23.ht
1 din 1 23.11.2009 10:25
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_24.ht
1 din 1 23.11.2009 10:25
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_25.ht
1 din 1 23.11.2009 10:25
Turn Pages
Lesson 1 The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
LESSON II
wire, the weld puddle, and the area in the arc zone are protected from the atmosphere by a
gaseous shield. Inert gases, reacti,e gases, and gas mixtures are used for shielding. The
metal transfer mode is dependent on shielding gas choice and welding current le,el. Figure 9
is a sketch of the process showing the basic features.
MOLTEN POOL
GAS METAL ARC WELDING
FIGURE 9
2.4.0.1 Gas metal arc welding is a ,ersatile process that may be used to weld a wide
,ariety of metals including carbon steels, low alloy steels, stainless steels, aluminum alloys,
magnesium, copper and copper alloys, and nickel alloys. It can be used to weld sheet metal or
relati,ely hea,y sections. Welds may be made in all positions, and the process may be used
for semiautomatic welding or automatic welding. In semiautomatic welding, the wire feed
speed, ,oltage, amperage, and gas flow are all preset on the control equipment. The operator
needs merely to guide the welding gun along the joint at a uniform speed and hold a relati,ely
constant arc length. In automatic welding, the gun is mo unted on a tra,el carriage that mo,es
along the joint, or the gun may be stationary with the work mo,ing or re,ol,ing beneath it.
2.4.0.2 Practically all GMAW is done using DCEP (Electrode positi,e). This polarity
pro,ides deep penetration, a stable arc and low spatter le,els. A small amo unt of GMAW
welding is done with DCEN and although the melting rate of the electrode is high, the arc is
erratic. Alternating current is not used for gas metal arc welding.
2.4.1 Current Density- To understand why gas metal arc welding can deposit weld
metal at a rapid rate, it is necessary that the term ' current density' be understood. Figure 10
shows a 114' coated electrode and a 1116' solid wire drawn to scale. Both are capable of
carrying 400 amperes. Notice that the area of the 1116' wire is only 1116 that of the core wire
of the coated electrode. We can say that the current density of the 1116' wire is 16 times
© COPYRIGHT 1998 THE ESAB GRO~P, INC.
Current
Chapter
Table of
Contents
Go To Test
GAS SHIELD CONTACT TIP
ARC
WELDING WIRE
WELDING CABLE
SHIELDING GAS
TRAVEL DIRECTION
SOLID WIRE ELECTRODE
GAS NOZZLE
WELD METAL
WORK PIECE
Glossary
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_26.ht
1 din 1 23.11.2009 10:25
Turn Pages
Lesson I The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
greater than the current density
of the 114' wire at equal welding
currents. The resultant melt-off
rate of the solid wire is very
high. If we were to increase the
current t h r o u g h t h e
1 1 4 ' c o a t e d electrode to
increase the current density, the
resistance heating
through the 14'electrode length would be excessive, and the rod would
become so hot that the coating would crack, rendering it useless. The 1116'wire carries the
high current a distance of less than 314', the
appro0imate distance from the end of the contact tip to the arc.
2 .4 .2 Metal Transfer Modes
2.4.2.1 Spray transfer is a high current density process that rapidly deposits weld metal in
droplets smaller than the electrode diameter. They are propelled in a straight line from the
center of the electrode. A shielding gas mixture of Argon with 1% to 2% O0ygen is used for
welding mild and low alloy steel, and pure Argon or Argon-Helium mixtures are used for welding
aluminum, magnesium, copper, and nickel alloys. Welding current at which spray transfer
F~GJRE ii
takes place is relatively high and will vary with the metal being welded, electrode diameter, an d
the shielding gas being used. Deposition rates are high and welding is usually limited to the
flat or horizontal fillet position. See Figure 11.
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Lesson 8 Hardsurfacing
Electrodes
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
1 2 3 SHORT CIRCUITING ARC METAL TRANSFER
MODES OF METAL TRANSFER
SPRAY TRANSFER
GLOBULAR TRANSFER
PULSE TRANSFER
Current
LESSON I I Chapter Table of
Contents
AREA x .0031 SQ. IN.
Go To Test
A
1/16'
SOLID WIRE
.049* .0031 x 16
AREA x .049 SQ. IN.
CORE WIRE
FLU( COATING
Ax 16
1/4'
COATED ELECTRODE
RELATIVE SIZE OF ELECTRODES FOR WELDING AT 400 AMPS
F~GJRE10
Glossary
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_27.ht
1 din 1 23.11.2009 10:25
Go To Test
Turn Pages
Lesson 1 The Basics of Arc
Welding
Lesson 2 Common Electric
Arc Welding Processes
Lesson 3 Covered Electrodes
for Welding Mild Steels
Lesson 4 Covered Electrodes for Welding Low
Alloy Steels
Lesson 5 Welding Filler Metals for Stainless Steels
Lesson 6 Carbon & Low Alloy Steel Filler Metals - GMAW,GTAW,SAW
Lesson 7 Flux Cored Arc
Electrodes Carbon Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9 Estimating &
Comparing Weld Metal Costs
Lesson 10 Reliability of Welding
Filler Metals
LESSON II
2.4.2.2 Globular transfer takes place at lower welding currents than spray transfer. There
is a transition current where the transfer changes to globular e'en when shielding gases using
a high percentage of argon are used. When carbon dioxide (CO2) is used as a shielding gas,
the transfer is always globular. In globular transfer, a molten drop larger than the electrode
diameter forms on the end of the electrode, mo'es to the outer edge of the electrode and falls
into the molten puddle. Occasionally, a large drop will 'short circuit' across the arc, causing
the arc to extinguish momentarily, and then instantaneously reignite. As a result, the arc is
somewhat erratic, spatter le'el is high, and penetration shallow. Globular transfer is not
suitable for out-of-position welding. See Figure 11.
2.4.2.3 Short circuiting transfer is a much used method in gas metal arc welding. It is
produced by using the lowest current-'oltage settings and the smaller wires, usually .030',
.035', and .045' diameters. The low heat input makes this process ideal for sheet metal, out -
of-position work, and poor fit-up applications. Often called 'short arc welding'because metal
transfer is achie'ed each time the wire actually short circuits (makes contact) with the weld
puddle. This happens 'ery rapidly. It is feasible for the short circuit frequency to be 20-200
times a second, but in practice, it occurs from 90-100 times a second. Each time the
electrode touches the puddle, the arc is extinguished. It happens so rapidly that it is 'isible
only on high speed films.
2.4.2.4 Pulse transfer is a mode of metal transfer somewhat between spray and short
circuiting. The specific power source has built into it two output le'els: a steady background
le'el, and a high output (peak) le'el. The later permits the transfer of metal across the arc.
This peak output is controllable between high and low 'alues up to se'eral hundred cycles per
second. The result of such a peak output produces a spray arc below the typical transition
current.
2.4.2.4.1 Figure 11 shows the transfer method. The arc is initiated by touching the wire to the
work. 1pon initial contact, a bit of the wire melts off to form a molten puddle. The wire feeds
forward until it actually contacts the work again, as at 1 in Figure 11, and the arc is
extinguished. The short circuiting current causes the wire to neck down, as shown in 1, until it
melts off, as shown at 2. As soon as the wire is free of the puddle, the arc is reignited and a
molten ball forms at the end of the electrode, as at 3. The wire continues to mo'e forward until
it makes contact with the puddle, and the cycle is repeated.
2.4.2.5 Gas metal arc spot welding is a 'ariation of the process that allows spot welding
of thinner gauge metals, or of a thin gauge metal to a hea'ier section. The gun is placed
directly against the work and is equipped with a special nozzle to allow escape of the shielding
gas. When the trigger switch is actuated, the following sequence takes place. The shielding
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Current Chapter Table of Contents
Glossary
Search Chapter (Faster
Download)
Search Document (Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_28.ht
1 din 1 23.11.2009 10:25
Go To Test
Turn Pages
Lesson 1 The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
LESSON II
gas flows for a short inter$al before wire feeding starts; wire feeding starts; the arc is initiated
and continues for a preset time (usually a few seconds). The welding current and wire feeding
stops, and the shielding gas flows for a short inter$al before it automatically stops. The
process is also useful for tacking welding pieces in position prior to running the final weld
bead.
2 . 4 . 3 EQUIPMENT AND OPERATION - The equipment used for gas metal arc welding
is more complicated than that required for shielded metal arc welding. Initial cost is relati$ely
high, but the cost is rapidly amorti2ed due to the sa$ings in labor and o$erhead achie$ed by
the rapid weld metal deposition.
2.4.3.1 The equipment necessary for gas metal arc welding is listed below6
1) Power source
2) Wire feeder
3) Welding gun
4) Shielding gas supply
5) Solid electrode wire
6) Protecti$e equipment
2.4.3.2 The basic equipment necessary for semiautoma tic gas metal arc welding is shown
in Figure 12.
SCHEMATIC DIAGRAM SEMI-AUTOMATIC GMAW EQUIPMENT
FIGURE 12
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Current
Chapter
Table of
Contents
Glossary
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
WELDING GUN
TRIGGER CONTROL LEAD FEED ROLLS
WELD CABLE
GAS HOSE
GROUND CABLE WORK
115V CONTACTOR ~ ~
MAGNETIC
VALVE
WIRE FEEDER
WIRE SPOOL
SHIELDING GAS
POWER SOURCE
FLOWMETER REGULATOR
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_29.ht
1 din 1 23.11.2009 10:25
Go To Test
2.4.4 Power Source - A direct current, constant voltage power source is recommended
for gas metal arc welding. It may be a transformer-rectifier or a rotary type unit. The lower
open circuit voltage and self-correcting arc length feature, as described in Lesson I, makes it m
ost suitable. Constant voltage power sources used for spray transfer welding and for flux cored
electrode welding (to be covered later) are the same. However, if the unit is to be used for
short-circuiting arc
w e l d i n g , i t m u s t h a v e
'slope' or slope control.
25
Slope control is a
m e a n s o f l i m i t i n g t h e 2 0 V
O
high short-circuit current L
T
that is characteristic of S
this type welder. Figure
10
13 shows the effect of
slope on the short-
5
circuiting current.
2.4.4.1 I f w e w e r e
s ho r t - a r c w e l d i n g a t approximately 150 amperes
and 18 v olts, as shown in Figure 13,
and had no slope comp onents in the power source, the current at short-circuit or when the wire
touches the work, would be over 1400 amperes. At this high current, a good length of the wire w
ould literally explode off the end, cause much spatter, and the arc would be erratic. With the
slope comp onents in the circuit, the short-circuiting current is in the neighborhood of 400
amperes, and the m olten ball is sort of pinched off the end of the wire m ore gently. For those
with an electrical background, it might be added that in some machines, slope is achieved by
adding a reactor in the AC secondary of the power source. In others, a slope resistor is added in
the DC output portion of the circuit. Slope may be adjustable for varying wire diameters or it
may be fixed, giving a good average value for .035' and .045' diameter wires, the two most
popular sizes.
2.4.4.2 Another factor influencing the arc in short-circuiting welding is the rate that the
amperage reaches the short-circuiting current level. Using the example in Figure 13, we know
that the current goes from 150 amperes to 400 amperes during each shorting period. If we
were to plot the current rise on a graph, as in Figure 14, we would see that the current rise if
very rapid, as shown by the broken line.
Lesson 1 The Basics of Arc
Welding
LESSON II
Current
Chapter
T a b l e o f
Contents
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
OPERATING POINT
CONSTANT VOLTAGE VIA CURVE
Glossary
SHORT CIRCUITING CURRENT NO SLOPE
SHORT CIRCUITING CURRENT WITH SLOPE
200 400 e00 800 1000 1200 1400
EFFECT OF SLOPE ON SHORT CIRCUITING CURRENT
FIGURE 13 Turn Pages
15
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_30.ht
1 din 1 23.11.2009 10:25
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_31.ht
1 din 1 23.11.2009 10:25
© COPYRIGHT 1998 THE ESAB GROUP, INC
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_32.ht
1 din 1 23.11.2009 10:25
TIIvE - MILLISECONDS
EFFECT OF IND~CTANCE ON CLRRENT RISE
FIGURE 14
Lesson 1 The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Cove red Electrodes
for Welding
Mild Steels
Lesson 4
Cove red Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
LESSON II
This rapid current rise can be
by using a device called an
(sometimes called a stabilizer)
output circuit of the welder. An
merely an iron core wound
turns of heavy wire. It does
c u r r e n t f l o w , b u t
i t a c t s somewhat like a fly
wheel or
damp er by retarding the rate
of rise as shown by the solid line.
By prev enting the rapid
current rise, the arc
becomes smoother,
spatter is reduced, and
b e a d s h a p e a n d
appearance are
improv ed. Because the inductor influences the time function, its design determines arc
on-off
time, and short-circuit frequency. Some power sources have a selector that can switch in
sev eral different inductance values to finely tune the arc.
2.4.4.4 Welding power sources designed for gas metal arc welding have a 115 volt outlet to
provide power to operate the wire feeder. They also have a receptacle to receive the electrical
power required to close the main contactor in the power source, which turns on the welding
power to the welding gun when the gun trigger is actuated.
2.4.4.5 Additional advancements in equipment technology have introduced many new
models. Inv erters, as well as microprocessor controls, have created the greatest attention. In
addition, multipurpose machines have provided the user with greater fle6ibility with a variety of
capabilities.
2.4.4.6 Global competition will continue to have a profound influence on future
advancements in arc welding equipment. As energy prices rise, greater demands for mor e
efficient equipment will follow.
2.4.5 Wire Feeder - When welding with a constant voltage power source, as is the case
in most gas metal arc welding applications, the prime function of the wire feeder is to deliv er
the welding wire to the arc at a very constant speed. Since the wire feed speed determines
the amperage, and the amperage determines the amount of heat at the arc, inconsistent wire
feed speed will produce welds of varying penetration and bead width. Advanced electronics
© COPYRIGHT 1998 THE ESAB GRO~P, INC.
Current
Chapter
Table of
Contents
Go To Test
Glossary
Turn Pages
WITHOUT IND~CTANCE
400 AIVPS
150 AMPS
WITH INDIJCTANCE
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_33.ht
1 din 1 23.11.2009 10:25
Lesson 1 The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
LESSON II
technology makes it possible to design motor speed controls that will produce the same
speed, e'en though the load on the motor 'aries or the input 'oltage to the motor may fluctuate.
2.4.5.1 A li mited amount of gas metal arc welding is performed with constant current type
power sources. In this case, the motor speed automatically 'aries to increase or decrease the
wire feed speed as the arc length 'aries to maintain a constant 'oltage.
2.4.5.2 The wire feeder also controls the main contactor in the power source for safety
reasons. This assures that the welding wire will only be energized when the switch on the
welding gun is depressed.
2.4.5.3 The flow of shielding gas is controlled by a solenoid 'al'e (magnetic 'al'e) in the
wire feeder to turn the shielding gas on and off when the gun switch is actuated. Most feeders
utilize a dynamic breaking circuit to quickly stop the motor at the end of a weld to pre'ent a
long length of wire protruding from the gun when the weld is terminated. Most feeders ha'e a
burn-back circuit that allows the welding current to stay on for a short period of time after wire
feeding has stopped, to allow the wire to burn back exactly the right amount for the next arc
initiation.
2.4.5.4 The feed rolls, sometimes called dri'e rolls, pull the wire off the spool or reel, and
push it through a feed cable or conduit to the welding gun. These rolls must usually be
changed to accommodate each different wire diameter, although some rolls are designed to
feed a combination of sizes.
2 . 4 . 6 Welding Gun - The function of the welding gun, sometimes referred to as a torch, is
to deli'er the welding wire, welding current, and shielding gas to the welding arc. Guns are
a'ailable for semi-automatic operation and for automatic operation, where they are fixed in the
automatic welding head.
2.4.6.1 Guns for GMAW ha'e se'eral characteristics in common. All ha'e a copper alloy
shielding gas nozzle, that deli'ers the gas to the arc area in a nonturbulent, angular pattern to
pre'ent aspiration of air. The nozzle may be water cooled for semiautomatic welding at high
amperage and for automatic welding where the arc time is of long duration. Welding current is
transferred to the weldingwire as the wire tra'els through the contact tip or contact tube
located inside the gas nozzle (Refer to Figure 9). The hole in the contact tip through which the
wire passes is only a few thousandths of an inch larger than the wire diameter. A worn contact
tip will result in an erratic arc due to poor current transfer. Figure 15 shows a few different
semiautomatic gun configurations that are commonly used for GMAW.
Lesson 10
Reliability of Welding
Filler Metals
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Current
Chapter
Table of
Contents
Go To Test
Glossary
Turn Pages
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_34.ht
1 din 1 23.11.2009 10:25
Turn Pages
Current
Chapter
Table of
Contents
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
FIGURE 15
2.4.6.2 The cur~e d neck or 'goose neck'type is probably the most commonly used. It
allows the best access to a ~ariety of weld joints. The wire is pushed to this type of gun by the
feed rolls in the wire feeder through a feed cable or conduit that usually is 10 or 12 feet in
length. The shielding gas hose, welding current cable, and trigger switch leads are supplied
with the welding gun.
2.4.6.3 The pistol type gun is similar to the cur~e d neck type, but is less adaptable for
difficult to reach joints. The pistol type is also a 'push' type gun and is more suitable for gas
metal arc spot welding applications.
2.4.6.4 The self contained type has an electric motor in the handle and feed rolls that pull the
wire from a 1 or 2 pound spool mounted on the gun. The need for a long wire feed cable is
eliminated, and wire feed speed may be controlled by the gun. Guns of this type are often
used for aluminum wire up to .045'diameter, although they may also be used for feeding steel
or other hard wires.
2.4.6.5 The pull type gun has either an electric motor or an air motor mounted in the handle
that is coupled to a feeding mechanism in the gun. The spool of wire is located in the control
cabinet that may be located as far as fifty feet from the gun. When feeding such long
distances, a set of 'push' rolls located in the control cabinet assist in feeding the wire. This
then becomes known as a push-pull feed system and is especially useful in feeding the softer
wires such as aluminum.
2 .4 . 7 SHIELDING GASES - In gas metal arc welding, there are a ~ariety of shielding
gases that can be used, either alone or in combinations of ~arying degrees. The choice is
dependent on the type of metal transfer employed, the type and thickness of metal, the bead
© COPYRIGI-T 1998 TI-E ESAB GROUP, INC.
Lesson 1 The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
LESSON II
CURVED NECK PISTOL TYPE
SELF CONTAINED PU:i TYPE
SEMI-AUTOMATIC GMAW GUN TYPES
Go To Test
Glossary
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_35.ht
1 din 1 23.11.2009 10:25
Lesson 1 The Basics of A Welding
Lesson 2 Common Electri
Arc Welding Processes
Lesson 3 Covered Electrodes
for Welding Mild Steels
Lesson 4 Covered Electrodes for Welding Low
Alloy Steels
Lesson 5 Welding Filler Metals for Stainless Steels
Lesson 6 Carbon & Low Alloy Steel Filler Metals - GMAW,GTAW,SAW
Lesson 7 Flux Cored Arc
Electrodes Carbon Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9 Estimating &
Comparing Weld Metal Costs
Lesson 10 Reliability of Welding
Filler Metals
LESSON II
profile (See Figure 16), penetration, and speed of welding. In our discussion, we will deal with
the more common choices used for the various transfer processes.
FERROUS METALS NON-FERROUS METALS
CO2 ARGON + CO2 ARGON + O2 ARGON HELIUvI
BEAD PROFILE
FIGURE 16
2.4.7.1 Short Circuiting Transfer - Straight carbon dioxide (CO2) is often used for short
circuiting arc welding because of its low cost. The deep penetration usually associated with
CO 2 is minimized because of the low amperage and voltage settings used with this process.
Compared to other gas mixes, CO 2will produce a harsher arc and therefore, greater spatter
levels. Usually, this is minimized by maintaining a short arc length and by careful adjustment of
the power supply inductance. The temperatures reached in welding will cause carbon dioxide
to decompose into carbon monoxide and oxygen. To reduce the possibility of porosity caused
by entrapped oxygen in the weld metal, it is wise to use electrodes that contain deoxidizing
elements, such as silicon and manganese. If the current is increased above the short circuiting
range, the use of carbon dioxide tends to produce a globular transfer.
2.4.7.1.1 Mixing argon in proportions of 50-75% with carbon dioxide will produce a
smoother
arc and reduce spatter levels. It will also widen the bead profile, reduce penetration, and
encourage 'wetting'. Wetting, i.e., a uniform fusion, along with joining edges of the base metal
and the weld metal, minimizes the
weld imperfection known as
undercutting (See Figure 17).
UNDERCUT WETTING
FIGURE 17
2.4.7.1.2 The 75% ArgonI25 CO2 mixture is often chosen for short circuit welding of thin
sections, whereas the 50-50 combination works well on thicker sections.
2.4.7.1.3 It should be noted that shielding gases can affect the metallurgy of the weld metal.
As an example, a combination of argon and carbon dioxide may be used for welding stainless
steel, but as the carbon dioxide breaks down, excessive carbon may be transferred into the
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Current Chapter Table of
Contents
Go To Test
Glossary
Turn Pages
Search Chapter (Faster
Download)
Search Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_36.ht
1 din 1 23.11.2009 10:25
Turn Pages
Lesson 1 The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
LESSON II
weld metal. Corrosion resistance in stainless steel is reduced as the carbon content
increases. To counteract this possibility, a less reactive mixture of 90% helium - 7-112% argon -
2-112% CO2 is sometimes chosen. This combination, known as a trimiç provides good arc
stability and wetting.
2.4.7.2 Spray Arc Transfer - Pure argon produces a deep constricted penetration at the
center of the bead with much shallower penetration at the edges (Figure 16). Argon performs
well on nonferrous metals, but when used on ferrous metals, the transfer is somewhat erratic
with the tendency for the weld metal to moveaway from the center line. To make argon suit -
able for spray transfer on ferrous metals, small additions of 1 to 5% oxygen have proven to
provide remarkable improvements. The arc stabilizes, becomes less spattery, and the weld
metal wets out nicely. If the percentage of argon falls below 80%, it is impossible to achieve
true spray transfer.
2.4.7.2.1 Pure helium or combinations of helium and argon are used for welding nonferrou
metals. The bead profile will broaden as the concentration of helium increases.
2.4.7.3 Pulse Spray Transfer - The selection of shielding gas must be adequate enough to
support a spray transfer. Material type, thickness, and welding position are essential variables
in selecting a particular shielding gas. The following is a list of recommended gases:
Carbon Steel ArgonICO20O20He (He less than 50%)
Alloy Steel ArgonICO20O20He (He less than 50%)
Stainless ArgonilO20CO2 (CO2max. 2%)
Copper, Nickel, & Cu-Ni Alloys ArgonlHelium
Aluminum ArgonlHelium
2 .4 .8 Electrodes - The solid electrodes used in GMAW are of high purity when they come
from the mill. Their chemistry must be closely controlled and some types purposely contain
high levels of deoxidizers for usewith CO 2 shielding.
2.4.8.1 The electrode manufacturer draws down the electrode to a finished diameter that,
with GMAW, is usually quite small. Diameters from .030' thru 1116' are common.
2.4.8.2 Most steel GMAW electrodes are copper plated as a means of protecting the
surface. The copper inhibits rusting, provides smooth feeding, and helps electrical
conductivity.
2.4.8.3 Information on types and classifications will be covered in a future lesson.
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Current
Chapter
Table of
Contents
Go To Test
Glossary
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_37.ht
1 din 1 23.11.2009 10:26
Go To Test
Turn Pages
Flux CoredArc Weld~ng (FCAW) is quite similar to GMAW as far as operation and
equipment are concerned. The major difference is that FCAW utilizes an electrode that is -e ry
different from the solid electrode used in GMAW. The flux cored electrode is a fabricated
electrode and as the name implies, flux material is deposited into its core. The flux cored
electrode begins as a flat metal strip that is formed first into a 'U shape. Flux and alloying
elements are deposited into the 'U' and then the shape is closed into a tubular configuration
by a series of forming rolls.
2.5.0.1 The flux cored electrode is a continuous electrode that is fed into the arc where it is
melted and transferred into the molten puddle. As in GMAW, the flux cored process depends on
a gas shield to protect the weld zone from detrimental atmospheric contamination. With FCAW,
there are two prima ry ways this is accomplished (See Figure 18). The gas is either a pplied
externally, in which case the electrode is referred to as a gas shielded flux cored electrode, or it
is generated from the decomposition of gas forming ingredients contained in the electrode's
core. In this instance, the electrode is known as a self-shielding flux cored
electrode. In addition to the gas shield, the flux co red electrode produces a slag co-e ring for
FIGURE 1
further protection of the weld metal as it cools. The slag is manually remo-ed with a wire brush or chipping
hammer.
2.5.1 Se l f Sh ie l de d Proces s - The main ad-antage of the se lf shie lding method is that
its operation is somewhat simplified because of the absence of external shielding equipment.
Lesson 1 The Basics of Arc
Welding 2 . 5 F LUX CORED ARC WELD ING
LESSON II
Current
Chapter
T a b l e o f
Contents
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Glossary
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
FLUX-CORED ARC WELDING
CONTACT TIP
GAS CUP
GAS SHIELD
FLUX CORE
GAS SHIELDED
CONTACT TIP
INSULATED GUIDE TUBE
FLUX CORE
SELF SHIELDED
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_38.ht
1 din 1 23.11.2009 10:26
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_39.ht
1 din 1 23.11.2009 10:26
© COPYRIGHT 1998 THE ESAB GROUP, IN
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_40.ht
1 din 1 23.11.2009 10:26
Turn Pages
Lesson 1 The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Although self shielding electrodes have been developed for welding low alloy and stainless
steels, they are most widely used on m ild steels. The self shielding method generally uses
a long electrical stick-out (distance between the contact tube and the end of the unmelted elec-
trode) commonly from one to four inches. Electrical resistance is increased with the long
extension, preheating the electrode before it is fed into the arc. This enables the electrode
to burn off at a faster rate and increases deposition. The preheating also decreases the
heat ava ilable for melting the base metal, resulting in a more shallow penetration than the
gas shielded process.
2.5.1.1 A major drawback of the self shielded process is the metallurgical quality of the
deposited weld metal. In addition to gaining its shielding ability from gas forming ingredients
in the core, the self shielded electrode contains a h igh level of deoxidizing and denitrifying
alloys, primarily aluminum, in its core. Although the alum inum performs well in neutralizing the
affects of oxygen and nitrogen in the arc zone, its presence in the weld metal will reduce
ductility and impact strength at low temperatures. For this reason, the self shielding method is
usually restricted to less critical applications.
2.5.1.2 The self shielding electrodes are more suitable for welding in drafty locations than
the gas shielded types. Since the molten filler metal is on the outside of the flux, the gases
formed by the decomposing flux are not totally relied upon to shield the arc from the
atmosphere. The deoxidizing and denitrifying elements in the flux further help to neutralize the
affects of nitrogen and oxygen present in the weld zone.
2.5.2 The Gas Shielded Process - A major advantage with the shielded flux cored
electrode is the protective envelope formed by the auxiliary gas shield around the molten
puddle. This envelope effectively excludes the natural gases in the atmosphere without the
need for core ingredients such as aluminum. Because of this more thorough shielding, the
weld metallurgy is cleaner which makes this process suitable for welding not only m ild steels,
but also low alloy steels in a wide range of strength and impact levels.
2.5.2.1 The gas shielded method uses a shorter electrical stickout than the self shielded
process. Extensions from 112' to 314' are common on all diameters, and 314' to 1 -112' on
larger diameters. Higher welding currents are also used with this process, enabling high
deposition rates to be reached. The auxiliary shielding helps to reduce the arc energy into a
columnar pattern. The combination of high currents and the action of the shielding gas
contributes to the deep penetration inherent with this process. Both spray and globular
transfer are utilized with the gas shielded process.
Lesson 10
Reliability of Welding
Filler Metals
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Current
Chapter
Table of
Contents
Go To Test
LESSON II
Glossary
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_41.ht
1 din 1 23.11.2009 10:26
CURRENT PATH
Lesson 1 The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
LESSON II
2.5.3 Current Density - Flux cored arc welding utilizes the same principles of current
density, as explained in section 2.4.1, but there is one significant difference between the flux
cored electrode and the solid electrode. With the flux cored electrode, the granular core
ingredients are poor electr ica l conductors and therefore, the current is carr ied primarily
through the outer metal sheathing. When an equal diameter cross
section of the two are compared (See Figure 19), it is seen that the
flux cored electrode has
a smaller current carrying area than the soli
electrode. This greater concentration of
current in a smaller area increases the
burnoff rate.
2.5.3.1 When all other factors are
equal,
the deposition rate of the flux cored
electrode is somewhat higher than the
solid electrode.
2.5.4 EQUIPMENT - The equipment used for flux cored arc welding is the same as
shown previously in Section 2.3.2.2, Figure 12, with the exception that the self shielded
method does not need the external gas apparatus.
2.5.4.1 Flux cored arc welding is done with direct current. All of the gas shielded electrodes
are designed for DCEP operation. The self shielded electrodes are either designed
specifically for DCEN or DCEP.
2.5.5 Power Source - The recommended power source is the direct current constant
voltage type. The constant current type can be used but with less satisfactory results.
2.5.6 Wire Feeder - The function of the wire feeder in FCAW is the same as discussed in
the section on GMAW. Since the flux cored electrode is tubular in construction, precautions
must be taken not to flatten the electrode. To facilitate feeding by means other than pressure
alone, specially designed feed rolls with knurled or groove d surfaces are used. Some feeders
use four feed rolls rather than two to minimize unit pressure on the electrode.
2.5.7 The Welding Gun - As compared to GMAW, the main difference in FCAW welding guns
is in those used with the self shielding process. The gun is somewhat more compact due to the
absence of an external gas shielding nozzle. Since the self shielding process normally requires
a longer electrode extension, the self shielding gun may have an insulated guide tube (Refer
back to Figure 18) to give stability to the electrode. Water cooled guns are available for high
duty semi-automatic welding and for automatic welding.
© COPYRIGHT 1998 THE ESAB GROUP, INC.
Current
Chapter
Table of
Contents
Go To Test
Glossary
Turn Pages
1/16 FLU?-CORED
ELECTRODE 1/16 SOLID ELECTRODE
FIGURE 19
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_42.ht
1 din 1 23.11.2009 10:26
Turn Pages
Lesson 1 The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
LESSON II
2.5.7.1 Flux cored welding generates fumes, that for environmental reasons, must be
removed from the welding area. This is usually done with an external exhaust system, but
welding guns with internal fume extractors have been developed. They are heavier than the
regular gun and must be properly maintained so that the extracting mechanism does not
disturb the shielding gas.
2 .5 .8 SHIELDING GASES - Carbon dioxide is the most widely used gas for auxiliary
shielding of the flux cored electrode. The other commonly used gas is a mixture of 75% Argon
and 25% CO2.
2.5.8.1 A ca rbon dioxide shield produces deep penetration and the transfer is globular. As
previously discussed, CO 2 will dissociate in the heat of the arc. To counteract this
characteristic, deoxidizing elements are added to the core ingredients of the electrode. The
deoxidizers react to form solid oxide compounds that float to the surface as part of the slag
covering.
2.5.8.2 The addition of Argon to CO2 will increase the wetting action, produce a smooth arc
arc, and reduce spatter. The transfer is spray-like, and the penetration is somewhat less than
with the straight carbon dioxide.
2.5.8.3 While some flux cored electrodes are designed to operate well on both the 100%
CO2 or the 75125 mixture, others are formulated specifically for the CO 2 shield or the Argonl
CO2 mixture. If the recommended gas is not used with these electrodes, the weld chemistry
may be affected. The reason for this is that inert gas, such as Argon, does not react with the
other elements; therefore, allowing them to be transferred across the arc into the weld metal.
An electrode designed for CO 2 shielding contains deoxidizing elements, such as silicon and
manganese. If a high percentage of Argon is used in the shielding medium, a large portion of
these elements may pass into the weld metal causing the weld metallurgy to be less ductile
than intended.
2.5.8.3 The opposite happens with electrodes formulated for a 75125 mixture. These
electrodes are usually designed for high yield and tensile strength. If a high percentage of CO 2
is used with them, the CO2 may react with the elements needed to attain these strength levels,
thereby preventing them from passing into the weld metal.
2.6 SUBMERGED ARC WELDING
Submerged Arc Welding (SAW) is different from the previously explained arc welding processes in
that the arc is not visible. The arc is submerged beneath loose granular flux. A continuous
electrode is fed by automatic drive rolls through an electrode holder where current
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Current
Chapter
Table of
Contents
Go To Test
Glossary
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_43.ht
1 din 1 23.11.2009 10:26
Lesson 1 The Basics of Arc
Welding
LESSON II
is picked up at the contact tube. The electrode mo'es into the loose flux and the arc is
initiated. The flux is deposited from a separate container that mo'es at the same pace as the
electrode assuring complete co'erage (See Figure 20).
2.6.1 Submerged Arc Flux - The flux helps form the molten puddle, slows the cooling
rate, and acts as a protecti'e shield. The fluç which is in close contact wi th the arc, is fused
into a slag co'er and that which is not fused is collected for reuse. The flux can contain alloying
elements that, when molten, will pass into the weld metal affecting the metallurgy. Some fluxes
are specifically prepared for their alloy altering capabilities while others, known as neutral
fluxes, are chosen when a minimal alloy change is desired. Although these latter fluxes are
called 'neutral', they still ha'e the ability to slightly alter the weld chemistry.
Current
Chapter
Table of
Contents
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Go To Test
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_44.ht
1 din 1 23.11.2009 10:26
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
FLUX HOPPER
LOOSE GRANULAR FLUX ELECTRODE
MOLTEN PUDDLE BASE METAL
Glossary
Turn Pages
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_45.ht
1 din 1 23.11.2009 10:26
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
SUBMERGED ARC WELDING
FIGURE 20
2.6.2 The Welding Gun - Although there are hand-held welding guns for the submerged
arc process, the majority of SAW is done with fully automa tic equipment. The basic compo-
nents include a wire feeder, a power source, a flux deli'ery system, and in some instances, an
automa tic flux reco'ery system.
2.6.3 Power Sources - The power source can be a constant current AC transformer, or i
may be a DC rectifier or generator of either the constant current or constant 'oltage 'ariety.
The power source must be rated for high current output. When current requirements exceed
the 'alue of a single machine, two or more of the same type may be connected in parallel.
2.6.4 Equipment - Most submerged arc welding is done wi th DCEP because it pro'ides
easy arc starting, deep penetration and excellent bead shape. DCEN pro'ides the highest
© COPYRIGHT 1998 THE ESAB GROUP, IN
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_46.ht
1 din 1 23.11.2009 10:26
Turn Pages
Lesson 1 The Basics of Arc
Welding
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
LESSON II
deposition rates but minimum penetration. Alternating current is often used as a trailing arc in
tandem arc applications. In this type of application, the leading DCEP arc provides deep
penetration, and the closely trailing AC arc provides high deposition with a minimum of arc
blow.
2.6.5 Electrodes - A variety of ferrous and nonferrous electrodes are used in submerged
arc welding. They are usually solid electrodes refined with the appropriate alloys at the steel
mill, and then shipped to electrode manufacturers where they are drawn down to a specific
diameter and packaged. There is another type of sub arc electrode known as a composite
electrode, that is fabricated in the same manner as a flux cored electrode. A chief adv antage
of this type is that the alloying elements can be added to the core of the electrode more
cheaply than a steel mill can produce those same alloys in a solid form. The electrodes for
SAW vary in diameter from 1116 inch to 114 inch with the larger diameters being the most
widely used.
2.6.6 Summary - Submerged arc welding has some advantages over other welding
processes. Since the radiance of the arc is blanketed by the loose flux, there is no need for a
protective welding hood (although safety glasses are recommended), there is no spatter and
only a very minim al amount of fumes escape from under the blanket. High welding currents,
quite commonly in the 300 to 1600 ampere range, are used. These high currents, combined
with fast travel speeds, m ake SAW a high deposition process that is especially suitable for
applications that require a series of repetitious welds. Some setups allow two or more elec -
trodes to be fed simultaneously into the joint, further increasing the deposition rate and speed.
2.6.6.1 Although SAW has these advantages, it does have some limitations. The flux must
be deposited and collected for every welding pass. This requires additional equipment and
handling. Also because of the loose fluç the process is limited to the flat and horizontal
positions. The equipment for SAW is commonly quite bulky which limits its mobility, and
although the process works well on thick m aterials, it usually is not satisfactory for thin gauge
m aterial. The process requires care in the operation. The amperages commonly used m ay
cause excessive heat buildup in the base metal, that m ay result in distortion or brittleness.
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Current
Chapter
Table of
Contents
Go To Test
Glossary
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_47.ht
1 din 1 23.11.2009 10:26
Go To Test
Turn Pages
Electroslag Welding (ESW) and Electrogas Welding (EGW) comprise only a minor portion of all welding
done in the country, but they are uniquely adapted to certain applications, primarily the joining
of -ery thick materials. The joining of a 12 inch material along a 40 foot line is not an
uncommon application for the Electroslag process.
2.7.1 Electroslag Welding (See Figure 21) is technically not an arc welding process,
although it utilizes a current carrying consumable electrode. The only time there is an arc
between the electrode and the work piece is when current is initially charged through the
electrode. This initial charge heats a layer of loose flux that becomes molten and extinguishes
the arc.
ELECTROSLAG WELDING
FIGURE 2
2.7.2 Flux - The flux used in ESW is high in electrical resistance. As current is applied,
enough heat is generated from this resistance to keep the fluç base metal, and electrode in a
molten state. This axis of the weld joint is on a -ertical plane. The two pieces of metal, usually of
the same thickness, are positioned so that there is an opening between them. One or more electrodes
are fed into the opening through a welding bead that tra-els -ertically as the joint is filled. To
contain the molten puddle, water cooled copper shoes or dam s are placed on the
sides of the -ertical ca-ity. As the weld joint solidifies, the dam s mo-e-ertically so as to
always remain in contact with the molten puddle.
2.7.3 Process - A -ariation of ESW is the consumable guide method. The process is the
same with this method except that the guide tube that feeds the electrode to the molten pool is
Lesson 1 The Basics of Arc
Welding 2 .7 ELECTROSLAG AND ELECTROGAS WELDING
LESSON II
Current
Chapter
T a b l e o f
Contents
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
Glossary
Search
Chapter
(Faster
Download)
Search
Document
(Slower
Download)
WATER INLET/OUTLET
ELECTRODE
COPPER SHOE
GUIDE TUBE (CONSUVIABLE GUIDE IvETHOD)
BASE IVETAL
MOLTEN FLUX
WELD POOL SOLIDIFIED METAL
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_48.ht
1 din 1 23.11.2009 10:26
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_49.ht
1 din 1 23.11.2009 10:26
© COPYRIGHT 1998 THE ESAB GROUP, INC.
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_50.ht
1 din 1 23.11.2009 10:26
Lesson 1 The Basics of Arc
Welding
LESSON II
also consumed. The chief ad antage with this method is the elimination of the electrode holder
which must mo e ertically with the weld pool. Also since the guide tube is consumed, the deposition
rate is slightly increased with this method.
2.7.4 Equipment - The equipment used in E S W is all automatic and of special design.
The power source may use either AC or DC current. The electrode may be either solid or flux
cored, although if the flux cored is used, it must be specially formulated so as not to contain its normal
amount of slag forming ingredients.
2.7.5 Summary - Electrogas Welding is similar to E S W as far as the mechanical as-
pects are concerned. The equipment is automatic, the welding head tra els ertically, and the
molten puddle is retained by shoes on the sides of the joint. The difference is that Electrogas Welding
utili2es an arc and it is externally gas shielded. The power source is also limited to
DC operation. The electrodes used in EGW can be either solid or flux cored.
Current
Chapter
Table of
Contents
Lesson 2
Common Electric
Arc Welding
Processes
Lesson 3
Covered Electrodes
for Welding
Mild Steels
Lesson 4
Covered Electrodes
for Welding Low
Alloy Steels
Go To Test
Glossary
Lesson 5
Welding Filler Metals
for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc
Electrodes Carbon
Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Turn Pages
Search
C h a p t e r
( F a s t e r Download)
Search D o c u m e n t
( S l o w e r Download)
Lesson 9
Estimating &
Comparing Weld
Metal Costs
Lesson 10
Reliability of Welding
Filler Metals
© COPYRIGHT 1998 THE ESAB GROUP, INC
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_51.ht
1 din 1 23.11.2009 10:26
LESSON II- GLOSSARY OF TERMS
Arc Blow - Deviation of the direction of the welding arc caused by magnetic fields in the
work piece when welding with direct current.
Straight - Welding condition when the electrode is connected to the negative terminal
Polarity and the work is connected to the positive terminal of the welding power source.
Reverse - Welding condition when the electrode is connected to the positive terminal
Polarity and the work is connected to the negative terminal of the welding power
source.
Slag - The brittle mass that forms over the weld bead on welds made with coated
e l e c t ro des , f lu x c o re d e l e c t r o des , s ub me r ge d a rc w e ld ing a nd
o t he r s l a g p r o d u c i n g w e l d i n g p r o c e s s e s . W e l d s m a d e w i t h
t h e g a s m e t a l a r c a n d t h e gas tungsten arc welding processes are slag
free.
Lesson 1 The Basics of Arc
Welding APPENDIX A
LESSON II
Current Chapter Table of Contents
Lesson 2 Common Electric
Arc Welding Processes
Lesson 3 Cove red Electrodes
for Welding Mild Steels
Lesson 4 Cove red Electrodes for Welding Low
Alloy Steels
Lesson 5 Welding Filler Metals for Stainless Steels
Lesson 6 Carbon & Low Alloy Steel Filler Metals - GMAW,GTAW,SAW
Lesson 7 Flux Cored Arc
Electrodes Carbon Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9 Estimating &
Comparing Weld
Metal Costs
Go To Test
Glossary
Turn Pages
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_52.ht
1 din 1 23.11.2009 10:26
- Welding with a coated electrode where the operator1s hand controls travel
speed and the rate the electrode is fed into the arc.
- Welding with a continuous solid wire or flux cored electrode where the wire
feed speed, shielding gas flow rate, and voltage are preset on the equipment,
and the operator guides the hand held welding gun along the joint to be
welded.
- A weld defect where slag is entrapped in the weld metal before it can float to
the surface.
Manual Arc
Welding
Semi-Automatic
Welding
Slag
Inclusion
Root Pass - The initial pass in a multi-pass weld, usually requiring 100% penetration.
Search Chapter (Faster
Download)
Search Document (Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_53.ht
1 din 1 23.11.2009 10:26
Lesson 10 Reliability of Welding
Filler Metals
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_54.ht
1 din 1 23.11.2009 10:26
Turn Pages
LESSON II
Gas Ions - Shielding gas atoms that, in the presence of an electrical current, lose one or
more electrons and therefore, carry a positi'e electrical charge. The pro'ide a
more electrically conducti'e path for the arc between the electrode and the
work piece.
High
Frequency - (as applied to gas-tungsten arc welding)
An alternating current consisting of o'er 50,000 cycles per second at high
'oltage, low amperage that is superimposed on the welding circuit in GTAW
power sources. It ionizes a path for non-touch arc starting and stabilizes the arc
when welding with alternating current.
Inert Gases - Gases that are chemically inacti'e. They do not readily combine with other
elements.
Flux - In arc welding, fluxes are formulations that, when subjected to the arc, act as
a cleaning agent by dissol'ing oxides, releasing trapped gases and slag and
generally cleaning the weld metal by floating the impurities to the surface
where they solidify in the slag co'ering. The flux also ser'e s to reduce spatter
and contributes to weld bead shape. The flux may be the coating on the
electrode, inside the electrode as in flux cored types, or in a granular form as
used in submerged arc welding.
Current
Density - The amperes per square inch of cross-sectional area of an electrode. High
current density results in high electrode melt-off rate and a concentrated, deep
penetrating arc.
Slope or Slope
Control - A necessary feature in welding power sources used forshort circuiting arc
welding. Slope Control reduces the short circuiting current each time the
electrode touches the weld puddle (See Section 2.5.3).
Inductance - (as applies to short circuiting arc welding)
A feature in welding power sources designed for short circuiting arc welding to
retard the rate of current rise each time the electrode touches the weld puddle.
Lesson 10 Reliability of Welding
Filler Metals
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Current Chapter Table of
Contents
Go To Test
Lesson 1 The Basics of Arc
Welding
Lesson 2 Common Electric
Arc Welding Processes
Lesson 3 Covered Electrodes
for Welding Mild Steels
Lesson 4 Covered Electrodes for Welding Low
Alloy Steels
Lesson 5 Welding Filler Metals for Stainless Steels
Lesson 6 Carbon & Low Alloy Steel Filler Metals - GMAW,GTAW,SAW
Lesson 7 Flux Cored Arc
Electrodes Carbon Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9 Estimating &
Comparing Weld
Metal Costs
Glossary
Search Chapter (Faster
Download)
Search Document (Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_55.ht
1 din 1 23.11.2009 10:26
Contact Tip - That part of a gas metal arc welding gun or flux cored arc welding
gun that
t r ans fe r s the we ld ing cur rent to the we ld ing wire immed ia te ly be fo r e the w ire
enters the arc.
Spray - Mode of metal transfer across the arc where the molten metal droplets are
Transfer smaller than the electrode diameter and are axially directed to the
weld puddle.
R e q u i r e s h i g h v o l t a g e a n d a m p e r a g e s e t t i n g s a n d a s h i e l d i n g g a s o f a t l e a s t
80% argon.
Lesson 1 The Basics of Arc
Welding
LESSON II
Current Chapter Table of Contents
Lesson 2 Common Electric
Arc Welding
Processes
Go To Test
Lesson 3 Covered Electrodes
for Welding
Mild Steels
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_56.ht
1 din 1 23.11.2009 10:26
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_57.ht
1 din 1 23.11.2009 10:26
Turn Pages
Lesson 4 Covered Electrodes for Welding Low
Alloy Steels
Lesson 5 Welding Filler Metals for Stainless Steels
Lesson 6 Carbon & Low Alloy Steel Filler Metals - GMAW,GTAW,SAW
Lesson 7 Flux Cored Arc
Electrodes Carbon Low Alloy Steels
Lesson 8 Hardsurfacing
Electrodes
Lesson 9 Estimating &
Comparing Weld Metal Costs
- Mode of metal transfer across the arc where a molten ball larger than the
electrode diameter forms at the tip of the electrode. On detachment, it takes
on an irregular shape and tumbles towards the weld puddle sometimes
shorting between the electrode and work at irregular intervals. Occurs when
using shielding gases other than those consisting of at least 80% argon and
at medium current settings.
- Mode of metal transfer somewhat between spray and short circuiting. The
specific power source has built into it two output levels: a steady background
level, and a high output (peak) level. The later permits the transfer of metal
across the arc. This peak output is controllable between high and low values
up to several hundred cycles per second. The result of such a peak output
produces a spray arc below the typical transition current.
- Mode of metal transfer in gas metal arc welding at low voltage and amperage.
Transfer takes place each time the electrode touches or short-circuits to the
weld puddle, extinguishing the arc. The short-circuiting current causes the
electrode to neck down, melt off, and then repeats the cycle.
- A shielding gas consisting of approximately 90% helium, 7-112% argon, and
2-112% carbon dioxide used primarily for short-circuiting arc welding of
stainless steels. Maintains corrosion resistance of the stainless steel and
produces good wetting and excellent weld bead shape.
Lesson 10 Reliability of Welding
Filler Metals
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C
Globular
Transfer
Pulse
Transfer
Short-circuiting
Transfer
Trimixor
Triple Mix
Glossary
Search Chapter (Faster
Download)
Search Document (Slower
Download)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_58.ht
1 din 1 23.11.2009 10:26
Lesson 2 Common Electric
Arc Welding Processes
Electrical
Stick-Out
- In any welding process using a solid or flux cored wire, the electrical stick -out
is the distance from the contact tip to the unmelted electrode end. Sometimes
called the 'amount of wire in resistance'. This distance influences melt-off
rate, penetration, and weld bead shape.
Go To Test
Lesson 1 The Basics of Arc
Welding
LESSON II
Current Chapter Table of Contents
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_59.ht
1 din 1 23.11.2009 10:26
Lesson 3 Covered Electrodes
for Welding
Mild Steels
Lesson 4 Covered Electrodes for Welding Low
Alloy Steels
Out-of-Position
Welds
Weld
Positions
- Welds made in positions other than flat or horizontal fillets.
-
Glossary
FLAT HORIZONTAL FILLET
Lesson 5 Welding Filler Metals for Stainless Steels
Lesson 6 Carbon & Low Alloy Steel Filler Metals -
GMAW,GTAW,SAW
VERTICAL OVERHEAD
Turn Pages
Lesson 7 Flux Cored Arc
Electrodes Carbon Low Alloy Steels
S e a r c h C h a p t e r
( F a s t e r Download)
Search D o c u m e n t
( S l o w e r Download)
Lesson 8 Hardsurfacing
Electrodes
HORIZONTAL
BUTT
POSITIONED FILLET
(FLAT)
Lesson 2 - Common Electric Arc Welding Processes http://www.esabna.con/EuWeb/AWTC/Lesson2_60.ht
1 din 1 23.11.2009 10:26
Lesson 9 Estimating &
Comparing Weld Metal Costs
Lesson 10 Reliability of Welding
Filler Metals
© C O P Y R IG HT 1 9 9 8 T H E E S AB G R O UP , I N C