2.
Manual Metal Arc Welding
2. Manual Metal Arc Welding
18
Figure 2.1 describes the burn-off of a covered stick electrode. The stick electrode
air
(O2, N2, etc.)
electrode core
consists of a core wire with a mineral cover-
electrode coating
ing. The welding arc between the electrode
and the workpiece melts core wire and covering. Droplets of the liquefied core wire mix
Smoke and gas
with the molten base material forming weld
metal while the molten covering is forming
slag which, due to its lower density, solidifies
on the weld pool. The slag layer and gases
which are generated inside the arc protect the
metal during transfer and also the weld pool
liquid slag
solid slag
from the detrimental influences of the surrounding atmosphere.
c ISF 2002
br-er2-01.cdr
Weld Point
Figure 2.1
Covered stick electrodes
have replaced the initially
applied metal arc and carbon arc electrodes. The
covering has taken on the
functions which are described in Figure 2.2.
Figure 2.2
2005
2. Manual Metal Arc Welding
19
The covering of the stick electrode consists of a multitude of components which are mainly
mineral, Figure 2.3.
coating raw material
effect on the welding characteristics
quartz - SiO2
to raise current-carrying capacity
rutile -TiO2
fluorspar - CaF2
to increase slag viscosity,
good re-striking
to refine transfer of droplets through the arc
to reduce arc voltage, shielding gas
emitter and slag formation
to increase slag viscosity of basic electrodes,
decrease ionization
calcareous- fluorspar K2O Al2O3 6SiO2
easy to ionize,
to improve arc stability
ferro-manganese / ferro-silicon
deoxidant
shielding gas emitter
magnetite - Fe3O4
calcareous spar -CaCO3
cellulose
kaolin Al2O3 2SiO2 2H2O
potassium water glass
K2SiO3 / Na2SiO3
lubricant
bonding agent
br-er2-03.cdr
© ISF 2002
Influence of the Coating Constituents
on Welding Characteristics
Figure 2.3
For the stick electrode manufacturing mixed ground and screened covering materials are
used as protection for the core wire which has been drawn to finished diameter and subsequently cut to size, Figure 2.4.
raw material storage
for flux production
raw wire
storage
jaw
crusher
1
magnetic
separation
wire drawing machine
and cutting system
2
3
descaling
inspection
example of a three-stage wire drawing machine
drawing plate
cone crusher
for pulverisation
Ø 6 mm
sieving
to further treatment like milling,
sieving, cleaning and weighing
sieving system
Ø 5,5 mm
Ø 4 mm
weighing
and
mixing
inspection
br-er2-04.cdr
to the
pressing
plant
electrode
compound
3,25 mm
wet mixer
inspection
© ISF 2002
Stick Electrode Fabrication 1
Figure 2.4
2005
2. Manual Metal Arc Welding
20
The core wires are coated
the pressing plant
with the covering material
which
inspection
electrodepress
electrode
compound
sion presses. The defect-
packing
inspection
core wire
magazine
nozzleconveying
wire wire pressing
belt
feeder
magazine
head
binding
agents in electrode extru-
inspection
compound
contains
free electrodes then pass
TO
DELIVERY
through a drying oven and
are, after a final inspection,
drying stove
automatically packed, Fig-
inspection
inspection
ure 2.5.
inspection
© ISF 2002
br-er10-33e.cdr
Stick Electrode Fabrication 2
Figure 2.5
Figure 2.6 shows how the moist extruded covering is deposited onto the core wire inside an
electrode extrusion press.
pressing cylinder
core rod
coating
pressing nozzle
pressing cylinder
pressing mass
core rod guide
br-er2-06.cdr
Production of Stick Electrodes
Figure 2.6
2005
2. Manual Metal Arc Welding
21
Stick electrodes are, according to their covering compositions, categorized into four different types, Figure 2.7. with concern to burn-off characteristics and achievable weld metal
toughness these types show fundamental differences.
cellulosic type
acid type
cellulose
40
rutile TiO2
20
quartz SiO2
25
Fe - Mn
15
potassium water glass
almost
no slag
droplet transfer :
medium- sized
droplets
toughness value:
good
slag solidification
time: long
droplet transfer :
fine droplets
to sprinkle
toughness value:
basic typ
rutile type
magnetite Fe3O4 50
SiO2 20
quartz
CaCO3 10
calcite
Fe - Mn
20
potassium water glass
rutile
TiO2
45
magnetite Fe3O4 10
SiO2
quartz
20
CaCO3 10
calcite
Fe - Mn
15
potassium water glass
fluorspar CaF2 45
CaCO3 40
calcite
SiO2 10
quartz
5
Fe - Mn
potassium water glass
slag solidification
time: medium
slag solidification
time: short
droplet transfer :
medium- sized to
fine droplets
toughness value:
droplet transfer :
medium- sized to
big droplets
toughness value:
good
very good
normal
© ISF 2002
br-er2-07.cdr
Characteristic Features of
Different Coating Types
Figure 2.7
The melting characteristics of the different coverings and the slag properties result in further
properties; these determine the areas of application, Figure 2.8.
coating type
symbol
cellulosic type
C
acid type
A
rutile type
R
basic type
B
~/+
~/+
~/+
=/+
very good
moderate
good
good
PG,(PA,PB,
PC,PE,PF)
PA,PB,PC,
PE,PF,PG
PA,PB,PC,
PE,PF,(PG)
PA,PB,PC,
PE,PF,PG
low
high
low
very low
moderate
good
good
moderate
slag
detachability
good
very good
very good
moderate
characteristic
features
spatter,
little slag,
intensive fume
formation
high burn-out
losses
universal
application
low burn-out
losses
hygroscopic
predrying!!
current type/polarity
gap bridging
ability
welding positions
sensitivity of
cold cracking
weld appearance
br-er2-08.cdr
© ISF 2002
Characteristics of
Different Coating Types
Figure 2.8
2005
2. Manual Metal Arc Welding
The
dependence
22
on
temperature of the slag’s
determines the reignition
behaviour of a stick electrode,
Figure
2.9.
ing slag
-contain
le
ti
u
r
high
r
nducto
semico
reignition
threshold
h ac
co igh id s
n d - te l a
uc mp g
to e r
r at
ur
e
hig bas
i
c
hs
co tem lag
nd pe
uc rat
to ur
r
e
conductivity
conductivity
electrical
The
electrical conductivity for a
rutile stick electrode lies,
also at room temperature,
temperature
above the threshold value
which
is
© ISF 2002
br-er2-09.cdr
necessary for
Conductivity of Slags
reignition. Therefore, rutile
electrodes are given pref-
Figure 2.9
erence in the production of
tack welds where reignition occurs frequently.
DIN EN 499 - E 46 3 1Ni B 5 4 H5
3
hydrogen content < 5 cm /100 g welding deposit
butt weld: gravity position
fillet weld: gravity position
suitable for direct and alternating current
recovery between 125% and 160%
basic thick-coated electrode
chemical composition 1,4% Mn and approx. 1% Ni
o
minimum impact 47 J in -30 C
2
minimum weld metal deposit yield strength: 460 N/mm
distinguishing letter for manual electrode stick welding
The complete designation
for filler materials, following European Standardisation, includes details–
partly as encoded abbre-
The mandatory part of the standard designation is: EN 499 - E 46 3 1Ni B
viation – which are rele-
© ISF 2002
br-er2-10.cdr
vant for welding, Figure
2.10.
The
Designation Example
for Stick Electrodes
identification
letter for the welding proc-
Figure 2.10
ess is first:
E
-
manual electrode welding
G
-
gas metal arc welding
T
-
flux cored arc welding
W
- tungsten inert gas welding
S
-
submerged arc welding
2005
2. Manual Metal Arc Welding
23
The identification numbers give information about yield point, tensile strength and elongation
of the weld metal where the tenfold of the identification number is the minimum yield point
in N/mm², Figure 2.11.
key number
minimum yield strength
N/mm2
tensile strength
N/mm2
minimum elongation*)
%
35
355
440-570
22
38
380
470-600
20
42
420
500-640
20
46
460
530-680
20
50
500
560-720
18
*) L0 = 5 D0
br-er2-11.cdr
© ISF 2002
Characteristic Key Numbers of Yield Strength,
Tensile Strength and Elongation
Figure 2.11
The identification figures for the minimum impact energy value of 47 J – a parameter for the
weld metal toughness – are shown in Figure 2.12.
characteristic figure
Z
A
0
2
3
4
5
6
7
8
0
minimum impact energy 47 J [ C]
no demands
+20
0
-20
-30
-40
-50
-60
-70
-80
The minimum value of the impact energy allocated to the characteristic
figures is the average value of three ISO-V-Specimen, the lowest
value of whitch amounts to 32 Joule.
br-er2-12.cdr
Characteristic Key Numbers
for Impact Energy
Figure 2.12
2005
2. Manual Metal Arc Welding
24
The chemical composition
alloy symbol
of the weld metal is shown
by the alloy symbol, Figure
The properties of a stick
electrode are characterised
by the covering thickness
Ni
-
0,3 - 0,6
0,3 - 0,6
0,3 - 0,6
0,6 - 1.2
1,8 - 2,6
2,6 - 3,8
0,6 - 1,2
0,6 - 1,2
£ 2,0
Mo
MnMo
1 Ni
2 Ni
3 Ni
Mn 1 Ni
1 Ni Mo
1,4
>1,4 - 2,0
1,4
1,4
1,4
>1,4 - 2,0
1,4
Z
other specified compositions
*) companion elements: Mo 0,2; Ni 0,5; Cr 0,2; V 0,08; Nb 0,05; Cu 0,3; Al 2,0
(applies only to self-shielded flux-cored electrodes).
single values are maxima
and the covering type. Both
details are determined by
br-er2-13.cdr
the identification letter for
electrode
Mo
_
Mn
without
2.13.
the
chemical composition*)
%
© ISF 2002
Alloy Symbols for Weld Metals
Minimum Yield Strength up to 500 N/mm2
covering,
Figure 2.13
Figure 2.14.
Figure 2.15 explains the additional identificakey letter
tion figure for electrode recovery and applica-
type of coating
ble type of current. The subsequent identifiA
acid coating
cation figure determines the application possi-
B
basic coating
bilities for different welding positions:
C
cellulose coating
R
rutile coated
(medium thick)
RR
rutile coated (thick)
RA
rutile acid coating
RB
rutile basic coating
RC
rutile cellulose coating
br-er2-14.cdr
1-
all positions
2-
all positions, except vertical down
postion
3-
© ISF 2002
flat position butt weld, flat position fillet
weld, horizontal-, vertical up position
4-
flat position butt and fillet weld
5-
as 3; and recommended for vertical
down position
Key Letters for
Electrode Coatings
Figure 2.14
2005
2. Manual Metal Arc Welding
25
The last detail of the Euro-
additional
characteristic number
deposition efficiency
%
current type*)
1
2
<105
<105
alternating and direct current
direct current
pean Standard designation
3
4
>105
>105
125
125
alternating and direct current
direct current
5
6
>125
>125
160
160
alternating and direct current
direct current
7
8
>160
>160
alternating and direct current
direct current
*) To prove the suitability for direct current,
the tests have to be run with a no-load voltage of max. 65 V.
determines the maximum
hydrogen content of the
weld metal in cm³ per 100
g weld metal.
Welding current amperage and core wire diameter of the stick electrode
are
© ISF 2002
br-er2-15.cdr
determined
by
the
thickness of the workpiece
Additional Characteristic Numbers
for Deposition Efficiency and Current Type
to be welded. Fixed stick
Figure 2.15
electrode lengths are assigned to each diameter,
Figure 2.16.
diameter
d
mm
l
length
2,0
2,5
250/300
350
3,25
4,0
350/450 350/450
5,0
6,0
450
450
mm
current
I
A
rule-of -thumb min.
for current[A] max.
Figure
2.17
shows
the
process principle of manual metal arc welding.
40-80
50-100
20 x d
40 x d
90-150 120-200 180-270 220-360
30 x d
50 x d
35 x d
60 x d
Polarity and type of current
depend
on
the
applied
electrode types. All known
power sources with a de-
br-er2-16.cdr
© ISF 2002
Size and Welding Current
of Stick Electrodes
scending
characteristic
curve can be used.
Figure 2.16
Since in manual metal arc welding the arc length cannot always be kept constant, a steeply
descending power source is used. Different arc lengths lead therefore to just minimally altered weld current intensities, Figure 2.18. Penetration remains basically unaltered.
2005
2. Manual Metal Arc Welding
26
Simple welding transformers are used for a.c. welding. For d.c. welding mainly converters,
rectifiers and series regulator transistorised power sources (inverters) are applied. Converters are specifically suitable
electrode holder
for site welding and are
mains-independent
stick electrode
- (+)
when
an internal combustion engine is used. The advan-
power source
= or ~
tages of inverters are their
+ (-)
small size and low weight,
arc
however, a more complicated electronic design is
necessary, Figure 2.19.
work piece
© ISF 2002
br-er2-17.cdr
Principle Set-up of MMAW Process
Figure 2.17
arc welding
converter
power source
characteristic
A2
U
A1
transformer
A2
2
rectifier
1
A1
21
characteristic
of the arc
br-er2-18e.cdr
inverter
type
I
© ISF 2002
br-er2-19.cdr
Operating Point at
Different Arc Lengths
Figure 2.18
© ISF 2002
Power Sources
for MMAW
Figure 2.19
2005
2. Manual Metal Arc Welding
27
45
cy
7
RA73
V
eff
ici
en
kg/h
sit
ion
6
30
B53
de
cy
0%
ie
n
22
ef
fic
io
n
po
sit
b
3
oa
ed
t
-c
ick
a
th
2
oa
d
te
c
inth
1
B15
25
de
RR12
RA12
X
4
0%
35
5
16
burn-off rate at 100% duty cycle
medium weld voltage
RR73
= RR12 =
=
=
=
20
c
po
40
100
200
300
3,25
4
5
6
A
X = RR73 -
0
400
medium weld current
br-er2-20.cdr
© ISF 2002
0
100
200
300
welding amperage
5 mm
5 mm
400 A 500
a = A- and R- coated electrodes, recovery 105%
b = basic-coated electrodes, recovery <125%
c = high-performance electrodes
br-er2-21.cdr
Medium Weld Current and
Voltages for Stick Electrodes
© ISF 2002
Burn-Off Rate
of Stick Electrodes
Figure 2.20
Figure 2.21
Figure 2.20 shows the standard welding paconstructional steels
shipbuilding steels
high-strength constructional steels
boiler and pressure vessel steels
austenitic steels
creep resistant steels
austenitic-ferritic steels (duplex)
scale resistant steels
wear resistant steels
hydrogen resistant steels
high-speed steels
cast steels
combinations of materials (ferritic/ austenitic)
steel:
cast iron:
cast iron with lamella graphite
cast iron with globular graphite
nickel:
pure nickel
Ni-Cu-alloys
Ni-Cr-Fe-alloys
Ni-Cr-Mo-alloys
copper:
Figure 2.22
besides the used current intensity, dependent
on the so-called “electrode recovery”, Figure
2.21. This describes the mass of deposited
up to 220% with metal covering components
in high-efficiency electrodes.
A survey of the material spectrum which is
suitable for manual metal arc welding is given
© ISF 2002
Suitable Materials for
Manual Metal Arc Welding
The rate of deposition of a stick electrode is,
cent. Electrode recovery can reach values of
pure aluminium
AlMg-alloys
AlSi -alloys
br-er2-22.cdr
and stick electrode types.
weld metal / mass of core wire ratio in per-
electrical grade copper (ETP copper)
bronzes (CuSn, CuAl)
gunmetal (CuSnZnPb)
Cu-Ni-alloys
aluminium:
rameters of different stick electrode diameters
in Figure 2.22. The survey comprises almost
all metals known for technical applications and
2005
2. Manual Metal Arc Welding
28
also explains the wide application
range
of
the
method.
In d.c. welding, the concentration of the magnetic
arc-blow
producing
forces can lead to the deflection of the arc from
power supply point on the
side of the workpiece, Fig-
br-er2-23e.cdr
ure
Arc Blow Effect through Concentration
of Magnetic Fields
2.23.
The
material
transfer also does not oc-
Figure 2.23
cur at the intended point.
Arc deflection may also occur at magnetizable mass accumulations although, in that
case, in the direction of the respective mass,
Figure 2.24.
inwards at the edges
Figures 2.25 and 2.26 show how by various
measures the magnetic arc blow can be
close to current-connection
compensated or even avoided.
close to large workpiece masses
The positioning of the electrodes in opposite
direction brings about the correct placement of
the weld metal. Numerous strong tacks close
in gaps towards the weld
the magnetic flux inside the workpiece. By additional, opposite placed steel masses as well
as by skilful transfer of the power supply point
br-er2-24.cdr
the various reasons for arc deflection can be
Arc Blow Effect
on Steel Parts
eliminated. The fast magnetic reversal when
a.c. is used minimises the influence of the
© ISF 2002
Figure 2.24
magnetic arc blow.
2005
2. Manual Metal Arc Welding
29
tilting of electrode
through additional blocks of steel
great number of tacks
through relocating the currentconnection (rarely used)
the welding
sequence
through using
a welding transformer
alternating current (not
applicable for all
types of electrodes)
tacks
br-er2-25.cdr
© ISF 2002
br-er2-26.cdr
© ISF 2002
Remedy Against
Arc Blow Effect 2
Remedy Against
Arc Blow Effect 1
Figure 2.25
Figure 2.26
Depending on the electrode covering, the water absorption of a stick electrode may vary
strongly during storage, Figure 2.27. The ab-
Water content of the coating
4,0
sorbed humidity leads during subsequent
20°C / 70% RF
%
welding frequently to an increased hydrogen
3,0
content in the weld metal and, thus, increases
cold cracking susceptibility.
2,0
1,0
0
0,1
1
10
Days
100
Time of storage
br-er2-27.cdr
© ISF 2002
Water Absorption of Different
Basic-Coated Electrodes
Figure 2.27
2005
2. Manual Metal Arc Welding
30
Stick electrodes, particularly those with a basic, rutile or cellulosic cover have to be baked
before welding to keep the water content of the cover during welding below the permissible
values in order to avoid
Water content of the coating
1,0
%
0,9
hydrogen-induced
0,8
Figure 2.28. The baking
basic-coated electrode
(having been stored at
18 - 20°C for one year)
0,7
temperature and time are
0,74
0,6
cracks,
specified by the manufac-
0,5
turer. Baking is carried out
0,4
0,39
0,3
in special ovens; in damp
0,28
AWS A5.5
0,2
0,1
working
storage and baking
40
50
and
only just before welding are
0
30
conditions
60
70
%
80
electrodes taken out from
© ISF 2002
br-er2-28.cdr
Water Content of the Coating
after Storage and Baking
electrically heated receptacles.
Figure 2.28
2005