Welding Technology (1)

ISF Welding Institute RWTH Aachen University

Lecture Notes

Welding Technology 1 Welding and Cutting Technologies

Prof. Dr.Ing. U. Dilthey

Table of Contents Chapter Subject Page

0. Introduction 1

1. Gas Welding 3

2. Manual Metal Arc Welding 13

3. Submerged Arc Welding 26

4. TIG Welding and

Plasma Arc Welding 43

5. Gas Shielded Metal Arc Welding 56

6. Narrow Gap Welding,

Electrogas - and

Electroslag Welding 73

7. Pressure Welding 85

8. Resistance Spot Welding,

Resistance Projection Welding

and Resistance Seam Welding 101 9. Electron Beam Welding 115

10. Laser Beam Welding 129

11. Surfacing and Shape Welding 146

12. Thermal Cutting 160

13. Special Processes 175

14. Mechanisation and Welding Fixtures 187

15. Welding Robots 200

16. Sensors 208

Literature 218

2003

0.

Introduction

0. Introduction 1

Welding fabrication processes are classified in accordance with the German Stan-

dards DIN 8580 and DIN 8595 in main group 4 Joining, group 4.6 Joining by

Welding, Figure 0.1.

Welding: permanent, positive joining

method. The course of the strain

lines is almost ideal. Welded joints

show therefore higher strength prop-

erties than the joint types depicted

in Figure 0.2. This is of advantage,

especially in the case of dynamic

stress, as the notch effects are

lower.

4.6.2Fusion welding

1Casting

5Coating Changing of

materialsproperties

62Forming

3Cutting

4Joining

4.4Joining by

casting

4.1Joining by

composition

4.7Joining bysoldering

4.6Joining bywelding

4.3Joining bypressing

4.2Joiningby filling

4.8Joining byadhesivebonding

4.6.1Pressure welding

4.5Joining by

forming

Production Processes acc. to DIN 8580

br-er0-01.cdr

Figure 0.1

ISF 2002

Connection Types

Screwing

Riveting

Adhesivebonding

Soldering

Welding

br-er0-02.cdr

Figure 0.2

0. Introduction 2

Figures 0.3 and 0.4 show the further subdivision of the different welding methods

according to DIN 1910.

Production processes

4Joining

4.6Joining by welding

4.6.2Fusion welding


4.6.1.1Welding

bysolid bodies

Heated toolwelding

4.6.1.2Weldingby liquids

Flow welding

4.6.1.3Weldingby gas

Gas pressure-/roll-/ forge-/

diffusionwelding

4.6.1.4Welding byelectrical

gas discharge

Arc pressurewelding

4.6.1.6Welding

by motion

Cold pressure-/shock-/ friction-/

ultrasonicwelding

4.6.1.7Welding by

electric current

Resistancepressurewelding

Joining by Welding acc. to DIN 1910Pressure Welding

ISF 2002br-er0-03.cdr

Figure 0.3

Production processes

4Joining

4.6Joining by welding

4.6.2Fusion welding


4.6.2.2Welding

by liquids

4.6.2.3Weldingby gas

4.6.2.5Weldingby beam

4.6.2.4Welding byelectrical

gas discharge

4.6.2.7Welding by

electric current

Cast welding Gas welding Arc welding Beam welding Resistancewelding

Joining by Welding acc. to DIN 1910Fusion Welding

br-er0-04.cdr

Figure 0.4

2003

1.

Gas Welding

1. Gas Welding 3

Although the oxy-acetylene process

has been introduced long time ago it

is still applied for its flexibility and mo-

bility. Equipment for oxyacetylene

welding consists of just a few ele-

ments, the energy necessary for weld-

ing can be transported in cylinders,

Figure 1.1.

Process energy is obtained from the

exothermal chemical reaction between

oxygen and a combustible gas, Figure

1.2. Suitable combustible gases are

C2H2, lighting gas, H2, C3H8 and natu-

ral gas; here C3H8 has the highest

calorific value. The highest flame in-

tensity from point of view of calorific

value and flame propagation speed is,

however, obtained with C2H2.

acetylene hose

oxygen cylinder with pressure reducer

welding rod

oxygen hose

welding nozzle

welding torch

acetylene cylinder with pressure reducer

welding flame

workpiece

1

9

7

2

6

45

3

8

19

7

2

64

5

3

8

br-er1-01.cdr

Figure 1.1

ISF 2002

27702850

3200

0

200

400

600645

0

ignition temperature [ C]O

oxyg

en

air

0.51.01.52.02.5

0

density in normal state [kg/m ]3

prop

ane

2.0

0.9ox

ygen

1.431.17

air

1.29

300335

510490

645

flame temperature with O2 flame efficiency with O 2

flame velocity with O 2

KW/cm2 cm/s

43

10.3

8.5

1350

370

330

br-er1-02.cdr

natu

ral g

as

prop

ane

C k

Figure 1.2

1. Gas Welding 4

C2H2 is produced in acetylene gas

generators by the exothermal trans-

formation of calcium carbide with wa-

ter, Figure 1.3. Carbide is obtained

from the reaction of lime and carbon

in the arc furnace.

C2H2 tends to decompose already at

a pressure of 0.2 MPa. Nonetheless,

commercial quantities can be stored

when C2H2 is dissolved in acetone

(1 l of acetone dissolves approx. 24 l

of C2H2 at 0.1 MPa), Figure 1.4.

Acetone disintegrates at a pressure of

more than 1.8 MPa, i.e., with a filling

pressure of 1.5 MPa the storage of 6m

of C2H2 is possible in a standard cylin-

der (40 l). For gas exchange (storage

and drawing of quantities up to 700 l/h)

a larger surface is necessary, therefore

the gas cylinders are filled with a po-

rous mass (diatomite). Gas consump-

tion during welding can be observed

from the weight reduction of the gas

cylinder.

ISF 2002

Acetylene Generator

loading funnel

material lock

gas exit

feed wheel

grille

sludge

to sludge pit

br-er1-03.cdr

ISF 2002

Storage of Acetylene

acetone acetylene

porous mass

acetylene cylinder

filling quantity :

acetone quantity :

acetylene quantity :

~13 l

6000 l

15 bar

up to 700 l/h

cylinder pressure :

br-er1-04.cdr

N

Figure 1.3

Figure 1.4

1. Gas Welding 5

Oxygen is pro-

duced by frac-

tional distillation

of liquid air and

stored in cylinders

with a filling pres-

sure of up to 20

MPa, Figure 1.5.

For higher oxygen

consumption, stor-

age in a liquid state

and cold gasifica-

tion is more profit-

able.

The standard cylinder (40 l) contains,

at a filling pressure of 15 MPa, 6m of

O2 (pressureless state), Figure 1.6.

Moreover, cylinders with contents of

10 or 20 l (15 MPa) as well as 50 l at

20 MPa are common. Gas consump-

tion can be calculated from the pres-

sure difference by means of the gen-

eral gas equation.

ISF 2002

Principle of Oxygen Extraction

air

cooling

nitrogen

gaseous

cylinder

bundle

oxygen

oxygenliquid

air

nitrogenvaporized

liquid

tank car

pipeline

cleaning compressor separationbr-er1-05.cdr

supply

Figure 1.5

br-er1-06.cdr

Storage of Oxygen

50 l oxygen cylinder

protective cap

cylinder valve

take-off connection

gaseous

p = cylinder pressure : 200 bar

V = volume of cylinder : 50 lQ = volume of oxygen : 10 000 l

content control

Q = p V

foot ring

user

gaseous

still

liquid

vaporizermanometer

safety valve

fillingconnection

liquid

N

Figure 1.6

1. Gas Welding 6

In order to prevent mistakes, the gas cylinders are colour-coded. Figure 1.7 shows a

survey of the present colour code and the future colour code which is in accordance

with DIN EN 1089.

The cylinder valves are also of different designs. Oxygen cylinder connections

show a right-hand

thread union nut.

Acetylene cylinder

valves are equipped

with screw clamp

retentions. Cylinder

valves for other

combustible gases

have a left-hand

thread-connection

with a circumferen-

tial groove.

Pressure regulators reduce the cylinder pressure to the requested working pres-

sure, Figures 1.8 and 1.9.

ISF 2002

Gas Cylinder-Identificationaccording to DIN EN 1089

br-er1-07.cdr

actual condition DIN EN 1089

oxygen techn.

white

blue (grey)

blue

acetylene

brownyellow

nitrogen

darkgreen

darkgreen

black

argon

dark green

grey

grey

actual condition DIN EN 1089

grey

grey

brown

helium

carbon-dioxide

grey grey

grey

grey

argon-carbon-dioxide mixture

vivid green

hydrogen

red

ISF 2002

Single Pressure Reducing Valve during Gas Discharge Operation

br-er1-08.cdr

cylinder pressure working pressure

Figure 1.7

Figure 1.8

1. Gas Welding 7

At a low cylinder pressure (e.g. acetylene cylinder) and low pressure fluctuations,

single-stage regulators

are applied; at higher cylinder pressures normally two-stage pressure regulators are

used.

The requested

pressure is set by

the adjusting

screw. If the pres-

sure increases on

the low pressure

side, the throttle

valve closes the

increased pressure

onto the mem-

brane.

The injector-type

torch consists of a

body with valves

and welding cham-

ber with welding

nozzle, Figure 1.10.

By the selection of

suitable welding

chambers, the

flame intensity can

be adjusted for

welding different

plate thicknesses.

ISF 2002

Single Pressure Reducing Valve,Shut Down

br-er1-09.cdr

discharge pressure locking pressure

ISF 2002

Welding Torch

br-er1-10.cdr

welding torchinjector or blowpipe

coupling nut hose connectionfor oxygenA6x1/4" rightmixer tube mixer nozzle oxygen valve

injectorpressure nozzle

suction nozzle

fuel gas valvewelding nozzle

hose connectionfor fuel gas

A9 x R3/8 left

welding torch head torch body

Figure 1.9

Figure 1.10

1. Gas Welding 8

The special form of the mixing chamber guarantees highest possible safety against

flashback, Figure 1.11. The high outlet speed of the escaping O2 generates a nega-

tive pressure in the acetylene gas line, in consequence C2H2 is sucked and drawn-in.

C2H2 is therefore available with a very low pressure of 0.02 up to 0.05 MPa -

compared with O2 (0.2 up to 0.3 MPa).

A neutral flame adjustment allows the differentiation of three zones of a chemical

reaction, Figure 1.12:

0. dark core: escaping gas mixture

1. brightly shining centre cone: acetylene decomposition

C2H2 -> 2C+H2

2. welding zone: 1st stage of combustion

2C + H2 + O2 (cylinder) -> 2CO + H2

3. outer flame: 2nd stage of combustion

4CO + 2H2 + 3O2 (air) ->

4CO2 + 2H2O

complete reaction: 2C2H2 + 5O2 ->

4CO2 + 2H2O

ISF 2002

Injector-Area of Torch

br-er1-11.cdr

acetylene

oxygen

acetylene

welding torch head injector nozzle pressure nozzle

coupling nut torch body

Figure 1.11

1. Gas Welding 9

By changing the mixture ratio of the

volumes O2:C2H2 the weld pool can

greatly be influenced, Figure 1.13. At a

neutral flame adjustment the mixture

ratio is O2:C2H2 = 1:1. By reason of the

higher flame temperature, an excess

oxygen flame might allow faster weld-

ing of steel, however, there is the risk

of oxidizing (flame cutting).

Area of application: brass

The excess acetylene causes the

carburising of steel materials.

Area of application: cast iron


welding flamecombustion

welding nozzlewelding zone

centre cone outer flame

3200C

2500C

1800C

1100C

400C

2 - 5

Figure 1.12

ISF 2002

excess ofacetylene

normal(neutral)

excess of oxygen

welding flameratio of mixture

effects in welding of steel

sparking foaming spattering

reducing oxidizingconsequences:

carburizinghardening

Effects of the Welding Flame Depending on the Ratio of Mixture

br-er1-13.cdr

Figure 1.13

1. Gas Welding 10

By changing the gas mixture outlet

speed the flame can be adjusted to

the heat requirements of the welding

job, for example when welding plates

(thickness: 2 to 4 mm) with the weld-

ing chamber size 3: 2 to 4 mm, Fig-

ure 1.14. The gas mixture outlet

speed is 100 to 130 m/s when using a

medium or normal flame, applied to

at, for example, a 3 mm plate. Using a

soft flame, the gas outlet speed is

lower (80 to 100 m/s) for the 2 mm

plate, with a hard flame it is higher

(130 to 160 m/s) for the 4 mm plate.

Depending on the plate thickness are

the working methods leftward weld-

ing and rightward welding applied,

Figure 1.15. A decisive factor for the

designation of the working method is

the sequence of flame and welding rod

as well as the manipulation of flame

and welding rod. The welding direction

itself is of no importance. In leftward

welding the flame is pointed at the

open gap and wets the molten pool;

the heat input to the molten pool can

be well controlled by a slight move-

ment of the torch (s = 3 mm).

ISF 2002

discharging velocity and weld heat-input rate: low

nozzle size: for plate thickness of 2-4 mmbalanced (neutral) flame

welding flame

2

soft flame

moderate flame

hard flame

discharging velocity and weld heat-input rate: middle

discharging velocity and weld head-input rate: high

3

4

br-er1-14.cdr

Effects of the Welding Flame Depending on the Discharge Velocity

ISF 2002

welding-rod flame welding bead

weld-rod flame

Rightward welding ist applied to a plate thickness of 3mmupwards. The wire circles, the torch remains calm.Advantages: - the molten pool and the weld keyhole are easy to observe- good root fusion- the bath and the melting weld-rod are permanently protected from the air- narrow welding seam- low gas consumption

Leftward welding is applied to a plate thickness of up to 3 mm.The weld-rod dips into the molten pool from time to time,but remains calm otherwise. The torch swings a little.

Advantages:easy to handle on thin plates

Flame Welding

br-er1-15e.cdr

Figure 1.14

Figure 1.15

1. Gas Welding 11

In rightward welding the flame is di-

rected onto the molten pool; a weld

keyhole is formed (s = 3 mm).

Flanged welds and plain butt welds

can be applied to a plate thickness of

approx. 1.5 mm without filler material,

but this does not apply to any other

plate thickness and weld shape, Fig-

ure 1.16.

By the specific heat input of the differ-

ent welding methods all welding posi-

tions can be carried out using the

oxyacetylene welding method, Figures

1.17 and 1.18

When working in tanks and confined

spaces, the welder (and all other per-

sons present!) have to be protected

against the welding heat, the gases

produced during welding and lack of

oxygen ((1.5 % (vol.) O2 per 2 % (vol.)

C2H2 are taken out from the ambient

atmosphere)), Figure 1.19. The addi-

tion of pure oxygen is unsuitable (ex-

plosion hazard!).

ISF 2002

gappreparations denotation

sym-bol

plate thicknessrange s [mm]from to

1,5

1,0

1,0 4,0

3,0 12,0

1,0 8,0

1,0 8,0

1,0 8,0

flange weld

plain buttweld

V - weld

corner weld

lap seam

fillet weld

1 - 2

1 - 2

Gap Shapes for Gas Weldings+

1~ ~ r =

s

br-er1-16.cdr

ISF 2002

PA

PB

PFPG

PC

PE

PD

butt-welded seams ingravity position

gravity fillet welds

horizontal fillet welds

vertical fillet and butt welds

vertical-upwelding positionvertical-down position

horizontal on vertical wall

overhead position

horizontal overhead position

Welding Positions I

br-er1-17.cdr

fs

Figure 1.16

Figure 1.17

1. Gas Welding 12

A special type of autogene method is

flame-straightening, where specific lo-

cally applied flame heating allows for

shape correction of workpieces, Figure

1.20. Much experience is needed to

carry out flame straightening processes.

The basic principle of flame straightening

depends on locally applied heating in

connection with prevention of expansion.

This process causes the appearance of a

heated zone. During cooling, shrinking

forces are generated in the heated zone

and lead to the desired shape correction.

ISF 2002

5. after welding: Removing the equipment from the tank

4. illumination and electric machines: max 42volt

3. second person for safety reasons

2. extraction unit, ventilation

1. requirement for a permission to enter

protective measures / safety precautions

Hazards through gas, fumes, explosive mixtures,electric current

Safety in welding and cutting inside oftanks and narrow rooms

br-er1-19e.cdr

Gas Welding in Tanks andNarrow Rooms

ISF 2002

welded parts

first warm up bothlateral plates, then belt

butt weld3 to 5 heat sourcesclose to the weld-seam

double fillet weld1,3 or 5 heat sources

Flame straightening

Flame Straightening

br-er1-20.cdr


PA

PB

PC

PD

PE

PG

PF

Welding Positions II

Figure 1.18

Figure 1.19 Figure 1.20

2003

2.

Manual Metal Arc Welding


Figure 2.1 describes the burn-off of a

covered stick electrode. The stick

electrode consists of a core wire with

a mineral covering. The welding arc

between the electrode and the work-

piece melts core wire and covering.

Droplets of the liquefied core wire mix

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 from the detrimental influ-

ences of the surrounding atmosphere.

Covered stick elec-

trodes have re-

placed the initially

applied metal arc

and carbon arc

electrodes. The

covering has taken

on the functions

which are described

in Figure 2.2.

br-er2-01.cdr ISF 2002c

Weld Point

Figure 2.1

ISF 2002

1. Conductivity of the arc plasma is improved by

2. Constitution of slag, to

3. Constitution of gas shielding atmosphere of

4. Desoxidation and alloying of the weld metal

5. Additional input of metallic particles

a) ease of ignitionb) increase of arc stability

a) influence the transferred metal dropletb) shield the droplet and the weld pool against atmospherec) form weld bead

a) organic componentsb) carbides

Task of Electrode Coating

br-er2-02.cdr

Figure 2.2


The covering of the stick electrode consists of a multitude of components which are

mainly mineral, Figure 2.3.

For the stick electrode manufacturing mixed ground and screened covering mate-

rials are used as protection for the core wire which has been drawn to finished di-

ameter and subsequently cut to size, Figure 2.4.

ISF 2002

Influence of the Coating Constituents on Welding Characteristics

br-er2-03.cdr

coating raw material effect on the welding characteristics

quartz - SiO2 to raise current-carrying capacity

rutile -TiO2to increase slag viscosity,good re-striking

magnetite - Fe O3 4 to refine transfer of droplets through the arc

calcareous spar -CaCO3to reduce arc voltage, shielding gas emitter and slag formation

fluorspar - CaF2to increase slag viscosity of basic electrodes,decrease ionization

calcareous- fluorspar -K O Al O 6SiO2 2 3 2

easy to ionize, to improve arc stability

ferro-manganese / ferro-silicon deoxidant

cellulose shielding gas emitter

kaolin -Al O 2SiO 2H O2 3 2 2

lubricant

potassium water glassK SiO / Na SiO2 3 2 3

bonding agent

Figure 2.3

1 2 3

raw wirestorage wire drawing machine

and cutting system

inspection

to the pressing

plant

electrodecompound

raw material storagefor flux production

jawcrusher

magneticseparation

cone crusherfor pulverisation

sieving

to further treatment like milling, sieving, cleaning and weighing

sieving system

weighingand

mixing

inspection

wet mixer

descaling

inspection

example of a three-stage wire drawing machinedrawing plate

6 mm 5,5 mm 3,25 mm 4 mm

ISF 2002

Stick Electrode Fabrication 1

br-er2-04.cdr

Figure 2.4


The core wires are coated with the

covering material which contains bind-

ing agents in electrode extrusion

presses. The defect-free electrodes

then pass through a drying oven and

are, after a final inspection, automati-

cally packed, Figure 2.5.

Figure 2.6 shows how the moist ex-

truded covering is deposited onto the

core wire inside an electrode extrusion

press.

Stick Electrode Fabrication 2

ISF 2002br-er10-33e.cdr

core wiremaga-

zine

electrodecompound

inspection

inspection inspection

inspectioninspection

the pressing plant

drying stove

TODELIVERY

packinginspection

electrode-press

compound

nozzleconvey-ingbelt

wiremagazine

wirefeeder

pressinghead

Figure 2.5

core rodcoatingpressing nozzlepressing cylinderpressing cylinder

pressing mass core rod guide

Production of Stick Electrodes

br-er2-06.cdr

Figure 2.6


Stick electrodes are, according to their covering compositions, categorized into

four different types, Figure 2.7. with concern to burn-off characteristics and achiev-

able weld metal toughness these types show fundamental differences.

The melting characteristics of the different coverings and the slag properties result in

further properties; these determine the areas of application, Figure 2.8.

ISF 2002

Characteristic Features of Different Coating Types

br-er2-07.cdr

cellulosic type acid type rutile type basic typ

celluloserutilequartzFe - Mnpotassium water glass

40202515

magnetitequartzcalciteFe - Mnpotassium water glass

50201020

rutilemagnetitequartzcalciteFe - Mnpotassium water glass

TiO2SiO2

Fe OSiOCaCO

3 42

3

TiOFe OSiOCaCO

23 4

23

fluorsparcalcitequartzFe - Mnpotassium water glass

4510201015

4540105

CaFCaCOSiO

23

2

almostno slag

slag solidification time: long

slag solidificationtime: medium

slag solidification time: short

droplet transfer :

toughness value:

medium- sizeddroplets

good normal good very good

fine dropletsto sprinkle

medium- sized to fine droplets

medium- sized to big droplets

droplet transfer : droplet transfer : droplet transfer :

toughness value: toughness value: toughness value:

Figure 2.7

ISF 2002

Characteristics of Different Coating Types

br-er2-08.cdr

coating typesymbol

gap bridging ability

current type/polarity

welding positions

sensitivity ofcold cracking

weld appearance

slag detachability

characteristic features

cellulosic typeC

acid typeA

rutile typeR

basic typeB

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

good very good very good moderate

spatter,little slag,

intensive fumeformation

high burn-outlosses

universalapplication

low burn-out losses

hygroscopic predrying!!

~ / + ~ / +~ / + = / +

Figure 2.8


The dependence on temperature of the slags electrical conductivity determines

the reignition behaviour of a stick electrode, Figure 2.9. The electrical conductivity for

a rutile stick elec-

trode lies, also at

room temperature,

above the thresh-

old value which is

necessary for reig-

nition. Therefore,

rutile electrodes

are given prefer-

ence in the

production of tack

welds where reig-

nition occurs fre-

quently.

The complete des-

ignation for filler

materials, following

European Stan-

dardisation, in-

cludes details

partly as encoded

abbreviation

which are relevant

for welding, Figure

2.10. The identifica-

tion letter for the

welding process 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

ISF 2002

Conductivity of Slags

br-er2-09.cdr

cond

uctiv

ity

temperature

reignition threshold

high rutile-conta

ining slag

semiconductor

acid

slag

high-

tempe

ratur

e

cond

uctor ba

sic sl

ag

high

-tem

pera

ture

cond

ucto

r

Figure 2.9

ISF 2002

Designation Example for Stick Electrodes

br-er2-10.cdr

The mandatory part of the standard designation is: EN 499 - E 46 3 1Ni B

hydrogen content < 5 cm /100 g welding depositbutt weld: gravity positionfillet weld: gravity positionsuitable for direct and alternating currentrecovery between 125% and 160%basic thick-coated electrodechemical composition 1,4% Mn and approx. 1% Niminimum impact 47 J in -30 Cminimum weld metal deposit yield strength: 460 N/mmdistinguishing letter for manual electrode stick welding

3

o

2

DIN EN 499 - E 46 3 1Ni B 5 4 H5

Figure 2.10


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/mm, Figure 2.11.

The identification figures for the minimum impact energy value of 47 J a parame-

ter for the weld metal toughness are shown in Figure 2.12.

ISF 2002

Characteristic Key Numbers of Yield Strength, Tensile Strength and Elongation

br-er2-11.cdr

key number minimum yield strengthN/mm2

tensile strengthN/mm2

minimum elongation*)%

35

38

42

46

50

355

380

420

460

500

440-570

470-600

500-640

530-680

560-720

22

20

20

20

18

*) L = 5 D0 0

Characteristic Key Numbers for Impact Energy

br-er2-12.cdr

characteristic figure minimum impact energy 47 J [ C]0

no demands +20 0 -20 -30 -40 -50 -60 -70 -80

ZA02345678

The minimum value of the impact energy allocated to the characteristicfigures is the average value of three ISO-V-Specimen, the lowest value of whitch amounts to 32 Joule.

Figure 2.11

Figure 2.12


The chemical

composition of

the weld metal is

shown by the alloy

symbol, Figure

2.13.

The properties of a stick electrode are

characterised by the covering thick-

ness and the covering type. Both de-

tails are determined by the identifica-

tion letter for the electrode covering,

Figure 2.14.

ISF 2002

Alloy Symbols for Weld MetalsMinimum Yield Strength up to 500 N/mm2

br-er2-13.cdr


key letter type of coating

A

B

acid coating

basic coating

C cellulose coating

R rutile coated (medium thick)

RR rutile coated (thick)

RA rutile acid coating

RB rutile basic coating

RC rutile cellulose coating

Figure 2.13

Figure 2.14


Figure 2.15 ex-

plains the additional

identification figure

for electrode recov-

ery and applicable

type of current.

The subsequent

identification figure

determines the ap-

plication possibili-

ties for different

welding positions:

1- all positions

2- all positions, except vertical down position

3- 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

The last detail of the European Standard designation determines the maximum hy-

drogen content of the weld metal in cm per 100 g weld metal.

Welding current

amperage and

core wire diame-

ter of the stick

electrode are de-

termined by the

thickness of the

workpiece to be

welded. Fixed stick

electrode lengths

are assigned to

each diameter,

Figure 2.16.

ISF 2002

Additional Characteristic Numbers for Deposition Efficiency and Current Type

br-er2-15.cdr

Figure 2.15

ISF 2002

Size and Welding Currentof Stick Electrodes

br-er2-16.cdr

Figure 2.16


Figure 2.17 shows

the process princi-

ple of manual

metal arc welding.

Polarity and type of

current depend on

the applied elec-

trode types. All

known power

sources with a de-

scending

characteristic curve

can be used.

Since in manual metal arc welding the

arc length cannot always be kept con-

stant, 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 unal-

tered.


U

1

2

2 1 I

A2 A1

A2

A1

characteristic of the arc

power source characteristic

ISF 2002

Principle Set-up of MMAW Process

br-er2-17.cdr

work piece

arc

stick electrode

electrode holder

power source= or ~

- (+)

+ (-)

Figure 2.17

Figure 2.18


Simple welding transformers are

used for a.c. welding. For d.c. welding

mainly converters, rectifiers and se-

ries regulator transistorised power

sources (inverters) are applied. Con-

verters are specifically suitable for

site welding and are mains-

independent when an internal com-

bustion engine is used. The advan-

tages of inverters are their small size

and low weight, however, a more

complicated electronic design is nec-

essary, Figure 2.19.

Figure 2.20 shows the standard weld-

ing parameters of different stick elec-

trode diameters and stick electrode

types.

The rate of deposition of a stick

electrode is, besides the used current

intensity, dependent on the so-called

electrode recovery, Figure 2.21. This

describes the mass of deposited

weld metal / mass of core wire ratio

in percent. Electrode recovery can

reach values of up to 220% with metal

covering components in high-efficiency

electrodes.


medium weld current

med

ium

wel

d vo

ltage

B15

B53

RA12RR12

RA73

RR73

100 200 300 400

6

3,2545

====

20

25

30

35

40

45

A

V


arc welding converter

transformer

rectifier

invertertype

Figure 2.19

Figure 2.20


A survey of the material spectrum which is suitable for manual metal arc welding is

given in Figure 2.22. The survey comprises almost all metals known for technical ap-

plications and 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,

Figure 2.23. The ma-

terial transfer also

does not occur at the

intended point.


c = high-performance electrodesb = basic-coated electrodes, recovery


Arc deflection may also occur at

magnetizable mass accumulations

although, in that case, in the direction

of the respective mass, Figure 2.24.

Figures 2.25 and 2.26 show how by

various measures the magnetic arc

blow can be compensated or even

avoided.

The positioning of the electrodes in

opposite direction brings about the

correct placement of the weld metal.

Numerous strong tacks close the

magnetic flux inside the workpiece. By

additional, opposite placed steel

masses as well as by skilful transfer


tilting of electrode

the weldingsequence

great number of tacks

tacks


through additional blocks of steel

through relocating the current-connection (rarely used)

through using a welding transformer alternating current (not applicable for all types of electrodes)


Arc Blow Effecton Steel Parts

inwards at the edges

close to current-connection

close to large workpiece masses

in gaps towards the weld

Figure 2.24

Figure 2.25 Figure 2.26


of the power supply point the various

reasons for arc deflection can be

eliminated. The fast magnetic reversal

when a.c. is used minimises the influ-

ence of the magnetic arc blow.

Depending on the electrode covering,

the water absorption of a stick elec-

trode may vary strongly during stor-

age, Figure 2.27. The absorbed hu-

midity leads during subsequent weld-

ing frequently to an increased hydro-

gen content in the weld metal and,

thus, increases cold cracking suscep-

tibility.

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 hydrogen-induced cracks, Figure 2.28. The

baking temperature

and time are speci-

fied by the manu-

facturer. Baking is

carried out in spe-

cial ovens; in damp

working conditions

and only just before

welding are elec-

trodes taken out

from electrically

heated receptacles.


Time of storage

Wat

er c

onte

nt o

f the

coa

ting

1 10 100Tage00

1,0

2,0

3,0

4,0

%

20C / 70% RF

ISF 2002

Water Content of the Coatingafter Storage and Baking

br-er2-28.cdr

basic-coated electrode(having been stored at18 - 20C for one year)

storage and baking

0,74

0,39

0,28AWS A5.5

Wat

er c

onte

nt o

f the

coa

ting

1,0

0,9

0,8

0,7

0,6

0,5

0,4

0,3

0,2

0,1

030 40 50 60 70 80%

%

Figure 2.27

Figure 2.28

2003

3.

Submerged Arc Welding


In submerged arc welding a mineral weld flux layer protects the welding point and

the freezing weld from the influence of the surrounding atmosphere, Figure 3.1. The

arc burns in a cavity filled with ionised gases and vapours where the droplets from

the continuously-

fed wire electrode

are transferred into

the weld pool. Un-

fused flux can be

extracted from be-

hind the welding

head and subse-

quently recycled.

Main components of a submerged arc welding unit are:

the wire electrode reel, the wire feed motor equipped with grooved wire feed rolls

which are suitable for the demanded wire diameters, a wire straigthener as well as a

torch head for current transmission, Figure 3.2.

Flux supply is car-

ried out via a hose

from the flux con-

tainer to the feeding

hopper which is

mounted on the

torch head. De-

pending on the de-

gree of automation

it is possible to in-

stall a flux excess

pickup behind the

torch. Submerged

Process Principle of Submerged Arc Welding

br-er3-01e.cdr

electrode

contact piece

flux hopper

Figure 3.1

ISF 2002

Assembly of a SA Welding Equipment

br-er3-02e.cdr

AC or DC current supplywire straightenerwire feed rollsflux supplyindicatorswire reel

power sourcewelding machine holder

Figure 3.2


arc welding can be operated using

either an a.c. power source or a d.c.

power source where the electrode is

normally connected to the positive

terminal.

Welding advance is provided by the

welding machine or by workpiece

movement.

Identification of wire electrodes for

submerged arc welding is based on

the average Mn-content and is carried

out in steps of 0.5%, Figure 3.3.

Standardisation for welding filler ma-

terials for unalloyed steels as well as

for fine-grain structural steels is con-

tained in DIN EN 756, for creep resis-

tant steels in DIN pr EN 12070 (previ-

ously DIN 8575) and for stainless and

heat resistant steels in DIN pr EN

12072 (previously DIN 8556-10).

The proportions of additional alloying

elements are dependent on the mate-

rials to be welded and on the me-

chanical-technological demands which

emerge from the prevailing operating

conditions, Figure 3.4. Connected to

this, most important alloying ele-

ments are manganese for strength,

molybdenum for high-temperature

strength and nickel for toughness.


DIN EN 756mat.-no.

Referenceanalysisapprox.weight %

Properties and application

S11.0351

CSiMn

= 0,08= 0,09= 0,50

CSiMn

= 0,11= 0,15= 1,50

CSiMn

= 0,10= 0,30= 1,00

CSiMnMo

= 0,10= 0,15= 1,00= 0,50

CSiMnNi

= 0,09= 0,12= 1,00= 1,20

CSiMnNi

= 0,10= 0,12= 1,00= 2,20

CSiMnMoNi

= 0,12= 0,15= 1,00= 0,50= 1,00

For lower welding joint quality requirements;in:boiler and tank construction, pipe production,structural steel engineering, shipbuilding

= 0,10= 0,10= 1,00

CSiMn

S21.5035

S31.5064

S2Si1.5034

S2Mo1.5425

S2Ni1

S2Ni2

S3NiMo1

For higher welding joint quality requirements; in:pipe production, boiler and tank construction,sructural steel engineering, shipbuilding.Fine-grain structural steels up to StE 380.

For high-quality welds with mediumwall-thicknesses.Fine-grain structural steels up to StE 420.Especially suitable for welding of pipe steels,no tendency to porosity of unkilled steels.Fine-grain structural steels up to StE 420.

For welding in boiler and tank construction andpipeline production with creep-resistant steels. Working temperatures of up 500 C. Suitablefor higher-strength fine-grain structural steels.

For welding low-temperature fine-grainstructural steels.Non-ageing.

Especially suitable for low-temperature welds.Non-ageing.

For quenched and tempered fine-grainstructural steels.Suitable for normalising and/or re-quenching and tempering.


commercial wireelectrodes

main alloying elementsMn Ni Mo Cr V

alloy type

Mn

MnMo

Ni

NiMo

NiV

NiCrMo

S1S2S3S4

0,51,01,52,0

S2MoS3MoS4Mo

1,01,52,0

0,50,50,5

S2Ni1S2Ni2

1,01,0

1,02,0

S2NiMo1S3NiMo1

1,01,5

1,01,0

0,50,5

S3NiV1 1,5 1,0 0,15

S1NiCrMo2,5S2NiCrMo1S3NiCrMo2,5

0,51,01,5

2,51,02,5

0,60,60,6

0,80,50,8

From a diameter of 3 mm upwards all wire electrodes have to be marked with the following symbols:

S1SiMo

S6:::

I IIIIII_ _

Example:S2Si:S3Mo:

IIIII

Figure 3.3

Figure 3.4


The identification

of wire electrodes

for submerged arc

welding is stan-

dardised in DIN EN

756, Figure 3.5.

During manufacture of fused welding fluxes the individual mineral constituents

are, with regard of their future compo-

sition, weighed and subsequently

fused in a cupola or electric furnace,

Figure 3.6. In the dry granulation proc-

ess, the melt is poured stresses break

the crust into large fragments. During

water granulation the melt hardens to

form small grains with a diameter of

approximately 5 mm.

As a third variant, compressed air is

additionally blown into the water tank

resulting in finely blistered grains with

low bulk weight. The fragments or

grains are subsequently ground and

screened thus bringing about the

desired grain size.

Identification of a Wire Electrodein Accordance with DIN EN 756

br-er3-05e.cdr

Wire e lec t rode DIN EN 756 - S2Mo

DIN main no.

Symbols of the chemicalcomposition:S0, S1...S4, S1Si, S2Si, S2Si2, S3Si,S4Si, S1Mo,..., S4Mo, S2Ni1, S2Ni1.5,S2Ni2, S2Ni3, S2Ni1Mo, S3Ni1.5,S3Ni1Mo, S3Ni1.5Mo


lime quarz rutile bauxite magnesite

silos

balance

roasting kiln

coke

coke

air

raw material

molten metal

tapping

coal-burning stoveelectrical furnace

granulation tub

foaming air

screen

balance

cylindrical crusher

drying oven

Figure 3.5

Figure 3.6


During manufacture of agglomer-

ated weld fluxes the raw materials

are very finely ground, Figure 3.7.

After weighing and with the aid of a

suitable binding agent (waterglass) a

pre-stage granulate is produced in the

mixer.

Manufacture of the granulate is fin-

ished on a rotary dish granulator

where the individual grains are rolled

up to their desired size and consoli-

date. Water evaporation in the drying

oven hardens the grains. In the an-

nealing furnace the remaining water is

subsequently removed at tempera-

tures of between 500C and 900C,

depending on the type of flux.

The fused welding fluxes are charac-

terised by high homogeneity, low sen-

sitivity to moisture, good storing prop-

erties and high abrasion resistance.

An important advantage of the ag-

glomerated fluxes is the relatively low

manufacturing temperature, Figure

3.8. The technological properties of

the welded joint can be improved by

the addition of temperature-sensitive

deoxidation and alloying constituents

to the flux. Agglomerated fluxes have,

in general, a lower bulk weight (lower

consumption) which allows the use of

components which are reacting among


rutile Mn - ore fluorspar magnesite alloys

sintering furnacesilos

ball mill

balance

mixer

dish granulator

gas

drying oven

heat treatment furnace

cooling pipe

screen

balance

Figure 3.7


Properties

uniformity of grainsize distribution

grain strength

homogeneity

susceptibilityto moisture

storing properties

resistance to dirt

current carrying capacity

slag removability

high-speed weldingproperties

multiple-wire weldability

flux consumption

1)assessment : -- bad, - moderate, + good, ++ very good2)core agglomerated flux

Fused fluxes1) Agglomeratedfluxes1)

+/++

+/++

+/++

+/++

+/++

+/++

-/++

-/+

-/++

-/++

-/++

-- /++2)

+/++

+/++

+/++

+/++

+/++

--/+

-/+

-/+

-/++

+/++

Figure 3.8


themselves during

the melting proc-

ess. However, the

higher susceptibil-

ity to moisture dur-

ing storage and-

processing has to

be taken intocon-

sideration.

The SA welding fluxes are, in accordance with their mineralogical constituents, clas-

sified into nine groups, Figure 3.9. The composition of the individual flux groups is to

be considered as in principle, as fluxes which belong to the same group may differ

substantially with regards to their

welding or weld metal properties.

In addition to the groups mentioned

above there is also the Z-group which

allows free compositions of the flux.

The calcium silicate fluxes are rec-

ognized by their effective silicon

pickup. A low Si pickup has low crack-

ing tendency and liability to rust, on

the other hand the lower current car-

rying capacity of these fluxes has to

be accepted. A high Si pickup leads to

a high current currying capacity up to

2500 A and a deep penetration. Alu-

minate-basic fluxes have, due to the

higher Mn pickup, good mechanical

Different Welding Flux TypesAccording to DIN EN 760

br-er3-09e.cdr

MS

CS

ZS

RS

AR

AB

AS

AF

FB

Z

MnO + SiOCaO

2 min. 50%max. 15%

manganese-silicate

CaO + MgO + SiOCaO + MgO

2 min. 55%min.15% calcium-silicate

ZrO + SiO + MnOZrO

2 2

2

min. 45%min. 15%

zirconium-silicate

TiO + SiOTiO

2 2

2

min. 50%min. 20% rutile-silicate

Al O + TiO2 3 2 min. 40% aluminate-rutilelAl O + CaO + MgOAl OCaF

2 3

2 3

2

Al O + SiO + ZrOCaF + MgOZrO

2 3 2 2

2

2

Al O + CaF2 3 2CaO + MgO + CaF + MoSiOCaF

2

2

2

min. 40%min. 20%max. 22%

aluminate-basic

min. 40%min. 30%min. 5%

aluminate-silicate

min. 70% aluminate-fluoride-basicmin. 50%max. 20%min. 15%

fluoride-basic

other compositions

Figure 3.9

ISF 2002br-er3-10ae.cdr

MS - high manganese and silicon pickup- restricted toughness values- high current carrying capacity/ high weld speed- unsusceptible to pores and undercuts - unsuitable - suitable for high-speed welding and fillet welds

for thick parts

CS acidic types

basic types

- highest current carrying capacity of all fluxes- high silicon pickup- suitable for welding by the pass/ capping method of thick parts with low requirements

- low silicon pickup- suitable for multiple pass welding- current carrying capacity decreases with increaseing basicity

ZS - high-speed welding of single-pass welds

RS - high manganese pickup/ high silicon pickup- restricted toughness values of the weld metal- suitable for single and multi wire welding- typical: welding by the pass/ capping pass method

AR - average manganese and silicon pickup- suitable for a.c. and d.c.- single and multi wire welding- application fields: thin-walled tanks, fillet welds for structural steel construction and shipbuilding

Figure 3.10a


properties. With the application of wire

electrodes, as S1, S2 or S2Mo, a low

cracking tendency can be obtained.

Fluoride-basic fluxes are character-

ised by good weld metal impact val-

ues and high cracking insensitivity.

Figures 3.10a and 3.10b show typical

properties and application areas for

the different flux types.

Figure 3.11 shows the identification

of a welding flux according to DIN

EN 760 by the example of a fused

calcium silicate flux. This type of flux

is suitable for the welding of joints as

well as for overlap welds. The flux can

be used for SA welding of unalloyed

and low-alloy steels, as, e.g. general structural steels, as well as for welding high-

tensile and creep resistant steels. The silicon pickup is 0.1 0.3% (6), while the

manganese pickup is expected to be 0.3 0.5% (7). Either d.c. or a.c. can be used,

as, in principle, a.c.

weldability allows

also for d.c. power

source. The hydro-

gen content in the

clean weld metal is

lower than the

10 ml/100 g weld

metal.

Identification of a Welding FluxAccording to DIN EN 760

br-er3-11e.cdr

weld ing f lux D IN EN 760-SF CS 1 67 AC H10

DIN main no.

flux/SA welding

method of manufacture F fused A agglomerated M mechanically mixed flux

flux type(figure 3.9)

flux class 1-3 (table 1)

metallurgicalbehaviour (table 2)

hydrogen content (table 4)

type of current

ISF 2002br-er3-10be.cdr

AB - medium manganese pickup- good weldability- good toughness values in welding by the pass/ capping pass method - application field:unalloyed and low alloyed structural steels- suitable for a.c. and d.c.- applicable for multilayer welding or welding by the pass/ capping pass method

AS - mainly neutral metallurgical behavior- manganese burnoff possible- good weld appearance and slag removability- to some degree suitable for d.c.- recommended for multi layer welds for high toughness requirements- application field: high-tensile fine grain structural steels, pressure vessels, nuclear- and offshore components

- mainly neutral metallurgical behaviour- however, manganese burnoff possible- highest toughness values right down to very low temperatures- limited current carrying capacity and welding speed- recommended for multi layer welds- application field: high-tensile fine-grain structural steeels

FB

AF - suitable for welding stainless steels and nickel-base alloys- neutral behaviour as regards Mn, Si and other constituents

Z - all other compositions

Figure 3.10b

Figure 3.11


The flux classes 1-3 (table 1) explain the suitability of a flux for welding certain ma-

terial groups, for welding of joints and for overlap welding. The flux classes also

characterise the metallurgical material behaviour. In table 2 defines the identification

figure for the

pickup or burn-off

behaviour of the

respective ele-

ment. Table 4

shows the grada-

tion of the diffus-

ible hydrogen

content in the

weld metal, Fig-

ure 3.12.

Figure 3.13 shows the identification of a wire-flux combination and the resultant

weld metal. It is a case of a combination for multipass SA welding where the weld

metal shows a

minimum yield

point of 460 N/mm

(46) and a mini-

mum metal impact

value of 47 J at

30C (3). The flux

type is aluminate-

basic (AB) and is

used with a wire of

the quality S2.

Parameters for Flux IdentificationAccording to DIN EN 760

br-er3-12e.cdr

unalloyed andlow-alloyed steelgeneralstructural steelhigh-tensile & creepresistant steels

welding of joints

hardfacing

stainless and heatresistant steelsCr- & CrNi steels

pickup of elementsas C, Cr, Mo

flux class1 2 3

table 1

table 2

metallurgialbehaviour

identificationfigure

proportion flux inall-weld metal

%

1234

over 0,70,5 up to 0,70,3 up to 0,50,1 up to 0,3

burnoff

5pickup orburnoff0 up to 0,1

6789

0,1 up to 0,30,3 up to 0,50,5 up to 0,7over 0,7

pickup

table 4

identificationhydrogen content

ml/100g all-weld metalmax.

H5

H10

H15

5

10

15

Figure 3.12

Identification of a Wire-Flux CombinationAccording to DIN EN 756

br-er 3-13e.cdr

chemicalcomposition of the wire electrode

wi re - f lux combina t ionD IN E N 756 - S 4 6 3 AB S2

standard no.

wire electrode and/orwire-flux combinationfor submerged arcwelding

strength andfracture strain

(table1 and 2)

impact energy(table 3)

type of flux(figure 3.10)

Figure 3.13


The tables for the identification of the tensile properties as well as of the impact en-

ergy are combined in Figure 3.14.

The chemical composition of the weld

metal and the structural constitution

are dependent on the different metal-

lurgical reactions during the welding

process as well as on the used mate-

rials, Figure 3.15. The welding flux

influences the slag viscosity, the pool

motion and the bead surface. The

different combinations of filler material

and welding flux cause, in direct de-

pendence on the weld parameters

(current, voltage), a different melting

behaviour and also different chemical

reactions. The dilution with the base

metal leads to various strong weld

pool reactions, this being dependent

on the weld parameters.

The diagram of the

characteristics for

3 different welding

fluxes assists, in

dependence of the

used wire elec-

trodes, to determine

the pickup and

burn-off behaviour

of the element

manganese, Figure

3.16. For example:

A welding flux with


table 2

identifi-cation

minimum base metalyield strength

N/mm2

minimum tensilestrengthN/mm2

2T

3T

4T

5T

275

355

420

500

370

470

520

600

Identification for strength properties of welding by thepass/ capping pass method welded joints

identification minimum yield pointn/mm2

tensile strengthN/mm2

minimum fracture strain%

440 up to 570

470 up to 600

500 up to 640

530 up to 680

560 up to 720

355

380

420

460

500

35

38

42

46

50

22

20

20

20

18

table 1 Identification for strength properties of multipass weld joints

table 3 Identification for the impact energy of clean all-weld metal or of welding by the pass/ capping pass method welded joints

Z

nodemands

A 0 2 3 4 5 6 7 8

-80-70-60-50-40-30-200+20

identificationtemp. for minimumimpact energy 47J

C

Figure 3.14

Metallurgical Reactions DuringSubmerged Arc Welding

br-er 3-15e.cdr

droplet reaction

dilution

weld pool reaction

welding flux welding filler metal

slag

weld metal

base metal

welding data

welding data

welding data

Figure 3.15


the mean charac-

teristic and when a

wire electrode S3

is used, has a neu-

tral point where

neither pickup nor

burn-off occur.

The pickup and burn-off behaviour is, besides the filler material and the welding

flux, also directly dependent on the welding amperage and welding voltage, Figure

3.17. By the example of the selected flux a higher welding voltage causes a more

steeply descending manganese char-

acteristic at a constant neutral point.

Silicon pickup increases with the in-

creased voltage. The influence of cur-

rent and voltage on the carbon content

is, as a rule, negligible.

Inversely proportional to the voltage is

the rising characteristic as regards

manganese in dependence on the

welding current, Figure 3.18. Higher

currents cause the characteristic curve

to flatten. As the welding voltage, the

welding current also has practically no

influence on the location of the neutral

point. Silicon pickup decreases with

increasing current intensity.

Manganese-Pickup and Manganese-BurnoffDuring Submerged Arc Welding

br-er 3-16e.cdr

S1

1,0% 3,0% Mn in wire2,0%

Mn-burnoff

Mn-pickup

S2 S3 S4 S5 S6

Figure 3.16


weld flux LW 280current intensity 580 Awelding speed 55 cm/min

neutral point

% Mn wire

% Si wire

% C wire

pick

up/ b

urno

ff X

in w

eigh

t %r

Figure 3.17


The Mn-content of the weld metal can be

determined by means of a welding flux

diagram, Figure 3.19.

In this example, the two points on the

axis which determine the flux characteris-

tic are defined for the parameters 600A

welding current and 29V welding voltage,

with the aid of the auxiliary straight line

and the neutral point curve (MnNP). In this

case, the two points are positioned at

0.6% DMn and 1.25% MnSZ. Dependent

on the manganese content of the used

filler material, the pickup or burn-off con-

tents can be recognized by the reflection

with respect to the characteristic line

(0.38% Mn-pickup with a wire contain-

ing 0.5%Mn, 0.2% Mn-burnoff with a

wire containing 1.75%Mn).

The structure of the characteristic line

for the determination of the silicon

pickup content, is, in principle, exactly

the same as described above, Figure

3.20. As silicon has only pickup prop-

erties and therefore no neutral point

exists, the second auxiliary straight

line must be considered for the deter-

mination of the second characteristic

line point.


weld flux LW 280arc voltage 29 Vwelding speed 55 cm/min

pick

up/ b

urno

ff X

in w

eigh

t %r

neutral point

% Mn wire

% Si wire

% C wire

450 A

Figure 3.18


flux diagramm LW 280,manganesewire electrode 4 mm acc. to Prof. Thier

= 580 A U = 29 V Mn = 0.48 % Mn Mn = 1.69 % Mn

example: I

SZ1

SZ2

Figure 3.19


Weld preparations for multipass fabrication are dependent on the thickness of the

plates to be welded, Figure 3.21. If no

root is planned during weld prepara-

tion and also no support of the weld

pool is made, the root pass must be

welded using low energy input.

When welding very thick plates which

are accessible from both sides, the

double-U butt weld may be applied,

Figure 3.22. Before the opposite side

is welded, the root must be milled out

(gouging/sanding). This type of weld

cannot be produced by flame cutting

and is, as milling is necessary, more

expensive, although exact weld

preparation and correct selection of

the welding parameters lead to a high

weld quality.

Another variation of

heavy-plate welded

joints is the so-called

steep single-V butt

weld, Figure 3.23.

The very steep edges

keep the welding vol-

ume at a very low

level. This technique,

however, requires the

application of special

narrow-gap torches.

The geometry during

slag detachment and


flux diagramm LW 280,siliconwire electrode 4 mm acc. to Prof. Thier

= 580 A U = 29 V Si = 0.16 % Si

example: I

SZ

auxiliarystraight line

auxiliarystraight line

Figure 3.20

Welding Procedure Sheets for Single-V Butt Welds, Single-YButt Welds with Broad Root Faces and Double-V Butt Welds

br-er 3-21e.cdr

preparation geometry weld buildup

manual metal arc welding

manual metal arc weldingmanual metal arc welding

andSASA

SASASASA

SASASASA

Figure 3.21


also during rework-

ing weld-related

defects may cause

problems. Here,

high demands are

made on torch ma-

nipulation and

process control.

Special narrow-gap

welding fluxes fa-

cilitate slag re-

moval.

The most important welding parameters as regards weld bead formation are weld-

ing current, voltage and speed, Figure 3.24. A higher welding current causes higher

deposition rates and energy input, which leads to reinforced beads and a deeper

penetration. The weld width remains roughly constant. The increased welding voltage

leads to a longer arc which also causes the bead to be wider. The change in welding

speed causes - on both sides of an optimum - a decrease of the penetration depth.

At lower weld speeds, the weld pool running ahead of the welding arc acts as a

buffer between arc

and base metal. At

high speeds, the

energy per unit

length decreases

which leads, be-

sides lower

penetration, also to

narrower beads.

ISF 2002

Welding Procedure Sheetfor Square-Edge Welds

br-er3-23e.cdr

GMA welding

GMA welding

SA welding

SA welding

oscillated

ISF 2002

Welding Procedure Sheetfor Double-U Butt Welds

br-er3-22e.cdr

preparation geometry weld buildup

manual metal arc weldingturning and sandingmanual metal arc welding

turn

turn

turn

side 1

side 2

SASA

SASA

SASA

SASA

Figure 3.22

Figure 3.23


Weld flux consumption is dependent on the selected weld type, Figure 3.25. Due to

geometrical shape, the flux consumption of a fillet weld is significantly lower than that

of a butt weld. Because of their lower bulk weight, the specific consumption of ag-

glomerated fluxes is

lower than that of

fused fluxes.

Two different control

concepts allow the

regulation of the arc

length (the principle

is shown in Figure

3.26). The applica-

tion of the appropri-

ate control system is


constant:

plate thickness:wire electrode:flux:

welding current ( )I

constant:

arc voltage (U)

constant:

welding speed (v)

pene

trat

ion

dept

h t

in m

mp

wel

d w

idth

b in

mm

w

tp

Iw

tp

I

w

te

Figure 3.24


2,42,22,01,81,6

1,6

1,4

1,4

1,2

1,2

1,0

1,0

0,8

0,8

0,6

0,6

0,4

0,4

0,2

0,2

0

400

400

0500

500

600

600

700

700

800

800

900

900

1000

1000

1100

1100

cons

umpt

ion

kg fl

ux /

kg w

ireco

nsum

ptio

n kg

flux

/ kg

wire

A) flat weld - I square butt joint

current intensity (A)

current intensity (A)

B) fillet weld

fused composition fluxes

fused composition fluxes

agglomerated fluxes

agglomerated fluxes

Figure 3.25

ISF 2002

Control of the Arc Length

br-er3-26e.cdr

1 2 3

direction of welding

L 1

L 2

L 3

Figure 3.26


dependent on the available power

source characteristics.

The external regulation of the arc

length by the control of the wire feed

speed requires a power source with a

steeply descending characteristic,

Figure 3.27. In this case, the shorten-

ing of the arc caused by some

process disturbance, entails a strong

voltage drop at a low current rise. As

a regulated quantity, this voltage drop

reduces the wire feed speed. Thus,

the initial arc length can be regulated

at an almost constant deposition rate.

In contrast, the internal regulation

effects, when the arc is reduced, a

strong current rise at a low voltage

drop (slightly descending characteris-

tic). At a constant wire feed speed the

initial arc length is independently regu-

lated by the increased burn-off rate

which again is a consequence of the

high current.

The reaction of the internal regula-

tion to process disturbance is very

fast. This process is self regulating

and does not require any machine ex-

penditure.

In submerged arc welding of butt

joints, it is, depending on the weld

preparation, necessary to support the


A

A

I

I

I

I

U

U

U0

U0

US

US

ID

ID

IS

IS IK I

I

external regulation D U-regulation)(

AA

UD

UD

internal self regulation D I-regulation)(

Figure 3.27

br-er3-28e.cdr

Examples of WeldPool Backups

backing flux

ceramic backing bar

flux copper backing

Figure 3.28


liquid weld pool with a backing, Figure 3.28. This is normally done with either a ce-

ramic or copper backing with a flux layer or by a backing flux. Dependent on the

shape of the backing bar, direct formation of the underside seam can be achieved.

When welding circumferential tubes,

the inclination angle of the elec-

trode has a direct influence onto the

formation of the weld bead, Figure

3.29. For external as well as for inter-

nal tube welds, the best weld shapes

may be obtained with an adjusted an-

gular position of the torch. If the ad-

vance is too low, the molten bath runs

ahead and produces a narrow weld

with a medium-sized ridge, too high

an advance causes the flowback of

the molten bath and a wide seam with

a formed trough in the centre. The

processes described here for external

tube welds are, the other way round,

also applicable to internal tube welds.

To increase the

efficiency of sub-

merged arc weld-

ing, different proc-

ess variations are

applied, Figure

3.30. In multiwire

welding, where up

to 6 wires are used,

each welding torch

is operated from a

separate power

source. In twin wire


b2 b3b1

t 1 t 2 t3

a3a2a1 = 0

0 - 30

inclusion

Figure 3.29

Process Variations ofSubmerged-Arc Welding

single wire tandem

parallel twinwire

tandem, twinwire


Figure 3.30


welding, two wire

electrodes are

connected in one

torch and supplied

from one power

source. Dependent

on the application,

the wires can be

arranged in a

parallel or in a tan-

dem.

In submerged arc welding with iron powder addition can the deposition rate be

substantially increased at constant electrical parameters, Figure 3.31. The increased

deposition rate is realised by either the addition of a currentless wire (cold wire) or of

a preheated filler wire (hot wire). The

use of a rectangular strip instead of a

wire electrode allows a higher current

carrying capacity and opens the SA

method also for the wide application

range of surfacing.

However, the mentioned process

variations can be combined over

wide ranges, where the electrode dis-

tances and positions have to be ap-

propriately optimised, Figure 3.32.

Current type, polarity, geometrical co-

ordination of the individual weld heads

and the selected weld parameters also

have substantial influence on the weld

result.


tandem welding

three-wire welding

three-wire, hot wire welding

four-wire welding

1. WH

1. WH

1. WH

2. WH

2. WH 3. WHHW

=

=

=

~

~

~~~~

3. WH

~

~

2. WH

~65

65

12..16

12..1635

10 101535 12..16

7580

1215 18

Process Variations ofSubmerged-Arc Welding

iron powder/chopped wire

hot wire

cold wire

strip


Figure 3.31

Figure 3.32


The description of these individual

process variations of submerged arc

welding shows that this method can

be applied sensibly and economically

over a very wide operating range,

Figure 3.33. It is a high-efficiency

welding process with a deposition

rate of up to 100 kg/h. Due to large

molten pools and flux application posi-

tional welding is not possible.

When more than one wire is used in order to obtain a high deposition rate, arc inter-

actions occur due

to magnetic arc

blow, Figure 3.34.

Therefore, the

selection of the

current type (d.c.

or a.c.) and also

sensible phase

displacements

between the indi-

vidual welding

torches are very

important.


0 500 1000 1500 2000 2500 A 35000

1020304050607080

kg/h100

depo

sitio

n ra

te

current intensity

wel

d m

etal voltage = 30 V

speed = 40 cm/min

wire protrusion = 10dlength

current intensity

3,0 mm

4,0 mm

5,0 mm

12

9

6

30 300 400 500 600 A 800

~~

kg/h

single wire+ metal powder

single wire+ hot wire

double wire

single wiretandem

three-wire

four-wire

Figure 3.33


+ +

( )_ ( )_

+ _ + ~

__ +( ) ( )_ _

elektrode

arc

workpiece

+ +

Magnetic Interaction of Arcs at SA Tandem Welding

Figure 3.34

2003

4.

TIG Welding and

Plasma Arc Welding

4. TIG Welding and Plasma Arc Welding 43

TIG welding and plasma welding belong to the group of the gas-shielded tungsten

arc welding processes, Figure 4.1. In all processes mentioned in Figure 4.1, the arc

burns between a

non- consumable

tungsten elec-

trode and the

workpiece or, in

plasma arc weld-

ing, between the

tungsten electrode

and a live copper

electrode inside

the torch. Exclu-

sively inert gases

(Ar, He) are used

as shielding gases.

The potential curve of the ideal arc, as shown in Figure 4.2, can be divided into

three characteristic sectors:

1.cathode- drop region

2.arc

3. anode-drop region

In the cathode-

drop region almost

50% of the total

voltage drop oc-

curs over a length

of 10-4 mm.

A similarly high

voltage drop oc-

curs in the anode-

drop region, here,

however, over a

length of 0.5 mm.

ISF 2002

Classification of Gas-Shielded Arc Welding acc. to DIN ISO 857

br-er4-01e.cdr

Plasma arc welding with

semi-transferred arc

Plasma arc welding

with transferred arc

Plasma arc welding with

non-transferred arc

CO welding2 Mixed gas welding

narrow-gap gas-shielded arc welding

plasma metalarc welding

electrogas welding

Metal inert-gas welding

MIG

Metal active gas welding

MAG

Gas-shielded arc welding

Tungsten hydrogen welding

Tungsten plasma welding with

electrode

Tungsten inert-gas welding

TIG

Gas-shielded metal arc welding

GMAW

Gas-shielded arc welding

tungsten

Figure 4.1

ISF 2002

Arc Potential Curve

br-er4-02e.cdr

U

V20

10

01 2 3 4 5

10-4 0,5

l

US

lmm

K

L

A+-

A:K:L:

l:

anode spot (up to 4000C)cathode spot (approx. 3600C)arc column (4500-20000C)arc length

arc potential curve(example)

Figure 4.2


The voltage drop on the remaining arc

length is comparatively low. Main en-

ergy conversion occurs accordingly in

the anode-drop and cathode-drop re-

gion.

Figure 4.3 shows the potential dis-

tribution by the example of a real TIG

arc under the influence of different

shielding gases. UA and UK have dif-

ferent values, the potential curve in

the arc is not exactly linear. There is

no discernible expansion of the cath-

ode-drop and anode-drop region

.

The electrical characteristics of the

arc differ, depending on the selected

shielding gas, Figure 4.4. As the ionisa-

tion potential of helium in comparison

with argon is higher, arc voltage must

necessarily be higher.

ISF 2002br-er4--03e.cdr

X

X

0

0

1

1

2

2

3

3

4

4

6

6

20

40

10

20

5

10

U

U

anode

anode

cathode

cathode

U = 6,5 VK

U = 6,5 VK

U = 3,5 VA

U = 6,1 VA

Argon60 A

Helium60 A

V

V

mm

mmARC

ARC

ARC

ARC

Figure 4.3


arc

volta

ge

25

20

15

10

arc

leng

th

4

2

4

2

helium

argon

weld current

50 100 150 200 250 3500

mmV

A

Figure 4.4


The temperature

distribution of a

TIG arc is shown in

Figure 4.5.

In TIG welding just approximately 30%

of the input electrical energy may be

used for melting the base metal, Fig-

ure 4.6. Losses result from the arc ra-

diation and heat dissipation in the

workpiece and also from the heat con-

version in the tungsten electrode.

ISF 2002

Temperature Distribution in aTIG Arc (at I=100 A)

br-er4-05e.cdr

TIG cathode

10 0

00 K

9 00

0 K

8 00

0 K

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

anodespot

weld pool

2

mm

4

6

8

2

mm

4

6

8 4 3 2 1 0 1 2 mm 4


melting of wire

welding direction

radiation

R.I2

P = U.I

thermal conductivity [W/m K]

fusion heat [kJ/kg]

specific heat [kJ/kg K]

Figure 4.5

Figure 4.6


Figure 4.7 describes the process principle of TIG welding.

Figure 4.8 explains by an example the code for a TIG welding wire, as stipulated in

the drafts of the European Standardisations.

A table with the chemical compositions of the filler materials is shown in Figure 4.9.

isf 2002

Tungsten Inert Gas Welding (TIG)

br-er4-07e.cdr

tungsten electrode

electric contact

shielding gas

shielding gas nozzle

filler metal

weld

arc

workpiece

welding powersource

Figure 4.7

ISF 2002

Designation of a Tungsten InnertGas Welding Wire to EN 1668

br-er4-08e.cdr

identification of filler rod as an individual product: W2

chemical composition table

rods and wires for tig-welding

minimum impact energy value 47 J at -30C

minimum weld metal yield point: 460 N/mm2

identification letter for TIG-welding

W 46 3 W2

Figure 4.8


According to Figure 4.10, a conventional TIG welding installation consists of a

transformer, a set of rectifiers and a torch. For most applications an electrode with a

negative polarity is

used. However, for

welding of alumin-

ium, alternating

current must be

used. For arc igni-

tion a high-

frequency high

voltage is super-

imposed and

causes ionisation

between electrode

and workpiece.

The central part of the torch for TIG welding is the tungsten electrode which is held

in a collet inside the torch body, Figure 4.11. The hose package contains the supply

lines for shielding gas and welding current. The shielding gas nozzle is more often

than not made of

ceramic. Manually

operated torches

for TIG welding

which are used for

high amperages as

well as machine

torches for long

duty cycles are

water-cooled.

ISF 2002

Chemical composition offiller rods and wires for TIG-welding

br-er4-09e.cdr

Figure 4.9

ISF 2002

Principle Structure of a TIG Welding Installation

br-er4-10e.cdr

selector switch

high-frequency choke coil

filte

r ca

paci

tor

transformerSC: scattering core for adjusting the characteristic curve

mai

ns

high voltage impulse generator~

O_

O+rectifier

St

L1L2L3NPE

=~

Figure 4.10


In order to keep the influence of torch distance variations on the current intensity and

thus on the penetration depth as low as possible, power sources used for TIG weld-

ing always have a steeply drooping characteristic, Figure 4.12.

The non-contact

reignition of the

a.c. TIG arc after a

voltage zero cross-

over requires ioni-

sation of the elec-

trode-workpiece

gap by high-

frequent high

voltage pulses,

Figure 4.13.

isf 2002br-er4-12e.cdr

current intensity

longer arc shorter arc

R and U rise R and Udrop

I drops I rises

volta

ge

U

arc length

long

shor

t

increasing

increasing

decreasing

decreasingi

Figure 4.12

torch capwith seal

handle of the torch

control switch

control cable

shieldinggas supply

cooling watersupply

cooling waterreturn withwelding currentcable

torch bodywith cooling device

electrode collet

colletcase

tungsten electrode

gas nozzle

br-er4-11e.cdr ISF 2002

Construction of a Water-CooledT TIG Welding orch for

Figure 4.11

ISF 2002

reignition of the arcby voltage impulses

++

- -

time

Welding Technology (1)

Documents

electroslag welding

tig welding

oxyacetylene welding

welding fixtures

shape welding

welding robots

pressure welding isf

plasma arc welding