ISF – Welding Institute RWTH – Aachen University Lecture Notes Welding Technology 1 Welding pps

Manual Metal Arc Welding 13 Figure 2.1 describes the burn-off of a covered stick electrode.. Droplets of the liquefied core wire mix with the molten base material forming weld metal whi

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ISF – Welding Institute RWTH – Aachen University

Lecture Notes Welding Technology 1 Welding and Cutting Technologies

Prof Dr.–Ing U Dilthey

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Table of Contents

Electrogas - and

Resistance Projection Welding

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2003

0

Introduction

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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

4.6.2 Fusion welding

1 Casting

5

materials properties

6 2

Forming

3 Cutting

4 Joining

4.4 Joining by casting

4.1 Joining by composition

4.7 Joining by soldering

4.6 Joining by welding

4.3 Joining by pressing

4.2 Joining

by filling

4.8 Joining by adhesive bonding

4.6.1 Pressure welding

4.5 Joining by forming

Production Processes acc to DIN 8580

Soldering

Welding

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Figure 0.2

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4.6.2 Fusion welding 4.6.1

Pressure welding

4.6.1.1 Welding by solid bodies

Heated tool welding

4.6.1.2 Welding

by liquids

Flow welding

4.6.1.3 Welding

by gas

Gas pressure-/

roll-/ forge-/

diffusion welding

4.6.1.4 Welding by electrical gas discharge

Arc pressure welding

4.6.1.6 Welding

by motion

Cold pressure-/

shock-/ friction-/

ultrasonic welding

4.6.1.7 Welding by electric current

Resistance pressure welding

Joining by Welding acc to DIN 1910

Pressure Welding

Figure 0.3

Production processes 4 Joining

4.6.2 Fusion welding 4.6.1

Pressure welding

4.6.2.2 Welding

by liquids

4.6.2.3 Welding

by gas

4.6.2.5 Welding

by beam

4.6.2.4 Welding by electrical gas discharge

4.6.2.7 Welding by electric current

Cast welding Gas welding Arc welding Beam welding Resistance

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2003

1

Gas Welding

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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 ing can be transported in cylinders, Figure 1.1

weld-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

calorific value The highest flame

in-tensity from point of view of calorific

value and flame propagation speed is,

200 400

6006450

1.29

300335

510 490

645

flame temperature with O 2

flame efficiency with O 2

flame velocity with O 2

1350 370 330

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1 Gas Welding 4

generators by the exothermal

trans-formation of calcium carbide with ter, Figure 1.3 Carbide is obtained from the reaction of lime and carbon

wa-in the arc furnace

a pressure of 0.2 MPa Nonetheless, commercial quantities can be stored

(1 l of acetone dissolves approx 24 l

Acetone disintegrates at a pressure of

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

pressure of 1.5 MPa the storage of 6m³

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

grille sludge

to sludge pit

~13 l

6000 l

15 bar

up to 700 l/h cylinder pressure :

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N

Figure 1.3

Figure 1.4

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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, 6m³ of

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

nitrogen vaporized

liquid

tank car pipeline

gaseous

p = cylinder pressure : 200 bar

V = volume of cylinder : 50 l

Q = volume of oxygen : 10 000 l content control

Q = p V foot ring

user

gaseous

still liquid

vaporizer

filling connection

liquid

N

Figure 1.6

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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

valves are equipped

with screw clamp

Pressure regulators reduce the cylinder pressure to the requested working

pres-sure, Figures 1.8 and 1.9

Gas Cylinder-Identification according to DIN EN 1089

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actual condition DIN EN 1089

oxygen techn.

white blue (grey) blue

acetylene

brown yellow

nitrogen

darkgreen

darkgreen black

argon

dark green grey grey

actual condition DIN EN 1089

grey

grey brown

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The injector-type

torch consists of a

body with valves

and welding

cham-ber with welding

coupling nut hose connection

for oxygen A6x1/4" right mixer tube mixer nozzle oxygen valve

injector pressure nozzle suction nozzle fuel gas valve welding nozzle

hose connection for fuel gas A9 x R3/8” left welding torch head torch body

Figure 1.9

Figure 1.10

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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

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

reaction, Figure 1.12:

Figure 1.11

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1 Gas Welding 9

By changing the mixture ratio of the

greatly be influenced, Figure 1.13 At a

neutral flame adjustment the mixture

higher flame temperature, an excess

oxygen flame might allow faster

weld-ing of steel, however, there is the risk

of oxidizing (flame cutting)

The excess acetylene causes the

carburising of steel materials

welding flame combustion

welding nozzle

welding zone centre cone outer flame

normal (neutral)

excess of oxygen

welding flame ratio of mixture

effects in welding of steel

sparking foaming

spattering reducing oxidizing

consequences:

carburizing hardening

Effects of the Welding Flame Depending on the Ratio of Mixture

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Figure 1.13

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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 weldweld-ing” 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)

discharging velocity and weld heat-input rate: low

nozzle size: for plate thickness of 2-4 mm

balanced (neutral) flame

discharging velocity and weld heat-input rate: middle

discharging velocity and weld head-input rate: high

Rightward welding ist applied to a plate thickness of 3mm

upwards 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.

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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

atmosphere)), Figure 1.19 The

addi-tion of pure oxygen is unsuitable

(ex-plosion hazard!)

gap preparations denotation sym-bol

plate thickness range s [mm]

PE

PD

butt-welded seams in gravity position

gravity fillet welds

horizontal fillet welds vertical fillet and butt welds vertical-upwelding position vertical-down position

horizontal on vertical wall

Figure 1.17

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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

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 of

tanks and narrow rooms

double fillet weld 1,3 or 5 heat sources

Flame straightening

Flame Straightening

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PA

PB

PC

PD PE

PG PF

Welding Positions II

Figure 1.18

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2003

2

Manual Metal Arc Welding

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2 Manual Metal Arc Welding 13

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

3 Constitution of gas shielding atmosphere of

4 Desoxidation and alloying of the weld metal

5 Additional input of metallic particles

a) ease of ignition b) increase of arc stability

a) influence the transferred metal droplet b) shield the droplet and the weld pool against atmosphere

c) form weld bead

a) organic components b) carbides

Task of Electrode Coating

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Figure 2.2

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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 ameter and subsequently cut to size, Figure 2.4

di-© ISF 2002

Influence of the Coating Constituents

on Welding Characteristics

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good re-striking

emitter and slag formation

decrease ionization calcareous- fluorspar -

K O Al O 6SiO2 2 3 2

easy to ionize,

to improve arc stability

kaolin

potassium water glass

Figure 2.3

1 2 3

raw wire storage wire drawing machine

and cutting system

inspection

to the pressing plant electrode compound

raw material storage for flux production

jaw crusher

magnetic separation cone crusher

for pulverisation sieving

to further treatment like milling, sieving, cleaning and weighing

sieving system

weighing and mixing inspection

wet mixer descaling

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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

core wire

zine

packing inspection electrode-

press

compound

nozzleing belt wire

convey-magazine wire feeder pressing head

Figure 2.5

core rod coating pressing nozzle pressing cylinder pressing cylinder

Production of Stick Electrodes

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Figure 2.6

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

four different types, Figure 2.7 with concern to burn-off characteristics and able weld metal toughness these types show fundamental differences

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

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

Characteristic Features of Different Coating Types

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cellulosic type acid type rutile type basic typ cellulose

rutile quartz

Fe - Mn potassium water glass

40 20 25 15

magnetite quartz calcite

50 20 10 20

rutile magnetite quartz calcite

TiO2SiO2

Fe O SiO CaCO

3 4 2 3

TiO

Fe O SiO CaCO

2

3 4 2 3

fluorspar calcite quartz

45 10 20 10 15

45 40 10 5

CaF CaCO SiO

2 3 2

almost

no slag

slag solidification time: long

slag solidification time: medium

slag solidification time: short droplet transfer :

toughness value:

medium- sized droplets

fine droplets

to 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

Characteristics of Different Coating Types

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coating type symbol

gap bridging ability current type/polarity

welding positions sensitivity of cold cracking weld appearance slag

detachability

characteristic features

cellulosic type C

acid type A

rutile type R

basic type B

PG,(PA,PB, PC,PE,PF)

PA,PB,PC, PE,PF,PG

PA,PB,PC, PE,PF,(PG)

PA,PB,PC, PE,PF,PG

spatter, little slag, intensive fume formation

high burn-out losses

universal application

low burn-out losses hygroscopic predrying!!

Figure 2.8

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The dependence on temperature of the slag’s electrical conductivity determines

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

a rutile stick 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

elec-The complete

des-ignation for filler

which are relevant

for welding, Figure

2.10 The

identifica-tion letter for the

welding process is

first:

high rutile-con

taining slagsemiconducto

r

acid

lag

high-tem

peratu

cond

uctor

Figure 2.9

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 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 minimum impact 47 J in -30 C

minimum weld metal deposit yield strength: 460 N/mm distinguishing letter for manual electrode stick welding

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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

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

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

Z A 0 2 3 4 5 6 7 8 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.

Figure 2.11

Figure 2.12

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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

Alloy Symbols for Weld Metals Minimum Yield Strength up to 500 N/mm 2 br-er2-13.cdr

Figure 2.13

Figure 2.14

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Figure 2.15

ex-plains the additional

identification figure

for electrode

The last detail of the European Standard designation determines the maximum drogen content of the weld metal in cm³ per 100 g weld metal

hy-Welding current amperage and core wire diameter of the stick

electrode are termined by the thickness of the workpiece to be welded Fixed stick electrode lengths are assigned to each diameter, Figure 2.16

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Figure 2.17 shows

the process

metal arc welding

Polarity and type of

current depend on

the applied

elec-trode types All

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

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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 independent when an internal com-bustion engine is used The advan-

mains-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 elecelec-trode

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

RA73 RR73

100 200 300 400

6

3,25 4 5

A

V

arc welding converter

transformer

rectifier

inverter type

Figure 2.19

Figure 2.20

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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 plications and also explains the wide application range of the method

ap-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 electrodes

b = basic-coated electrodes, recovery <125%

a = A- and R- coated electrodes, recovery 105%

ated

thin-c

oated

220

%

eposition e

ciency

constructional 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

Ni-Cu-alloys Ni-Cr-Fe-alloys Ni-Cr-Mo-alloys copper: electrical grade copper (ETP copper)

bronzes (CuSn, CuAl) gunmetal (CuSnZnPb) Cu-Ni-alloys

AlMg-alloys AlSi -alloys

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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

through additional blocks of steel

through relocating the connection (rarely used)

current-through using

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

Arc Blow Effect

on Steel Parts

inwards at the edges

close to current-connection

close to large workpiece masses

in gaps towards the weld

Figure 2.24

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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 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

18 - 20°C for one year)

storage and baking

0,74

0,39 0,28

30 40 50 60 70 % 80

%

Figure 2.27

Figure 2.28

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2003

3

Submerged Arc Welding

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3 Submerged Arc Welding 26

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 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

continuously-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

power source welding machine holder

Figure 3.2

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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 756 mat.-no.

Reference analysis approx.

weight %

Properties and application

S1 1.0351

C Si Mn

= 0,08

= 0,09

= 0,50

C Si Mn

= 0,11

= 0,15

= 1,50 C Si Mn

= 0,10

= 0,30

= 1,00 C Si Mn Mo

= 0,10

= 0,15

= 1,00

= 0,50 C Si Mn Ni

= 0,09

= 0,12

= 1,00

= 1,20 C Si Mn Ni

= 0,10

= 0,12

= 1,00

= 2,20 C Si Mn Mo Ni

= 0,10

= 1,00

C Si Mn

S2 1.5035

S3 1.5064 S2Si 1.5034

S2Mo 1.5425

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 and pipeline production with creep-resistant steels Working temperatures of up 500 °C Suitable for higher-strength fine-grain structural steels For welding low-temperature fine-grain structural steels.

commercial wire electrodes

main alloying elements

0,5 1,0 1,5 2,0 S2Mo

S3Mo S4Mo

1,0 1,5 2,0

0,5 0,5 0,5 S2Ni1

S2Ni2

1,0 1,0

1,0 2,0 S2NiMo1

S3NiMo1

1,0 1,5

1,0 1,0

0,5 0,5

S1NiCrMo2,5 S2NiCrMo1 S3NiCrMo2,5

0,5 1,0 1,5

2,5 1,0 2,5

0,6 0,6 0,6

0,8 0,5 0,8

From a diameter of 3 mm upwards all wire electrodes have

to be marked with the following symbols:

Figure 3.3

Figure 3.4

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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

grains are subsequently ground and

screened – thus bringing about the

desired grain size

Identification of a Wire Electrode

in Accordance with DIN EN 756

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W i r e e l e c t r o d e DIN EN 756 - S2Mo

DIN main no.

Symbols of the chemical

composition:

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

air

raw material molten metal tapping

coal-burning stove electrical furnace

granulation tub

foaming airscreen

balance

cylindrical crusher

drying ovenFigure 3.5

Figure 3.6

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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 ished on a rotary dish granulator where the individual grains are rolled

fin-up to their desired size and 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 500°C and 900°C, depending on the type of flux

consoli-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 furnace

silos ball mill

balance mixer

dish granulator

gas drying oven

heat treatment furnace

Properties

uniformity of grain size distribution grain strength homogeneity susceptibility

to moisture storing properties resistance to dirt current carrying capacity slag removability high-speed welding properties multiple-wire weldability flux consumption

1)

assessment : bad, - moderate, + good, ++ very good

2) core agglomerated flux

Fused fluxes 1) Agglomerated

fluxes 1)

+/++

+/++ +/++ +/++ +/++ +/++

Trang 36

themselves during the melting proc-ess However, the higher susceptibil-ity to moisture dur-ing storage and-processing has to

be taken sideration

intocon-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 Types According to DIN EN 760

Figure 3.9

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

Trang 37

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 ues and high cracking insensitivity Figures 3.10a and 3.10b show typical properties and application areas for the different flux types

val-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

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

Trang 38

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/mm² (46) and a mini-mum metal impact value of 47 J at –30°C (3) The flux type is aluminate-basic (AB) and is used with a wire of the quality S2

Parameters for Flux Identification According to DIN EN 760

table 2 metallurgial behaviour

identification figure proportion flux in all-weld metal

% 1

2 3 4

over 0,7 0,5 up to 0,7 0,3 up to 0,5 0,1 up to 0,3 burnoff

5 pickup or

6 7 8 9

0,1 up to 0,3 0,3 up to 0,5 0,5 up to 0,7 over 0,7 pickup

table 4 identification

hydrogen content ml/100g all-weld metal

max.

H5 H10 H15

5 10 15

Trang 39

The tables for the identification of the tensile properties as well as of the impact ergy are combined in Figure 3.14

en-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

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

minimum tensile strength N/mm 2 2T

3T

4T

5T

275 355 420 500

370 470 520 600

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

identification minimum yield point

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

Z

no demands

-80 -70 -60 -50 -40 -30 -20 0 +20

welding flux welding filler metal

slag

weld metal

base metal welding data welding data welding data

Figure 3.15

Trang 40

the mean teristic and when a wire electrode S3

charac-is used, has a tral point where neither pickup nor burn-off occur

neu-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-Burnoff During Submerged Arc Welding

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

Tiêu đề	Welding and Cutting Technologies
Người hướng dẫn	Prof. Dr.–Ing. U. Dilthey
Trường học	RWTH Aachen University
Chuyên ngành	Welding Technology
Thể loại	Lecture Notes
Năm xuất bản	2003
Thành phố	Aachen

Định dạng
Số trang	247
Dung lượng	18,44 MB