3. Submerged Arc Welding - hcmut.edu.vndantn/WT/WT1-c3.pdf · Submerged Arc Welding 26 ... Main...

2003

3.

Submerged Arc Welding

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 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.

© ISF 2002br-er3-04e.cdr

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 500°C and 900°C,

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 2

CaO + 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/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 IdentificationAccording to DIN EN 760

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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 orburnoff

0 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% ∆Mn 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

Ø

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

Ø

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

I∆

I∆

IS

IS IK I

I

external regulation ∆ U-regulation)(

AA´

U∆

U∆

internal self regulation ∆ 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 t 3

α3α2α1 = 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

75°80°

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

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