Welding technology

1 The classification of the welding methods

Welding is a non-demountable joint between two or more pieces of metal. From the

chemical and physical point of view, the phenomenon is explained by bringing the atoms from

the pieces in connection into the mutual sphere of attraction by heating with or without

pressing, with or without using and additional welding material. Welding, as a technological

procedure, have several possibilities of carrying out.

The classification of the welding procedures follows specific criteria (see Figure 1):

I) Classification based on the method of the welding process:

a) Welding by smelting the pieces;

b) Welding by pressing the pieces, with or without heating them, with or without additional

welding material.

II) Classification based on the energy used for welding:

a) Thermo-chemical energy transferred through solids;

b) Thermo-chemical energy transferred through liquids;

c) Thermo-chemical energy transferred through gases.

d) Electric arc welding;

e) Radiations welding;

f) Welding with mechanic energy;

g) Thermo-electric energy welding (electric resistance welding).

III) Classification on the basis of how the welding is done:

a) Manual;

b) Manual - mechanized;

c) Mechanized;

d) Automatic.

Figure 1. Methods for welding by smelting

Figure 2. Methods for welding by pressure

Welding by pressure

With sclips With liquids With gases With electric

arc With mechanic

energy

By

diffu

sion

By

rolli

ng

By

drill

ing

With

term

it

Ligh

ting

Lase

r

Pen

cil o

f el

ectro

ns

Turn

ing

With electric

resistance

Welding by smelting

With liquids With gases With electric

arc

With radiations With electric

resistance

With liquids

Fusi

ng

elec

trode

Coa

l

Term

o-co

mpr

essi

on

Spa

rkin

g

elec

trode

Flux

c

ored

Turn

ing

Gas

sh

ield

ed

Ligh

ting

Pen

cil o

f el

ectro

ns

Turn

ing

Turn

ing

Lase

r

Non-fusing

electrode (W)

Fusing

electrode (M)

Pla

sma

+ in

ert

Act

ive

gas

Iner

t gas

(W

IG)

Pla

sma

Ato

mic

h y

drog

en )

Iner

t gas

(M

IG)

(MA

G)

gas

(MIG

IV) Classification on the basis of the combination of the welding procedures:

a) Mechanized flux cored;

b) With plasma;

c) Half mechanized gas shielded;

d) Automatic in points;

e) Mechanized with plasma.

2. Classification of the welded connections I) Joint elements may be assembled with: (fig. 3-10):

- Groove welded joints;

- Fillet welded joints;

- Welds between two or more elements meeting in angle and forming a joint.

II) By the cross section of the welds there can be:

- groove welds: continuous, having the edges pressed or not. The edges cannot be

processed when their thickness is beyond 4 mm for a manual welding and 8 mm for an

automatic welding. The processed edges are obtained by cutting the pieces with special

automatic machine, then sharing and milting them, thus the throats having certain forms,

angles and dimensions;

- fillet welds: they are made without processing the edges of the pieces. Their cross sections

may be various: plat, convex, concave, triangular with a wider side on the direction of

transferring the effort. The fillets can be: frontal, lateral, oblique in angle α.

Figure 3. Groove welds: a) ….c) lengths for welding; d) … h) cross sections trough welding throats.

Figure 4. Fillet welds: a) frontal weld; b) lateral weld; c) lateral weld with returns; d) inclined weld.

Figure 5. Welds between two or more elements intersected in angle (a) …(c).

Figure 6. “K” and half “K” groove welds.

Figure 7. Fillet welds.

Figure 8. Discontinuous fillet welds: 15t 120 150mmmin = … ; e 15 mint− ≤ for elements in

compression; e 30 mint− ≤ for elements in tension.

Figure 9. Welds in holes and in slots. a) ;

for circular holes:

2 ; 25mm; 25mm; 0 7 ; <101 md t t d a . t t≥ < ≥ < in min

)(L 21 a d a= + − ( ) and =a L d a= π − ; b) ( )2 10 253t t 1, t≤ = … .

Figure 10. Welding positions (STAS 7365-74); . o o o0 90 ; 0 180α = β =… … o

In the case of static loading or in the case of light weight loading, the elements can be

welded with discontinuous fillet welds or with partial penetration groove welds. The welds can

be vertical or horizontal, the angles α and β referring to the inclination respectively, the

rotation of the welded pieces during the execution; standard regulations STAS 7365-74 gives

the principal positions of welding for both groove welds and fillet welds and, STAS 735-79

shows the plotting pattern of welding.

3. Welding supplies

Along with the basic material (metal), welding means also the addition material which is

continuously feeding the welding place or intermittently in the end making together a strong

system.

The additional welding materials, whose characteristics depend on the basic material and

the procedure of welding, are:

- main addition welding materials, which are parts of the welding (metals and metallic

alloys);

- auxiliary materials, which do not make part of the welding (the cover of the electrodes,

the fluxes, the gas for the shielding).

The functions of the cover of the electrodes are:

a) ionization: kipping the stability of the electric arc;

b) protection: the metal smelt zone is protected against the action of the oxygen and the

nitrogen from the atmosphere;

c) moderation: the slag on the welding is a thermal insulation, improving the plasticity;

d) purification: removing the unwanted elements (like sulfur, phosphors, gases), the smelt

zone will be an approach of the basic element;

e) alloying: metals (in powder) are sent from the electrodes to the smelt metal during

welding, thus forming alloyed constituents.

The welding wires are wires made of carbon steel, low alloyed steel, alloyed steel or high

alloyed steel. The wires have the same functions as the wires inside the electrodes have.

The fluxes are additional welding materials, in fact homogeneous deposits in the welded

zone during the process of the welding with the same functions as the functions of the cover

of the electrodes.

The materials for welding (or cutting) with gas depend on the methods that are chosen

and which they can be: welding by gas-shielding with a protection gas-MIG, MAG, WIG, PL

(SP) or gas-shielding with an active gas – GA with non-fusible electrode (W), see Figure 2.

So the gases used for welding and cutting are: active or inert. The inert gases are: argon,

helium, nitrogen. The active gases can be: carbon dioxide, oxygen, hydrogen, acetylene.

4. Arc welding

4.1. The principle of arc welding

Arc welding is a welding method which uses the heat in order to fuse the edges of the

welding and the addition material. The heat is generated by the electric arc between the

electrodes and the welding piece or between two independent electrodes, connected to two

poles of the source of electric current.

The principle of an arc welding is the principle of electric arc process: when the electrode

is closely situated to the piece of metal, the electrons trespass the space between these

elements; when the electrode is removed away slowly, the electrons are passing trough the

inter-space and hit the gas particles in atmosphere. These particles become ions and so all

this space is ionized. The temperatures increase dramatically: from 500oC at the edge of the

electrode to 2500oC at the surface of the melted metal. When solidifying, all the metal fuses

together. The electric arc must by kept constant (the intensity of the current Is and the tension

Ua). The electrode moves with its own speed, a specific and constant value Ve and

consequently, the welding must be also done with a constant speed, Vs.

The arc welding can be:

- with covered fusing electrodes;

- with fusing electrodes for flux cored arc welding;

- gas shielded arc welding with fusible or non fusible electrodes.

During the electric arc process in the welding area the following distinct zones appear

(figure 11, 12 and 13):

1. the seam formed by the welding metal and the addition material melted together;

2. the zone which is thermal influenced;

3. the part of metal non-affected by the heat.

Fig. 11. The method of welding with electric arc: 1 – electric arc; 2 – metal pieces; 3 – addition material

(electrode)l; 4 – electric current for feeding the arc; 5, 6 – the smelt zone; 7 – the weld seam.

Figure 11. Electric arc welding area: 1 – seam (additional material);

1’ – seam (melted metal piece); 2 – heat affected zone (ZIT); 3 –

the metal part not affected by welding process.

Figure 12. The ZIT structures of the steel (arc welding): a) hypoeutectic steel: C% = (0.02% …0.83%);

b) eutectic steel c% = 0.83%; c) hypereutectic steel, C% = (0.83% …6.7%); d) lattice structure whose

crystallization depend on the cooling speed; e) the structure changes depend on the carbon content and

on the cooling speed.

4.2. The technology of flux cored arc welding

The electrode is made of wire and it conducts electricity, bringing in the same time the

addition material. It is not cored, so it must be protected. The protection is achieved by

welding under a layer of flux. The flux is a homogeneous mineral mixture, whose

characteristics are directed towards protection of the welding and stabilizing the electric arc.

The equipment used for all these processing phases is either entirely or half automatic. When

the equipment is automatic, we use a device also called tractor which moves along rails on

the direction of the fillet welds (see Figure )

i. The equipment in the laboratory

Mainly, the equipment for the automatic welding with flux cored arc welding are:

a) the source of current (continuous) RSAR 1000;

b) the panel (operating and control) under continuous current;

c) the welding device – tractor AST 3.

a) The source for continuous current, RSAR 1000 (Figure 15) is a rectifier whose

characteristics are: the tension for feeding (3x380V; 50 Hz); the maximum current

(110A), the extreme values for the intensity of the welding current (1000 ÷ 250A); the

time for continuous work is no more than 60 min.

The destination of the rectifier is to convert the current supplied by the source into a

current whose characteristics depend on the thickness of the pieces of metal that

must be welded, on the distance between the pieces and on the type of the welds.

Adjusting the intensity of the current and also its tension means to decide upon the

principal parameters for the welding. They are: Is and Ua, the intensity and the tension

of the welding current Vs, the welding speed, and respectively Ve, the advancing

speed of the electrode.

Indeed, if we know the thickness of the metal piece t, we then decide the thickness of

the welding arc: tde 3,1= . Both Is and Ua are depending on de, that is:

and . 26.5 154.25 135s e eI d d= ⋅ + ⋅ − 22.125 10 16.5aU Is−= ⋅ +

Both the speed of the wire advancing and the speed of welding depend on the

thickness of the cross-section of the seam (the throat) and in fact, on the thickness of

the electrode, so both Vs and Ve must be priori decided.

It is very important to know that the values of all these parameters decide upon the

quality of the seam, so they must not be either non-adequate or varying (Figure 14).

Figure 13. The influence of the welding parameters on the quality of welding: a) Is, Ua, Vs suitable; b) Is –

small; c) Is – big; d) Ua – small; e) Ua – big; f) Vs – small; g) Vs – big.

b) The operating and control panel is a bonding part between the source and the

welding tractor, so it makes the link between the rectifier of the current and the

welding pieces, or the welding head situated on the tractor, with several cables.

c) The welding – device - tractor AST 3, is used for welding fillet-welds or for groove

welds, for pieces of metal with thickness greater than 2mm and heaving the diameter

1200mm for circular welds. It has four wheels for traveling and worm-gear wheels

(creepers) which determine the modification of the speed of advancing of the

electrode and of the tractor. Also it has a system of assembling of cog wheels in

series which makes possible for obtaining more than 6 steps of variation of the speed

for the tractor and for the wire, too.

≥

Figure 15. The equipment for the automatic flux cored arc welding method: a)-source

of continuous current RSAR 1000; b), b’) – control and command panel (front and

back); c)- automatic welding device; d)- welded pieces

1-feeding cable (380V); 2- protection cable (contact to earth); 3- switch on contact; 4-

signal lamp; 5- switch for welding current; 6- voltmeter; 7- kilo-ampere meter; 8-

release button; 9- plugs for remote command control; 10- welding cable; 11- vent; 12-

panel of the source current; 13- indicator for the intensity Is; 14- gauge for

measurement of Is; 15- cable for remote control-command of the current; 16- feeding

cables from 380V source; 17- flexible electric conductor for the tractor ASTM-3; 18-

welding cable; 18’- protection conductor; 19- on switch for the command panel; 20-

ampere-meter; 21- voltmeter; 22- start signal lamp; 23- cut off; 24- rolling wheels; 25-

supporting bars; 26- worm gear wheels; 27- tractor ASTM-3; 28- motor wheels; 29-

taps for the joint between the motor wheels and the shaft of the rectifier; 30- motor;

31- box with command buttons; metallic box containing the welding wire; 33-roller for

the welding wire; 35- support and guiding mechanism; 36- tap for activating the worm

gear wheel; 37- flux bunker; 38- cog wheels for the advance of the welding wire; 39-

cog wheels for the advancing speed of the tractor; 40- welding wire; 41- welding

head.

Figure 16. Flux cored arc welding method: 1 – electric arc; 2 – welding wire; 3 – admission pipe for

flux; 10 – welding wire bobbin; 11 – flux bunker; 12 – electric contact; 13 – electric energy sources; 14 –

command and control panel; p – on –button; o – off button; Re – rheostat for fixing the speed of the wire;

Rs – rheostat for fixing the speed of welding; A – ampere-meter V – voltmeter; S – speed-meter.

Figure 17. The final part of the welding head of AST- 3: 1 – motor roll; 2 – pressing roll; 3 – welding wire;

4 – rolls for strengthening the wire; 5 – handle for the action of the eccentric axis; 6 - worm gear body; 7

– washer; 8 – rod for the transmission of the pressing force; 9 – compressing arc; 10 – articulated lever;

11 – welding head; 12 – supporting plate; 13 – support for the welding head.

Figure 18. The cinematic scheme of the welding tractor AST – 3: M – electric engine; 21 – 26 – worm-

gear serial mechanisms for the displacement of the tractor; 2A, 2B – cog wheels for change used to fix

the speed of the tractor; Z7 – Z10 – worm gear serial mechanism for advancing the wire; 2c, ZD – cog

wheels for change used to fix the speed of the advancing of the wire; D – the diameter of the motor

wheel for the displacement of the welding tractor; d – the diameter of the motor roll for advancing the

wire; Rm – motor roll for advancing the wire; Rp – pressing roll; A – pressing arc.

ii. More about …

When installing the source of continuous current, we have to check the connections according

to all regulations, and this is done by the qualified personnel. The RSAR source has the

possibility to set up the intensity of the arc welding Is, and this can be put in evidence by a

gauge or a vertical rule situated on the front of the source. There are also a voltmeter and a

kilo ampere-meter.

The operating and the control panel contains several circuits, relays, measure instruments,

magnetic amplifiers, contacts, all necessary in work processing.

The metallic box is mobile and its place is between the source of current and the equipment

for welding. The panel is connected to the 380 V source for alternating current and it is also

connected to the welding tractor with the help of a flexible conductor of electricity. From the

outlet champs (+, -), two electric cables make the connection with the welding pieces, or with

the table for welding, or with the welding head.

The welding tractor AT-3 is used with several characteristics: tension voltage for feeding

3x380V/50Hz; nominal current 1000A; diameter of the welding wire 1.5 … 5mm; speed of

advancing of the wire 1 … 7.5m/min; speed of welding 0.26-2m/min.

Also, the possibility to weld under inclined positions is achieved but for angles no more than 30o from the vertical one. In fact, this electric device is constructed by an electric engine, a

worm-gear wheel necessary to incline to the welding head, a bunker for flux, two driving

wheels for moving the tractor on the surface of the process of metal or along rails, two wheels

for rolling in the front of the welding head and a metallic circular box for the welding wire,

which is advancing with the help of some devices in a long curve in order not to be bent or

broken. The mechanism of advancing the wire consists in a couple of pressing rolls and the

pressing bearing. They are situated on an eccentric axis are part of the front of the tractor

(see Figure 17).

In fact, both the advancing speed of the arc and the moving speed of the tractor are obtained

with the help of worm-gear mechanisms in order to have big ratios for transmissions – the

exchange wheels 2A, 2B an 2C, 2D, whose sum of the number of cogs is always constant

(the number of cogs are between 14 and 39 and makes the value: 2A + 2B =2C+2D=53,

(Figure 18).

The steps of an arc welding are:

- we decide upon the type of the throat thickness, dimensions and form, all depending

on the thickness of the welded metal;

- we decide upon the principal parameters of welding: the diameter of the wire (de), the

intensity of the welding current (Is), the effective tension (Ua), the welding speed (Vs)

and the speed of advancing of the wire (Ve). These parameters depend on the

thickness of the metal (1) and the relations between them are:

5 2ed t= − ; and de, the diameter of the wire is

.The tension of the electric arc is:

26.5 154.75 138.5s e eI d d= ⋅ + ⋅ −

2mm2 1ed≤ ≤ 22.125 10 16.5aU Is−= ⋅ +

We can also decide the speed of the welding (Vs), on the basis of the cross section of

the throat of the weld taking into account that A is the cross area, 2

22

/ 4

62.5073 620.8161.1044 2.5243 56.1364

e

s

e eee

A dk V

d ddd

π== ⋅

≈ + + + +

In fact, these values are already calculated and can be taken from special charts.

Then we can have the speed of advancing of the wire Ve from the condition that: 2

4e

t s e e sdA V V V k Vπ

⋅ = ⋅ ⇒ = ⋅ , where At is the cross section of a fillet weld made on a

single passing of the electrode along the welding line.

Changing the parameters of the welding influences the diameters and the quality of

the weld fillets, so:

a) if Is grows more than a limit value for the same de, the arc welding is unstable;

b) if Is drops under a minimum permitted value, the arc welding is unstable and

the wire is not melt so the fillet is interrupted and in short circuit;

c) if we need a greater value of the speed welding and a bigger throat thickness

we need to use a welding continuous current with inverted polarity (cc)+;

d) if we want a greater speed of making the deposit of the welded metal we will

use the welding with (cc)- ( direct polarity) but the strength of the welding is

smaller – this method is used for fillet welding which are smaller;

e) changing the polarity from (cc)+ to (cc)- and keeping Is and de constant, the

tension Ua of the arc welding must increase with 4 in order to kip constant the

form of the welding throat;

f) Grossing the vales over recommended determines the grooving of the width

of the welding and drops its depth, so the flux is used in a greater amount,

determining an un-uniform fillet welding width a fragile tendency.

iii. The advantages and disadvantages automatic flux cored arc welding

A. Advantages

1) -being automatic, the weld is uniform and homogeneous;

2) -the drops of metal or slag are inexistent;

3) -the quantity of burned gases is diminished;

4) -the wire is not wasted;

5) -the productivity of the execution is bigger;

6) -the intensity of the welding current Is is bigger than using covered carbon steel arc

welding electrodes.

B. Disadvantages

1) -the fillets are horizontally and for special positions of fillet welding in corners;

2) -the weld must by always longer than a meter.

3) -the slag means supplementary expenses (it has to be brushed with steel wire brush

afterwards).

5. The technology for welding with Gas-shielded arc welding

5.1. Welding in an atmosphere of an active gas

The active gas (carbon dioxide, CO2) is a shield which allows the welding with a fusible,

non cored electrode. The lock of flux, also, makes the welding to be visible, less expensive.

The procedure is adequate for all positions of welding and it is half mechanized – man makes

the entire job, except bringing the wire and the gas in the middle of the arc welding. It can be

entirely mechanized by using a welding tractor. The welding material can be sent on the

surface of the basic metal in two ways (Figure 21):

- “spa” – spray or in short circuit;

- “sha” – in short arc.

The “spa” welding is for bigger welding currents and consists in very tiny drops of metal

which flow with a great speed trough the arc in a continuous jet gases and metallic melt

powder. The method is used for pieces of metal whose thickness is bigger than 3 … 5 mm.

The “sha” welding is made by welding current with Is smaller and consists of:

a) forming of big drops of metal at the end of the welding fillet;

b) because of the shortest electric arc, drops tie up the two welding components and

makes a metallic link;

c) this so called metallic “deck” stops the electric potential (Ua = 0) and the intensity of

the current growing instantly, determines a short circuit. The electro-magnetic forces

strangle the metallic “deck”.

d) The strangulation of the metallic “deck” under a rapidly increased temperature is cut

off, thus the electric arc being re-established and the process continuing.

The number of short circuits is 100 – 200/sec. Both the minimum and the maximum values of

the intensity of the current depend in the diameter of the wire.

5.2. The equipment for welding with gas-shielded arc method (MAG/CO2) (fig. 19, 20, 21, 22, 23, 24, 25)

This equipment that can be seen in the laboratory and which is a half automatic system is

made of the following main parts: the source of continuous current (A) which is in fact a

rectifier; a gas cylinder (B) to which the rectifier are attached the pressure reducing gear and

the discharging for the protection gas (s). The gas in the cylinder is CO2. So there is also a

heater for the gas (IG) whose function is to prevent from forming carbonic ice when installing

the cylinder and instantly extending of the CO2; a filter having hygroscopic elements for the

gas, retaining the water vapors (DG). The access of the gas is depending on electric vent

(EV). The wire advances with the help of a mechanism for the electrode (the wire). The

mechanism is put in action by the continuous electric current engine (M) and reducing gear.

The command and control panel sets up the steps of rotation of the engine (M). The wire is

placed on a bobbin from where is pulled out with the help of wire advancing rolls ® and it is

connected to the welding pistol through an electric gas-protecting water cooling big diameter

cable made of flexible elements puts together in the same rubber tube.

Figure 19. The advancing system of the wire (electrode)

Figure 20. The advancing mechanism system SAM630: 1 –support plate; 2 – damping pistons for the

advance of the welding wire; 3 – bolt; 4 – washer; 5 – compression arc; 6 – pressing roll; 7 – support for

balance; 8 – lever for transmitting the pressing force; 9 – pressing roll; 10 – roll; 11 – lever for unblock

the welding wire; 12 – MRF – water rectifier block; 13 –motor roll; 14 – motor roll; 14 – advancing pinion;

15 – damping pistons; 16 – motor roll; 17 – bolt for supporting the pressing roll; 18 – bearings; 19 –

security rings.

Figure 21. The sequences of sending the additional material trough the electric arc space by “spa” or

“sha” methods

Figure 22. Welding pistol MIG/MAG: 1 – nozzle; 2 – the current neck of the pistol; 3 – damping pistons

system; 4 – the handle of the pistol; 5 – micro switch; 6 – rubber pipe; 7- metallic body with canals; 8 –

pieces for contact.

Figure 23. The dryer of CO2 system: 1 – main conduit; 2 – resistor; 3- metal box; 4 – water sealing; 5-

Dutch washer; 6 – arc; 7 – water sealing; 8 – dryer fixing washer; 9 – body of the dryer; 10 – elements

filled up with hygroscopic substances; 11- metallic washers; 12- water sealing.

Figure 24. The system of working the equipment of half mechanized gas shielded arc welding: A –

Source of current for welding (rectifier); B – gas cylinder for shielding gases; CO2 – carbon dioxide, Ar –

argon; HG – gas heater; Dg – gas dryer; RP – pressure reducer; D – debit-meter; DS – wire un-roller; M

– electric engine; R – reducer; r – wire advancing roll; Ev – electric valve; Vac – the speed advancing of

the wire (ELECTRODE); H2O- water cooling; f – flexible cables; s – switch; Sp – support for the source

of current and the gas cylinder.

5.3. The technology of welding with the half mechanized of gas shielded arc welding

The stages of welding are:

1. The determination of the parameters for welding: de, Is, Ua, Vs, Ve, i.e.,

. m, then . for “sha” circuit and for “spa”

circuit. After that Ua is determined depending on the welding currents, Is:

⋅ I (for

≤ ≤e0 8 d 2 4.

= +13 34 0U .

= −eIs 1 25d 32 5.

a s

= − + −2e eIs 67d 37d 78

050508. ≤ ≤500 sI 1000A );

The area of the welding deposit (kg/h) depends on Is:

0.3 − −= ⋅ + ⋅ +4 20 3 10 0 1 10 0 52s s sA . I . I . (for ≤ ≤100 600AsI );

The speed is similarly determined with the method of flux cored arc welding. s

determined with the help of the value and the way of sending the melt metal on the basic

metal, so:

sk×V

- for “sha” circuit: = − + 2e

31 7 135127 8se

.k×V .d d

- for “spa” circuit: = − + − +2e 2

e

368 163 537 402 1177 5s ee

.k×V d d .d d

The speed of advancing of the wire, =e sV k×V . The time of welding is = 100 ts

s

ntV

,

where nt is the number of times when the electrode goes on a line along the weld. There,

generally can be one or far many more times when making a bigger cross-section weld (“a” is

bigger); ts is specified here for a meter of welding. So: for vertical

groove welds, where t is the thickness of the welded material and for

lateral fillet welding; .

= − + +42 23 553 25562sI t t

= − +7 4 1542sI t + 408t

−= ⋅6 508 10 122a sU . I +

2. The discharging of the protection gas, which also depend on the thickness of the

welded elements, t: DG = 8 … 10l/min for ≤ ≤1 5mm t mm ; DG = 8 … 12l/min for

. ≤ ≤5 12mm t mm

Figure 25 . The equipment for half mechanized gas shielded (CO2) arc welding with fusible electrode

(MAG/Co2):

a- SR630 (continuous current source); b-b’ – SAM630 (wire advancing device for minimal welding

current of 630A); b – back see; b’ – front see; c) welding pistol; d – CO2 gas cylinder; e – piece of metal

to be welded; 1 – feeding cable for the electric resistance; 2 – ground connecting cable; 3 – feeding

cable for the electric resistance; 4 – gas heater; 5 – gas dryer; 6 – pressure reducer; 7 – debit-meter; 8 –

rubber pipe with CO2; 9 – gas admittance vent; 10- gas exit vent; 11 – SAM630 commander; 12 –

switch for fixing the tension; 14 – voltmeter;; 15 – kilo-ampere-meter; 16 – water admittance vent; 17 –

water exit vent; 18 – welding cable; 19 – cable for connecting the ground; 20 – rubber cable; 21 – CO2 –

admittance vent; 33 – water exit vent; 24 – lateral movable wall; 25 – switch for fixing the speed of the

advancing of the wire or for starts for spot welding; 29 – flexible pipe for all the tubes which contain

CO2; 30 – micro switch; 31- gas and wire exit vent; 32 – device for hanging up the source of current; 33

– device for manipulating the advancing wire device; 34 – ventilator; 35 – signal lamp for the rectifier –

on position.

The diameter de of the electrode, depending on t:

( )( )( )

=⎧⎪

=⎪⎨ =⎪⎪ =⎩

0 8 for t = 1 ;0 8 1 for t = 2 5 ;

0 8 1 2 for t = 6 ;

1 1 2 for t = 7 12

… …

…

… …

e

e

e

e

d . mm mmd . , , mm , , mm

d . , , . mm mm

d , , . mm , , mm.

The throat thickness and the method of sending the melt material depend also on t:

( )⎧

( ) ( )( )

≤⎪

=⎪⎨

=⎪⎪⎩

t 3 r = 0 1 6 for "sha" (I) weld;

t 3 5 for r = 1 6 2 4 (I) weld;

t 5 25 for (X) weld;t>25 for (U) weld.

…

… …

…

mm, , , . mm

, , mm . , , . mm

, , mmmm

all these but for the first kind, being in “spa” circuit.

The quality of the welding line depends on how close is the head of the pistol by the

welded metal.

When the welding with the equipment we must do the following steps:

(1) set up the Is, Ua values from the SR630 rectifier;

(2) set up the speed Ve and install the advancing device at the end of the welding wire;

(3) check the pressure of the protection gas to be ≥ 10 daN/cm2;

(4) check the welding wire to be covered with a shiny copper film and the surface of the

welded elements to be clean;

(5) check the position of the welding pistol to be in a 15o … 25o angle of inclination.

i. The advantages and disadvantages of the method

A. Advantages

a) Any position is possible for welding;

b) The wire is not wasted;

c) The fillet is not covered with slag;

d) The ratio of depositing AD and the productivity are bigger than for covered electrodes.

B. Disadvantages

a) The equipment is (2 … 5) times more expensive than the equipment for all other

methods;

b) The pistol is heavier;

c) The cables are heavier.