SUBMERGED
SUBMERGED ARC ARC WELDING WELDING (SAW)(SAW) 1
1. Mode of Operation. Mode of Operation: Usually automatic but it can be : Usually automatic but it can be semi-automatic.semi-automatic. 2.
2. Principle of OperationPrinciple of Operation: Granular flux & bare solid wire is used. Arc is submerged: Granular flux & bare solid wire is used. Arc is submerged hence no visible sign of arc. Arc melts the electrodewire, flux & some base metal to form hence no visible sign of arc. Arc melts the electrodewire, flux & some base metal to form weldpuddle.
weldpuddle. 3
3. Basic equipment . Basic equipment requirementsrequirements:: (i
(i)) TraTransnsfoformermer / r / rerectctififieier (cor (consnstatant vont voltltagage( fle( flat )cat )chaharacracteteririststicic)) ((iiii)) HHeeaadd//HHoosse ae asssseemmbbllyy
((iiiiii)) PPoowweer rr reettuurrn n ccaabbllee ((iivv)) WWiirre e ffeeeed d uunniitt (v)
(v) Flux Flux hopper hopper / / delivdelivery ery / / recoverecovery ry systsystemem ((vvii)) RRuun n oonn//oofff f ttaabbss
((vviiii)) TTraraccttoor cr caarrririaaggee ((viviiiii)) FFumume exe exttraractctioion.n. 4.
4. Arc StrikingArc Striking:: Wire contact is
Wire contact is made by the amade by the advancement of the wire by dvancement of the wire by bmechanical bmechanical drive.drive. 5.
5. Arc & Weld shieldingArc & Weld shielding::
Granular flux uses to generate protective gases & slag, & to addalloying elements to the Granular flux uses to generate protective gases & slag, & to addalloying elements to the weld pool.
weld pool. 6.
6. Weld refining & cleaningWeld refining & cleaning: Refining & cleaning compounds within the flux: Refining & cleaning compounds within the flux 7.
7. Process variable parametersProcess variable parameters:: a)
a) OCV (Open Circuit OCV (Open Circuit Voltage Voltage ): Required to ini): Required to initiate or re-ignite the eltiate or re-ignite the electric arc.ectric arc. b)
b) Arc Voltage Arc Voltage : Changes with a: Changes with arc length. Arc is rc length. Arc is submerged any changes in submerged any changes in arc lengtharc length will change in weld metal composition .
will change in weld metal composition .
c) Current / WFS (Wire Feed Speed): Increasing the wire feed speed automatically c) Current / WFS (Wire Feed Speed): Increasing the wire feed speed automatically
increases the current in the wire. increases the current in the wire. d)
d) Polarity: Polarity: AC/DC AC/DC +/- +/- .. e) Flux type & size: e) Flux type & size:
(i)
(i)
Fused Fused fluxes fluxes : acidi: acidic typc type.e.(ii)
(ii)
AgglomeAgglomerated fluxes (Bonderated fluxes (Bonded fluxes) d fluxes) : : basic type.basic type. The shapeThe shape of the of the flux is flux is granulargranular
f)
f)
Electrode wire type Electrode wire type & diameter & diameter : High quality wire : High quality wire in 2.4 – in 2.4 – 6 mm diameter 6 mm diameter in coils.in coils. Large diameter reduces penetration.Large diameter reduces penetration.
g)
g)
Electrode wire Electrode wire / flux / flux specification: C specification: C omposition & omposition & grading is grading is selected to selected to suit thesuit the electrode & parent metal.electrode & parent metal.
h)
h)
Wire Feed Wire Feed Speed( WFS) Speed( WFS) : Increasing : Increasing the wire the wire feed speed feed speed automatically increasesautomatically increases the current in the wire.the current in the wire. 8) Consumables
8) Consumables: High quality drawn wire & granular flux.: High quality drawn wire & granular flux.
i)
i)
Typical welding imperfectionsTypical welding imperfections:: a.a. CentCenterlierline crne crackacks : Des : Deep & naep & narrow rrow welwelds.ds. (ii)
(ii) Shrinkage cavities: caused by a weld depth / width ration of > 3/2Shrinkage cavities: caused by a weld depth / width ration of > 3/2 9) )
9) )AdvantagesAdvantages a)High productivity a)High productivity
b)No visible arc light b)No visible arc light
10)
10)DisadvantagesDisadvantages a.
a. ResRestritrictected in pd in posiositiotional nal weldweldinging b.
b. VarVariabiable comle compospositiitions (Aons (Arc lenrc lengthgth)) Positional Capabilities
TUNGSTEN INERT GAS (TIG) WELDING PROCESS
Mode of Operation: Manual but can be semi-automatic
2) Principle of operation: Small diameter solid wire and shielding gas (inert gas) is used. The arc is produced between a non-consumable electrode (tungsten) & the work piece. Operator must control the arc length & also add filler metal into the weld pool if needed.
3) Basic equipment requirements:
a) Transformer / Rectifier (constant current (drooping) characteristic) b) Head / Hose assembly.
c) Power return cable. d) Torch head assembly
e) Gas cylinder, hoses, regulators, flow meter. f) Visor with lens.
g) Fume extraction.
4) Arc Striking : The arc striking (scratch start) the core wire onto the plate and withdrawing cause contamination of the tungsten and weld metal to work on this high frequency arc is used cause interference. To work on this, lift arc is used where the electrode is touched on to the plate & is withdrawn slightly.
5) Arc and Weld Shielding: Inert gas (pure argon & helium) is used to shield arc & weld. Gas cut-off delay is used to shield weld metal at the end of a run.
6) Weld refining & Cleaning: Very clean high quality drawn wire is used. 7) Process variable parameters:
a) Voltage : Changes with change in arc length & type of gas being used. b) Current : Changes with change in tungsten diameter. Slope in & slope out
controls the current at the start & end of the weld. c) Polarity : DC –ve for steels.
AC for Aluminum.
d) Inert Gas type: Pure gases argon & helium are used. Nitrogen added for copper welding. Mixture (Arg+Heli) gives good gas cover & penetration. e) Gas Flow rate : Should be correct for given joint design & position as given
in approved welding procedures.
f) Purging : Purging gas pure argon used to reduce atmospheric root oxidation.
g) Tungsten type : Thoriated tungsten for DC and zirconated tungsten for AC. Too fine vertex angle will melt the tungsten tip. With AC, the tungsten end is chamfered & forms a ball end during aluminum welding
8) Consumable : High quality drawn wire & inert gas (pure argon or helium or mixture of both)
9) Typical imperfection:
a) Tungsten inclusions: Caused by a lack of welder skill, too high current & incorrect vertex angle.
b) Crater pipes : Caused by poor weld finish technique or incorrect use of current decay.
c) Weld/root oxidation : If using insufficient gas cut-off delay or purge pressure.
10) Advantages:
a) High quality weld b) All positional
c) Low inner run cleaning 11) Disadvantages:
a) Small range of consumables. b) High ozone levels.
c) Low productivity
Manual Metal Arc Process (MMA)
1) Mode of Operation : Manual
2) Principle of Operation: Arc is struck between short flux bonded metal electrode & the work piece. Both the electrode & work piece surface melt to form a weld pool. Simultaneously melting of flux coating on the rod will form a gas & slag which protects the weld pool from the surrounding atmosphere. One of the weld run is completed the slag must be chipped off.
3) Basic Equipment requirement:
) Transformer rectifier (constant current (dropping) characteristic) ) Power / Power return cables
) Electrode holders. ) Visor with lens
) Electrode
Electrode oven (bakes up to 350°C)
)
Holding oven (temp. up to 200°C)4) Arc striking: The arc is struck by striking the electrode on the surface of the plate & withdrawing it a small distance. Maintain short, constant arc length.
5) Weld refining & cleaning : Refining & cleaning compounds within the bonded flux. 6) Process variable parameters:
a) OCV (Open Circuit Voltage) Requirement to initiate or re-ignite the arc & change with type of electrode being used. Arc voltage changes with change in arc length.
b) Current : Type & value of current will be determined by the choice of electrode classification, diameter, material type, thickness & welding position.
c) Polarity : AC/DC+/- (Electrode + or - & polarity reversible or straight) or electrode coating being used.
d) Full electrode specification & diamter : Should be correctly written on electrode & electrode box.
e)
Electrode pre-use: Basic coated electrodes (i) should be baked at 350°C for 1Hr. (ii) Held in holding ovens at 150°C (iii) Finally in a heated quiver (around
70°C0 with welder for welding.
f) Speed of travel: High dependant on the skill of a welder.
7) Consumables: Core solid wire between 350 & 450mm & 2.5-6mm diameter, covered with bonded flux coating core wire generally low quality steel. Electrodes are grouped depending on the main constituent in their flux coating. The common groups arc
Basic – Calcium carbonate & calcium fluoride (Electrode no. ending with5,6&8) Cellulosic – Cellulose (Electode no. ending with 0 &1)
Rutile – Titania (Electrode no. ending with 2,3, &4) 8) Typical imperfections:
i) Slag inclusions : Poor welding technique & insufficient inter run cleaning. ii) Hydrogen cracks : Incorrect electrode type or baking procedure.
9) Advantages:
i) Range of consumables. ii) All positional.
10) Disadvantages
i) High level of generated fumes. ii) Hydrogen control
Metal Inert Gas (MIG) Welding Process or Metal Active Gas (MAG) Welding Process
1. Mode of Operation : Semi-automatic
2. Principle of Operation : Copper coated or uncoated small diamter solid continuous wire from a spool & shielding gas (Argon + Co2) is used. Arc is produced between a metal electrode wire & the work piece to form a weld pool.
3. Basic equipment requirements:
a) Transformer / Rectifier (constant voltage (flat) characteristic) b) Head / hose assembly
c) Wire liner
d) Power return cable
e) Wire feed unit, wire spool
f) Gas cylinder, hoses, regulators, flow meter g) Visor with lens
h) Fume extraction.
4. Arc Striking: The arc is struck in three different metal transfer modes.
i) Dip transfer : The wire short circuits the arc & the molten metal forming on the wire is transferred by the wire dipping into the weld pool.
ii) Spray transfer : The wire does not make contact with the weld pool. The molten metal at the tip of the wire transfers to the weld pool in the form of spray of small droplets.
iii) Pulsed transfer : Uses pulses of current to fire a single global of metal across the arc gap.
5. Arc & Weld shielding : Cylinder fed inert / active gas shield for arc & weld. 6. Weld refining & cleaning : Very clean, high quality drawn wire.
7. Process variable parameters:
a) OCV (Open Circuit Voltage): Require to initiate or re-ignite the arc. Depend on type of gas being used & type of transfer achievable.
b) Current /Wire feed speed (WFS): Increasing the wire feed speed automatically increases the current in the wire.
c) Polarity : DC –ve (Electrode positive – Reversible)
d) Gas type : Mixture of argon & Co2 (5-20%) to get good penetration, stable arc, very little spatter.
e) Gas flow rate : Adequate to give good coverage over solidifying & molten metal to avoid oxidation & porosity.
f) Inductance: Causes a backpressure of voltage to occur in the wire & operates only when there is a change in current. Reduce level of spatter.
g) Electrode diameter: (Generally produced in 0.6/0.8/0.1/1.2/1.4&1.6mm diameter.
h) Contact tip/drive roller & liner sizes: Both should be of correct size for the wire being used. Loss in contact between the wire & contact tip will reduce current pick. Contact tip should be replaced regularly. The drive roller pressure is only hand tight just to drive the wire. Liner should be of correct type & size for the wire.
i) Wire Feed Speed (WFS) : Incrasing the wire feed speed automatically increases the current in the wire.
8. Consumables : High quality drawn wire & inert active gas. 9. Typical imperfections:
i) Burn through : Incorrect metal transfer mode.
ii) Solica inclusions : Caused by poor inter run cleaning. 10. Advantages:
i) Material thickness range ii) High productivity (o/f) iii) Continuous electrode 11. Disadvantages
i) Small range of consumables ii) High ozone levels
iii) Protection for site working. 12. Positional Capabilities:
Dip – All positional Spray – Flat only
