Gas Tungsten Arc Welding

By L D Poyyara

GTAWFusion Welding ProcessArc Between Non-Consumable Tungsten Rod And WorkArc & Weld Pool Shielded By ArgonFiller Wire Separately Added To Weld PoolWelding Torch & Tungsten Rod Cooled by Flow OF Argon / Cooling Water

Shielding GasInert Gas - Argon , HeliumCommon Shielding Gas ArgonWhen Helium Is Used Called Heli Arc WeldingWhen Argon Is Used Called Argon Arc WeldingInert Gas Prevents Contamination Of Molten MetalIt Prevents Oxidation Of Tungsten RodIt Ionizes Air Gap and Stabilizes ArcIt Cools Welding Torch & Tungsten Rod

Equipment & Accessories +Argon Gas InFlow MeterWelding Cable & Cooling Water In TubeHF Unit & Water Cooling SystemArgon CylinderPressure RegulatorCooling Water InCooling Water OutArgon ShieldingTungsten RodPower Source Work Arc+High Frequency Connection Solenoid ValveCeramic CupPedal Switch

GTAW Equipment & AccessoriesPower Source Inverter, Thyrester,Rectifier, GeneratorHigh Frequency UnitWater Cooling SystemWelding Torch- (Ceramic Cup, Tungsten Rod, Collet, Gas-lense) Petal SwitchArgon Gas Cylinder Pressure Gauge, Regulator, Flow Meter Earthing Cable With Clamp

Types Of GTAW Power SourceInverter- DC

Thyrester DC

Motor Generator DC

Rectifier DC

Transformer AC (For Aluminium Welding Only)

Power Source Provides Electric Energy Arc Heat

Drooping Characteristic

OCV Appx. 90V, Current Range 40 A to 300 A ( Capacity Of M/s)

Arc Voltage 18V to 26V

Characteristic Of GTAW Power Source

AVertical CurveV1V2A1A2V

Drooping Constant Current

High Frequency Unit Provides High Voltage Electric Energy With Very high Frequency 10000 Cycles / Sec.

Initiates low energy Arc & ionize Air Gap.

Electrically charges Air Gap For welding Current to Jump Across the Tungsten Tip & BM to Form An Arc.

HF Gets Cut Off, Once Welding Arc Struck.

Water Cooling System

Provides Cooling Water To Welding Torch.

Cools Tungsten Rod, Torch handle & Welding Cable.

Cooling Water Returns through Flexible Tube Which Carries welding cable within.

GTAW TORCHTungsten RodCeramic CupArcArgon Gas InletCooling Water OutletCooling Water Inlet Tube with cableBase MetalTorch HandleCap with collet For Holding TungstenArgon Shielding GasEarthing Cable

Petal SwitchSwitches system on And off in sequenceWhen Petal PressedSolenoid valve opens, Argon gas flowsHigh Frequency starts jumping from tungsten rodWelding current flows generating an arc across tungsten rod and work. High frequency gets cut off from the system & welding continues. When Petal ReleasedCurrent gets cut off, Arc extinguishes Gas flow remains for few more seconds before it stops.

Argon Gas Cylinder- Pressure Regulator + Flow MeterCylinder Stores Argon At High Pressure

Regulator Regulates Cylinder Pressure to Working Pressure

Flow Meter Controls Flow RateArgon CylinderFlow MeterPressure RegulatorFlow RegulatorPressure gaugesCylinder ValveConnection To Torch

Shielding GasArgon - Purity 99.95%

Impure Argon Results In Porosities

Purity Verified by Fusing BQ CS plate

Leakage of Argon in Torch Results in Porosity.

Check Leakage by Closing the Ceramic Cup With Thump

Argon Gas CylinderLight Blue In Colour

Full Cylinder Pressure: 1800 psi ( 130 Kgs / Cm2 ) Volume Of Argon In Full Cylinder: 7.3 M3

Commercial Argon (99.99%) Cost: Rs 70/- Per M3

High Purity Argon (99.999) Cost: Rs 87/- Per M3

Back PurgingPurging Gas Commercial Argon or NitrogenApplicable to Single Sided full penetration Prevents oxidation of root pass from opposite side of weldEssential for high alloy steels, nonferrous metals and alloysDesirable For All MaterialWelding TorchRoot PassPurging Gas InPurging Gas OutPurging chamberFiller Wire

Tools For GTAW

Head Screen

Hand gloves

Chipping Hammer

Wire Brush

Spanner Set

Tungsten Rod

Non Consumable Electrode.

Maintains Stable Arc

Tip to be Ground to a cone Shape of 60 to 30 angle

Thoriated Tungsten for General Application, Zerconiated Tungsten for Aluminium Welding

Sizes :- 2, 2.4 & 3 mm Tungsten RodGround to 50 ankle

Filler Wire

Added Separately to the weld pool.

Compatible to base metal

Used in cut length for manual welding.

Used from layer wound spool for automatic welding.

Sizes :- 0.8, 1, 1.2, 1.6, 2, 2.4 & 3 mm

ASME Classification Of Filler WireSS Filler Wire:SFA-5.9, ER 308, 308L, 316, 316L, 347, 309 LAS Filler Wire:SFA 5.28, ER 70S A1, ER 80S B2, ER90S D2, ER 80S Ni2 CS Filler Wire: SFA- 5.18 , ER 70S2 C = 0.07%, Mn = 0.9% 1.4%, Si = 0.4 0.7%, P = 0.025%, S = 0.035%

Dos & Don'ts In GTAWAlways Connect Electrode VeKeep Always Flow Meter VerticalCheck & Confirm Argon PurityClean Groove & Filler wire With Acetone Grind Tungsten Tip to PointDont Strike Arc With Electrode + VeDont strike Arc Without Argon FlowDont Strike Arc By touching Tungsten Rod Dont Touch Weld Pool With Tungsten Rod Dont Lift and break Arc

Dos Donts

Dos & Don'ts In GTAWBreak The Arc Only By Pedal SwitchLift The Torch only After 5 Sec Of Arc Break.Ensure Pre Purging & Post Purging of 5Sec Ensure Argon Flow & Water Circulation To Torch When Arc is Stopped Dont Lift Torch immediately.Dont Weld With Blend Tungsten RodDont Weld With Argon Leaking TorchDont Weld Without Water CirculationDos Donts

Dos & Don'ts In GTAWProvide Back Purging For Single Sided Full Penetration WeldsUse N2 or Argon as Back Purging Gas For CS & LASUse Argon As Back Purging Gas For SS & Non Ferrous Alloys Dont Weld Single Sided Full Penetration Welds Without Back PurgingDont Use N2 As Back Purging Gas For Non Ferrous AlloysDont Empty Ag Cylinders Fully

Dos Donts

Defects In GTAW 1. Cracks 2. Lack Of Fusion 3. Porosity 4. Undercut 5.Lack Of Penetration 6. Excess Penetration 7.Overlap 8. Suck Back 9. Under Flush 10. Burn Through 11. Tungsten Inclusion 11.Stray Arcing

Crack

CauseRemedyWrong ConsumableWrong ProcedureImproper PreheatInadequate Thickness In Root PassUse Right Filler WireQualify ProcedurePreheat UniformlyAdd More Filler Wire in root Pass

Lack Of FusionLack Of Fusion

CauseRemedy Inadequate Current Wrong Torch angle Improper bead placement Use Right Current Train /Qualify welder Train/Qualify Welder

Porosity

CauseRemedy Impure Argon Gas Argon Leak Within Torch Defective Filler Wire Wet surface of BM Rusted / Pitted Filler wire Improper Flow Of Argon Replace Argon Cylinder Replace Leaking Torch Replace Filler Wire Clean & Warm BM Clean Filler Wire Provide Gas lense

UndercutUnder cut

CauseRemedy Excess Current Excess Voltage Improper Torch angle Reduce the Current Reduce Arc length Train & Qualify the Welder

Lack Of Penetration*LOP* Applicable to SSFPW

CauseRemedy Excess Root Face Inadequate Root opening Over size Filler Wire Wrong Direction of Arc Improper bead placement Improper weaving technique Reduce Root Face Increase Root Opening Reduce Filler Wire size Train / Qualify Welder Train / Qualify Welder Train & Qualify Welder

Excess Penetration*Excess Penetration* Applicable to SSFPW

CauseRemedyExcess root opening Excess Current Inadequate root face Excess Weaving Wrong Direction Of ArcReduce root gapReduce Current Increase Root faceTrain Welder Train Welder

Overlap Overlap

CauseRemedy1) Wrong Direction Of ArcInadequate CurrentExcess Filler WireTrain & Qualify WelderIncrease CurrentReduce Filler Metal

Suck Back*Suck Back* Applicable to SSFPW in 4G, 3G & 2G

CauseRemedy Excess weaving in root Excess Current Inadequate root face Wrong Electrode angle Reduce weaving Reduce Current Increase root face Train / Qualify Welder

Under flushUnder flush

CauseRemedy Inadequate weld beads in final layer2) Inadequate understanding on weld reinforcement 3) Wrong selection of filler wire size Weld some more beads in final layer2) Train / Qualify welder

3) Train / Qualify Welder

Burn through*Burn trough*Applicable to root pass

CauseRemedy Excess Current Excess Root opening Inadequate Root face Improper weaving Reduce the Current Reduce root opening Increase root face Train / Qualify Welder

Tungsten InclusionTungsten Inclusion

CauseRemedy Ineffective HF Improper Starting of Arc

3) Tungsten Tip Comes in Contact With Weld Rectify HF Unit Never Touch Weld With Tungsten Rod3) Train / Qualify welder

Stray ArcingArc Strikes

CauseRemedy HF Not In Operation Inadequate Skill of Welder Rectify HF Unit Train the Welder

Thanks