Gas Tungsten Arc Welding

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Gas Tungsten Arc Welding

By HARDISH TRIVEDI

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GTAW

• Fusion Welding Process

• Arc Between Non-Consumable Tungsten

Rod And Work

• Arc & Weld Pool Shielded By Argon

• Filler Wire Separately Added To Weld Pool

• Welding Torch & Tungsten Rod Cooled by

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Shielding Gas

• Inert Gas - Argon , Helium

• Common Shielding Gas – Argon

• When Helium Is Used – Called “Heli – Arc” Welding • When Argon Is Used – Called “Argon Arc” Welding • Inert Gas Prevents Contamination Of Molten Metal • It Prevents Oxidation Of Tungsten Rod

• It Ionizes Air Gap and Stabilizes Arc

• It Cools Welding Torch & Tungsten Rod

3

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Equipment & Accessories

– + Argon Gas In

Flow Meter

Welding Cable & Cooling Water In Tube HF Unit & Water Cooling System Argon Cylinder Pressure Regulator Cooling Water In

Cooling Water Out Argon Shielding

Tungsten Rod

Power Source Work

Arc

+ High Frequency Connection

Solenoid Valve Ceramic Cup Pedal Switch Gas Lens Collet

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GTAW Equipment &

Accessories

• Power Source – Inverter, Thyrester,Rectifier, Generator

• High Frequency Unit • Water Cooling System

• Welding Torch- (Ceramic Cup, Tungsten Rod, Collet, Gas-lens)

• Pedal Switch

• Argon Gas Cylinder

• Pressure Gauge, Regulator, Flow Meter • Earthing Cable With Clamp

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Types Of GTAW Power Source

• Inverter- DC

• Thyrester – DC

• Motor Generator – DC • Rectifier – DC

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Power Source

• Provides Electric Energy – Arc – Heat • Drooping Characteristic

• OCV – Appx. 80V,

• Current Range 40 A to 300 A ( Capacity Of M/s) • Arc Voltage 18V to 26V

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Characteristic Of GTAW

Power Source

A Vertical Curve V1 V2

Drooping – Constant Current V

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High Frequency Unit

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

• Initiates low energy Arc / Spark & Ionize Air Gap. • Electrically charges Air Gap For welding Current to Jump Across the Tungsten Tip & BM to Form An Arc.

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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.

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GTAW TORCH

Tungsten Rod Ceramic Cup

Arc

Argon Gas Inlet Cooling Water Outlet

Cooling Water Inlet Tube with cable Base Metal

Torch Handle Cap with collet For

Holding Tungsten

Argon Shielding Gas Earthing Cable

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Pedal Switch

Sequence

When M/c On

• Power source gets energized

• Pump starts pumping cooling water to torch

When Pedal Switch Pressed with tungsten rod held close to BM within 3mm

• Solenoid valve opens, Argon starts flowing

• After 5 seconds of pre-purging, high Frequency current jumps from tungsten rod generating sparks

• Immediately welding current makes arc across tungsten rod and work through the HF sparks.

• High frequency gets cut off from the system when welding arc is initiated and welding is started.

When Pedal Released without lifting the torch

1 Current gets cut off, Arc extinguishes, Gas flow continues as post purging. 2 Gas flow remains for few more seconds before it stops.

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Argon Gas Cylinder- Pressure

Regulator + Flow Meter

• Cylinder Stores Argon

At High Pressure

• Regulator Regulates

Cylinder Pressure to Working Pressure

• Flow Meter Controls

Flow Rate Argon Cylinder Flow Meter Pressure Regulator Flow Regulator Pressure gauges Cylinder Valve Connection To Torch

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Shielding Gas

• Argon - Purity 99.99%

• 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

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Argon Gas Cylinder

• Light Blue In Colour

• Full Cylinder Pressure: 1800 psi ( 135 Kgs / Cm2 ) • Volume Of Argon In Full Cylinder: 7.3 M3

• Commercial Argon (99.99%) Cost: Rs 90/- Per M3 • High Purity Argon (99.999) Cost: Rs 110/- Per M3

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Back Purging

Purging Gas Commercial

Argon or Nitrogen • Applicable to Single Sided full penetration • Prevents oxidation of

root pass from

opposite side of weld • Essential for high

alloy steels,

nonferrous metals and alloys

• Desirable For All Material Welding Torch Root Pass Purging Gas In Purging Gas Out Purging chamber Filler Wire

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Tools For GTAW

• Head Screen • Hand gloves • Chipping Hammer • Wire Brush • Spanner Set

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Tungsten Rod

• Non Consumable Electrode.

• Maintains Stable Arc

• Tip to be Ground to a cone Shape of 60º

to 30º angle

• Thoriated Tungsten for General

Application, Zerconiated Tungsten for Aluminium Welding

• Sizes :- 2, 2.4 & 3 mm Ø

Tungsten Rod

Ground to 50º ankle

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Pulsed GTAW

• Power Source Provides Two different Current Levels“Background” and “Peak”at regular

interval

• “Background” & “Peak” are above and below the Average Current

• Best Suitable for Full Penetration Open Root Pass Welding

• Ideal for Root Pass by Automatic Machine Welding

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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.

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ASME Classification Of Filler Wire

SS 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

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Dos

&

Don'ts

In

GTAW

• Always Connect Electrode – Ve

• Keep Always Flow Meter Vertical

• Check & Confirm Argon Purity

• Clean Groove & Filler wire With Acetone

• Grind Tungsten Tip to Point

• Don’t Strike Arc With Electrode + Ve

• Don’t strike Arc Without Argon Flow

• Don’t Strike Arc By

touching Tungsten Rod • Don’t Touch Weld Pool

With Tungsten Rod

• Don’t Lift and break Arc

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Dos

&

Don'ts

In

GTAW

• Break The Arc Only By Pedal Switch

• Lift 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 Don’t Lift Torch

immediately.

• Don’t Weld With Blunt Tungsten Rod

• Don’t Weld With Argon Leaking Torch

• Don’t Weld Without Water Circulation

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Dos

&

Don'ts

In

GTAW

• Provide Back Purging For Single Sided Full Penetration Welds

• Use N2 or Argon as

Back Purging Gas For CS & LAS

• Use Argon As Back

Purging Gas For SS & Non Ferrous Alloys

• Don’t Weld Single Sided Full Penetration Welds Without Back Purging

• Don’t Use N2 As Back

Purging Gas For Non Ferrous Alloys

• Don’t Empty Ag Cylinders Fully.

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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

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Crack

Cause Remedy 1) Wrong Consumable 2) Wrong Procedure 3) Improper Preheat 4) Inadequate Thickness In Root Pass

1) Use Right Filler Wire 2) Qualify Procedure

3) Preheat Uniformly

4) Add More Filler Wire in root Pass

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Lack Of Fusion

Cause Remedy

1) Inadequate Current 2) Wrong Torch angle

3) Improper bead placement

1) Use Right Current

2) Train /Qualify welder 3) Train/Qualify Welder

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Porosity

Cause Remedy

1) Impure Argon Gas

2) Argon Leak Within Torch 3) Defective Filler Wire

4) Wet surface of BM

5) Rusted / Pitted Filler wire 6) Improper Flow Of Argon

1) Replace Argon Cylinder 2) Replace Leaking Torch 3) Replace Filler Wire

4) Clean & Warm BM 5) Clean Filler Wire 6) Provide Gas lens

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Undercut

Cause Remedy

1) Excess Current 2) Excess Voltage

3) Improper Torch angle

1) Reduce the Current 2) Reduce Arc length

3) Train & Qualify the Welder

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Lack Of Penetration

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Cause Remedy

1) Excess Root Face

2) Inadequate Root opening 3) Over size Filler Wire

4) Wrong Direction of Arc 5) Improper bead placement

6) Improper weaving technique

1) Reduce Root Face

2) Increase Root Opening 3) Reduce Filler Wire size 4) Train / Qualify Welder 5) Train / Qualify Welder 6) Train & Qualify Welder

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Excess Penetration

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Cause Remedy

1)Excess root opening 2) Excess Current

3) Inadequate root face 4) Excess Weaving

5) Wrong Direction Of Arc

1) Reduce root gap 2) Reduce Current

3) Increase Root face 4) Train Welder

5) Train Welder

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Overlap

Cause Remedy

1) Wrong Direction Of Arc 2) Inadequate Current

3) Excess Filler Wire

1) Train & Qualify Welder 2) Increase Current

3) Reduce Filler Metal

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Suck Back

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Cause Remedy

1) Excess weaving in root 2) Excess Current

3) Inadequate root face 4) Wrong Electrode angle

1) Reduce weaving 2) Reduce Current 3) Increase root face

4) Train / Qualify Welder

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Under flush

Cause Remedy

1) Inadequate weld beads in final layer

2) Inadequate understanding on weld reinforcement

3) Wrong selection of filler wire size

1) Weld some more beads in final layer

2) Train / Qualify welder 3) Train / Qualify Welder

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Burn through

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Cause Remedy

1) Excess Current

2) Excess Root opening 3) Inadequate Root face 4) Improper weaving

1) Reduce the Current 2) Reduce root opening 3) Increase root face

4) Train / Qualify Welder

Burn trough

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Tungsten Inclusion

Cause Remedy

1) Ineffective HF

2) Improper Starting of Arc

3) Tungsten Tip Comes in Contact With Weld

1) Rectify HF Unit

2) Never Touch Weld With Tungsten Rod 3) Train / Qualify welder

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Stray Arcing

Cause Remedy

1) HF Not In Operation

2) Inadequate Skill of Welder

1) Rectify HF Unit 2) Train the Welder

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Figure

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References

Related subjects : Gas Tungsten Arc Welding