1. This Presentation is provided to you by: WeldCanada
This Presentation is provided to you by: WeldCanada.com Industry Standard Welding Procedures Software CSA, AWS, ASME and API Welding Codes

2. Choice of Shielding Gases
CWA-Toronto 4th Nov 2003
Choice of Shielding Gases
Applications of Shielding Gases & Modes of Metal Transfer
Viwek Vaidya

3. Too many choices! Too many base metals Too many processes
Too many brands
Variety of opinions!
Gas compositions often unknown
A shielding gas standard

4. Shielding gas components
CO2 - Dirty gas needs cleaning
Argon – From cryogenic processing
Oxygen - From cryogenic processing
Helium – From mines of Natural gas
Hydrogen – Chemical processing
Nitrogen – From cryogenic processing

5. The functions of shielding gases are
Protect the weld pool from atmosphere
Provide a gas plasma - ionised gas
Support metal transfer and bead wetting

6. Physical properties of pure gases
Size and shape of the plasma column depends on:
thermal conductivity
specific gravity:
determines the heat content of the gas
Ionization potential:
ease of carrying electrical energy

7. High thermal conductivity gases
CO2 and He have high thermal conductivities
For equal energy into the plasma
less surface needed to transmit heat
Plasma column remains narrow
Localised under the molten tip of wire
This produces globular transfer

8. Globular transfer High thermal conductivity Narrow plasma column
CO2 and Helium produce globular transfer
Impossible to produce spray transfer!

9. Thermal conductivity and plasma shape
Thermal Conductivity is the ease with which the gas will dissipate heat
Argon has low thermal conductivity
It is used for low R-Value windows
Argon

10. Low thermal conductivity gases
Argon has low thermal conductivity
For equal energy into the plasma
more surface is needed to transmit heat
Plasma column expands
Reaches beyond the molten tip of wire
Rapid melting with high electron condensation heating
This produces spray transfer

11. Spray Transfer Low thermal conductivity Expanded plasma column
Electron condensation heating

12. Spray Transfer Wire melts in a fast fine droplet stream
Wire end becomes pointed
Spray transfer results in high deposition and good penetration
Argon gives spray transfer!

13. Penetration profiles
Argon has a finger nail penetration profile consistent with spray transfer
CO2 and He have elliptical penetration consistent with the globular transfer

14. The 90/10 rule To ensure a smooth spray transfer remember this rule!
90% Innert gas (Ar/He)
10% Active gas (Active gas component)
These could be CO2/O2 combinations
For welding steel or stainless base materials some oxygen or CO2 is needed for arc stability

15. Spray transfer limits
Below 85% Argon content, spray transfer is not possible
Beyond 5% Oxygen levels, fume emissions become a problem
Although He is innert, it promotes globular transfer
Any gas mixture that will spray transfer, will generally pulse and short circuit
Hydrogen will provide heat and clean oxides

16. Shielding gas choice
Quiz time!

17. Argon – Helium mix
75%Ar+25% He
Applicable to what base metals?

18. Argon – Helium mix 50%Ar+50% He What is the bead shape?
What is the advantage with respect to Blue Shield 1?

19. Argon – Helium mix* 25%Ar+75% He
*Can one spray transfer with this gas? Why?
What application ? Automatic or manual?

20. Argon – Oxygen mix 98%Ar+2%O2
This gas can be applied to what base metals?
What would be the bead shape?

21. Argon – Oxygen mix* 95%Ar+5% O2 Can one spray transfer with this gas?
*Can this be applied to Stainless steels?

22. Argon – CO2 mix*
90%Ar+10%CO2
Bench mark composition for spray transfer.
*What would be the weld bead shape compared to Ar-5%O2

23. Argon – CO2 *
85%Ar+15% CO2
Can this gas be used for GMAW spray transfer?
*Can this gas be used for FCAW mild steel, and stainless steel?

24. Argon – CO2 * 75%Ar+25% CO2 Can one spray transfer with this gas?
How will the bead shape look compared to CO2
*What will the fillet weld penetration be like compared to CO2? What about fumes?

25. Helium – Argon – CO2 mix* 90%He+7.5%Ar+2.5% CO2
*Can one spray transfer with this mixture? Why?
What base metal should be welded with this mix?

26. Argon – CO2 – H2 mix 96.25%Ar+2.75% CO2+1%H2
Can this gas be used for short circuit and spray transfer for dissimilar welds?

27. Argon – H2 mix *
97.5%Ar+2.5% H2
*Can this gas be used for GTAW of ferrous metals?

28. Argon – H2 mix *
95%Ar+5% H2
*Can one spray transfer with this gas?

29. Argon – H2 mix *
65%Ar+35% H2
*Is this a welding grade gas? Where is this applied?

30. Nitrogen – H2 mix *
95%N 2+5% H2
*Can you weld with this gas? In what application?

31. Argon – CO2 – O2 mix* 91%Ar+5% CO2 +4% O2
Can one short circuit and spray with this gas?
* How will it weld on non blasted plate, GMAW? Why?

32. Argon – Helium – CO2 mix* 81%Ar+18%He+1% CO2
Where would this gas composition be used?
Magnesium, copper, mild steels or SS?
*Can one short circuit and spray transfer with this mix? Why?

33. Argon – CO2 – Helium mix* 75%Ar + 15% CO2 + 10%He
*What advantage would this gas have over a 85% Argon + 15% CO2?

34. Thank you for your attention!
Questions?