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This Presentation is provided to you by: WPS America .com Industry Standard Welding Procedures Software for AWS and ASME Codes. Choice of Shielding Gas es. Applications of Shielding Gases & Modes of Metal Transfer. CW A - Toronto 4 th Nov 200 3. Viwek Vaidya . Too many choices!.

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This Presentation is provided to you by:

WPSAmerica.com

Industry Standard Welding Procedures Software for AWS and ASME Codes


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Choice of Shielding Gases

Applications of Shielding Gases & Modes of Metal Transfer

CWA-Toronto 4th Nov 2003

Viwek Vaidya


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Too many choices!

  • Too many base metals

  • Too many processes

  • Too many brands

  • Variety of opinions!

  • Gas compositions often unknown

  • A5.32 - shielding gas standard


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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


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The functions of shielding gases are

  • Protect the weld pool from atmosphere

  • Provide a gas plasma - ionised gas

  • Support metal transfer and bead wetting


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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


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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


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Globular transfer

  • High thermal conductivity

  • Narrow plasma column

  • CO2 and Helium produce globular transfer

  • Impossible to produce spray transfer!


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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


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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


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Spray Transfer

  • Low thermal conductivity

  • Expanded plasma column

  • Electron condensation heating


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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!


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Penetration profiles

  • Argon has a finger nail penetration profile consistent with spray transfer

  • CO2 and He have elliptical penetration consistent with the globular transfer


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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


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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



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Argon – Helium mix

  • 75%Ar+25% He

  • Applicable to what base metals?


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Argon – Helium mix

  • 50%Ar+50% He

  • What is the bead shape?

  • What is the advantage with respect to Blue Shield 1?


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Argon – Helium mix*

  • 25%Ar+75% He

  • *Can one spray transfer with this gas? Why?

  • What application ? Automatic or manual?


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Argon – Oxygen mix

  • 98%Ar+2%O2

  • This gas can be applied to what base metals?

  • What would be the bead shape?


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Argon – Oxygen mix*

  • 95%Ar+5% O2

  • Can one spray transfer with this gas?

  • *Can this be applied to Stainless steels?


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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


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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?


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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?


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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?


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Argon – H2 mix *

  • 97.5%Ar+2.5% H2

  • *Can this gas be used for GTAW of ferrous metals?


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Argon – H2 mix *

  • 65%Ar+35% H2

  • *Is this a welding grade gas? Where is this applied?


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Nitrogen – H2 mix *

  • 95%N 2+5% H2

  • *Can you weld with this gas? In what application?


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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?


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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?


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Argon – CO2 – Helium mix*

  • 75%Ar + 15% CO2 + 10%He

  • *What advantage would this gas have over a 85% Argon + 15% CO2?