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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

choice of shielding gas es

Choice of Shielding Gases

Applications of Shielding Gases & Modes of Metal Transfer

CWA-Toronto 4th Nov 2003

Viwek Vaidya

too many choices
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
shielding gas components
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
the functions of shielding gases are
The functions of shielding gases are
  • Protect the weld pool from atmosphere
  • Provide a gas plasma - ionised gas
  • Support metal transfer and bead wetting
physical properties of pure gases
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
high thermal conductivity gases
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
globular transfer
Globular transfer
  • High thermal conductivity
  • Narrow plasma column
  • CO2 and Helium produce globular transfer
  • Impossible to produce spray transfer!
thermal conductivity and plasma shape
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

low thermal conductivity gases
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
spray transfer
Spray Transfer
  • Low thermal conductivity
  • Expanded plasma column
  • Electron condensation heating
spray transfer12
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!
penetration profiles
Penetration profiles
  • Argon has a finger nail penetration profile consistent with spray transfer
  • CO2 and He have elliptical penetration consistent with the globular transfer
the 90 10 rule
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
spray transfer limits
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
argon helium mix
Argon – Helium mix
  • 75%Ar+25% He
  • Applicable to what base metals?
argon helium mix18
Argon – Helium mix
  • 50%Ar+50% He
  • What is the bead shape?
  • What is the advantage with respect to Blue Shield 1?
argon helium mix19
Argon – Helium mix*
  • 25%Ar+75% He
  • *Can one spray transfer with this gas? Why?
  • What application ? Automatic or manual?
argon oxygen mix
Argon – Oxygen mix
  • 98%Ar+2%O2
  • This gas can be applied to what base metals?
  • What would be the bead shape?
argon oxygen mix21
Argon – Oxygen mix*
  • 95%Ar+5% O2
  • Can one spray transfer with this gas?
  • *Can this be applied to Stainless steels?
argon co 2 mix
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
argon co 2
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?
argon co 224
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?
helium argon co 2 mix
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?
argon h 2 mix
Argon – H2 mix *
  • 97.5%Ar+2.5% H2
  • *Can this gas be used for GTAW of ferrous metals?
argon h 2 mix27
Argon – H2 mix *
  • 65%Ar+35% H2
  • *Is this a welding grade gas? Where is this applied?
nitrogen h 2 mix
Nitrogen – H2 mix *
  • 95%N 2+5% H2
  • *Can you weld with this gas? In what application?
argon co 2 o 2 mix
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?
argon helium co 2 mix
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?
argon co 2 helium mix
Argon – CO2 – Helium mix*
  • 75%Ar + 15% CO2 + 10%He
  • *What advantage would this gas have over a 85% Argon + 15% CO2?
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