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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!.
This Presentation is provided to you by: WPSAmerica.com Industry Standard Welding Procedures Software for AWS and ASME Codes
Choice of Shielding Gases Applications of Shielding Gases & Modes of Metal Transfer CWA-Toronto 4th Nov 2003 Viwek Vaidya
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 • 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 • Protect the weld pool from atmosphere • Provide a gas plasma - ionised gas • Support metal transfer and bead wetting
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 • 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 • High thermal conductivity • Narrow plasma column • CO2 and Helium produce globular transfer • Impossible to produce spray transfer!
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 • 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 • Low thermal conductivity • Expanded plasma column • Electron condensation heating
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 • 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 • 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 • 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
Shielding gas choice Quiz time!
Argon – Helium mix • 75%Ar+25% He • Applicable to what base metals?
Argon – Helium mix • 50%Ar+50% He • What is the bead shape? • What is the advantage with respect to Blue Shield 1?
Argon – Helium mix* • 25%Ar+75% He • *Can one spray transfer with this gas? Why? • What application ? Automatic or manual?
Argon – Oxygen mix • 98%Ar+2%O2 • This gas can be applied to what base metals? • What would be the bead shape?
Argon – Oxygen mix* • 95%Ar+5% O2 • Can one spray transfer with this gas? • *Can this be applied to Stainless steels?
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 – 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 – 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 – 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 – H2 mix * • 97.5%Ar+2.5% H2 • *Can this gas be used for GTAW of ferrous metals?
Argon – H2 mix * • 65%Ar+35% H2 • *Is this a welding grade gas? Where is this applied?
Nitrogen – H2 mix * • 95%N 2+5% H2 • *Can you weld with this gas? In what application?
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 – 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 – CO2 – Helium mix* • 75%Ar + 15% CO2 + 10%He • *What advantage would this gas have over a 85% Argon + 15% CO2?
Thank you for your attention! Questions?