simplifying shielding gas selection
TRANSCRIPT
-
8/3/2019 Simplifying Shielding Gas Selection
1/4
Search our Site Search
Advanced Search
Hom e Tech Cells Article Archiv e Industry Dire ct ory Subscript ions Advertise Media Cent er Login/Re gist er
Consumables Tech Cell - Article
Order Reprint
Print Friendly
Published in...
Practical WeldingToday
Subscribe to PWT
View This Issue
Related TechCells
Arc Welding
Art and Sculpture
Repair and Field
Welding
Aluminum Welding
Tags
sheilding, gtaw, gas ,garth-stapon, fcaw, co2,argon
Home \ Consumables \ Articles \ Simplifying shielding gas selection
Simplifying shielding gas selectionHow different gases and gas blends affect your welding application
By Kevin A. Lyttle , W.F. Garth Stapon
January 11, 2005
Have you ever asked yourself any of the following questions:
1. Why is welding affected by the shielding gases used?
2. Why are so many blends available for carbon steel?
3. Why can I use some gases for some materials and not
others?
Answering these questions will help you take the mystery out
of gas selection and make a choice that meets the needs of
your job.
You can choose from a variety of gas blends for gas metal arcwelding (GMAW), gas tungsten arc welding (GTAW), or flux
cored arc welding (FCAW). For each of these processes, the
shielding gas performs multiple tasks. It not only protects the
molten weld pool from exposure to the atmosphere, but it also
can promote a stable arc, determine the type of metal transfer
obtained, affect the welding travel speed, and impact the
quality of the finished weld deposit. Proper shielding gas
selection is critical to the ultimate success of the joining
operation.
You can take several approaches to selecting a gas, but to
make the best selection, you should know what your finished weld requirements are.
Ask yourself:
1. What kind of material must be joined?
2. How important is weld appearance?
3. Is spatter a concern?4. Is productivity improvement a prime interest?
5. Is deep penetration required, or should penetration be minimized to reduce burn-through in the joint?
6. Is it important to reduce welding fumes?
Keep these questions in mind as you address how to choose the best shielding gas for your application.
Which Process Is Best for This Application?
When deciding which welding process works best in your application, consider base material type, base material
thickness, and welding position.
As a rule of thumb, use GTAW for the most consistent joining results for materials thinner than 0.040 in. For thicker
materials, GMAW usually is a more economical process. FCAW should be considered in some instances to
enhance production rates, especially on scaled or rusty material or when welding out of position.
Additional considerations include joint penetration, welding position, and weld quality. It's more economical to weld
in the flat, horizontal, or slightly downhand positions because higher deposition rates are achieved. With FCAW or
pulsed and conventional spray GMAW, productivity can increase. Optimum weld quality can be achieved with
GTAW, but it requires greater welder skill and deposits less weld metal at slower speeds than GMAW or FCAW.
Sponsors
Advertising Information
12/21/2010 Simplifying shielding gas selection - Co
thefabricator.com//simplifying-shieldi 1
-
8/3/2019 Simplifying Shielding Gas Selection
2/4
Note: The multiple gas recommendations for the same process and material type and
thickness indicate that the selection will be based on the specific needs of the application
being considered.
One Gas, Two Gases, or Three Gases?
Three pure gases form the foundation for shielding arc welding processes: argon (Ar), helium (He), and carbon
dioxide (CO2). In many cases, other gases such as oxygen (O2), nitrogen (N2), and hydrogen (H2) may be added to
modify arc characteristics, the molten weld pool, or the weld. They also can affect the metal transfer and the overall
performance obtained in GMAW and FCAW. Tailoring the blend composition helps meet job requirements.
The next question to ask is which gases do what with GMAW, GTAW, and FCAW.
Argon. Argon is heavier than air, has low thermal conductivity, and can ionize easily in a welding arc. This means
that argon blankets the weld zone (so lower flow rates are needed), providing a relatively narrow arc characteristic
with good electrical conductivity (which means easy arc-starting). It can be used alone in GTAW and for GMAW of
aluminum and other nonferrous materials. Argon is a major component of shielding gas when spraylike, high-
productivity welding is desired in GMAW or FCAW for joining steel and stainless steel.
Helium. Helium is considerably lighter than air, which means higher flow rates are required than for argon or carbon
dioxide. It offers good thermal conductivity but lower electrical conductivity when compared to argon (arc-starting
requires higher voltage). Helium generally is combined with other gases to optimize performance characteristics.
Helium-enhanced mixtures can join all material types using GMAW, GTAW, or FCAW.
Carbon Dioxide. Carbon dioxide dissociates at arc temperatures and recombines as it contacts the cooler base
material, t ransferring arc energy t o the weld puddle. Additions of carbon dioxide provide wider and deeper bead
penetration. The oxidizing atmosphere produced within the arc zone results in more slag on the surface of the
solidified GMAW bead. Carbon dioxide can be used alone or as a major component (typically 5 to 25 percent)
mixed with argon for GMAW and FCAW.
Oxygen. Oxygen can improve arc performance in GMAW by enhancing arc stability while reducing the surface
tension of the weld puddle. This causes the puddle to be more fluid and have better wetting characteristics. Since
oxygen reacts with components of the welding wire or electrode, it contributes to the slag deposit found on the weld
bead surface. It's typically used as a 2 to 5 percent addition to an argon-based blend.
Nitrogen and Hydrogen. Nitrogen and hydrogen typically are used only for welding 300 series (austenitic) or duplex
stainless steels. Nitrogen can increase weld penetration and arc stability. Hydrogen can improve weld puddle fluidity
and surface cleanness. Their use generally is confined to stainless steel applications, because nitrogen can cause
porosity in carbon steel, while hydrogen can increase cracking potential in some of the same materials.
How Are Gases Blended to M ee t Application Needs?
To understand how different gas blends work in different applications, first it's important to understand the differencebetween two- and three-part blends.
Two-part Blends. Traditional two-part blends for GMAW of carbon steel are mixtures of argon with controlled
amounts of oxygen or carbon dioxide. Argon/oxygen blends were a s tandard choice for conventional or pulsed-spray
transfer, but in many applications, they have been replaced by argon/carbon dioxide mixes.
When argon/carbon dioxide blends are used in place of argon/oxygen mixtures, bead appearance improves with less
surface oxide and better bead shape and wetting control. Simultaneously, it can provide a more easily controlled,
broader, less fingerlike penetration profile. As the carbon dioxide level increases, penetration deepens, which can
cause burn-through on thin materials. Spatter and fume levels increase as the carbon dioxide content of the blend
increases. Converting from oxygen-enhanced blends to argon/carbon dioxide mixt ures generally produces more
consistent, higher-quality results. Travel speed increases of 15 to 20 percent can be achieved by selecting argon
with 5 to 15 percent carbon dioxide in applications in which argon with 1 to 5 percent oxygen has been used
previously.
For FCAW of carbon or stainless steel, argon with 25 percent carbon dioxide can be used to improve out-of-position
performance and reduce weld spatter. In special circumstances, lower carbon dioxide additions can be used with
specially formulated cored wires to reduce welding fumes. To prevent weld quality problems, the flux-cored wire
12/21/2010 Simplifying shielding gas selection - Co
thefabricator.com//simplifying-shieldi 2
-
8/3/2019 Simplifying Shielding Gas Selection
3/4
Author
must be used following the manufacturer's shielding gas recommendation.
Argon with 25 to 50 percent helium can be used to shield both GMAW and GTAW of aluminum and some other
nonferrous materials. Helium increases the heat input to the base material to enhance penetration and improve weld
puddle fluidity. Hydrogen (less than 10 percent) also can be added to argon for GTAW of austenitic stainless steel
to increase weld puddle fluidity and improve travel speeds by 10 to 25 percent while providing good weld bead
appearance.
Three-part Blends. To further enhance bead appearance, improve ease of operation when some base material
contamination is present, and increase flexibility and overall welding productivity, three-part shielding gas blends
may be a good choice.
Three-part blends can work well with short-circuiting, spray transfer, and pulsed-spray transfer. Benefits include
improved arc stability for reduced spatter and better weld bead wetting characteristics.
Argon with carbon dioxide and oxygen can provide versatility to join different types and thicknesses of carbon steel.Argon/helium/carbon dioxide mixes (25 to 35 percent helium, 1 to 10 percent carbon dioxide) can increase travel
speed. Argon/helium blends with controlled carbon dioxide content (1 to 2 percent) are suitable for joining stainless
steels when weld metal carbon control is important. For best results with GMAW, pulsed-spray transfer often is
recommended.
FCAW also is suitable for joining stainless steels, especially when welding out of position. Using cored wires
typically results in cost savings via higher weld metal deposition rates. They are suitable for joining material thicker
than 14 in. or when pulsed transfer isn't an option.
When joining 300 series alloys, optimum bead color and shape can be obtained by using argon/carbon
dioxide/hydrogen blends because of the reducing atmosphere created by the presence of the hydrogen. This mixture
minimizes ox ide formation on the bead surface and enhances the fluidity of the weld puddle. Hydrogen-enhanced
mixtures are not recommended for joining plain carbon steel.
The industry standard for short-circuiting GMAW of stainless steel has been a helium-based (85 to 90 percent) mix
with small additions of argon (5 to 10 percent) and carbon dioxide (2 t o 5 percent). This blend provides good bead
shape and color match, but it's not as versatile as some other mixtures. An argon/carbon dioxide/nitrogen blend can
be used in its place while also permitting use in high-productivity spray and pulsed-spray transfer. When combined
with high-silicon filler metals, weld puddle fluidity and wetting action can improve. Mixtures containing nitrogen arenot recommended when joining stainless to carbon steel.
What Is the Optimal Gas Flow?
Shielding gas flow rates are determined by the process, welding position, and operating parameters. With GTAW,
flow rates typically are from 10 to 20 cubic feet per hour (CFH). For GTAW, using a torch with a gas lens will help
ensure a laminar flow, which contributes not only to better weld quality, but also to 10 percent or lower gas
consumption rates.
With GMAW and FCAW, recommended flow rates vary widely30 to 45 CFHdepending on the welding position,
operating current, and shielding gas composition. For flat-position welding, helium-enhanced mixtures will require
slightly higher flow rates than argon-based blends. Gas flow rates may be reduced if the nozzle-to-work distance is
kept as close as possible. In many instances, production site surveys determine that shielding gas flow rates
typically are set in excess of 50 CFH. This can contribute to poor weld quality as atmospheric gases are drawn into
the arc zone because of excessive gas turbulence. Optimized flow enhances quality and reduces shielding gas
usage.
Shielding Gas and Cost-effective Joining
Shielding gas selection is critical to achieving cost-effective joining of carbon steel, stainless steel, and aluminum.
You can select one gas, such as argon for aluminum welding, to provide suitable arc stability, minimum spatter, and
good bead shape.
Two-part blends, such as argon/carbon dioxide mixtures, can perform well in most carbon steel and stainless steel
welding applications in which you use conventional or pulsed-spray t ransfer.
Lower carbon dioxide content will reduce the amount of welding fumes generated. Where you require enhanced bead
appearance, low spatter, and less postweld cleanup, three-part gas blends can provide good results while still
improving welding productivity.
Base metal thickness, welding position, operator skill level, and production demands require careful consideration
when selecting and optimizing the joining process. With an understanding of shielding gases, you can optimize your
welding process to reduce cost and improve quality.
Kevin Lyttle is manager of welding research and development for Praxair Inc., and Garth Stapon is marketing
manager, metal fabrication, eastern region, for Praxair Distribution Inc., 39 Old Ridgebury Road, Danbury, CT
06810, 800-772-9247, fax 800-772-9985, [email protected], [email protected],
www.praxair.com.
Related Company Showrooms:Praxair Inc.
Additional Information
Kevin A. LyttleManager, Welding Research and Deve lopmentPraxair Inc.
39 Old Ridgebury Road
Danbury, CT 06810
USA
12/21/2010 Simplifying shielding gas selection - Co
thefabricator.com//simplifying-shieldi 3
-
8/3/2019 Simplifying Shielding Gas Selection
4/4
Phone: 800-PRAXAIR
Contact via email
W.F. Garth StaponMarketing Manager, Metal FabricationPraxair Inc.
39 Old Ridgebury Road
Danbury, CT 06810
Phone: 800-225-8247
Contact via email
Showing 0 comments
Sort by Popular now Subscribe by email Subscribe by RSS
Add New Comment
Optional: Login be low.
Trackback URL http://disqus.com/forum
blog comments powered by DISQUS
Tools and Resources
Supplier Search
Article Archive
Buyer's GuidesSuperDeck
Subscriptions
Media Center
Useful Links
My Account
Login/Register
Contact Us
Learn and Connect
Industry Tradeshows
Educational Events
FMA StoreJob Board
Podcasts
Affiliations
FMA
TPA
FABTECH
Nuts & Bolts Foundation
Policies
Privacy
Copyright
Legal
Follow us on:
Facebook
Twitter
LinkedIn
FMA Communications, Inc.
833 Featherstone Road
Rockford, IL 61107815-399-8700
E-mail: [email protected]
Thefabricator.com provides metal
fabrication professionals with marke t
news, the industry's best a rticles,
product news, and conference
information from the Fabricators &
Manufacturers Association, Intl.
Thefabricator.com covers technologies in the following areas:
Coil Process ing Tube and Pipe Fabrication Fab Stories Automation and Robotics Cutting and Weld Prep Welding Stamping Saw ing Welding Inspection Training and Retention Power Tools Roll Forming
Resistance Welding Safety Industry Trends and Analys is CAD/CAM Softw are Laser Cutting Shop Strategies Waterjet Cutting Plasma Cutting Assembly Tube and Pipe Production For CEOs Press
Technology Finishing Repair and Field Welding Bending Machining Tes ting and Measuring Materials Handling Press Feeding Folding Tool and Die For Engineers Shop Management Laser Welding
Consumables Cutting Oxyfuel Cutting Aluminum Welding Hydroforming Art and Sculpture Metals/Materials Arc Welding Punching Shearing
12/21/2010 Simplifying shielding gas selection - Co
thefabricator.com//simplifying-shieldi 4