shield gas selection for welding

Discussion in 'Welding Tips and Welders' started by grumpyvette, Jan 27, 2009.

  1. grumpyvette

    grumpyvette Administrator Staff Member

    read these, links below,
    keep in mind that allowing outside air to enter the molten metal weld pool, generally results in a far less dense and as a result noticeably weaker weld structure, some what like a sponge if you could examine it under an electron micro scope, use of a surrounding barrier of outer shield gas allows the molten metal to cool as a much stronger and denser more or less solid crystalline structure, this will generally result in a weld that looks better and provides a good deal stronger bond between the two welded original structures and a weld that requires noticeably less mechanical cleaning of its outer surfaces with grinding to clean its exposed outer surface.
    this is especially helpful on processes like welding two thin sheet metal body panels as it will almost always require significantly less panel prep with grinding, sanding, bondo etc.
    if you get a chance weld two scrap body panels one with flux core and one with MIG or even better TIG welds with the proper matched shield gases.
    I think, youll notice a very obvious difference in both the surface of the welds and if you bend the welded joint several times, the effort it takes to crack the welded joint resulting it the welded area failing due to physical stress on that joint.
    a properly welded MIG or even better TIG weld, will generally duplicate or even exceed the structural strength of the two parent panels you joined

    viewtopic.php?f=60&t=77 ... fm?ID=1024

    welding rods usually 36" long so 37" pipe with one end glued is not a bad idea

    look here



    ask questions here, because they know more than I do about many parts of the welding arts ... ay.php?f=4
    "Stainless should be welded with 100% argon. It is practical for most shops and hobbyist. There is a helium mix that is better but way expensive and it has to be purchased in larger quantities you would never use so forget that. Stainless is welded with straight polarity or NCEN (Direct Current Electrode Negative).

    One thing you should consider is back gassing the weld joint. Tape up the ends of the collector with cardboard (away from the welding heat) and run a hose inside to fill it with argon. The back side of a non back gassed stainless joint will crystallize due to oxygen exposure. A common term is sugar behind the joint. It is also important to be very aware of pre flow and post flow when welding stainless. It is hard to make yourself hold the torch over the weld for 5 seconds after the arc stops but you got to do it.

    I bought stainless wire for my mig and tried it with 75/25 once. It will weld stainless but it isn’t pretty. Hence the tig purchase.

    Aluminum is welded with 100% argon and AC current. Most welders have an adjustable balance control (time at DCEN/DCEP) to achieve the best cleaning action and penetration. That is the reason AC current is used.

    when your talking about mig/tig shield gas flow rates
    gauge on right side indicates tank pressure
    gauge on left side indicates flow pressure
    15-20 psi flow pressure is usually adequate, but ask your local miller dealer for tips/advice, and gas mix info


    if you buy a bottle of shield gas like argon for mig welding, the cost is usually "at least around here "about $240 one time plus $45 to fill (first fills usually included) and about every 6 years you need to pay about $50 -$60 to get the tank re certified as safe to fill, be VERY SURE YOU BUY A TANK STAMPED PRIVATE OWNED or it will be swapped out for a rental tank when its refilled, and get your tank REFILLED or your very likely to get someone elses tank that needs to be certificated.
    "yes that can mean making two trips or waiting an hour or more to get it filled"
    most gas tank supplys will only refill their tanks or some ones they have an exchange agreement with, and the tanks you find at pawn shops frequently FAILED the last re-certification and can,t be refilled ANYPLACE

    OR you can rent a tank, generally theres a security deposit that varies , and a monthly charge , that can run $15-$30 per tank, plus you pay for tank swaps (your empty for their full each time about $34, around here, but you never pay for re-certification, so it depends on what your doing which is better.

    how long a tank will last obviously depends on usage but a full size tank lasts about 2, 8 hour days of fairly heavy welding or several months to a year of small jobs
    "IF your going to weld a great deal its more than likely cheaper to rent, it cost me about $240 for a full size tank filled that I OWN, but if you own a tank about every six years you need to pay about $60 to get it re-certified, and it costs about $45 per refill, and you need to wait to get the tank refilled, which can take a few hours if they are busy so you get the same tank back.
    if you rent cost varies wildly but $10-$20 a month on tank rental and $30 per refill is rather common, and a 100$ tank security deposit that you get back if you return the tanks common.
    BTW if your looking for a light duty mig that will weld up to 3/16" millers got this on sale
    and it will do about 80% of the automotive welding that most guys get into,
    but keep in mind, when you purchase a MIG welder you still need a shield gas tank ,gauges , mig wire, a face shield etc, with any welder so that price of the welder alone is not all inclusive
    120 volt feed $549
    I know a couple guys who bought these lincoln mig welders and they find they have zero complaints, but then , keep in mind I find that, its almost universal, that unless you do a good bit of welding on a nearly constant basis, with several different welders, and know what your looking at when the welds are done, youll tend to think darn near any welder you own is doing a decent job regardless of reality, simply because youve got little to use as a comparison.
    230 volt feed $878
    yes I admit Im a tool junky but after using a buddies 252 miller I saved up for over a year to get one, yes I rarely use it to near its max capacity but keep in mind duty cycle limitations are nearly something you can ignore on most welding
    230 volt feed $2450

    Last edited by a moderator: Nov 2, 2018
  2. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    [quote="sz0k30 Said:"
    NEVER EVER get a welder that does not use gas. A total waste of money. No matter how good of a deal it may seem, its not.
    yeah Id be inclined to agree that the MIG welders correctly used with shield gas are capable of producing noticeably better weld quality than FLUX CORE "welders"[/quote]

    something like this is in my opinion a frustrating P.I.T.A. ...
    learning to correctly TIG weld with a decent TIG welder will open your eyes,
    too huge field of options, and a myriad of potential and until then un-dreamed of ideas
    owning a decent MIG and TIG welder and a heavy duty drill press or better yet a MILL and lathe ,
    leaves you open to the potential to build a huge assortment of custom, & unique and in most case's,
    project's with a great deal more performance potential than your limited too buying components off the shelf.

    a bit more spent will result in noticeably better results, but remember youll still need tanks and gas and wire, a face shield etc a-out... ing-h... ckets... uot-co... /8201-... g-fr-p... -half-...

    In welding, there is no single universal welding process that is used for all applications. The process used must be varied depending on the type of material being welded.

    Whether or not that material is ferrous or non-ferrous, magnetic or non-magnetic, and what the end use application of the metals is.

    These considerations will also influence the type of gas used in the welding process.

    What Welding Processes Use Gas?
    Table of Contents [show]

    Two of the most common types of welding use gases in their process.

    Gas Metal Arc Welding - (GMAW or MIG Welding) uses a wire welding electrode on a spool that is automatically fed onto the two weld piece ends to be joined together and an arc created by an electrical current between the metal and the wire shielded by a shielding gas to heat the wire to the melting point.

    Gas Tungsten Arc welding - (GTAW or TIG welding) uses a tungsten electrode and shielding gas to heat the filler metal placed on two weld piece ends to be joined together. A constant current power supply produces the energy to create an arc through a column of ionized gas and metal vapors (plasma).

    What Purpose Do Gases Serve In MIG And TIG Welding
    Shielding gases are commonly used in gas metal arc welding (MIG) and gas tungsten arc welding (TIG) to protect the weld area from oxygen and water vapor.

    Oxygen and water in the atmosphere can make the welding process more difficult and cause a deterioration in the quality of the weld.

    Shielding gases are typically denser than air so they can wrap around the weld and will require low flow rates to distribute the gas. They fall into two categories- inert (noble gases) or semi-inert.

    Helium and argon are the only two noble gases used in welding.

    They are sometimes used in 100% pure form but can also be mixed or blended with other semi-inert gases such as carbon dioxide hydrogen or nitrogen to improve weld characteristics on certain types of metals.

    The use of shielding gases provides several advantages in the welding process:

    • It Protects the welding arc.
    • It is possible to weld at higher temperatures without the material oxidizing.
    • There is very little loss of alloying elements as the metal transfers across the arc.
    • Side effects such as burn-in and spatter can be reduced.
    • Individual gases can be adjusted to the requirements of the material being welded.
    Why Gas Blends Are Important
    Shielding gases protect the liquid metal pool created in the welding process from atmospheric contamination.

    They essentially remove potentially reactive gases such as oxygen and nitrogen as well as water vapor from the vicinity of the weld. They can also stabilize the arc and enhance the metal transfer mode.

    In addition, the shielding gases can change the basic mechanical properties of the weld area through their interaction with the base metal and filler metal. This affects the strength, hardness and corrosion resistance.

    The various shielding gases used in welding have specified properties and functions. Those most commonly used are in this table.

    Gas Effect produced Arc behavior Cost
    Hydrogen (H2) Better bead surface, higher arc temperature, good ignition, higher weld speed Stable, concentrated arc Cheap
    Argon (Ar) Inert noble gas, improves oxide breakdown, improved control of the weld pool, confined penetration Stable arc Moderate
    Helium (He) Inert noble gas, supplies more heat input, improves penetration and fluidity of weld pool Unstable, wandering arc Expensive
    Nitrogen (N2) Can build nitrides in high temperatures Wandering arc Cheap
    Carbon Dioxide ( CO2) Used in small ratio to oxidize and stabilize the arc, improves wettability of the weld bead,deep weld penetration Unstable arc Cheap
    Oxygen (O2) Used in small ratio to oxidize and stabilize the arc, improves weld pool fluidity & weld penetration Never used alone Cheap
    Quite often, blends of two or three gases are used to improve the efficiency and quality of the weld for specific base metals and filler metals.

    By adjusting the composition of the shielding gas, you can influence the distribution of heat to the weld. This, in turn, can influence the shape of the weld metal cross-section and the speed of welding.

    The increase in welding speed can be substantial. As labor costs make up a considerable amount of overall welding costs, this can relate to a potential for significant savings.

    Gases Used In MIG Welding
    Many types of gases and gas blends can be used in MIG welding.

    The choice of which to use largely depends on the type of material you are welding.

    Argon mixed with CO2 in a 75%/25% blend will increase the weld penetration and bead wetting characteristics and can be used to join carbon steel and low alloy steels.

    Tri-mix blends of argon, helium and CO2 in a 90%/7.5%/2.5% ratio are ideal for welding stainless steel because it provides good arc stability and depth of fusion.

    Welding of aluminum is typically done with 100% Argon. However, if the aluminum being welded is thicker than ½ of an inch there may be Helium added to the mix to increase the heat penetration.

    Either 100% pure argon or a blend of argon and helium in a 60% /40% mix are the most common gases used to weld nickel alloys to improve penetration and weld pool flow.

    Pure argon or a blend of argon and helium in a 75% /25% mix are the most common gases used to weld copper alloys. This helps to improve penetration and weld pool flow.

    Gases Used In TIG Welding
    Unlike MIG welding, relatively few gases can be used for TIG welding.

    Pure Argon is probably the most popular type of shielding gas for TIG welding because it can be used on every type of metal including aluminum.

    Pure argon provides good arc stability and requires less cleaning action as the arc is narrow and concentrated so you can get a precise weld without a lot of bead rollover. It will typically produce a completed weld with a brighter, shinier surface appearance.

    Argon and helium, where helium is 50% of the mix, allows for hotter welds while working which can create a wider heat profile and better conduction of heat.

    It is probably the second most common type of shielding gas for TIG welding and it is used for some specialized applications. The extra heat comes at a price though, so you’ll have to carefully monitor the weld to make sure you are not burning through the metal.

    Pure helium or high percentages of helium (He-90%, Ar-10%) shielding gas are used primarily for TIG welding with direct current electrode negative (DCEN).

    Often designed as seam welders, the combination of GTAW - DCEN. The high heat input from the gas used can provide fast welding speeds and outstanding penetration.

    Finally, there’s straight hydrogen. In some case, welders may opt to work with hydrogen because it increases the heat input while welding.

    It creates a hotter, wider bead that penetrates deeper into the metal. This is particularly advantageous in working with stainless steel.

    Safety With Your Welding Gases
    Since gases are invisible their presence is not readily identifiable. But they do have the potential to asphyxiate, burn or harm users.

    The following safety precautions and tips should be noted by weld operators.

    The National Ag Safety Database offers the following safety precautions:

    • Inspect equipment for leaks at all connections using approved leak-test solution.
    • Inspect hoses for leaks and worn places.
    • Replace bad hoses.
    • Protect hoses and cylinders from sparks, flames and hot metal.
    • Use a flint lighter to ignite the flame.
    • Stand to the side (away from the regulators) when opening cylinder valves.
    • Open cylinder valves very slowly to keep sudden high pressures from exploding the regulators.
    • Only open the acetylene cylinder valve 1/4 - 3/4 turn; leave wrench in place so the cylinder can be quickly closed in an emergency.
    • Open and light acetylene first, then open and adjust oxygen to a neutral flame.
    • Close the acetylene torch valve first when shutting off the torch ( a "pop" might occur as the oxygen "blows out" the flame, but this eliminates the possibility of the flame burning up the acetylene line).
    • When finished, close cylinder valves, bleed the lines to take pressure off regulators, then neatly coil hoses and replace equipment.
    • Have a fire extinguisher easily accessible at the welding site.

    National Ag Safety Database

    The shielding gas used during the MIG or TIG welding process is a key component in its success.

    In order to achieve proper penetration, uniform beading and good welding results the correct shielding gas must be used when welding using the MIG or TIG welding methods.

    Using incorrect shielding gas results in poor penetration, irregular bead shapes, excessive splatter, overheating, lack of arc control and quick burning of the electrode.

    It’s important to learn about the proper gases to use and take due caution while using them.

    Hi, my name is Gregory! I have been welding practically all of my life and love it. As I have gotten older I have started to weld less and less, so in order to continue my love for welding I created this website. I like to write about my experiences and help you all become welders. I hope that you enjoy the site!

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    Last edited: Oct 21, 2018
  3. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member guide.html


    Acetylene (C2H2) is a colorless, highly flammable gas. Mostly used for oxy-fuel applications, acetylene has a high heat release in the primary flame and a low heat in the secondary flame. It has the hottest flame temperature of the commercially available fuel gases (6,300 °F/3, 480 °C) and is an excellent choice for welding, brazing and cutting of steel alloys less than 1 inch thickness.

    Interesting Info: An Acetylene cylinder has a tank pressure of 250 psi at 70 Degrees F

    Air is a colorless, odorless, nonflammable gas. Industrial air is used in air carbon arc gouging and in plasma arc cutting (PAC) processes.

    Colorless, odorless, tasteless and non-toxic, argon (Ar) is a noble gas that comprises 0.93% of the earth's atmosphere. Argon can provide an inert and clean environment free from nitrogen and oxygen for annealing and rolling metals and alloys. In the casting industry, argon is used to flush porosity from molten metals to eliminate defects in castings. In the metal fabrication industry, argon is used to create an inert gas shield during welding. Argon is frequently blended with carbon dioxide (CO2), hydrogen (H2), helium (He) or oxygen (O2) to enhance the arc characteristics or facilitate metal transfer in Gas Metal Arc Welding (GMAW or MIG).

    Because 100% argon can be used to TIG weld all metals and thicknesses you only need one type of gas in your shop to handle all of your welding projects. MIG welding aluminum is different than welding steel when it comes to shielding gas requirements. For aluminum, 100 percent argon is the gas of choice.

    Carbon Dioxide (CO2) is a tasteless, colorless, odorless, nonflammable gas. It is commonly utilized with argon (Ar) as a shielding gas during welding or in some cases it is used in pure vapor state. This prevents atmospheric contamination of molten weld metal during gas shielded electric arc welding process.

    Helium (He) is the second lightest elemental gas next to hydrogen. Colorless, odorless, tasteless, nontoxic and chemically inert, helium is nonflammable and has a high thermal conductivity. It is used to create an inert gas shield and prevent oxidation during welding of metals such as aluminum, stainless steel, copper and magnesium alloys. The addition of helium generally increases weld pool fluidity and travel speed.

    Hydrogen (H2) is the lightest of all gases. Colorless, odorless, tasteless and nontoxic, hydrogen exists as a gas at atmospheric temperatures and pressures. In metal fabrication, hydrogen serves as a protective atmosphere in high-temperature operations such as stainless steel manufacturing; commonly mixed with argon for welding austenitic stainless. Hydrogen is used to enhance plasma welding and cutting operations.

    Nitrogen (N2) is a diatomic gas which comprises 78% of the earth's atmosphere. Colorless, odorless, tasteless, and nontoxic, nitrogen exists as a nonflammable gas at atmospheric temperatures and pressures. Nitrogen is utilized as a purge gas with stainless steel tube welding. Nitrogen can enhance plasma cutting, food processing, heat-treating. Small additions to argon based shielding gases can be used for welding stainless steel by the Gas Metal Arc Welding (GMAW or MIG) process.

    Oxygen (O2), which comprises 21% of the earth's atmosphere, supports life and makes combustion possible. Colorless, odorless and tasteless, oxygen is used to support oxyfuel cutting operations. Oxygen may be added in small quantities to shielding gases. Oxygen is also used as the plasma cutting gas (with Hafnium electrodes) on carbon steel.

    Propane (C3H8) is a colorless, flammable, liquefied gas with a natural gas odor. The flame temperature of the oxy-propane flame is lower than acetylene and propylene. The primary flame releases low BTU when compared to propylene or acetylene, which increases preheat time. Propane is commonly used by scrap yards for cutting carbon steel, where the cut quality is not critical. Where cut quality is not a concern, propane may be a cost-effective fuel gas.

    Interesting Info: A Propane cylinder has a tank pressure of only 110 psi at 70 Degrees F

    Propylene (C3H6) is a colorless, flammable, liquified gas with a faintly sweet odor. It has high heat release in its primary and secondary flames. The heat release in the primary flame cone is similar to acetylene. The BTU capacity of the outer flame is superior to that of acetylene. Propylene combines the qualities of an acetylene flame with the secondary heating capacity of propane. The fuel gas burns hotter than propane; however, the cutting speed should be calculated on a case-by-case-basis before choosing this as the most economical choice as your fuel gas.

    Interesting Info: A Propylene cylinder has a tank pressure of only 137 psi at 70 Degrees F

    Argon/carbon dioxide blends are versatile mixtures for welding Carbon, Low-Alloy and some Stainless Steels. Increasing the CO2 content will increase weld penetration and bead wetting characteristics. At higher current levels and CO2 content, increased spatter may result. Ar/CO2 blends can be used to join a wide range of material thickness while utilizing a variety of modes of metal transfer.

    Principal Applications
    Ar/CO2 blends are used for all kinds of structural steel, farm implements and machinery. Lower levels of CO2 can be used for pulsed arc or spray arc welding, while higher levels > 20% are used for short arc welding and the shielding of some flux-cored wires.

    ARGON 95% - 5% Co2
    This blend is used for pulsed spray transfer and short-circuiting transfer on a variety of material thicknesses. A 5% mixture may be used for GMAW-P of Low Alloy Steels for out-of-position welding. The arc forces that develop give this mixture more tolerance to mill scale and a more controllable puddle than an argon-oxygen blend.

    This blend performs similarly to the 5% blend, but with increased heat input providing a wider, more fluid weld puddle in either short-circuit or spray transfer.

    ARGON 85% - 15% Co2
    This blend has been used for a variety of applications on Carbon and Low-Alloy Steels. In the short-circuit mode of transfer, maximum productivity on thin gauge metals can be achieved with this blend. This is done by minimizing the excessive melt-through tendency of higher carbon dioxide mixes, while increasing deposition rates and travel speeds. As the carbon dioxide percentages are lowered from the 20% range (maximum spray arc levels), improvements in deposition efficiency occur due to decreasing spatter loss. This blend will support the spray arc mode of transfer.

    ARGON 80% - 20% Co2
    May be used for short circuiting or spray transfer welding of Carbon Steel.

    This blend is commonly used for GMAW with short-circuiting transfer on Low Carbon Steel. It was formulated to provide optimum droplet frequency on short-circuiting transfer using .035 and .045 diameter wire. This blend operates well in high current applications on heavy base metal. It promotes good arc stability, weld pool control, and weld bead appearance. This blend will not support the spray type mode of metal transfer.

    Argon/oxygen blends are mostly widely used for conventional and pulsed spray transfer on clean (little or no scale or residual oil), plain Carbon and Stainless Steel. These blends, typically 1, 2 or 5% oxygen, provide good arc stability and very low levels of spatter and fume. Higher levels of oxygen will also increase puddle fluidity that may make out-of-position welding more difficult.

    Principal Applications
    Generally used for welding heavy section Carbon Steel for farm equipment, military transports, ships and automotive assemblies. These blends are also used for spray arc welding of both ferritic and austenitic Stainless Steel components.

    ARGON 99% - 1% OXYGEN
    This blend is primarily used for spray transfer on Stainless Steels. One percent oxygen is usually sufficient to stabilize the arc and improve the droplet rate and bead appearance.

    This blend is used for spray arc welding of Carbon Steels, Low-Alloy Steels and Stainless Steels. It provides greater wetting action than the 1% oxygen mixture. Weld mechanical properties and corrosion resistance of welds made with 1% and 2% oxygen additions are similar. However, bead appearance will be darker and more oxidized for the 2% blends with stainless steels.

    ARGON 95% - 5% OXYGEN
    This blend provides a more fluid but controllable weld pool. It is the most commonly used argon-oxygen mixture for general Carbon Steel welding. The additional oxygen also permits higher travel speeds.

    This tri-mix blend is widely used for short-circuiting transfer welding of Stainless Steel in all welding positions. The carbon dioxide content is kept low to minimize carbon absorption and assure good corrosion resistance, especially in multipass welds. The argon and carbon dioxide additions provide good arc stability and depth of fusion. The high helium content provides significant heat input to overcome the sluggish nature of the stainless steel weld pool.

    TRI-MIX – 66% Argon – 26.5% Helium – 7.5% Co2
    This tri-mix blend has been developed for spray and pulsed spray arc welding of both Carbon and Low-Alloy Steels. It can be used on all thicknesses in any position. This high-speed blend will produce higher quality welds over rust, oil, and mill scale than conventional two-part mixtures. It produces good mechanical properties and weld puddle control.

    TRI-MIX – 66.1% Argon – 33% Helium – 0.9% Co2
    This tri-mix blend is used for short arc, spray, and pulsed spray arc welding of Stainless Steel. It provides a higher welding speed, a broad weld with a flat crown and good color match, reduced porosity, and excellent alloy retention with good corrosion resistance.

    Laser gases are produced to meet the stringent requirements of the laser processing industry. Available as pure gases or as pre-blended mixtures of helium, nitrogen, carbon dioxide, and occasionally, carbon monoxide, Laser gases are used to generate the laser beam in a wide variety of CO2 lasers. Carbon dioxide lasers must be protected from the problems created by moisture, hydrocarbons, and other contaminants which can be introduced through the gas supply system. These impurities can reduce laser power, create unstable operating characteristics, damage expensive optics, and cause costly downtime. With a properly designed delivery system, the use of Laser gases help assures optimum laser performance, maximum operating duty cycle, and minimum maintenance costs.
  4. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

  5. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

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