This article explores the different welding gases and how they are used. We are beginning with a clearer understanding of the functions of industrial gases and how they are applied in the welding process, and we explain their various characteristics and why they are used for their purposes of welding. For a piece of robust information, you can also read about types of welding gases and their purpose. It will amaze you that many gases have different applications, including medical purposes. More surprising is the air we breathe daily; they contain substantial industrial gases applied in welding applications.
The first step is to know that gases are classified as reactive and nonreactive or inert gases in scientific terminology.
The main difference between inert and reactive gases is in the names:
- Inert gases – are stable gases with very low to zero chemical reactivity with their surroundings. They work strictly as a protectant and do not impact the final consequences of the weld. Helium and argon are commonly used inert gases for welding.
- Reactive gases – well–react. Reactive gases combine chemically with the elements in the weld pool and can affect or change the properties of the metals in the weld. You can use these gases to change the nature of your weld. Reactive gases include nitrogen, oxygen, hydrogen, and carbon dioxide. These reactive gases are used in the welding process: They can be used pure or as a blend; When mixed in appropriate proportion. When the right quantities are applied, semi-inert gases can improve the quality of a weld.
The inert gas controls the weld and protects your metals from unwanted chemical processes. We can combine an inert gas with one or two reactive gases at a very low concentration in welding techniques. The reactive gases will make slight changes like adding more heat or changing the consistency of the filling metals.
While it’s essential to understand the difference between inert and reactive gases, It is necessary to know why and when to use each gas for its specific purpose.
Why Gas Used In Welding
Gases used in welding are for four primary purposes, and they are:
- Gas for Shielding
- Gas for Purging
- Gas for Blanketing
- Gas for Heating
We should not get this confused during the welding process gases, and fumes are produced; however, what we are discussing here is what gas is used to influence the welding processes. These gases are essential to achieving a great weld; after all joining two metals adequately is a success in welding.
Welding creates substantial heat, and as it is applied to the weld, it causes all manner of chemical reactions with the weld pool and the air surrounding it; this means if the welding environment is controlled adequately, we can get a great weld but a bad weld if we cannot control the weld environment. Why is the welding environment important, we will find out shortly.
Let us begin with the shielding gases as explained by Tulsa welding school
- Argon and helium are the two inert gasses used in welding. The properties of Internet gasses determined why they are used as shielding gases. We will briefly explain the properties of both gasse to appreciate why they are used for shielding during welding.
- Argon accounts for one percent of air and is a by-product of the air-reduction processes used to produce oxygen. This gas is suitable for shielding welds in flat and deep groves.
- Argon is suitable for easier starts and alternating current applications and longer arcs at lower voltages. 7 In pure form, argon is often used with aluminum and nonferrous metals.
- The addition of helium improves argon’s heat transfer properties, and combining argon with carbon dioxide or oxygen can help stabilize the arc.
- Helium is effective for mechanized applications but less forgiving for manual welding. Since pure helium creates an erratic arc, it can result in spatter when working with steel.
- When mixed with argon, helium can provide cathode cleaning. Even so, pure helium is ideal for magnesium, copper and aluminum. Other blends can be used on aluminum and stainless steel.
- Now that we have discussed the inert gasses or nonreactive gases, let us discuss the reactive gases of Hydrogen, Nitrogen, oxygen, and carbon dioxide.
Hydrogen is often used in combination with other gases. When added to argon, it can deepen penetration and increase welding speeds. On grades of stainless steel sensitive to oxygen, it can result in cleaner weld surfaces and better bead profiles.
The mixture of argon, carbon dioxide and hydrogen can raise arc temperature, narrow the arc and improve weld penetration.
Hydrogen isn’t perfect, though. If misused, it can cause weld porosity, a phenomenon brought on by too much-trapped gas, resulting in the formation of round holes. Cracking can also occur under the bead in carbon and low-alloy steel.
Nitrogen increases weld penetration and arc stability. Gas blends containing nitrogen can improve alloys’ mechanical properties and prevent pitting corrosion and nitrogen loss from the metal. 14
Like hydrogen, oxygen is usually used with other gases to shield the weld.
For example, oxygen is usually used in combination with argon during the welding process for these benefits 15:
- Arc stabilization
- Spatter minimization
- Metal transfer improvement
However, this gas can cause oxidation, so it can’t be used with copper, aluminum, or magnesium.
And be conservative with using it: An abundance of oxygen can result in brittleness.
Carbon dioxide is best suited for steel and is especially useful in inert metal gas (MIG) welding because it increases weld speed, penetration, and mechanical properties.
While inexpensive, carbon dioxide is not without its faults when used in welding. It causes a shakier arc and spatter loss, and working with it can produce a lot of smoke fumes on a job site. Mixing carbon dioxide with argon, however, can reduce spatter.
Carbon dioxide should also not be used for thin metals like aluminum. It’s usually too hot for thin metal to sustain.
Shielding Gases for Welding?
Shielding in welding is a process mainly used to protect the molten metal from the contamination and oxidation caused by harmful gases from the atmosphere such as Oxygen, Carbon dioxide, Nitrogen, and Water vapor; these gases also impact essential parts of the welding process such as
- Arc and metal transfer characteristics
- Fusion zone width
- Welding speed
- Weld penetration
- Surface shape patterns
- Undercut tendency
- Shielding gasses are also known as noble gasses, and inert gasses are colorless, odorless, and non-chemically reactive. Understanding this is fundamental because the properties of various gasses used in welding training are applied in real-world welding projects. It also means that choosing the wrong gas can result in defects and discontinuities.
- Shielding is by far the most common use for gasses in welding. Shielding gasses do precisely what it sounds like they do – shield your weld from unwanted contaminants.
- Think of it as a dome-like shield of gas over the welding pool, which is the place where the metals melt together. Although that’s not physically what’s happening, it’s a helpful mental picture.
- You can supply shielding gasses from an external source or burn the electrode. Electrodes in specific welding processes have a coating that releases the gas under heat. The electrode is the conductor.
- Why does a weld need shielding? to prevent effects of contaminants.
- By “contaminants,” we mean properties that will interact with the chemical processes or metals in the weld. Depending on the type of metals you’re welding, contaminants could include oxygen, nitrogen, water vapor, or other chemicals and elements in the environment around you.
- Purging gas is similar to shielding gas but is used underneath the weld joint rather than above it. Instead of a protective shield, purging gas pushes the unwanted contaminants away from the weld joint.
- Purging gas is mainly used for a new weld where you’re combining two separate pieces for the first time. Once you get that first weld stable, you probably won’t need to use purging gas underneath.
- Purging is usually applied while welding stainless steel. You seal the base of the joint and then literally blow the purging gas across it to keep the area clear of contaminant elements.
- Purging gases can be the same as shielding gases.
- Blanketing gas protects the metals after the weld is complete and as it cools. Think about it – you’ve put all this work into safeguarding your weld from contaminants – but when you finish welding, it’s still scorching and vulnerable to unwanted reactions from the air around it.
- Blanketing gas can be added to the tank or space where your weld is cooling. The gas ensures the purity of the area around the weld and keeps any unwanted gasses or reactions from occurring.
- Heating gas preheats metals before welding. You will typically see this in gas welding or brazing, for example.
- Cracks can develop during the cooling process if it cools too quickly, depending on the metal. Applying heat before the weld will ensure the metal cools more slowly and maintains its structure.
- Heating gas is most often used when gas welding steel, which is most susceptible to cold cracks.