There are several welding processes available, with different advantages and applications, and some are better than others. But one thing all these welding processes have in common is the use of gases.
Welding gases play crucial roles in welding processes, such as shielding the weld pool from contaminants in the air and heating the filler electrode and parent metal. Welding gases include inert and active gases alike, and the most commonly used ones are Argon, Carbon dioxide, Helium, and Oxygen.
This article discusses welding gases in greater detail, covering the purpose of gases in welding and the different gases used. It also gives the prices of the most widely used gases and discusses gas safety precautions as well.
What’s The Purpose of Welding Gas?
The primary purpose of welding gas is to prevent contaminants like oxygen, water vapor, and dust in the air from getting into the weld pool. The gas is also used to clean the weld and for heating metals.
Welding gases can be either inert or reactive. Inert gases are inactive; they don’t change or cause any change to the weld, remaining the same throughout the welding process. These gases mainly shield the weld pool, allowing the weld to form without any defects.
On the other hand, reactive gases are active, reacting to different circumstances like temperature and metal type. These gases cause changes to the weld and themselves and enhance the way the weld is formed.
The primary purpose of welding gas is to shield the weld pool from elements in the air. In this role, the gas is called a shielding gas, keeping away impurities that can negatively affect the finished weld’s appearance and quality. For instance, oxygen in the air can oxidize the weld pool’s molten metal, reducing its corrosion resistance properties and causing a blackened weld bead.
Similarly, porosity, which significantly reduces the weld’s strength, happens when oxygen, nitrogen, and hydrogen in the air get into the weld pool.
As such, it’s nearly impossible to do MIG or TIG welding without shielding gases unless the filler metal used is flux-cored, which produces a slag that functions like shield gases.
Shielding gases can be inert, which allows them to remain stable, despite the extreme heat produced during the welding process. They can also be active, reacting with the metal and electric arc to affect weld speed, filler metal transfer, arc stabilization, weld penetration, and weld geometry.
Inert shielding gases are used for TIG welding, while active gases are used for MIG/MAG welding.
Purging gases help to remove impurities from the joint to be welded. Water vapor, oxygen, and other gases can react negatively with the hot metal as it’s being welded, resulting in a distorted and weaker weld.
In most cases, the purging gas is the same as the shielding gas. But while shielding gases act from above the weld, purging gases are applied from below, cleaning the joint as the weld progresses.
Instead of an electric arc, some welding processes use gas-fueled flames to heat the metal and filler rod to make the weld rather than an electric arc.
What Type of Gas is Used in Welding?
There are a limited number of gases used in welding processes, and these include:
Argon is an inert gas and one of the most abundant gases on Earth. The gas is used majorly as a shielding gas to keep out air from the weld pool and electric arc. It can also serve as a purging gas.
Hundred percent argon is used as shielding gas when MIG welding non-ferrous metals like aluminum, titanium, and copper. But with ferrous metals, you’ll need to add another gas like C02.
When used as a shielding gas, argon produces a thin penetration profile beneficial for fillet and butt welds.
Carbon Dioxide (CO2)
C02 is what we breathe out, and plants breathe in. Additionally, The gas is also released from decomposing organic matter. As a result, carbon dioxide is one of the most abundant gases on Earth and the least expensive shielding gas.
Carbon dioxide is a reactive gas and the only one that can be used in its pure form without mixing with an inert gas. As a shielding gas, C02 produces deep weld penetrations, making it ideal for welding thick metals. However, it creates a lot of spatter, which is one reason it’s commonly used with other gases to reduce the amount of spatter.
Hydrogen is the simplest gas, and it’s abundant on Earth. It’s also relatively simple to produce and burns without emission, with water as the byproduct.
The gas is only used in small quantities with other shielding gases because hydrogen is highly reactive to other elements. When used in small amounts with other gases, hydrogen produces increased heat in the weld, enhancing penetration and creating a much cleaner weld.
Helium is the second most abundant gas in the universe, but it’s in short supply on the Earth and is difficult to produce. As a result, helium is one of the more expensive welding gases.
Like argon, helium is chemically inert and used as shielding gas for non-ferrous metals and stainless steel. It produces a wide and deep penetration profile, making it suitable for use when welding thicker materials.
Helium also produces a hotter arc, allowing for faster metal transfer and higher deposition rates. The gas is commonly used with Argon and Oxygen in varying proportions.
Oxygen is a colorless, odorless, and tasteless gas, but also very reactive.
It’s mixed in small quantities (not more than nine percent) with other shielding gases, as too much of it will cause brittleness. Oxygen adds fluidity to the weld pool and increases the welding speed.
The gas causes oxidation and so should not be used with aluminum, copper titanium, and magnesium.
Nitrogen is the most abundant gas in our atmosphere, making up about 80 percent of the air we breathe.
It can be used alone as a shielding gas in laser welding and plasma cutting, increasing weld penetration arc stability.
Shielding gas blends containing nitrogen can increase the mechanical properties of metals that contain nitrogen. Nitrogen also serves as a blanketing gas for tanks and similarly enclosed spaces.
Acetylene is a highly flammable gas. In gas welding, It is used with oxygen to make a hot enough flame to melt most metals and filler rods.
No gas is perfect for all applications and situations, as they each have their shortcomings. Mixed gases create a balance by combining two gases so that one makes up for the other’s lapses and vice-versa.
For instance, consider two different gases, A and B, where A produces deeper penetration and much spatter, while gas B produces no spatter but a shallow penetration profile. By combining the two gases, you get the best of both worlds – a gas blend that’s better than either of its components, producing less spatter and good penetration.
Mixed gas blends aren’t limited to just two gases and can also be made from Three gases. Some gas mixtures used in welding include:
Argon and Carbon Dioxide
Shielding gas mixtures of 75 to 95 percent argon and 5 to 25 percent CO2 produce a smooth weld with minor spatter. The amount of C02 in the mix depends on the thickness of the steel to be welded. In other words, the thinner the steel, the lesser the amount of C02.
Unlike pure CO2, this mixture allows using the more efficient spray mode of metal transfer, resulting in higher deposition rates and productivity.
Argon, Carbon Dioxide and Oxygen
This shielding gas mixture is much like the Argon and CO2 mixture, producing smooth welds and minimal spatter. But with not more than five percent oxygen added to make the weld pool fluid and increase travel speed during the welding process.
Helium and Argon
A Helium and Argon gas mix is best for non-ferrous metals. Gas blends with 75 percent or more helium are ideal for aluminum and other alloys. You can also use a similar mixture with argon making up 75 percent or more.
Adjusting the proportions of either gas will change the penetration, shape of the weld, and travel speed. Use a mix with more helium when welding thicker metals. On the other hand, use more argon for thinner metals requiring narrow penetration.
Argon, Helium and Carbon Dioxide
There’s a wide range of mix ratios available for this combination, some with more argon and others with more helium. By varying the percentages, you can use this mixture for carbon steel, stainless steel, and aluminum.
Argon and Oxygen
Oxygen can be added to argon in amounts not more than five percent. The added oxygen significantly stabilizes the welding arc while increasing weld fluidity and filler metal droplet rate. It also influences the shape of the bead.
One percent oxygen added to argon is used for welding stainless steel using the spray mode of metal transfer. Increasing oxygen to two percent allows spray transfer mode on carbon steel and low alloy steels.
One percent and two percent oxygen additions yield similar results, but the weld bead will be darker and more oxidized with two percent oxygen added.
Finally, five percent oxygen mixed with argon is the most commonly used argon/oxygen gas blend for MIG welding carbon steel. The increased oxygen in the mix permits greater weld fluidity and higher travel speeds.
How Much is a Bottle of Welding Gas
The price of welding gas depends on two main factors: the size of the cylinder and the type of gas. Gas cylinders are available commercially in three sizes; 40, 80, and 125 Cubic feet (Cu/ft). There are larger cylinders than these three, but they’re only available on special orders or leased out for large-scale projects.
CO2 is the most inexpensive gas you can get. Gas blends with 75 percent argon and 25 percent CO2 are more expensive than pure CO2 and generally cost the same as 100% argon.
The table below shows price ranges for different gasses and cylinder sizes.
|75 Ar/ 25 CO2
|$235 – $240
|$315 – $320
|$360 – $365
|$235 – $240
|$315 – $320
|$360 – $365
Note that CO2 is sold in pounds rather than cubic feet, and 1 lb = 8.741 Cu/ft. So 40, 80, and 125 Cu/ft are approximately 5, 10, and 15 lbs, respectively. Prices for these amounts of CO2 are given below:
- 5 lb = $70
- 10 lb = $80
- 15 lb = $90
These prices include the cost of the gas as well as the cylinder. Refill prices are, of course, much lower.
How Much Welding Gas do You Need?
The amount of shielding gas you’ll need for a project depends on the amount of time it will take to make the weld and the flow rate of the gas per hour. Mathematically this is given as:
Gas needed = welding time X flow rate.
Welding time is given in hours, while the flow rate is in cubic feet per hour (CFH)
For instance, if you’ll use a flow rate of 20 CFH for four hours of welding, the volume of gas needed will be 80 Cu/ft (20 X 4).
It means you will need two 40 Cu/ft tanks or one 80 Cu/ft tank of shielding gas to complete the Job.
Where To Get Welding Gas
You can buy welding gas from places like TractorSupply and Airgas. These two are some of the biggest retailers and will usually have a store nearby.
However, If by chance none of them are available in your area, you can ask around at welding workshops, as they’ll likely know the best way to get the gas.
Still, another way to go is to check online on sites like Amazon and eBay.
All welding gases have the potential to be dangerous, depending on their characteristics. Handle flammable gases like hydrogen and especially acetylene with great care.
Moreover, always keep flammable gases away from the welding area unless when using them. And when you use them, be sure to have a class B fire extinguisher ready at hand.
With inert gases, there is no risk of a fire as they rarely react with other elements. However, there’s a risk of oxygen deprivation and unconsciousness if you weld in an enclosed area for too long. So when working in such conditions, make sure you take regular breaks and use gas detectors and extractor fans.
Finally, take care when moving gas cylinders around. Although they’re durable and can withstand some hits and falls, you shouldn’t place them in positions where they’re likely to drop or be hit by other objects, as the valve is a weak spot that can break off easily. A broken valve can be as dangerous as a bullet, as it will go off with the force of the gas trapped in the tank.
Frequently Asked Questions:
What Is the Best Gas for Welding Steel?
You can weld steel using both TIG and MIG welders. Argon is the best gas for Tig welding steel, as it’s cheaper and produces minimal spatter and better heat transfer.
When MIG welding steel, the best gas to use is a mix of 75% argon and 25% carbon dioxide (also called C25), this gas blend produces minimal spatter, good penetration, and weld geometry and won’t burn through thin Metals.
Can You TIG Weld With Mig Gas?
You can’t do TIG welding with MIG gases, as these gases are either active or semi-inert like CO2. TIG welding with any gas that’s not entirely inert like Argon and Helium will ruin your blow torch by oxidizing the tungsten inside.
Can You Mig Weld With Tig Gas?
The MIG welding process, despite its name, doesn’t use inert gases but Active gases or a combination of inert and active gases. The active gases like oxygen and C02 make the arc hotter and produce deeper penetration. If you use a TIG gas, you will end up with very little penetration.
Pure argon is the only inert (and TIG) gas that can be used for MIG welding. And even then, only use argon for MIG weld non-ferrous metals like aluminum, titanium, or copper.
Welding gases are used primarily to shield the weld pool from oxygen, water vapor, and dust in the air, which can deform and weaken the weld. The gases can also be used as purging gases to clean the joint to be welded and as fuel for scorching flames that can melt metal.
The most common gases used for welding include argon, CO2, oxygen, and helium. These gases are either inert like argon, nitrogen, and helium or active like oxygen, acetylene, and CO2.
When using active gases, ensure that there is a fire extinguisher nearby in case of a fire. There is the risk of unconsciousness with inert gases after long periods in enclosed spaces, so take regular breaks and use gas detectors and extractor fans.
Finally, take care when hauling gas tanks. The valve is a weak point, easily broken, and has the potential to become a dangerous projectile.