When planning a welding job, from big to small, your choice of shielding gas can make or break the quality of your weld and ease of your work. The right shielding gas can make all the difference in the shape, transfer of heat, alloy content, fume generation, and a host of other details that will impact your finished weld.
As a fabricator, you will do well to have a basic understanding of the chemistry involved in shielding gases. So today, we want to remove some of that confusion for you by giving you a very brief, yet informative look at shielding gases 101. After beefing up your knowledge in this area, you will produce stronger, smoother welds in no time.
Basics of Shielding Gases
Before we get started you will want to keep these three things in mind about the way that shielding gases work. The simple properties of these gasses that will influence your weld are as follows:
- The thermal properties of your gas at high temps.
- The chemical reaction each gas will have with the materials in your welding plate and wire.
- How each gas will affect the method of transfer between metals.
Now that we have these three basics in mind, let’s take a look at the most commonly used shielding gases and their applications.
Argon is one of the pure gases used for welding, and is the most popular, the others include helium and carbon dioxide and we will get to those later. Argon is a noble, single atom gas that is used in welding because it is affordable, available and has minimal to no chemical reactions, leaving you with a strong weld and no fumes.
Argon gas is often mixed with a bit of oxygen and is ideal when welders want deeper penetration and a more concentrated arc. You will want to use it in MIG welding and TIG welding when working with non-ferrous materials such as aluminum, copper and zinc.
Here are a few helpful, binary shielding gas mixtures using argon.
- Argon-1% O2- -This mixture is useful for spray transfer on stainless steels, 1% oxygen is sufficient not only to stabilize the arc but to improve appearance and droplet rate.
- Argon-2% O2-Useful for spray arc welding on carbon steels, low alloy steels and stainless steels, this mixture will give you increased wetting over the 1% mixture while still providing the same quality weld.
- Argon-5% O2-Providing a weld pool that is more fluid, yet easier to control, this mixture is general carbon steel welding as the extra oxygen provides higher transfer speeds.
Let’s talk about Helium, another monoatomic noble gas that is commonly used in TIG welding on non ferrous materials. Unlike argon, helium has a high ionization potential and a greater conductivity, offering the opposite effects of welding with argon. This can give you a bit of trouble when striking an arc if you are not using high frequency arc starting. This gas is rarely used for TIG welds, unless working with copper.
Carbon Dioxide is a fairly complex, compound molecule that is typically used in flux-cored arc welding (FCAW). When working with CO2 keep in mind the way it will react in your arc, the carbon and oxygen will separate and if you are not careful they could oxidize your base metals and cause dealloying of your weld bead or puddle.
Working with CO2 can produce a nicely balanced width to depth penetration profile but in MIG welding it is unable to give you a spray transfer and it can give you a globular transfer with a fair amount of spatter.
Other Gases Used In Mixtures (The Basics)
Oxygen– A polyatomic molecule, generally used at mixtures of less than 10% in MIG applications.
Hydrogen– Generally used with austenitic stainless steels at a mixture of less than 10%
Nitrogen– Not generally used in shielding mixtures unless needed to improve corrosion resistance in duplex and super-duplex steels.
So, after your whirlwind education in shielding gases you can feel a bit more confident when deciding which to use in your next welding project. We hope that this has inspired you to learn more about the amazing chemistry happening on your welding table.