Welding is an essential process in various industries, and selecting the appropriate shielding gas is crucial for ensuring the quality of the weld.
One of the most common gases used in welding, particularly in Metal Inert Gas (MIG) welding, is carbon dioxide (CO2). This blog will explore why CO2 is used in welding, its advantages, and how it compares to other gases.
Let’s get straight to the point.
CO2 is widely used in MIG welding due to its cost-effectiveness, deep penetration, and ability to oxidise impurities. This makes it ideal for welding thicker carbon steel.
While it offers economical and practical benefits, such as rust removal and improved weld toughness, CO2 can cause increased spatter and arc instability when used alone. Blending CO2 with argon can mitigate these drawbacks.
However, CO2 is unsuitable for welding non-ferrous metals like aluminium or magnesium, whereas argon or helium is preferred. Proper ventilation is essential to avoid health risks from CO2 breakdown products.
The Role Of Shielding Gas In Welding
What Is Shielding Gas?
Shielding gas plays a vital role in welding by protecting the weld pool from atmospheric contaminants, such as oxygen, nitrogen, and hydrogen.
Without shielding gas, these elements could react with the molten weld, leading to defects like porosity and excessive spatter.
The choice of shielding gas can significantly impact the welding process, affecting the final weld’s arc stability, penetration, and mechanical properties.
Why CO2 Is Commonly Used
Carbon dioxide (CO2) is the most widely used reactive gas in welding, particularly in MIG welding. Its popularity stems from several factors:
- Cost-Effectiveness: CO2 is the most economical of the common shielding gases, making it a cost-effective option for many applications, especially when the primary concern is minimising production costs.
- Penetration: CO2 allows deep weld penetration, especially when welding thicker materials. The increased arc voltage facilitates this deep penetration.
- Oxidising Properties: When exposed to the high temperatures of the welding arc, CO2 breaks down into carbon monoxide and oxygen, promoting oxidation. This controlled oxidation can help with fluxing and preventing porosity, which are critical in achieving a strong and clean weld.
CO2 And Arc Stability
While CO2 is beneficial in many ways, it does have some drawbacks. Pure CO2 creates a less stable arc and more spatter when blended with other gases.
However, many industries find that a mixture of 75–95% argon and 5–25% CO2 provides a more desirable combination of arc stability, puddle control, and less spatter.
This blend also enables spray transfer welding, boosting productivity while enhancing the weld’s appearance.
Comparing CO2 With Other Gases
Different gases can be used in welding, each offering unique benefits and drawbacks. Here’s how CO2 compares to other common shielding gases:
- Argon: Pure argon is often used for welding non-ferrous metals like aluminium, magnesium, and titanium. It provides excellent arc stability and smooth welds but lacks the deep penetration that CO2 offers.
- Helium is another common shielding gas known for its broad and deep penetration profile, making it ideal for thick materials. However, helium is more expensive than CO2 and requires a higher flow rate.
- Oxygen: Often used in small quantities (less than 9%), oxygen can improve the fluidity, penetration, and arc stability in welding mild carbon, low alloy, and stainless steel. However, it is not suitable for reactive metals like aluminium and magnesium.
What Are The Key Advantages Of Using CO2 In Welding?
1. Increased Penetration
One of the primary benefits of using CO2 in welding is the increased penetration it provides. This is particularly advantageous when working with thicker materials, as the deeper penetration ensures a strong bond between the workpieces.
The increased arc voltage facilitated by CO2 allows for effective root and sidewall penetration, which is crucial in structural welding applications.
2. Cost-Benefit Analysis
CO2 is significantly less expensive than other shielding gases like argon and helium. This makes it an attractive option for large-scale welding operations where cost efficiency is a priority. Despite its lower cost, CO2 still provides sufficient protection against oxidation and other atmospheric contaminants, making it a practical choice for many applications.
3. Safety Considerations
While CO2 is generally safe to use, it is important to be aware of potential safety concerns.
Under the intense heat of the welding arc, CO2 can break down into carbon monoxide and pose health risks if not adequately ventilated.
Therefore, it is crucial to ensure that the welding area is well-ventilated to avoid the accumulation of harmful gases.
4. Rust Removal And Surface Preparation
Another advantage of using CO2 in welding is its ability to assist in rust removal. The oxidising properties of CO2 can help clean the surface of the metal, preventing common welding defects like porosity, poor fusion, and insufficient penetration.
This makes CO2 an excellent choice for welding applications involving carbon steels, which are prone to rusting.
5. Improvement In Toughness And Weld Quality
The toughness of a weld is a critical factor in its overall strength and durability. Using CO2, especially in combination with other gases, can improve the toughness of the weld by reducing surface tension and enhancing penetration outcomes.
This is particularly beneficial when working with carbon steels, where achieving the desired toughness can be challenging.
The Limitations And Challenges Associated With CO2 In Welding
Arc Stability And Spatter
One of the main challenges of using pure CO2 as a shielding gas is the need for arc stability and the increased spatter. This can make welding more challenging and require additional cleanup after welding.
However, these issues can be mitigated by blending CO2 with inert gases like argon, resulting in a more stable arc and less spatter.
Not Suitable For All Materials
While CO2 is highly effective for welding carbon steels, it is unsuitable for all materials.
For example, CO2 should not be used for welding non-ferrous metals like aluminium, magnesium, or titanium, as it can lead to oxidation and other welding defects.
For these materials, pure argon or argon-helium mixtures are more appropriate.
Conclusion
Carbon dioxide (CO2) is critical in welding, particularly in MIG welding of carbon steels. Its cost-effectiveness, ability to provide deep penetration, and oxidising properties make it a popular choice in many industrial applications.
However, it is important to understand its limitations, such as arc stability issues and unsuitability for non-ferrous metals. By carefully selecting the appropriate shielding gas based on the specific welding application, welders can achieve high-quality results that meet the required standards.
Frequently Asked Questions
Why Is Argon CO2 Used In Welding?
An Argon/Co2 mix produces superior results. The arc is softer and smoother, and the resulting weld deposit is slightly softer and more malleable than when pure Co2 is used.
Why Is CO2 Added To Argon?
Adding 20 per cent CO2 to argon produces a blend that can be used for short-circuit or spray transfer welding of carbon steel, but it can produce more spatter than the 15 per cent mix. The 25 per cent CO2 blend and argon are commonly used for GMAW with short-circuit transfer on low-carbon steel.
What Gas Is Best For Welding?
Argon (Ar) is the basic gas for MIG/MAG welding. Helium (He) can be added to increase the penetration and fluidity of the weld pool. Argon or argon/helium mixtures can be used for welding in all grades.
Can CO2 Be Used Alone For Welding?
Yes, CO2 can be used as the sole shielding gas in MIG welding. However, pure CO2 produces a hotter, less stable arc than mixed gases, which might increase spatter. Due to its deep penetration capabilities, it is commonly used in heavy fabrication.
How Does CO2 Affect Weld Quality?
While CO2 helps achieve good weld penetration and strength, the increased spatter and arc instability compared to argon or argon blends may require additional post-weld cleaning. However, with proper settings, it still produces reliable, high-quality welds.