The arc welding process requires electrodes, and every method has a specific electrode coating type to achieve the arc that’s required for fusion. The electrodes will look different depending on the types of arc welding you’re planning to use.
Each family of electrodes will have variations that are designed for specific applications. A prime example: Some electrodes have an electrode coating which is a chemical mixture which is ideal for certain types of welding, including: stick welding and Shielded Metal Arc Welding (SMAW).
Why are Welding Rods Coated?
There are few reasons, better arc control, cleaner and stronger welds, and extra protection against impurities for the molten metal pool. In this article, we will take a closer look at electrode coating options and the benefits to choosing specific coatings for certain applications.
What Is the Electrode Coating Called?
There are specific electrode coating types with characteristics that make them an ideal job for certain applications.
Five of the most common coatings that you will see in use today:
1. Cellulose Welding Electrodes
These electrodes leave behind a thin layer of slag that’s easy to remove. The cellulose coating will break down into carbon dioxide and hydrogen during heating. This creates the shielding gas layer that protects the welding pool. But there is a risk of hydrogen embrittlement in the weld and these coatings work better with DC. Adding different coating elements may be possible to work with AC too. Cellulose electrodes are a good choice for vertical position with deeper penetration, rutile coating and less slag.
2. Rutile Electrodes
These are very similar to cellulose electrodes, but they have a higher percentage of titanium dioxide to create a gas shield of carbon hydrogen, nitrogen and oxygen. This makes the rutile electrodes a good choice for welding low carbon steel. But, rutile electrodes can leave behind trace amounts of titanium in the slag. Adding cellulose to the rutile electrode coating will improve protection for the weld pool, reduce spatter and lower the fume emissions. Rutile electrodes are a great choice for welding in all positions.
3. Iron Oxide Electrodes
These electrodes work with AC and DC current, and they produce easy to remove slag. The composition of this coating is high in oxygen which creates weaker weld deposits. There is a risk of hydrogen embrittlement too, but it’s lower than cellulose electrodes. The iron oxide electrodes have superior arc control which is ideal for precise bead placement and neater welds.
4. Iron Powder Electrodes
These are variations of other electrode coatings which add iron powder to the mix to improve weld quality and efficiency. These are a common variation type used with cellulose electrodes to use them with AC current.
5. Basic Electrodes
These are also known as hydrogen-controlled electrodes, and they need extra care before you weld with them. They must be stored in a dry area, and they are baked before you use them. If these requirements are ignored these electrodes can create an unstable composition that will compromise the welds. They deposit controlled low levels of hydrogen to minimize porosity and cracking. Basic electrodes are a good option to weld steel if they are stored properly.
What Is the Role of Electrode Coating In SMAW?
Why are welding rods coated when used with SMAW? There are few key advantages when a coated electrode is used. The flux will decompose on the top of the weld pool and this makes the process less prone to air movement that shields gas arc welding. This makes the welding process more predictable to prevent porous and weak welds.
The welder could use flux core MIG welding to achieve the same control and results by utilizing similar electrode principles. But TIG welding and to a lesser degree MIG welding require a wind-free environment for the welding process and to prevent defects caused by poor gas shielding for the weld pool.
There are certain metals that can be used to coat the electrodes for SMAW, and this can create a controlled current that’s stronger. This will make the penetration deeper, and the welds will be much stronger. Every electrode coating will add specific properties to the process, and this makes the selection of electrodes important.
Three Main Reasons Why using Coated Electrodes are Preferred for Welding:
First Reason: Current Control
All electrode coatings improve the control of the current that will be used to fuse the material together. There are bare electrodes, but they are rarely used because they create an arc that can be unpredictable and harder to control. The heavy coatings offer more control than light coatings, but even a light electrode coating is more controllable than a bare electrode. More control reduces spatter and it’s easier to create neater and smoother welds. The electrode coating will facilitate deeper penetration, and this will improve the strength of the welds.
Second Reason: Slag
The material that is left after the welding is completed can offer protection to the metal as it cools. This will improve the quality of the weld and it will be much stronger. There are many types of coated electrodes, and they all offer different advantages for a project. Understanding what every coating does is beyond the scope of this article, but many make it easier to clean slag when you’re finished.
Third Reason: Shielding Gas
There are specific electrode coatings that reduce impurities in the weld. When the coatings melt they produce shielding gasses that protect the weld pool from impurities, such as: oxygen, sulfur and other contaminants that can damage the weld. This cleans the metals of oxides and other impurities that can compromise the process.
What Is Heavy Electrode Coating
There are light and heavy (shielded arc) coatings that have certain properties in common. But, the main difference between them is that the heavy electrode coatings have greater strength properties. For this reason, heavy shielded arc coatings are often used in heavy-duty fabrication applications.
Electrode Coating-In Conclusion
Welding with an electrode coating can be beneficial if you understand the options and the characteristics of the electrode. There are many factors to consider, including: core metals, tensile strength, position and more. Choosing the right electrodes to meet the needs of the project will require research that takes these factors into account.