Electrodes are essentially a coated metal wire that should generally be made out of materials similar in nature and composition to the metal being welded, and there are a variety of factors that go into selecting the right electrode for your particular project.
While Shielded metal arc welding (SMAW) or ‘stick’ electrodes are consumable and become a part of the weld, other electrodes such as those used in TIG welding are non-consumable, meaning they do not melt and stay separate from the weld, in these circumstances the use of a welding rod is required.
At Eng-weld, we know that selection of the right electrode is essential when it comes to the strength of the weld, bead quality, minimising splatter and cleanup.
Cellulosic electrodes are welding electrodes that are covered in a coating that contains organic materials. Generally, roughly 30% of the coating’s weight is cellulose, however in some countries around the world paper pulp and wood powder may be added to the coating in order to reduce the amount of pure cellulose.
The various organic compounds in the electrode will decompose in the arc, forming carbon dioxide, carbon monoxide and hydrogen, each of which increases the tension within the arc creating a stronger and harder arc. Due to this, a cellulosic electrode can penetrate up to 70% deeper than compatible electrodes with the same current values.
Generally produced with a thin or medium thickness coating, while this does produce slag, which can be cleaned after the welding process is complete, it can lead to significant spatter loss. However, due to coating the gap filling, vertical down welding and penetration capabilities of this type of electrode are very good.
The main features of Cellulosic Electrodes are:
- Deep penetration.
- Capable of welding vertically downwards.
- You are able to weld metal with good mechanical properties.
- The weld pool developed is smaller.
Low Hydrogen Electrodes
A low hydrogen electrode is essentially a Shielded metal arc welding (SMAW) consumable that contains a moisture content of less than 0.6%, compared to the more traditional 4-6% moisture content found in cellulosic electrodes.
As a general rule, low hydrogen electrodes such as E7018 stick electrodes offer the user low spatter levels combined with a smooth, stable and quiet arc. These features make these electrodes a great choice for experienced welders or beginners to learn with. The characteristics of these filler metal electrodes give the welder good arc control and minimise the need for a post-weld clean up.
Unlike other electrodes, such as E6010 or E6011, low hydrogen electrodes provide excellent rates of deposition and penetration, allowing the welding operator to add more weld metal into a joint at any time, thereby increasing the strength of the weld while simultaneously avoiding weld defects, lack of fusion for example.
The main features of Low Hydrogen Electrodes are:
- Good penetration.
- Good deposition.
- Quiet arc characteristics.
- Low spatter levels.
- Good fusion.
Mild Steel Electrodes
As a general rule of thumb, mild steel electrodes offer a quiet and stable arc, that offers low penetration which makes them ideal for bridging wide gaps and for working with thin plates. There are however, various different types of mild steel electrodes, each of which has slightly different properties which make them better suited for different applications.
For example, grade 6013 is a general-purpose, mild steel electrode that provides deep penetration, whilst retaining a smooth and stable arc. The arc of this electrode is easily regenerated, with a beautiful bead appearance and low spatter, combined with easy slag control for vertical-down welding.
Whereas the 7018 arc welding rod is again a mild steel electrode, engineered to weld high-tensile carbon-steel materials this rod is often used in structural welding due to the crack-resistant properties of the weld. It will however produce a large amount of slag, making it unsuitable for vertical-down welding.
The final mild steel electrode we will look at is the 6011. This versatile and deep penetrating electrode gives you a smooth and stable arc, used for the welding of mild steels galvanised and some other low alloy steels. Its coating produces a forceful and deep penetrating arc, while the slag layer is thin and easily removable.
Stainless Steel Electrodes
As with the other electrodes we have seen above, stainless steel electrodes again come in an array of variations, each slightly different than the last.
Here, we’ll be looking at 3 different grades of stainless steel welding electrodes, 308, 309, and 316, and when you should use them.
If you’re working with types 301, 302, 304, 305, and cast alloys CF-3 and CF8, then we would recommend you use 308L, including ER308LSi welding electrodes. These stainless steel electrodes are ideally suited for use on austenitic stainless steels, but for applications such as in the electrical power industry, we would recommend 308H, as this high carbon electrode provides better creep resistance for higher temperature applications.
When joining a low or mild steel alloy to stainless steel you should use 309L, including ER309LSi. This is also true when joining stainless steels that are dissimilar, for example, 409 to itself or to 304L stainless. In addition to this, they should be used for joining 309 base metals.
When it comes to working with 316L and 316 base metals, and their cast equivalents, CF-8m and CF-3M, you should only use 316L, including ER317LSi as your filler metal.
Some 308L applications may be substituted with 309L as the filler metal as they do not require molybdenum, unlike in 316 or 316L applications which do need molybdenum, and as such you cannot substitute 309 for 316.
Typical applications of various stainless steel electrodes include:
- Heat exchangers.
- Furnace parts.
- Expansion joints.
- Aircraft exhaust manifolds.
- Heating element tubing.
- Woven screen welding for high temperature processing of minerals.
Repair and Maintenance Electrodes
As we have seen above, there are a wide variety of electrodes available. Each one has slightly different properties and therefore a slightly different and unique function. When carrying out any repair and maintenance work you must ensure that the electrode you are using has the desired properties.
First, establish what the metal is that you will be repairing or maintaining. Then, you have to establish if you need universal electrodes or electrodes with specific attributes. Once you have all this information collected, you can then begin to weld, if you do not, and you use the wrong electrode your weld is liable to either fail or you may burn right through the metal you are working with.