Welding flux is crucial as a prime anti-oxidising agent most commonly associated with arc welding. Choosing the right one will play an important role in the final quality of the weld. As anyone in the industry knows, becoming a welder is no easy feat as they are put to the test with extensive training. Welders must familiarise themselves with the various weld types, practices and the components for each welding method.
Did you know that flux core welding is known as one of the oldest arc welding methods? In this case, age has no bearing as is it remains one of the most effective and widely used methods for joining metal. The way it works is pretty straightforward as flux prevents welds from interacting with the environment, including air. Without flux, the base and filler material will interact with the atmosphere forming oxides or other unwanted compounds.
The Importance Of Flux In Arc Welding
When you weld something, the base metal and the filler will undergo substantial temperature changes in a short space of time. As mentioned earlier, if the heated metal interacts with air, it could result in oxidation. This essentially means that the weld now has an oxide layer which could reduce the overall strength.
In addition to oxygen creating poor welds, sulphides and nitrides can also affect the weld strength. Remember, the abundance of nitrogen in the atmosphere can result in metals being affected by inclusions. If the weld is not done properly and an oxide layer forms, it nullifies the metal’s corrosion resistance.
How Does It Work?
Because it can affect weld strength, technicians and engineers need to ensure that oxygen never reaches the weld seam when welding. In order for flux to work, it should be inert to the metals being joined. In laymen’s terms, there should be no reaction between the flux and the metals.
A good weld is a result of choosing the right flux material for the specific metals being used. Not only does weld flux prevent oxidisation but it also
- creates a protective slag over the molten metal
- removes impurities from the molten metal
- greatly reduces splatter
- prevents hardening by slowing down cooling time
The primary applications for flux are in Shielded Metal Arc Welding (SMAW), Flux-Cored Arc Welding (FCAW), and Submerged Arc Welding (SAW). Find out more about custom fabrication, coded welding and finishing.
What Are The Different Types Of Flux?
In welding, flux is mostly used with the electrode, often a 1mm to 3mm coating. There are also some electrodes where the flux is in a hollow cavity which means the electrode actually covers the flux.
Among others, the main benefit of flux-core welding is that it offers greater penetration which is ideal for thicker joints. That’s not all though as welders can also hold the torch and travel in a number of directions. Where arc welding is concerned, flux-cored electrodes are classified into four different types.
1. Rutile Electrode (R, RR)
Rutile is a mineral which mainly consists of titanium dioxide. Rutile electrodes offer a softer arc with lighter penetration compared to cellulosic electrodes. Here, welders can easily control the slag while the arc ignites and restrikes easily, often making it the preferred method, especially for out-of-position welds. This is the standard electrode for universal use with fine to medium droplet transfer and good overall mechanical properties.
2. Low Hydrogen Electrode
Basic flux consists of calcium carbonate, calcium fluoride, magnesium carbonate and a few other compounds. Using basic flux will result in enhanced mechanical properties and low levels of hydrogen diffusion. The fact that basic flux wires solidify slag means less support for the weld pool. While basic flux is preferred for high strength steels, they are less operable for out-of-position welding. Flux-core welding is commonly used for general repairs, shipbuilding and other types of manufacturing.
3. Cellulose Electrodes
Cellulose electrode coating offers much better penetration due to the combination of cellulose and other organic compounds generally produced with thin or medium coating thickness. When cellulose is exposed to high welding temperatures, it decomposes and produces carbon monoxide and hydrogen. It’s the production of these two gases that provide the weld with shielding from the atmosphere.
The high moisture content results in the weld metal containing high dissolved hydrogen levels. This requires special methods of welding and at elevated temperatures of 100–250 °C even when welding relatively thin materials. Cellulosic electrodes are widely used in welding of oil or natural gas pipelines using the vertical down position.
4. Iron Oxide Coating
Iron oxide coatings are a mixture of metallic oxides including iron, manganese and silica. When they are exposed to welding heat, they produce a molten acidic slag. The iron oxide coating improves arc behaviour and bead appearance helping to increase the metal deposition rate and arc travel speed.
The high levels of oxygen generated with iron oxide coating mean that it is not suitable for metals that easily undergo oxygen inclusion. Welders can prevent weld oxidation by adding deoxidizing agents with the welding core. Slag can easily be removed and it is highly suitable for positional welding.
Iron powder is added to all types of coating to increase the overall efficiency of electrodes. Adding the Iron powder will increase the deposition rate, reduce the voltage and enables the cellulosic electrodes to cope with alternating current.
What’s The Difference Between MIG Welding and Flux-Cored Arc Welding?
MIG welding, also known as Metal Inert Gas welding, is a process where the electrode is fed into the weld using an electrode gun. It is considered a semi-automatic process with a very high production rate. Compared to flux-cored arc welding, MIG welding doesn’t need a flux coated electrode as it uses shield gas as protection from environmental forces. This means operators can weld outdoors without the weather impacting the final product.
Cost, Equipment And Usability
Generally, MIG welding equipment is more expensive than for arc welding which contributes to the higher initial investment required for a MIG welding setup. The equipment for flux-cored arc welding is not only cheaper but it’s also easier to transport. It has fewer components as the system doesn’t need to provide air for the weld.
Compared to flux welding, MIG welding is much easier for beginners as the welder only needs to use one component at a time. While it has several benefits, MIG welding is not suitable for outside use as wind or rain can significantly impact the weld strength. Argon is possibly one of the most popular MIG shielding gases due to its affordability and inert chemical characteristics.
Interesting Read: ‘Underwater Welding: One Of The Most Dangerous Occupations’
Final Thoughts On Arc Welding
Welding is more than just joining metals as it involves a series of conscious decisions factoring in all the necessary details. Flux-cored arc welding is the most productive in terms of the amount of weld per hour.
A MIG welder typically produces 5 to 8 pounds of weld per hour while an FCAW welder can do around 25 pounds or more. Flux core arc welding can weld on half-inch plates in a single pass with full penetration on both sides, making it ideal for the shipbuilding industry.
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