Flux core welding is a popular arc welding process that relies on a tubular wire electrode with a special inner core filled with flux material. During the welding process, this flux melts to protect the weld pool from atmospheric gasses.
If you want to find out more about flux core welding, its types, and how it works in addition to its advantages and disadvantages, keep on reading this guide.
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What Is Flux Core Welding?
Flux Core Arc Welding, also known as (FCAW), is a welding process involving an electric arc between the workpiece and a wire electrode.
In principle, this process is very similar to Metal Inert Gas (MIG) welding, in which a continuous consumable electrode is fed through the welding gun and a high voltage electric arc melts it during the welding.
The main difference here is that, unlike MIG welding, where the shielding process is carried out by an inert gas that is fed through the gun, this process depends on the flux contained within the tubular electrode.
As the high voltage arc passes through the electrode, the flux core also melts, creating a shielding cloud that prevents atmospheric gasses from reacting with the molten weld.
However, different types of flux have various degrees of shielding, depending on the type of Flux core welding.
Since the flux core contributes to the shielding process, flux core arc welding is also called “dual shield welding”.
The extra shielding properties of the flux core make it a highly portable and convenient welding technique in outdoor and windy conditions.
How the Welding Process Works
In flux core welding, the welding machine produces a high voltage electric arc that travels through the electrode.
This arc generates enough heat to melt the electrode and the flux material over the base metal to create the weld pool and fuse it to the joint area.
Since the electrode is consumable, the machine provides a continuous feed of the flux-filled wire using knurled rollers, which makes it a major improvement on standard stick welding or manual metal arc welding (MMA).
Similar to MIG welding, this type of welding relies on shielding gasses for protection against atmospheric gasses, particularly oxygen and nitrogen that can oxidize and weaken the weld.
However, in some types of flux core welding, the shielding is created by the melted flux itself by forming a layer of slag as well as protective gasses that provides enough protection to the weld.
Types of Flux Core Welding
The process of flux core welding can take two different routes, depending on the method by which the weld pool is shielded from the atmosphere. As a result, we now have two different types of flux core welding, so here’s a quick look at each one of them:
Self Shielded Flux Core
This one is known as FCAW-S. In this type, the electrode’s flux agent is designed to melt and create a protective cloud that completely protects the weld pool from reacting with atmospheric gasses like oxygen and nitrogen.
This eliminates the need for using gas shielding equipment, which is not only large and inconvenient to move around, but also adds to the overall costs.
As a result, self shielded flux core welding is remarkably convenient for welding just about anywhere due to its portability.
In addition to its convenience, since this method doesn’t rely on gasses for shielding, it’s quite practical for welding in particularly windy areas, such as open sites.
Gas Shielded Flux Core
In gas shielded flux core welding, the flux within the wire still creates a protective cloud that shields the molten metals like self shielded flux core welding.
However, its shielding capabilities are secondary and may not be enough for full protection, so high pressure shielding gasses are the primary method of shielding.
This one is known as FCAW-G, and in this type, the flux agent is mainly there to deoxidize the weld pool while high pressure gas is mainly responsible for shielding the weld.
Although this one may not be as reliable as self shielded flux core welding, the gas shielded counterpart is better suited for thicker welds that require advanced shielding because it’s relatively faster and more penetrating power.
It’s also a better option for supporting the weld while working in awkward positions, such as vertically up or overhead.
How to Flux Core Weld
Now that you know more about the principle of flux core welding, here’s a simple guide that shows you how to do it:
1. Gather Your Equipment and Put On Your Safety Gear
Flux core welding involves high voltage and flashing electric arc, so make sure that you prepare all the necessary tools and safety equipment before you start. This includes:
- The flux welder machine
- Flux core wire
- Welding gloves
- Welding mask
- Safety goggles
- Wire brush
- Slag chipping hammer
- Cleaning rag for the surface
2. Prepare the Working Surface
Flux core welding can work through rust and dust. However, cleaning your surface gives you more consistent welds and cleaner results.
Wipe the surface with a dry cloth and/or wire brush, and make sure that the clamping areas are also clean before connecting the ground clamp to the workpiece.
3. Load the Proper Flux Wire in the Feed
There are different flux wire thicknesses out there. A good all-around choice here would be .030 inch diameter wires. Larger wires like .0350 inch will leave more slag on the weld, so only use them for thicker welds.
4. Set the Machine to the Right Settings
Refer to the welding machine’s manual in order to find out more about the right settings for your welding machine.
This includes adjusting the machine’s amperage, voltage, and wire feed speed that is suitable for the project and your skills.
5. Pull the Trigger to Start Welding
Press the trigger to start the feeding process until the flux wire pokes out of the welding gun (about 1/2 to 3/4 inches is enough).
Tap the flux wire to the workpiece where you want to weld in order to strike the arc. Use the “strike and pull” technique as you continue to move through the joint area.
Keep pressing the trigger to release more wire for welding. If you’re a beginner, maintaining proper drag angle and pace might take some trial and error, but you’ll eventually get the hang of it.
6. Remove the Slag
After you’re done, turn off the welding machine and inspect the weld, then use the chipping hammer to remove the layer of slag left by the flux wire. You can also use a wire brush for a cleaner finish and remove tiny slag leftovers.
Whether it’s a gas shielded or self shielded system, most flux core arc welders will include the following equipment:
- The welding gun with flux releasing trigger
- The power supply unit
- The flux core welding wires
- Wire feeder unit
- Controls that are responsible for voltage, polarity, wire feeding speed
In advanced flux core welders with advanced features, additional items like motion sensors and seam followers might also be included within the main unit.
In addition to the previously mentioned equipment, the gas shielded welders will also include the gas shielding system itself.
Advantages of Flux Core Welding
Flux core welding comes with many benefits that make them suitable for elaborate weld projects. In this section, I’ll walk you through some of them:
Easy to learn
Compared to TIG and stick welding, flux core welding is quite easy, as you can grasp flux core welding in a short time, especially if you have previous experience in MIG welding.
Suitable for Outdoor Applications
Flux core welding, especially the self shielded type, creates reliable protection against wind drafts and powerful air currents, which makes it suitable for welding in open areas, such as construction sites and farms.
Since self shielding flux core welders don’t require additional gas shielding systems, they’re easily moved around in the form of a single unit.
Versatile and Convenient
You can easily choose between self shield and gas shielded wire depending on the project you’re working on, which allows you to work on a wider variety of conditions without making drastic changes to your setup.
Flux core welding also gives you the ability to work at various angles and in awkward positions, even with rusty metals.
Provide Thicker Welds
Flux cored wire, especially gas shielded type, has a high penetration power and creates a larger weld pool with a relatively large deposition rate, so it can work on thick metals that solid core welders can’t.
Flux core wire isn’t necessarily cheap, but it gives you more versatility and penetrating power while saving the added costs of gas shielding (while using self shielded wire), so it can end up saving you money in the longer run.
Disadvantages of Flux Core Welding
Despite all its merits, flux core welding is not perfect, so here’s a quick look at some of the disadvantages of using this technique:
The special design of the flux core wire makes it a bit more expensive than regular solid core wires used in other types.
It produces more Spatter
Another major drawback of flux core welding is that its welding beads are bulky and unappealing due to high penetration power. The flux core also leaves a layer of slag that you need to clean away after welding. I have written a guide to reduce spatter that you may find interesting.
Not Suitable for Thin Workpieces
While the high penetration power is great for thicker metals, you’re better off using solid wires while welding thin metals (anything smaller than 3/16 inches thick)
When to Use Flux Core Welding?
Flux core is not always the optimal choice for welding, but there are some applications where it displays relatively better results than other types of welding. These conditions include:
- You do most of your work in open areas with plenty of wind (self shielding)
- You do your welds on-site where portability is essential for you (self shielding)
- You typically work on unclean or rusty workpieces
- You typically work on thick metals (gas shielding)
- You don’t mind after-weld cleanup and finishing
Power Source in Flux Core Welding
When it comes to Flux Core welding, most power supplies are either single phase or three phases with a frequency of around 50 to 60 Hz, and provide a power source of 230 or 460 volts and 200 or 575 volts to a lesser extent.
Ideally, all flux core welders use battery-like direct current to operate but can operate at different polarities.
The operation methods depend on the type of flux core welder and work as follows:
- Self Shielded Flux Core: The wire is usually the negative pole while the workpiece is usually positive. This is called “Straight Polarity” or “DCEN”
- Gas Shielded Flux Core: The wire is usually the positive pole while the workpiece is usually negative. This is called “Reverse Polarity” or “DCEP”
Different manufacturers may have different polarity systems, so make sure that you check the operating manual before setting the polarity of your system.
Shielding Gasses in Flux Core Welding
Carbon dioxide is the most popular gas used in shielding flux core welding, available in cylinders or bulk form.
Argon is also used in combination with carbon dioxide for improved shielding, with 75% Ar and 25% CO2 being the most common blend, especially for thick and challenging welds.
Electrodes in Flux Core Welding
The most common electrode wires used in flux core welding are steel wires with carbon inner flux.
As the arc passes through the wire, the steel melts and the carbon oxidizes into carbon dioxide to shield the metal from reacting with atmospheric gasses.
Stainless steel electrodes are also used because they break down into steel and carbon. They’re more resistant to corrosion but they’re more expensive than regular carbon flux steel wires.
To sum up, flux core welding is an arc welding process that relies on a consumable tubular electrode with an inner flux material designed to either fully shield the weld pool or provide extra shielding to support the CO2 gas.
The process is similar to MIG welding, but the flux core’s additional shielding greatly saves the costs of shielding gasses and provides a remarkably high deposition rate. However, the process creates more smoke and spatter chances than other types.