What is a Flux Core Welder? Learn Exactly In 10 Minutes

By Bill Byers / January 14, 2019
What Is A Flux Core Welder Title Image

Need to know what is a flux core welder. I tell you in words, images and a video so that you know exactly what a flux core welder is.

Forney Easy Weld 125 FC Front

​An Example of a Flux Core Welder

​What is a Flux Core Welder?

​It is either an automatic or semi automatic welding machine that welds using electricity to produce a powerful electric arc.

Inside the flux core welder is a spool of wire containing flux core welding wire.

The wire in flux core welding is special as it is made like a tube. On the outside of this tube is metal and inside are special compounds called flux.

This wire is continuously fed through a drive mechanism inside the welder and then through a cable (also known as a hose) attached to the welder, up to the gun where it feeds out to the weld you are making.

When the welder is powered or the trigger on the gun is pressed electrical energy is passed to and along the flux core wire to its very tip.

When the welding gun with its flux core welding wire is brought close to the metals to be welded known as the base metals, an arc is formed. This arc is what melts the base metal and the flux core welding wire and creates the weld pool - a molten pool of metal.

The metal on the outside of the flux core wire melts into the pool.

The flux from the core of the flux core wire does two things;

1. It forms a gas that protects the molten metals in the weld pool from the surrounding air.

2. The flux also drips into the pool of metal taking impurities to the top of weld where they solidify and form a protective covering called slag.

​YouTube Video Of A Flux Core Welder

​This short two minute fourteen second video describes the common points of a flux core welder. The video covers what is in the cabinet, where the wire is fed, the welding gun and ground clamp. It's a good 101 on what is a flux core welder.

Forney Easy Weld 125FC

​Video Credit: Forney Industries

​Why is a Flux Core Welder Different?

​​There are other types of welders that use an electrical arc - TIG, MIG and Stick welders. Only Stick welders and Flux core welders use tubular welding wire - a wire that has a flux core and that flux core produces slag that covers the weld pool.

Where stick welders use rods of specific lengths and diameters of flux core wire.

Unique to flux core welders a spool of flux core welding wire that sits inside the welder and is continuously fed into the weld.

A flux core welder uses the FCAW (Flux Core Arc Welding) process to weld. I have a full description of the flux core welding process on the site, if you want to know more then please follow the text link to the document. ​

​Two Types of Flux Core Welding Wire

​Yes, there are two types of flux core welding wire and it is important to choose the right type as then you will know the kind of flux core welder you need to weld with. I have an article that goes into more detail on the types of flux core welding wire "What is Flux Core Wire, Know When to Use and Why" so I will give a brief overview here.

One type of flux core wire is called self shielded, the core of the wire produces gas that shields the hot metal from the surrounding air as you weld. (If you want to know why, take a look at my what is flux core welding article).

No separate tank of high pressure gas is needed with this type of wire. You have your flux core welder, your wire and a power supply and you can weld.

The other type of Flux core wire is called gas shielded or dual shielded. With this type of flux core wire a separate tank of high pressure gas needs to be used. This makes this type of flux core welder very similar to a MIG welder. Indeed many MIG welders will feed flux core wire and MIG wire with just a few changes made inside the welder. I go into more detail later.

​The Flux Core Only Welder for Self Shielded Wire

First I cover a flux core only welder so that you know what that is.

There will be an electrical power lead to connect the welder up to external power. I cover later on in the article the considerations around providing your flux core welder with power.

The power lead goes into the flux core welder.

The cabinet will have front and back vents. Those vents will need 12 to 18 inches clear around them as air is most often used to cool the internals and there is a fan inside that will run to cool the flux core welder.

Forney Place to Put Wire

Place to Put Flux Core Wire in

​Also inside the cabinet, is a place to put the spool of flux core wire. A flux core welder can also be known as a wire feed welder and this spool of flux core is an important feature that makes the flux core welder what it is.

A wire feed mechanism feeds the wire through from the spool out to a hose or cable.

Forney Feeding Wire Through Wire Feed

Feeding Wire Through Wire Feed Mechanism

​There is a wire tension control used to set the tension on the wire. It should be set to grip but not so tight as to crush the delicate flux core wire.

The wire feeds across a set of rollers and on a flux core welder these rollers will be knurled, U shaped grooves with teeth that grip the wire so that is feeds smoothly.

The electrical current is fed to the wire here.

The wire runs inside a liner within the welding cable or hose. It feeds up to the welding gun

Flux Core Welding Gun

Flux Core Welding Gun

​The cord or hose is typically 8 to 10 feet in length and the wire is fed when the welder is switched on and the trigger on the welding gun is pressed.

The wire feeds out through a contact tip at the end of the welding gun and often but not always as it depends on the welder and the preference of the person welding a nozzle goes over the end of the contact tip.

This is half of the electrical circuit.

The other half has a grounding clamp

Forney Ground Clamp

Ground Clamp

​This ground clamp is attached to the piece to be welded or to the welding table if you have a metal table. Preferably as close to your work as possible. There is a lead that runs from your ground clamp back to your welder.

The ground clamp takes the electrical circuit back into your welder where it returns to ground through your plug socket.

On the front of the flux core welder are dials or buttons where the volts or amperage is set. This is where the welding output; the heat output of the welder is set according to the thickness or gauge of metal welded.

Along with the output settings there will be a dial for the wire feed speed.

GoPlus Front

Inside the cabinet of most well known brands of flux core welders you will find a welding parameters chart. This chart outlines the manufacturers suggested output setting and wire feed speed for the gauge of metal welded.

Forney Welding Parameters Chart

Welder Welding Parameters Chart

​You can use these as your starter settings but you may need to adjust for the welding conditions, your workshop and metal you are welding.

Incorrect settings will produce more spatter as you weld. Not sure what spatter is? find out here​.

These are the main components of a flux core welder.

​Note that: A flux core only welder will not be able to feed gas and so you will not be able to weld with or use dual shielded or gas shielded flux core wire.


​A Flux Core Welder and a MIG Welder?

​MIG welders will often also feed self shielded flux core wire as well as solid wire.

A MIG welder is at its foundations very similar to my description above of a flux core only welder, with some key differences.

It has the ability to feed external shielding gas, change drive rollers and the ability to change polarity.

If you are using a MIG welder to weld with self shielded flux core wire then a knurled drive roller will need to be installed to feed the flux core wire.

Knurled Drive Roll

Knurled Drive Roll

​MIG welder drive rollers for solid MIG wire have V shaped grooves that will crush flux core wire. If your MIG welder does not have a knurled roller then one will need to be purchased.

And while you are looking at the set up check the contact tips are the right size to feed the flux core wire as contact tips for solid wire are often different sizes.

This is a brief overview of the differences. You can read more detail on the differences between a flux core welder and a MIG welder here.

​What Polarity is Used for Flux Core Welding?

The Flux in self shielded flux core wire chemically needs the polarity set to DCEP (Direct Current Electrode Positive). Flux core only welders will be set up this way by default.

A MIG welder set up to feed solid wire will have its polarity set to DCEN (Direct Current Electrode Negative).  MIG welders that can also use shelf shielded flux core wire will have terminals inside the MIG welder that you can change.

Example of MIG Polarity Terminals

Example of Polarity Terminals

​Be sure to change these terminals to DCEP as incorrect polarity is often a cause for the flux core wire spitting but not welding.

​A Flux Core Welder for Dual Shielded Flux Core Wire

​A welder capable of welding dual shielded flux core wire will be to the high end of most home workshop welders, demanding power input of 220 volts as a minimum, which is why this type of wire is often used in fabrication shops.

The welder itself will be sold as and is capable of feeding an external cylinder of shielding gas.

Which means that you will need to buy and source a tank of high pressure gas.

Argon Tank Welding

Argon Tank

​If you are using dual shielded flux core wire it will need to be protected with separate gas. I go over later on in this article the type of gasses that can be used.

On the tank of gas a regulator will need to be installed to regulate the pressure and speed the gas is fed out at.

The gas is fed via a hose connected into the welder. The external shielding gas feeds through the welder and up along the hose or cable that leads to the welding gun.

The nozzle at the end of the welding gun helps direct the gas so that is covers the weld pool providing the dual shielding the wire needs.

The polarity for welding dual shield flux core wire is the same as MIG welding, which is DCEP (Direct Current Electrode Negative).

​Specific Capabilities of a Flux Core Welder

​It is useful to know the general capabilities of and features of a flux core welder. Of course your particular welder may have less or more capabilities depending on its features and price.

​What Metals can you Weld with a Flux Core Welder

​A flux core welder is mainly used for welding mild steel or low alloy steel.

Stainless steel can also be welded using specialist flux core wire designed to weld stainless steels. It is worth knowing that flux core wires capable of welding stainless steel typically demand DCEP polarity settings. The same as welding with gas.

With many of the cheaper flux core only welders incapable of changing polarity they will not be able to use this wire despite what their marketing may say.

To weld with this wire at home a reasonably powerful MIG welder (230 volts) that can also weld with flux core wire will be needed.

Some users report great results with this wire, others not so much - link to stainless steel welding flux core wire.

Galvanized steel can also be welded with a flux core welder, which is a boon, because with the MIG process you would need to grind all the galvanization off before attempting to weld.

This is a great feature of a flux core welder.

In addition some low nickel alloys can also be welded with flux core welders.

A flux core welder is not used for welding Aluminum, as there is no flux core Aluminum wire suitable. Want to find out why? Go over to my article all about why

​Metal Thicknesses Welded

​The thickness of metal - the gauge of metal - that can be welded with a Flux core welder depends how powerful your flux core welder is, and the power you can supply your flux core welder with.

What I mean by this is the cheapest flux core welders on the market will run on the power available in a domestic home and may need 110 volts or 115 volts to work.

That type of welder may weld 20 gauge to 1/8th thick metal.

Quarter inch to 3/16th size metal with joint preparation such as beveling could be attempted by those welder operators with the skill to do multiple weld passes.

Welding quarter inch and above with a single weld pass will see you looking for a welder that runs on 230 volts. Which in a home environment may need separate power put in to support your flux core welder.

Flux core welders are used because they are generally good at welding thicker metals compared to MIG welding.  And particularly gas shielded flux core welding is used in the ship building and construction industry where thick metal needs welding in a short amount of time.

Because Flux core welding is a 'hot' process compared to MIG welding, welding thinner than 20 gauge will take skill or risk blowing holes through your metal.

​Powering Your Flux Core Welder

​I've just covered that metals thicknesses welded depend on the power you can supply your flux core welder with. Flux core welding is an electrical arc process. The thicker the metal, the stronger the arc must be to weld well.

Check the electrical supply the flux core welder you are planning to use needs - 110 volt, 115 volt or 230 volt.

Provide a circuit at the right level of power, dedicated to the welder while you are welding. Other devices in use on the same circuit takes away power your welder needs to use. Potentially destabilizing the arc and so affect the weld quality.

Check that the fuse on the circuit is large enough for the welder you are using. For example, many of the 115 volt home use flux core welders need a 30 Amp fused circuit to use them at their maximum power output.

And while you are checking those things check that the power point your welder is using has a good earth connection as without that the welding arc will be poor or not at all.

Lincoln EIectric InnerShield NR-211-MP

​Choosing Your Flux Core Wire

​The flux core wire whether self shielded or dual shielded is chosen to match the type of metal welded.

And of course choose wire that your flux core welder is capable of feeding and welding.

For example, choose mild steel wire for welding mild steel. ​

Most lower priced flux core welders will feed 0.030 and 0.035 diameter wires. There are larger flux core wire diameter sizes 0.045 and above however they need a flux core welder able to feed them, with the power to melt and weld successfully with them. Those types of flux core welders would normally need 220 volt or above.

Which is best 0.030 or 0.035 for home welding is hotly debated. If you're trying to decide and need some advice take a look at my article on the subject. ​

​Flux Core Welding Positions

​As flux core welder operator your welding task may be laid flat on a work table. A flat, horizontal weld is a position a beginner welder should start off practicing in as it is the easiest.

What is more challenging are welds that need to be made vertically or overhead. The beauty of flux core wire is that the wire itself is suitable for all positions. Flat - horizontal, vertical and overhead.

​Flux Core Welding Multiple Passes

​Particularly if you have a low powered flux core welder, welding 1/4 inch thick steel will see you needing to prepare the joint with beveling and making your weld with multiple passes. This means laying each weld bead one on top of the other in a structured way to build up the weld in the joint.

What is key to this method of welding is Flux core welding wire capable of making multiple passes - not all flux core wire can. Check your flux core wire is rated for multiple passes.

And because key to flux core welding is welding slag and good slag coverage of your weld, each pass needs good slag coverage and the slag completely removed once the weld has cooled before the next pass is made or you risk your weld failing due to slag inclusion and porosity

Looking for more information on this? Head over to my document that goes into detail on welding slag and why it is so key to flux core welding.

​Duty Cycle of a Flux Core welder and What is it?

​The duty cycle of a given flux core welder is an important consideration when choosing your welder.

The duty cycle covers how long the flux core welder can weld for before it needs to be rested. It is measured over a 10 minute period and at a certain amperage of the welder. 20% at 80 Amps. Tells you the user that this welder can be used for two minutes (20% of a ten minute period) at its 80 Amp setting.

This duty cycle may not be stated at the maximum Amp output the welder can be set to.

Use a higher Amp setting than the duty cycle stated and your 2 minute weld period will drop dramatically.

The flux core welder will normally be cooled by an internal fan. The fan will need to be on during the welder's resting period till the welder cools.

Most Flux core welders have thermal sensors that will automatically switch the welder off if the duty cycle is exceeded or the welder overheats. And not reset until the welder has cooled sufficiently.

​The Semi-Automatic Flux Core Welder

​On the front of the flux core welder will be dials or switches, sometimes an LED readout that allow you to set the voltage output or Amperage of the welder.

There will be a dial where the wire feed speed is set.

Super Deal MIG 130 Front Controls

​Flux Core Welder Front Controls

​This is the semi automatic part of the flux core welder I mentioned at the start of the article.

Set the controls and the welder will weld at those settings when you push the trigger on the welding gun. And it will continue to weld, feeding the wire at these settings and the wire feed speed until you let go of the trigger and stop.

This is the automatic part of the process. It is down to the the human operator to control the settings used, the welding materials, the speed of travel along the weld, the distance from the weld and the angle welded at.

​What Shielding Gas is used with Dual Shielded Flux Core Wire?

Welding Dual shield flux core wire needs a cylinder of high pressure gas to weld successfully. As well as a welding machine that can feed that gas and a machine powerful enough to produce enough Amps to melt the wire and the base metals.

The gasses typically used in gas shielded flux core wire are;

  • 100% Carbon Dioxide
  • Argon, Carbon Dioxide mixes such as C25 (75% Argon, 25% Carbon Dioxide)

Be guided by the recommendation of the flux core wire manufacturers on the type of gas and cubic feet per minute to feed the gas out at detailed in their wire welding parameters charts.  These charts are normally found on the manufacturers web pages.

​Other Considerations Before You Start Welding

​You have your flux core welder. You now have a clue about what is a flux core welder. What other things are important needs to knows before you start.

  • A Flux core welder is more tolerant of dirty steel - steel that can't be perfectly cleaned before you weld. Even so it is best to prepare your metal for welding by grinding or brushing off any oil, rust, mill scale or paint that you can
  • Use the recommended wire feed speeds for your flux core welder and the wire you are using. Too slow a speed will cause burnback, where the flux core wire melts onto the contact tip causing a world of pain and cleanup
  • Use your flux core welder within its capability. This means its voltage and Amp are set according to the thickness of the metal it is capable of welding. If you're not sure of the gauge of the metal use a metal thickness gauge
  • Set your wire stickout for flux core welding. Flux core wire needs around 1/2 to 3/4 inch stickout, about twice the recommended stickout compared to MIG welding. If you are not sure what stickout means, it is literally the amount of wire sticking out from the end of your contact tip
Welding Wire Stickout

Welding Wire Stickout

  • ​Set the controls on your flux core welder to those recommended on its welding parameter chart on the inside of its cabinet. If there isn't one go by the chart of your chosen flux core wire. Failing that consult an online welding calculator for general parameters​.
    The right settings will keep the spatter produced while welding to a minimum
  • Then practice, practice practice. Do some test welds to see what suits your particular situation. The material your using, its thickness and your workshop environment
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