Flux Core Welding
For over five decades now, flux core welding provided engineers with a strong, versatile solution to their needs. Strictly speaking, flux core is actually a distinct type of electrode, which is used within a standard MIG welding unit. An MIG unit on its own relies on a separate shielding gas, meaning that it cannot be used in windy outdoor conditions. On the other hand, shielding gases are generated from a flux core as the wire melts. By keeping the electrode protected from the air in this way, flux core welders can be used in a wider range of situations and circumstances.
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Flux core welding uses a hollow wire with the center containing a flux. This allows the welder to work quickly, while also giving a remarkably high-quality weld. When compared to a standard MIG unit, the results are astonishing- while an MIG unit might generate between five and eight pounds of weld each hour, a flux core unit can instead provide over 25 pounds in the same amount of time! What’s more, flux core units can also weld half inch plates, making it the primary choice within the shipbuilding industry.
How Flux Core Welding Works
AS with MIG welders, flux core welding has three main requirements: a shield, a filler metal, and an electrical supply. The electrode is supplied continuously to the joint in order to weld it together. The electrode is supplied by the wire feeder with an electrical charge. As the electrode comes into contact with the metal joint, a short circuit is created, which heats the electrode and causes it to melt, as does the metal it is in contact with. In a very short space of time, both of these which simultaneously melts the flux and form a puddle to provide an air shield and a slag to prevent any contamination.
Why Use Flux Core Welding
Flux core units are used because they provide results which are simply impossible to achieve with an MIG unit. For instance, flux core units can provide a faster, stronger weld in galvanized, flat, vertical up and steel welding. In addition, it is more productive when welding mild steel.
Flux core welders provide better shielding even in dirty environments, making them the ideal choice for work in the field. In addition since there is no tank of gas to carry around, the unit is also lighter, so workers are able to carry it around with them with ease. Finally, flux core units burn hotter than MIG units, so they can weld materials that are thicker in a single pass.
By far the greatest advantage of flux core units, though, is that they are a much more-cost effective solution than MIG units. If you have the necessary budget, then you can even purchase an MIG welder which also provides flux core welding, offering you a wide range of applications.
What To Consider
As with any equipment, there are multiple factors that you’ll need to keep in mind when choosing the optimum flux core welder for your needs. These are as follows:
The first thing you’ll want to consider with your flux core welder is the type of shielding used. There are two main options here: self-shielded, gas shielded. They both come with flux filling and external sheath made of a compound of deoxidizers and alloys to keep pollutants out. The main difference between the two lies in the electrode. A self-shielded unit has an electrode in the form of a tubular wire, which lies in the center and is coated with a shielding power. A gas shielded unit, on the other hand, has an additional gas bottle, to provide an extra layer of shielding. This shielding gas works to protect the area of the weld.
Self shielded units have a flux wire which is extremely portable, making them a solid choice for things like bridge and ship construction, and structural steel welding. Gas shielded wires often are a superior choice for vessels, petrochemical piping, and more general fabrication. Nonetheless, both types of wire work well in both all-position and flat or horizontal welding on a wide range of different steel types and other metals which are alloy based. They can even be used to repair worn-out welds and to provide extra protection from abrasion.
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Although a flux core unit uses the same sort of electrode as in MIG welding, the main difference is that these electrodes are tubular, or come with a hollow tube with the flux in the center, whereas MIG electrodes are typically robustly metallic.
Flux core electrodes come in numerous sizes. Some of these are the same size as MIG electrodes, whereas others are closer in size to that of a stick electrode. The most common sizes for industrial use are .035, .052, and .0625. These wires also have their own special classifications from the American Welding Society, which you should also look at as well as the size.
A standard flux core electrode would be classified like this: E71T. The E stands for electrode, the 7 refers to the minimum tensile strength in 10,000lbs per square inch of weld, the 1 means that it is if an all position welding ability (flat and horizontal welds have a 0 instead), and finally the T tells you that it is a tubular electrode.
With shielding gas, the classification would be the same, with the addition of C or C/M at the end. A C means that only carbon dioxide shielding gas, whereas C/M means that argon gas may also be used.
You will also need to think about the diameter of the wire you are using. The standard diameter for a wire is .03 inches, since this allows you to weld a wide range of different metal thicknesses. If you will be welding particularly thick metal, then consider using a .35-inch diameter wire instead, which will put up with the additional heat needed for this. Furthermore, look for the stick out length of the electrode- flux core welding needs almost three-quarters of an inch of stick out, which is double that of standard MIG welding.
Dual shielding units can only use a relatively limited range of gases for shielding: argon, carbon dioxide, a mix of these two gases, argon and oxygen. On the other hand, gas shielded flux core units require either pure carbon dioxide or a combination of carbon dioxide and argon. The difference between the two is that the former provides better penetration, the latter results in less scatter and a superior arc quality. This is because the flux in the wire reacts negatively to carbon dioxide, meaning the arc is less stable. While argon also has a similar reaction to the wire, the effect is not as severe, and therefore it works to stabilise some of the effects of the carbon dioxide reaction. Nevertheless, both gases will deliver a weld that looks good.
The most common gases used in dual shielding units are argon plus carbon dioxide, or oxygen plus argon. The majority of welders use 75% argon with 25% of carbon dioxide, as this is the optimum amount for a stable arc with superior spray transfer and minimal splatter. We recommend that you seek out the manufacturer’s recommendations for both gas and electrodes.
There are two different metal transfers used in flux core welding: spray transfer and globular. The former is more widely used, and as the name suggests, metal from the electrode is heated so that it “sprays” liquid metal into the joint to fill it. Globular, meanwhile, involves heating the electrode, and then allowing the metal to “glob” down from the electrode to the joint. The main differences between the two transfer types are the wire speed, the gas used, and the voltage setting
Flux cored welders require voltage supply that is constant in order to function properly. Whereas stick welders and TIG welding units, which maintain a steady amperage, flux cores instead maintain a constant voltage. The reason for this is that flux core units alter their amperage along with the speed of the wire feed- the faster the feed, the higher the electrode’s contact, which generates more heat. To do this requires additional amperage, so the power supply needs to be somewhat flexible. However, most flux core units have a restricted amperage range, so this flexibility is somewhat limited.
All flux core welders use direct current (DC), much like a typical battery. In most cases, the polarity will be DC-electrode positive, meaning that electricity flows from metal to handle. Again, this is fairly standard when larger electrodes are being used. However, when thinner sheet metals are being welded, a smaller electrode is needed, so the polarity needs changed to DC-electrode negative.
Flux core welders use much more power than MIG welders- in essence, the former is a vastly more powerful version of the latter. In fact, there are some flux core welders out there which can run with over a thousand amps of power! Generally, though, these welders are 110v, and therefore generate 140amps- less than a gas model or alternator. This is plenty enough power for most users’ needs, and it’s possible for such models to work 24-guage steel up to ¼ thick. However, if you’re looking for something a bit more powerful, then there are also numerous 220v flux core units out there, too.
Naturally, a welder with a higher voltage is a more powerful and robust piece of equipment than one with a lower voltage. Not only is it able to generate a greater amount of heat, but it can also weld thicker materials. A high voltage welder is essential for working on aluminum, which requires additional amperage compared to steel of the same thickness. Compared to a low-amperage 110v unit, a 220v unit has a higher duty cycle, meaning it is easier to use and provides faster results. You should therefore carefully consider this duty cycle when choosing a welder. The duty cycle essentially tells you how many minutes (within 10) you can weld for, before you have to recharge the unity
So, if the duty cycle of a welder is 30%, that means you can use it for three minutes at a time, before waiting another 10 minutes to use it again. The duty cycle is dependent on the amperage load, so the measurement will be for a specific amperage rating- for example, that 30% duty cycle might be for 90A.
The amperage rating is the very highest amperage that the welder can possibly emit. If a welder’s specifications were 30-120A with 30% at a 90A duty cycle, it would mean that while it is possible to use 120A for welding thicker metal, the device would nonetheless also run comfortably at 90A for three minutes’ worth of use.
Duty cycle is certainly something you should look at, but remember not to compare units of different duty cycles. If you know what kind of amperage load you need, then look within those boundaries- if you need 90A, then a unit with 30% at 70A probably isn’t going to cut it. What’s more, while you can buy cheaper welders with a duty cycle of 60A or below, these won’t give you enough power to get through steel for basic fabrication. Check out our multi process welder reviews.
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When welding, there are two angles you need to think about: work and travel. The travel angle is relative to the gun when held at a 90-degree angle to the flat part of the joint. In most cases, this will be somewhere between 5 and 15 degrees. However, in extreme conditions, it may exceed 20 degrees- and this can lead to increased spatter, an instable arc, and decreased penetration.
The work angle, meanwhile, is the position of the gun in context with the flat surface of the joint. This is therefore a lot more variable, since it depends not only on the position of welding, but also the joint configuration itself. The measurement refers to flat, horizontal, and vertical positions, since it is a variable angle.
Finally, it’s vital that you choose a welder which has adequate protection against overheating, or else you’ll only be able to use it for a limited amount of time. If the welder overheats, then you’ll have to wait a long time for it to cool down again- not what you want to happen when you’re in the middle of a job. You should therefore seek out a welder which comes with thermal overload protection.