When the end goal is to get to clean metal on a workpiece, carbon arc gouging is a frequently used process across many welding applications in the shop and in the field.
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Carbon arc gouging, commonly referred to as air arc gouging, is often chosen for material removal because it’s a portable process that can quickly remove a lot of material. Sometimes gouging is necessary to complete a specific type of weld for the weld joint design.
Following some gouging best practices can help improve the efficiency of the process and the results you see.
Get answers to frequently asked questions about gouging.
The process is often a required step in the weld procedure for many full-penetration welds, which are frequently used for joints that will be subjected to high stress, such as those in structural construction. A procedure may require a gouge process to remove steel backing, burn off weld tabs or back gouge.
Gouging is necessary for many tasks related to welding when the operator is trying to remove material to get to clean metal. The most obvious use of gouging is to remove large amounts of metal or welds that need to be repaired. In these cases, gouging is much faster than removing this material with a grinding wheel, which is typically used to remove surface defects or excess reinforcement.
Casting work may also frequently require this process. If a casting has a defect or flaw, operators can gouge out the defect then fill it back up with weld metal.
You can gouge in constant voltage (CV) mode, but it will result in a shallower penetration profile that is wider and flatter than gouging in constant current (CC) mode. Although a CV process can provide satisfactory performance, most industries prefer the arc characteristics of a CC process, which provides arc consistency and a deeper, cleaner trough. For this reason, many Miller® industrial power sources have a dedicated CC gouge process, which optimizes the arc for gouge applications.
Gouging electrodes are available in a range of sizes, so understanding your machine’s capabilities is key to avoid using too large of an electrode. The spec sheet or owner’s manual for some machines will specify the electrode diameter ranges that can be run and list the maximum electrode size that can be used for carbon arc gouging. Or, as best practice, get the amperage ratings from the carbon electrode manufacturer.
Electrode size should be about 1/8 inch smaller than the desired groove width. Depth of the groove will be dictated by travel speed and travel angle. Keep in mind that the capabilities of your power source typically limit your maximum electrode diameter, but you can also perform multiple passes to create larger grooves.
Typical cylindrical electrodes, also known as pointed electrodes, are best for all-purpose gouging. Flat electrodes are good for achieving a flush surface, as in removing weld reinforcement or creating rectangular grooves. Jointed electrodes allow the ends to connect — eliminating stub loss — and hollow electrodes allow for increased travel speed.
If you are making forceful contact into the workpiece, it means your amperage isn’t high enough. If you’re using a dedicated gouge mode (CC), increase the amperage. If you are gouging in CV mode, increase the voltage.
Gouging is a process just like stick or MIG welding. Just as with those welding processes, technology in Miller engine-driven welder/generators and plug-in welding power sources that include a gouging mode has resulted in optimized gouging performance. Reference the owner’s manual for your power source to find the gouging setup, if applicable.
A dedicated gouge mode enables operators to keep the arc lit more consistently and makes it easier to manipulate the arc. Otherwise, the arc going out can cause the operator to struggle.
Choosing a machine with a dedicated gouging process can help ensure you are best equipped to meet all the needs and unexpected repairs of the job.
While this used to pose a problem with older inverter machines, today’s inverter-based power sources from Miller have been engineered, designed and tested for the gouging process, providing exceptional reliability and operation.
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Carbon arc gouging is an important part of many welding applications — from structural steel construction to field repairs. Understanding the gouging process and how to choose the right equipment and electrodes for the job can help improve efficiency and optimize results with this process. To learn more about challenges and solutions in structural construction welding and fabrication, visit MillerWelds.com/construction.
The main difference between this gouging technique and the others is that a separate air jet is used to eject molten metal from the groove.
As air carbon arc gouging does not rely on oxidation it can be applied to a wide range of metals. DC (electrode positive) is normally preferred for steel and stainless steel but AC is more effective for cast iron, copper and nickel alloys. Typical applications include back gouging, removal of surface and internal defects, removal of excess weld metal and preparation of bevel edges for welding.
Air carbon arc gouging works as follows. An electric arc is generated between the tip of a carbon electrode and the workpiece. The metal becomes molten and a high velocity air jet streams down the electrode to blow it away, thus leaving a clean groove. The process is simple to apply (using the same equipment as MMA welding), has a high metal removal rate, and gouge profile can be closely controlled. Disadvantages are that the air jet causes the molten metal to be ejected over quite a large distance and, because of high currents (up to 2000A) and high air pressures (80 to 100 psi), it can be very noisy.
The electrode is a graphite (carbon) rod which has a copper coating to reduce electrode erosion. Electrode diameter is selected according to required depth and width of gouge. Cutting can be precisely controlled and molten metal/dross is kept to a minimum.
A DC power supply with electrode positive polarity is most suitable. AC power sources which are also constant current can be used but with special AC type electrodes. The power source must have a constant current output characteristic. If it does not, inadvertant touching of the electrode to the workpiece will cause a high current surge sufficient to 'explode' the electrode tip. This will disrupt the operation and cause carbon pick-up. As arc voltage can be quite high (up to 50V), open circuit voltage of the power source should be over 60V.
The gouging torch is normally operated with either a compressed air line or separate bottled gas supply. Air supply pressure will be up to 100psi from the air line but restricted to about 35psi from a bottled supply. Providing there is sufficient air flow to remove molten metal, there are no advantages in using higher pressure and flow rates.
Although carbon is picked up by the molten metal, the air stream will remove carbon-rich metal from the groove to leave only minimal contamination of the side walls. Poor gouging technique or insufficient air flow will result in carbon pick-up with the risk of metallurgical problems, e.g high hardness and even cracking.
Typical operating data for air carbon arc gouging:
Electrode diameter (mm)Current AGouging is commenced by striking the electrode tip on to the workpiece surface to initiate the arc. Unlike manual metal arc (MMA) welding the electrode tip is not withdrawn to establish arc length. Molten metal directly under the electrode tip (arc) is immediately blown away by the air stream. For effective metal removal, it is important that the air stream is directed at the arc from behind the electrode and sweeps under the tip of the electrode. The width of groove is determined by the diameter of electrode, but depth is dictated by the angle of electrode to the workpiece and rate of travel. Relatively high travel speeds are possible when a low electrode angle is used. This produces a shallow groove: a steep angle results in a deep groove and requires slower travel speed. Note, a steeply angled electrode may give rise to carbon contamination.
Oscillating the electrode in a circular or restricted weave motion during gouging can greatly increase gouging width. This is useful for removal of a weld or plate imperfection that is wider than the electrode itself. It is important, however, that weave width should not exceed four times the diameter of the electrode. The groove surface should be relatively free of oxidised metal and can be considered ready for welding without further preparation. Dressing by grinding the side-walls of the gouge should be carried out if a carbon rich layer has been formed. Also, dressing by grinding or another approved method will be necessary if working on crack-sensitive material such as high strength, low alloy steel.
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