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In welding, gouging has been a requirement for many years in several industries and applications, and is one method to explore. Especially in maintenance and repair, the ability to gouge or groove metal is critical and deserves full consideration. Gouging electrodes are made of artificial graphite and have a pure copper coating. The gouging electrodes are available in a variety of shapes and diameters to meet the various applications.
Gouging 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 Unlike Manual Metal Arc (MMA) welding the electrode tip is not withdrawn to establish arc length.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.
Table of Contents
Introduction
Features of Gouging Electrodes
Methods of Gouging
Plasma gouging
Air Carbon-Arc Gouging
Types of Carbon Electrodes
Frequently Asked Questions about Gouging Electrodes
Conclusion
Gouging electrodes are made of carbon and have a copper coating. Gouging carbon rods are used for metal removal at fast rates with low power consumption. It is generally used to remove welding defects, excess welds and foundry risers from cast products.
Features of Gouging electrode
Pure copper coated – good electric conductivity.
High density (made of artificial graphite) –leads to high metal removal rate.
Less consumption of electrodes – cost reduction.
Constant quality – for a safe process.
High metal removal rate – effective process.
Extreme low burn back rate.
Methods of Gouging
Two of the most common methods of gouging are:
Plasma gouging
Air carbon-arc gouging electrode.
Plasma gouging is a variation of plasma cutting, in which the arc is "defocused" slightly by increasing the whole size in the constricting orifice. A cutting arc is directed downward through the metal to blow the molten metal down and out through the kerf, forcing the two pieces of metal to separate. In plasma gouging, the torch is inclined at an angle to the work piece, and the arc plows out a groove on the metal surface and blows the molten metal off to the side. A more intense cutting arc causes a groove too deep and narrow for most applications, so the defocused arc is used for gouging.
The plasma cutting process was invented in 1954 at the Tonawanda Laboratory of the Linde Division of Union Carbide. A young scientist, Robert Gage, discovered that by forcing a gas tungsten arc through a small orifice in a process similar to focusing a beam of light through a lens, the temperature and intensity of the arc could be increased. By passing a fairly high gas flow through this focused arc, it could cut metal.
Air Carbon-Arc Gouging
The main goal of air arc gouging is to remove defective or old welds to repair or dismantle equipment. Unlike oxy-fuel cutting, air arc gouging avoids the need for oxidation of the metal to cut. The rate of metal removal depends on the efficiency of the air jet in removing molten metal and the melting rate. The process of air carbon-arc gouging is generated between the tip of a carbon electrode and the work piece. The metal becomes molten and a high velocity air streams down the electrode to blow it away and thus leaves a clean groove. It is a simple process to apply, has a high metal removal rate, gouge profile and it can be closely controlled.
However, there are disadvantages: 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.
This type of gouging 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.
Applications of Gouging
Plasma gouging was developed as a tool for weld removal and weld preparation. Back gouging was used to remove metal from the reverse side of arc-welded joints to eliminate defects and improve strength. Weld defects such as cracks, porosity, and lack of fusion could be gouged out using a plasma torch and then repaired with a new, sound weld.
Today plasma arc gouging has wider industrial applications, from shipbuilding and maintenance, to heavy equipment manufacturing and repair, to manufacturing of truck bodies, tanks, and steel structures. Plasma gouging removes strong backs, lifting lugs, temporary brackets, tack welds, and rivets. It is also suitable for demolition or salvage operations to disassemble welded structures. In foundries, it removes excess material from castings. Anywhere surplus metal, excess weld, or defects need to be removed, plasma gouging can be used.
Types of Electrodes
There are three types of carbon electrodes:
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AC coated electrodes (for use with AC power sources),
DC plain electrodes and
DC copper-coated electrodes.
The latter is most widely used because of their comparatively long electrode life, stable arc characteristics and groove uniformity.
This process is the best alternative to traditional gouging more particularly when precision and safety are priorities. With a removal capability of up to 8 kg/h, Plasma gouging improves operating conditions by reducing noise and fumes.
Using the same process as plasma cutting, it enables the removal of metal efficiently, precisely and cleanly.
Efficiency
The plasma arc produces a very accurate groove.
Suitable for application on all ferrous and non-ferrous materials.
Easy to use.
Gouge all conductive materials.
No carbon filler.
Heated area reduced.
Instantaneously wieldable without preparing the edges.
Less noise and fumes.
Professional finishing.
Higher consumable life
Frequently Asked Questions about Gouging Electrodes
Q1- What are gouging electrodes made of?
Gouging electrodes are made of carbon and have a copper coating.
Q2- What are the uses of gouging carbon rods?
It is used to remove welding defects, excess welds and foundry risers from cast products
Q3- What is the gouging process?
The gouging process is characterized by the large amount of gas which is generated to eject the molten metal.
Q4- How does arc gouging work?
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Conclusion
The importance of gouging in the field of welding cannot be overemphasized. These gouging electrodes are made of carbon and have a copper coating. The gouging carbon rods play a major role in metal removal at fast rates with low power consumption. It is generally used to remove welding defects, excess welds and foundry risers from cast products.
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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.
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.
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.
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