Air carbon-arc gouging removes metal through the intense heat of an arc created between a carbon electrode and the workpiece. As the material melts, compressed air, which is directed through outlets in the lower jaws of the torch holding the electrode, lifts the molten metal clear of the arc before the metal solidifies.
The air carbon-arc gouging process does not require oxidation to maintain the cut, so it can gouge or cut metals that the oxyfuel process cannot. In fact, most common metals (carbon steel, stainless steel, high-alloy wear plate, copper alloys and cast irons) can be cut using air carbon-arc gouging.
Typical applications include the back-gouging of weld seams to reach the deposited weld metal from the other side of the workpiece, the removal of gates and risers from castings, the removal of old or excess weld metal so that equipment can be repaired and the reshaping of torn metal prior to welding repair, notably on construction equipment.
The inventor of carbon-arc gouging, Myron Stepath, originally developed the process for removing defective welds in stainless steel armor plate on U.S. warships; conventional methods such as chipping and grinding proved unfeasible due to time and cost factors. Stepath did his original work with the Navy during World War II before founding Arcair Co. in 1949. Today, Arcair is part of the ESAB family of brands, and the name Arcair is synonymous with the gouging process.
The rate at which metal is removed is based on the efficiency of the air stream, diameter of the carbon electrode, output of the welding power source and skill of the operator. Fortunately, learning the air carbon-arc gouging process only takes practice. Here are eight tips to improve results.
1. Choose an electrode
There are three types of carbon electrodes: 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.
These electrodes are made from mixing carbon and graphite with a binder. Baking this mixture produces dense, homogeneous graphite electrodes of low electrical resistance, which are then coated with a controlled thickness of copper.
Copper-coated carbon electrodes come in three shapes and multiple sizes: round electrodes in diameters ranging from 1/8 in. to 1 in., half-round electrodes in 5/8-in. diameters and flat (rectangular) electrodes measuring 5/32 in. by 3/8 in. or 3/16 in. by 5/8 in. Rectangular electrodes are used to make rectangular grooves and remove weld reinforcements, while half-round electrodes provide the versatility of creating a round or flat gouge depending on their orientation.
The depth and contour of the groove produced are controlled by the electrode diameter and travel speed. Groove depths greater than 1.5 times the diameter must be made in multiple passes. The width of the groove is determined by the electrode diameter and is typically 1/8 in. wider than the diameter. A wider groove may be made with a small electrode by oscillating the electrode in a weaving motion.
The diameter of the carbon electrode is limited by the output of the power source. Table 1 suggests current ranges for commonly used DC copper-coated electrodes.
2. Choose a torch
A manual gouging torch and cable assembly includes connections for the welding lead and compressed air line. Be sure to size the torch and ground cable appropriately based on amperage and length of the cable. An insulated connection boot and hookup kit simplifies torch hookup and eliminates the possibility of arcing when contacting electrically hot parts.
The manual torch holds the carbon electrode in a swiveling head so that the air jets stay aligned with the electrode regardless of angle. Most torches have one set of air jets, but some have air jets on two sides of the electrode, which are better for some uses, such as removing pads and risers from large castings (padwashing).
Traditional manual torch models require a fair amount of grip pressure to open, about 27 lbs. or more. Arcair’s newest torch, the AirPro X4000, uses the compressed air already flowing through the torch to pneumatically open the torch jaws. The operator pushes a rocker switch, the jaws open and the operator can insert, adjust and remove carbon electrodes without effort. As an added benefit, elimination of a lever assembly creates a lower profile torch for improved access.
The rocker switch also controls the compressed air on/off function so that no air flows through the torch or cable without the operator initiating flow through the rocker switch. A latch mechanism locks air flow on when in use to reduce hand fatigue, while a “no leak” air valve saves electricity and maintenance costs of maintaining the shop air compressor.
Manual torches are usually air-cooled. For high-current applications, water-cooled cable assemblies may be used with heavy-duty torches.
3. Position the electrode
When using copper-coated carbon electrodes, position the electrode in the torch so that the uncoated end points toward the workpiece. Set the air pressure to 80 to 100 psi, which is a flow sufficient enough to prevent trapping carbon in the gouge.
In normal conditions, position the electrode so that no more than 7 in. of carbon sticks out past the torch head. For aluminum, this extension should be 3 in. The source of air blast is always positioned between the electrode and workpiece. If there is sufficient airflow, cleaning the joint is not a problem.
4. Strike an arc
Strike an arc by lightly touching the carbon electrode to the workpiece. Let the arc start and slowly move it forward or side to side as needed to accomplish the goal. Striking the arc is a little bit different and slightly easier than with a welding electrode. Prior to striking, take the necessary time to get into a comfortable position, and do not draw the electrode back once the arc is struck.
The air carbon-arc gouging process operates between 35 V to 55 V. Listen for a loud arc, which indicates sufficient voltage (note: wear hearing protection when gouging). A muffled arc means the voltage is too low, which could result in carbon deposits.
5. Angle of travel
Hold the torch so that the carbon electrode slopes back from the direction of travel with the air blast blowing past the tip of the electrode to evacuate the molten metal. The proper torch-to-workpiece angle is 35 to 45 degrees.
6. Depth of the gouge
Travel speed determines the depth of the gouge. The faster the travel speed, the shallower the gouge. A slow travel speed produces a deeper gouge. A short arc must be maintained by progressing in the direction of the cut fast enough to keep up with the metal removal and electrode consumption. The steadiness of the progression controls the smoothness of the resulting surface.
7. The push technique
Always use a push technique with air carbon-arc gouging. Move continuously forward with the air blowing from behind the arc. Never back up. This prevents carbon deposits in the base material that cannot be welded without first re-gouging or grinding to completely clean the base material.
8. Focus on the line
When back-gouging a weld joint, focus on the joint line, which is visible just in front of the carbon electrode. This allows you to follow the weld seam. To better control gouging results, hold your head behind the arc.
With this advice in mind, and with a little bit of practice, air carbon-arc gouging can be a simple, inexpensive and highly effective way to remove almost all metals in a variety of metal fabrication and repair applications.