Guide to Carbon Arc Cutting

Photo courtesy of ALan Jiménez from Pixabay

Carbon arc cutting (CAC) is a method of cutting or gouging metal that uses heat generated from a carbon electrode supplemented by a stream of compressed air to remove material cleanly and efficiently. It is a process that, due to its versatility, simplicity, and relatively low cost of operation, is used in many applications in the welding industry.

How Carbon Arc Cutting is Used

Carbon arc cutting and gouging are common in heavy equipment maintenance and repair, mining, shipbuilding, structural steel, and even non-ferrous metal applications. A skilled welder can gouge welds out of a completed or worm assembly quickly and cleanly with little to no damage to the base metal.

Carbon arc cutting is suitable for preparing plates for welding by gouging a “U” groove joint into a single plate or multiple sections that have been tacked together. CAC may also back-gouge a double-bevel groove weld.

It’s important to understand the distinction between carbon arc cutting and gouging. While the processes share the same principles, equipment, and basic characteristics, they are not identical. The only difference is the application.

Carbon arc cutting cuts through the workpiece, creating two separate pieces from one.

Carbon arc gouging involves removing material, typically a weld, from the workpiece without piercing the base metal. but does not pierce the base metal at any point. This method allows for the quick and clean removal of parts like brackets, bearing housings, and other attachments from larger assemblies.

How Carbon Arc Cutting Works

Carbon arc cutting uses heat generated by the electric arc when the carbon electrode contacts the workpiece to melt metal. A stream of compressed air, connected to the carbon arc electrode holder, then blows the molten material away from the workpiece.

Carbon arc electrodes are available in sizes ranging from ⅛ inch to ¾ inch. Flat carbon electrodes are also available and are commonly used to “wash off” or “scarf” weld metal from a welded assembly without significantly impacting the base metal.

Types of Carbon Arc Cutting

Carbon arc cutting can be done manually and automatically, depending on the specific application and project requirements.

Manual Carbon Arc Cutting

In manual carbon arc cutting, the welder holds the electrode holder and starts the arc by touching the workpiece. The welder controls the work angle and travel speed to make the cut or gouge. This method is used for irregular shapes and dimensions where automation is impractical, such as field repairs on heavy equipment.

Automatic Carbon Arc Cutting

In automatic carbon arc cutting, specialized equipment controls the movement of the carbon arc electrode holder. Depending on the workpiece's size and shape, either the electrode moves around the part, or the part moves to the electrode.

The machine controls parameters such as amps, volts, travel speed, work angle, and travel angle. This method is ideal for heavy industrial settings needing consistent, high-volume cutting.

Advantages of Carbon Arc Cutting

There are numerous advantages of carbon arc cutting.

Efficiency and Speed

Carbon arc cutting and gouging can cut or remove high amounts of metal relatively quickly due to the high amperage and large electrode availability.

Versatility in Metals

Unlike oxy-acetylene cutting and gouging (which relies on oxidation as its means of cutting), carbon arc cutting can cut and gouge non-ferrous metals, such as stainless steel.

Cost-Effectiveness

Carbon arc cutting is cost-effective for several reasons. For instance, it doesn’t use a shielding gas and the cost of the carbon arc electrodes is reasonable compared to the consumables other welding processes require.

This process can be performed with relatively simple and basic equipment: a constant-current welding machine with sufficient amperage capability, an air compressor, and a carbon arc electrode holder.

Potential Disadvantages of Carbon Arc Cutting

There are some disadvantages to the carbon arc cutting process, which welders should consider.

Noise Levels

CAC is notoriously loud, which may make it unsuitable for some environments. The loud noise also means adequate hearing protection is a must! The noise levels of the carbon arc cutting process may reach 118 dB and have been described as comparable to an airplane at takeoff.

Sparks and Molten Metal

Carbon arc cutting can quickly remove large amounts of metal, but it also throws hot sparks and molten metal over long distances due to high-pressure compressed air. This increases the risk of injury and fire.

Perform carbon arc cutting in a large, open space or with proper barricades (weld curtains or sturdy, non-flammable materials) to protect against sparks hitting combustible materials. Be mindful of the direction in which sparks are thrown.

Safety Precautions

As with any other welding process, it is important to wear your PPE, but there are some additional hazards associated with carbon arc cutting that welders should be aware of.

Personal Protective Equipment (PPE)

For carbon arc cutting, a welding hood with the right shade lens is essential. Use a shade #12 lens for operations under 500 amps and a shade #14 for over 500 amps. Start with the darkest shade that still lets you see the workpiece clearly and adjust as needed.

Carbon arc cutting also produces high noise levels, often exceeding 118 dB. Hearing protection is necessary; foam ear plugs are the minimum, but double protection (ear plugs plus headphone-style ear muffs) may be needed, especially in loud environments.

Welders should also wear a heavy leather welding jacket to protect against sparks, along with:

Safety glasses with side shields or goggles
Heavy leather gloves
Sturdy canvas or denim work pants
Steel-toed work boots

Ventilation and Fume Control

Carbon arc cutting and gouging generate large amounts of fumes and airborne particulates. To minimize exposure:

Work in a well-ventilated area.
Use fans to direct fumes away from your breathing zone.
Use a portable fume extractor, a powered air-purifying respirator (PAPR) welding hood, or a respirator with the correct filter under your welding hood.

Lighting

Ensure the lighting is bright enough to see the workpiece clearly. If there's no natural light, use portable halogen work lamps, positioned safely out of the path of cutting and gouging operations.

Equipment and Materials

The carbon arc cutting process requires only basic tools and equipment:

An adequate power source
A constant-current welding machine with sufficient amperage capacity (minimum 200 amp)
An air compressor of sufficient size to deliver adequate pressure to the carbon arc electrode holder for the duration of the cutting or gouging process

Step-by-Step Carbon Arc Cutting Process

As with most other welding processes, welders must take some simple steps to ensure consistent, quality workmanship.

Preparation

Prior to the start of carbon arc cutting, consider making these steps part of the pre-job checklist.

Inspecting Equipment and Materials

Is the welding machine in good operating condition? Check cables and connections to ensure the equipment will perform the process properly. Check the consumable carbon electrodes to ensure they are clean and dry.

Check the air compressor and hoses. Look for any leaks that may result in loss of pressure during the cutting process.

Setting the Power Supply

Adjust the amperage on the power source to the manufacturer’s recommendations, based on the size of the electrode and the thickness of the material.

Positioning the Workpiece

To the greatest extent possible, safe, and practical, position the piece such that you can comfortably access the entirety of the joint while remaining safely out of the line of fire of sparks and debris.

Execution

With the welding equipment set up, it is time to initiate the cutting or gouging process.

Striking the Arc

Like stick welding, start the arc by touching the electrode to the workpiece. A solid ground connection is essential. If cutting old, rusty, or dirty material, clean the base metal where you'll start the arc.

Manipulating the Electrode

For a clean cut, focus on the work and travel angle. The cut area should have a symmetrical "U" shape. If the cut leans to one side, adjust the work angle. Side-to-side movement is usually unnecessary; if more metal needs to be removed, make another pass or use a larger electrode.

Controlling the Arc Length and Angle

The arc length will require just the right balance to maintain. An arc that is too long will be quickly lost. An arc that is too close may likewise extinguish and have to be restarted.

The travel angle will be a push angle, often as steep as 45 degrees or more, to remove the molten metal cleanly and efficiently.

Finishing

To complete the carbon arc cutting or gouging operation, take the following steps.

Extinguishing the Arc

Similar to SMAW (stick welding), when you’re at the end of the cut, simply move the carbon electrode out and away from the workpiece in a quick but steady motion. This will all but eliminate the chances of an arc strike or cutting and gouging outside the area of the joint, which could require repair.

Inspecting the Cut

Visually inspect the cut to make sure you’ve cut the material cleanly and that it is not being held by slag from the cutting process or by missed areas in the joint. If you were gouging out old weld metal, check you have removed the entire weld with minimal damage and gouging to the base metal.

Cleaning Up

Prior to any further welding operations after the cutting or gouging process, remove all slag from the joint. If you cut the joint properly, only a minimal amount of grinding should prove necessary. You can also use a wire brush to remove any residual debris from the cut surface.

Common Challenges and Solutions

The carbon arc process produces some unique challenges.

Poor Arc Stability

If you're experiencing poor arc stability, first check the ground connection. Arc blow is often due to resistance from a poor circuit. Clean the workpiece where the ground clamp attaches and ensure it's secure. If problems persist, inspect the welding cables and connections back to the power source, and clean or replace any worn or damaged parts.

Excessive Sparking

Excessive sparking when you are removing very little metal from the joint could be the result of the airways of the carbon arc electrode holder being plugged or misaligned relative to the joint. Try these steps to resolve the issue:

Stop cutting and turn off the power source.
Disconnect the airline to ensure any debris lodged in the electrode holder will not strike the welder, once freed.
Clean holes and check the electrode holder for debris that could be holding the carbon electrode at the incorrect angle.

Inconsistent Cuts

Multiple factors, like technique or power source fluctuations, can cause inconsistent cuts. If this continues, consider these possibilities:

Operator error: Use an angle guide to steady your hand during cutting.
Incorrect amperage: Too little amperage won't melt enough material, while too much will create excess molten metal and slag, affecting the cut.
Dirty or rusty material: Clean the base metal with a wire brush, as impurities can disrupt a consistent arc.
Machine output: If the machine is at maximum capacity, it might overheat or reduce output, affecting cut consistency.

Excessive Buildup of Slag and Debris in the Joint

If there is an abnormally high amount of slag building up in the joint and it becomes necessary to periodically stop and chip away the slag before resuming cutting operations, consider one or more of the following means of mitigation:

Make smaller cuts but more individual passes, which will result in less molten metal piling up
Use a larger carbon arc electrode
Increase air pressure to blow away more of the molten metal from the cut
Increase the work angle by laying the electrode angle down at a steeper angle

Maintenance and Care of Equipment

With the amount of amperage and subsequent heat inherent to the carbon arc process, there is the potential for tremendous wear and tear on the equipment.

Cleaning the Electrode Holder

You should clean the electrode holder as often as necessary with a small, handheld wire brush or even a file to remove sparks and debris from the cutting process. Keeping the electrode holder clean will ensure the carbon electrode has a secure electrical connection and is properly aligned with the air holes in the electrode holder.

Applying a small amount of WD-40 to the electrode holder will leave a thin, oily layer, which will delay the buildup of sparks on the electrode holder.

Inspecting Cables and Connections

Cables and connections show signs of wear and damage if you use them in high-amperage applications for extended periods. Inspect the cable and cut out and replace sections that have become worn, frayed, or burned from excessive heat.

Consider stepping up to a larger size cable (as per the manufacturer’s recommendations) if you will be using the carbon arc cutting process extensively and repeatedly on a project or in a facility.

Use only quality connectors rated for the amperage requirements for the carbon arc electrodes.

Use dielectric grease (available at any auto parts store) when installing new cable connections. This will ensure a clean, solid electrical connection that will allow the proper flow of current and offer some protection against overheating and corrosion.

Storing Equipment Properly

Store all equipment (including the power source, cables, electrode holder, air hose, compressor, and consumables) in a dry place, away from any inclement weather that may cause rust, dirt, and debris build-up, which would inhibit the efficient operation of the welding equipment.

Replacing Worn Components

Repair or replace any cables, connections, hoses, or any part of the carbon arc cutting system that shows excessive wear or damage.

Calibration and Testing of Equipment

Use an amp/voltmeter to check that the power source output matches the requirements for carbon arc cutting and can consistently produce the necessary amps.

If the output doesn't match the machine settings, inspect electrical connections for wear or damage. If no issues are found, contact a welder repair service for further evaluation, as there could be internal damage needing professional attention.

Advanced Techniques and Tips

Cutting Thick Materials

One of the advantages of the carbon arc cutting process is the capability to cut and gouge thick sections of material productively and efficiently. You can accomplish this in a few ways.

Techniques for Deep Cuts

For cutting thick pipes or plates, or gouging large welds, you may need multiple passes. Trying to cut too much in one pass can cause excessive slag and sparks. Two or three passes are often cleaner and better than a single pass that needs multiple starts and stops.

Managing Heat and Distortion

To reduce distortion, avoid concentrating heat in one area for too long. Move the part around and make passes in different areas rather than staying on one joint until completion. This helps maintain a uniform temperature and reduces distortion.

Precision Cutting

Some applications may require more precision in cutting than merely removing large amounts of metal quickly. Plus, a neater, more accurate cut means less cleanup.

Tips for Accurate Cuts

For precise cuts, use a smaller carbon electrode to remove less material at a time, which improves accuracy and reduces cleanup.

Using Guides and Templates

Use an angle iron or tubing as a guide for more accurate cutting. Clamping the guide to the workpiece helps keep the cut straight. Magnetic torch-cutting guides and jigs or templates for frequent cuts can also improve precision. Always mark a chalk line or use soapstone to increase visibility and guide the cut.

FAQ

What materials can you cut with the carbon arc cutting process?

Although carbon arc cutting is primarily used for ferrous metals like iron and steel alloys, it is also suitable for non-ferrous alloys, such as stainless steel. This is because the carbon arc cutting process uses an electric arc, whereas oxy-acetylene torch cutting, in contrast, relies on oxidation.

What are some of the main advantages of the carbon arc cutting process?

The main advantages of using the carbon arc cutting process include the capability to cut and gouge thick sections of metal, its portability due to the basic equipment needed, and the comparatively low cost of the equipment.

What are some disadvantages of carbon arc cutting?

The main drawbacks of carbon arc cutting are its high noise levels, the risk of sparks and molten metal traveling farther (increasing fire hazards), and the need for more operator skill compared to simpler methods like plasma or laser cutting. Additionally, it often requires more post-cut cleanup than plasma or laser cuts.

Is it true that the carbon arc cutting process is “harder” on the welding machine and may cause excessive wear and tear on internal components?

Carbon arc cutting can strain older welding machines, especially if power surges occur or the machine runs at high amperages beyond its duty cycle. Newer machines with overload protection are less affected. To avoid damage, follow the manufacturer's amperage guidelines and ensure the machine and cables are rated correctly.

Featured photo courtesy of gabrielroma // Pixabay