Why plasma is better for industrial gouging: carbon arc vs. plasma

In the industrial welding and cutting industry, a few processes dominate the industrial gouging market. For almost 80 years, carbon arc gouging was the go-to for most industrial gouging applications. Recently, plasma gouging has made several advances in consumable technology. With an ever-evolving market, shifting regulatory requirements, and increasing work environment concerns, many companies need the increased flexibility and safer working conditions plasma provides.

What is carbon arc gouging?

Carbon arc gouging removes metal by heating the metal using an electric arc that travels between the tip of a carbon electrode and a conductive metal workpiece. The metal becomes molten, and a high-velocity air jet streams down the electrode to blow the metal away, leaving a clean groove. This metal gouging technique is used to remove metal for back gouging cracked or damaged welds, joint preparation, and for fabrication and repair.

Common industry applications for carbon arc gouging include ship building, rail car manufacturing, pressure vessel fabrication, structural steel manufacturing, and pipe and tube fabrication.

History of carbon arc gouging   

Myron Stepath developed the process of carbon arc gouging with compressed air to remove defective welds in stainless steel armor plates on US warships during World War II. Prior to Stepath’s invention, carbon arc gouging had been used to remove defective welds in overhead and vertical locations where gravity could be used to remove molten metal. Stepath realized that adding an air jet to the process could remove metal on flat objects as well.

The original process was a two-person job. One person would melt the metal and a second would use an air nozzle and direct an air blast at the molten metal. It worked, and molten metal could now be removed from flat surfaces. In 1948, Stepath introduced the first air carbon arc torch to the welding industry and carbon arc gouging soon became a single-operator job. This new tool saved time on weld back gouging, crack removal, and weld defect repairs on carbon, alloy, and stainless steel.

Technical requirements of carbon arc gouging   

Carbon arc gouging requires specialized tools for effective welding and worker safety, including: 

  1. Hand-held torch or automated fixture

  2. Compressed air source

  3. Welding power supply

  4. Electrodes

  5. Safety equipment for protection from fumes and heat:

      • Hearing protection

      • Suitable welding helmet

      • Proper ventilation system

      • Heat resistant clothing – jackets, aprons, and leggings 

Benefits of carbon arc gouging   

Carbon arc gouging is widely adopted because of its ease of use and efficiency. Specifically, carbon arc gouging: 

  1. It is portable. The torch can be used for operations at greater distances from a power supply than other methods

  2. Has lower initial costs

  3. Can be used on dirty or rusty metal

  4. Can more easily produce specific gouging profiles and more predictable gouging profiles

  5. Electrodes have a specific shape, making it easy to predict the size, shape, and width of the gouge

Drawbacks of carbon arc gouging   

Carbon arc gouging is more hazardous than plasma gouging. The air jet causes the molten metal to be ejected over a significant distance, so extra care must be taken to ensure worker safety from molten metal. The force of the air blast tends to vaporize much of the molten metal into fine droplets, creating fumes consisting of metal vapor, carbon dust, and metallic byproducts. Because of high currents (up to 2000A) and high air pressures (80 to 100 psi), carbon arc gouging can be very noisy, requiring ear protection. 

Most electrodes are made from a mixture of graphite and pure carbon. As the electrode is consumed, it releases carbon into the base material. This carbon becomes brittle as it cools and must be removed before welding, requiring extensive secondary operations, including grinding and sanding. These secondary operations are labor intensive, increasing both the time required to finish the job and costs.   

What is plasma gouging?   

Plasma gouging removes metal by using gas and an electric current to create a plasma arc. Heat from the transferred arc rapidly melts the metal and high gas pressure blows the molten metal away. The plasma gouging process removes any amount of material from a work piece, regardless of shape or rate, without severing or piercing the material. 

Industrial plasma gouging in the 125-to-200-amp range has been quickly adopted for applications equating to carbon arc welding with electrodes from 6 mm, ¼ inch, to 10 mm, 3/8 inch, in diameter. 

History of plasma gouging 

Robert Gage invented the plasma cutting process at the Tonawanda Laboratory of the Linde Division of Union Carbide in 1954. 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. When they passed a fairly high gas flow through this focused arc, it could cut metal. Plasma gouging is an application of plasma cutting that uses a slightly defocused arc to increase the hole size in the constricting orifice and produce a somewhat wider and less intense arc. Instead of severing the metal, only some of the material is removed.

Technical requirements of plasma gouging 

Plasma gouging requires specific equipment, including: 

  1. A dedicated power supply with a specific gouging mode designed for the gouging process

  2. A plasma torch that houses a special set of consumables designed for gouging. Gouging can be done freehand with a hand-held torch, with mechanical aids such as a track cutter, custom gantry, fully automated CNC cutting table, or robot

  3. Gas supply. Many options can be used depending on the application and tool, including air, nitrogen, oxygen, an argon and hydrogen mix, and other combinations

  4. Safety equipment: 

      • Hearing protection

      • Eye protection

      • Ventilation

      • Heat resistant clothing

Benefits of plasma gouging 

Plasma gouging has several benefits that can reduce costs, save time, and improve working conditions.

  • Plasma gouging is generally FOUR times faster than carbon arc gouging with rod sizes from 6 mm (1/4 inch) to 16 mm (5/8 inch)

  • Plasma gouging creates cleaner gouge profiles, requiring little to no secondary work

  • Plasma gouging delivers consistent gouge profiles

  • Process adoption is easier, with a shorter learning curve for new operators. Operators require less training, so new hires are productive faster and companies save on training costs  

  • The work environment is safer:

      • Typically, when measured at conditions that create a similar gouge size, plasma gouging is 5 to 10 decibels quieter than carbon-arc gouging

      • Plasma gouging has fewer toxic fumes and less arc spatter. The plasma gas pushes the molten metal out of the groove less violently than carbon arc gouging air jets, so arc spatter is reduced and less molten metal vaporizes, reducing the metallic vapor and reaction with the surrounding atmosphere

  • Flexible integration with mechanized options, carriages, stationery fixtures, robots, etc. make plasma gouging more versatile and useful in more applications than carbon arc  gouging

  • Customized consumable gouging charts make system set up easier for new and  experienced operators

Why is plasma gouging a better choice?

Plasma gouging provides more consistent and repeatable gouge profiles. It delivers safer work environments and minimizes secondary operations, which reduces costs. Plasma systems can be fitted with numerous torch options to fit a variety of automated applications where carbon arc technology cannot be used. In short, plasma is safer, more versatile, faster, more precise, and more cost effective. 

 

For more training, visit: https://www.hypertherm.com/HCI

 

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