In my June 28th blog post titled “Low-tech, High-impact!” I discussed work completed by EWI’s Steve Massey highlighting the benefits of mechanization of backgouging and welding as they relate to productivity. In this post I will review the basics of carbon arc gouging and discussing other benefits of mechanizing the process.
Carbon arc gouging is a process whereby an arc is struck between a consumable carbon-graphite electrode and the base material. As the arc melts the base material, a jet of air travels along the under-side of the electrode and blows away the melted base material. Carbon arc gouging is an efficient method of removing a large amount of material and is often used to prepare joints for welding of heavy sections. A common application is backgouging the second side of T-joints to ensure adequate root penetration as shown in Figure 1.
While the carbon arc gouging process is often applied manually, a high level of skill is required to achieve a consistent groove shape and depth. Improper operation can lead to an inconsistent gouge depth and shape as well as excessive clean-up time. Either of these issues can have a significant negative effect on productivity. In trials conducted by EWI, mechanization decreased the gouging time by 68% and post-gouge clean-up time was decreased by 22%. Figure 2 shows a joint after mechanized backgouging, while Figure 3 shows the same joint after being cleaned up with a chipping hammer.
In addition to higher travel speeds and material removal rates, mechanization allows for more precise control, eliminating the unintentional removal of excess material. This leads to a significant decrease in the cross-sectional area of the subsequent multi-pass weld (see Figures 4 and 5).
Additional benefits to reducing the cross-sectional area of the weld are decreased welding time, a reduction in weld consumable use, and a reduction in distortion.
In summary, mechanization of the carbon-arc gouging process for the backgouging of weld joints yields the following benefits:
- Less operator skill required
- Less gouging time
- Less clean-up time
- More precise control, resulting in a smaller gouge cross-sectional area
- Less weld consumable cost
- Less second-side welding time
- Less distortion