Tech Tip: Gouging - Environmental & Safety
Gouging and cutting metal are important operations in the welding world. Welders must often remove welds or metal to replace worn or defective parts, repair defects in a weld, or remove worn hardfaced deposits so new hardfacing can be reapplied. Back gouging can also be necessary when both sides of a plate are to be welded. Unfortunately, these important operations also raise concerns about environmental and safety issues.
Two of the most popular methods of gouging are plasma gouging and carbon-arc gouging. Is one safer than the other?
In carbon-arc gouging, an electric arc at the end of a consumable carbon rod melts the metal, and a continuous blast of compressed air violently blows the molten metal away. The constituents of the molten metal react strongly with air, and the force of the blast tends to vaporize much of the molten metal into fine droplets, creating a high level of fume consisting of metal vapor, carbon dust and metallic byproducts. Typically the fume level is higher than the allowed exposure level to welding fumes in a workplace. Depending on the material to be gouged, exposure to particular toxins may also be a problem.
Plasma gouging is a variation of plasma cutting in which the arc is slightly "defocused" by increasing the hole size in the constricting orifice. The torch is inclined at an angle to the workpiece, so that the arc plows out a groove on the metal surface and blows the molten metal off to the side. Plasma gouging uses an electric arc to melt the metal, but the plasma gas itself pushes the molten metal out of the groove. This operation is less violent than air carbon-arc gouging, so less molten metal vaporizes, reducing the vapor level and its reaction with the surrounding atmosphere. If air is used for the plasma gas, some reaction occurs but the volume of air is lower than what is used for air carbon-arc gouging. If inert gas is used, the molten metal is protected from the surrounding atmosphere and has little chance to react with the air.
Plasma gouging is typically 5 to 10 decibels quieter than air carbon-arc gouging. This still normally requires hearing protection for the operator but may eliminate the need for hearing protection for nearby workers. Actual measurements should always be taken to assure that proper safety procedures are implemented.