Plasma technology isn’t just for cutting
July 23, 2012
More welders are realizing the benefits of using plasma technology to perform gouging in heavy industrial applications where versatility, speed, and safety are important.
Plasma arc gouging has wide capabilities in industrial applications, including shipbuilding and maintenance; heavy equipment manufacturing and repair; and truck body, tank, and steel structure manufacturing. It can remove strong backs, lifting lugs, temporary brackets, tack welds, and rivets, and it can be used for demolition or salvage operations. In foundries, it removes excess material from castings. It provides a means to fix and maintain bridges, heavy equipment, and pipelines, but it is also handy for removing weld cracks and imperfections and preparing plate edges for welding by removing extra metal that may be on the plate.
Today more welders are realizing the benefits of using plasma technology to perform routine gouging applications, and it’s easy to understand why. Plasma gouging is a fast, simple, and quiet way to remove metal. Four different gouging methods are in common use today: mechanical, oxyfuel, carbon arc, and plasma.
Mechanical grinding can involve hand grinding, hand milling, routing, or chipping.
Oxyfuel gouging involves using fuel gas to heat steel to its ignition temperature. Once the metal is nice and hot, it is rapidly combusted, then blown away by a jet of oxygen gas. Its use is limited to carbon steel.
In the carbon arc gouging process, an electric arc is generated between the tip of a carbon electrode and the metal workpiece. A jet of air is then directed around the tip to remove molten metal from the area, forming a groove. This process is versatile because it is capable of performing on mild steel, cast iron, nickel alloys, copper, and aluminum.
The final method is plasma gouging. Like plasma cutting, the plasma gouging process uses a constricted jet of high-temperature gas to melt the metal. It is relatively quiet and doesn’t cause excess smoke. With just a bit of practice, it is possible to achieve a smooth, clean, consistent gouge. And just like its cutting counterpart, plasma gouging can be done on mild steel, stainless steel, aluminum, and copper.
Plasma gouging works similarly to plasma cutting. In plasma cutting, a plasma arc is formed between a negatively charged electrode inside the torch and a positively charged workpiece. Heat from the transferred arc melts the metal quickly, and a high-velocity gas jet blows away the molten material. The process is nearly identical for gouging; the only difference is that you blow away only some of the material by holding the torch at an angle and using gouging-specific consumables that are designed to produce a wider and softer arc. In addition, many plasma systems have a dedicated operation mode for gouging, which enables the arc to stretch without going out. Some manufacturers include gouging consumables in the start-up kit with new machines.
Plasma cutting and gouging require almost the same equipment. For hand gouging, all you need is a plasma system consisting of a power source, a gas supply (often just air), a torch, and lead. Cut charts and instructions in the operator’s manual explain safety, parts, and operating parameters for gouging. Many manufacturers supply accessories specifically designed for gouging, such as metal heat shields to surround and protect your hands and leather lead protectors. These generally do not come standard with a new system, but are worth the investment if you expect to do a lot of gouging.
A number of different plasma and shielding gases—including air, nitrogen, oxygen, an argon / hydrogen mix, and other combinations—can be used when gouging with plasma. You should check the operator manual first just to be sure the gas you want to use is compatible with your particular plasma system. There are a few rules to follow to help you decide which gas to use.
Modern air plasma torches provide good cooling characteristics, high cutting capacities, long consumables life, and consistent gouge quality, all attributes which improve gouging performance and allow for a more controlled gouging process. Another feature of modern air plasma torches is their design.
In the past all hand plasma torches were designed with a 75- or 90-degree angle. Today straight torches are available to provide a variety of options that suit different ergonomic needs. Some plasma systems include a quick-disconnect feature that makes it easy to switch between the different torches. For example, you can have two torches—a standard 75- to 90-degree torch with cutting consumables and a straight torch, ready with gouging consumables—and then quickly and easily switch between the two depending on the job at hand.
Operators use a variety of techniques to achieve different gouge profiles and sizes, whether they’re gouging by hand or using a mechanized method like a track cutter. The most common way involves positioning the torch at a 40- to 60-degree angle to the work surface while the pilot arc forms and transfers to the plate.
Once you’ve made contact, simply aim or feed the arc into the area you want gouged while moving the torch forward. Variations in the torch angle and speed, along with amperage levels, are used to control the gouging depth. A steeper torch angle and slow forward movement form a deeper gouge angle, while a lower torch angle and fast forward movement form a gouge angle that is shallow.