Gouging with Plasma
The switch to plasma wasn’t exactly planned, but more welders are now realizing the benefits of gouging with plasma. Michelle Avila of Hypertherm explains the reasons why.
The switch to plasma wasn’t exactly planned, but more welders are now realizing the benefits of gouging with plasma. Here’s why.
They’ve been mining in Grant County, New Mexico since before the Civil War. Huge copper mines like Chino and Tyrone still drive the local economy that has been in high gear the past couple years thanks to the rising copper prices that have prompted mine owners to run their operations around the clock, three shifts a day, seven days a week.
While this non-stop activity is undoubtedly good for the economy, it means there is no time to rest. Huge dump trucks and other heavy equipment are in constant demand, moving hundreds of thousands of tons of material a day. Maintenance crews are constantly busy, fixing one thing or another.
Often their work involves gouging out old welds, a necessary first step before they can begin the actual work of repairing a truck bed or replacing a mold board liner on a track dozer. In the past, the crew would reach for carbon arc, but not anymore. Today these professionals use plasma to make better repairs in less time.
The switch to plasma wasn’t exactly planned. It came after a supplier insisted on demonstrating the process. A senior supervisor explains his initial reaction, “I thought they were wasting my time because plasma can’t be used for gouging. Well, we were wrong. You can gouge with plasma. We now use it in every application where we used to use carbon arc.”
Today, more and more welders are realizing the benefits of gouging with plasma. It’s easy to understand why. Plasma gouging is faster, easier, safer, and quieter than other metal removal methods; benefits that ultimately save companies a considerable amount of money.
Another company sold on plasma gouging is Rockland Marine Corporation (Rockland, ME), a business that fabricates, repairs, and services a range of different boats. The company’s first attempt at plasma gouging began more than 14 years ago with the purchase of a Hypertherm MAX100.
Rockland Marine first purchased the system to cut metal because, as welder Francis Dennison explains, “Plasma can cut through rusted and painted metal and about 90 percent of our work is done outside in the elements.” To them, gouging was just considered an added benefit. Now it’s a necessity. “Plasma is a lot faster than carbon arc and grinding. The metal removal rate is faster. It takes less time and the clean-up is easier because there is little to no mess,” adds Dennison.
His comments are echoed by Miller-St. Nazianz, Inc. (Nazianz, WI), a company that fabricates and manufactures spray-application agricultural equipment. Brian Schad, the leader of the company’s special projects team, uses plasma to cut and gouge daily. “The plasma is cleaner, faster, and not nearly as loud. We use fewer consumables too.”
DIFFERENT GOUGING PROCESSES
There are four different gouging methods in common use today: mechanical grinding, oxyfuel, carbon arc, and plasma.
Mechanical grinding can involve hand-grinding, hand-milling, routing or chipping. As you might imagine, while mechanical grinding eventually gets the job done, the process is time-consuming, loud, and dangerous. Just ask the crew working to construct the 680-mile long Ruby Pipeline in the western United States. They have seen their share of injuries, especially eye injuries, a common occurrence in the pipeline industry, which sees at least one eye injury per day in the United States.
The next method, 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. Oxyfuel is quieter and faster than mechanical gouging, but the process is often hard to control, even if you have years and years of experience. Also, its use is limited to carbon steel.
In the carbon arc process, an electric arc is generated between the tip of a carbon electrode and the metal work piece. A jet of air is then directed around the tip to remove molten metal from the area, forming a groove. This process is more versatile than oxyfuel gouging as it works on a number of different metal types: mild steel, cast iron, nickel alloys, copper, and aluminum. It’s also easier to learn, and overall does a good job of removing metal.
The problem though is that, like mechanical gouging, it is loud. In addition, the carbon arc process creates a lot of smoke and fumes, and like oxyfuel gouging, carbon-arc is hard to control. It’s not uncommon to remove too much metal or to wind up with extra carbon deposits or inclusions on the base metal.
Another problem: carbon arc gouging is tedious and time consuming because the process requires operators to repeatedly stop and re-feed the rod. Rockland Marine’s Dennison explains it like this, “You have to keep adjusting your rod. The rods are only about 12 in long, so you adjust it once or twice and then it’s time to replace it.”
The final method of gouging involves plasma. Like plasma cutting, plasma gouging uses a constricted jet of high temperature gas to melt the metal. With just a bit of practice, it is possible to achieve a smooth, clean, consistent gouge. Plus plasma gouging is relatively quiet and doesn’t cause a bunch of smoke.
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