August 29, 2002
Many fabricators use plasma arc cutting torches every day, either to replace or complement saws, cut-off wheels, snips, and oxyfuel rigs. It can be used in a variety of applications—installing or remvoving HVAC/R equipment, plumbing systems, and industrial equipment; reparing equpment and systems; and cutting shapes consistently.
Many fabricators use plasma arc cutting torches every day, either to replace or complement saws, cut-off wheels, snips, and oxyfuel rigs. Fabricators say the use of this equipment has grown because it can be used in a variety of applications, from installing heating, ventilation, air conditioning, refrigeration, and plumbing systems, to demolishing old industrial wash systems and erecting new ones, to cutting shapes to repair excavator booms or consistently cutting shapes.
When it comes to cutting, what's in your toolbox? These days some fabricators and contractors complement or replace their saw, cutoff wheel, snips, or oxyfuel rig with a portable air plasma arc cutting machine.
These machines are about the size of a small carry-on suitcase; weigh 40 to 80 lbs. depending on their output; and slice through mild steel, stainless steel, and aluminum. A 55-amp plasma cutter, a popular size, can cut 1/4-inch steel at a rate of 70 inches per minute (IPM).
Contractors of all sizes can use plasma cutters to fabricate metal in the field. This includes mechanical contractors; general contractors; heating, ventilation, air-conditioning, and refrigeration (HVAC/R) contractors; and those responsible for maintenance, repair, and operating (MRO). Some shop fabricators also use plasma cutters, especially if they can't afford mechanical shears or CNC equipment.
With labor costs comprising 80 to 85 percent of a typical fabrication project, saving time means big money. For this reason, fabricators look for tools that can reduce costs.
"When I bid a job, I bid the hours. So if a tool can save us time, I certainly want to use it," said Jeff Beyersdorf, project manager at U.S. Plumbing and Heating, Combined Locks, Wis. This firm designs and installs HVAC/R and plumbing systems.
Steven Young Sr., supervisor and maintenance manager at Murphy Concrete & Construction Company Inc., Appleton, Wis., also takes a business perspective.
"If you can incorporate a plasma cutter into your operation, it will save you half the repair time," he said. "That's worth a lot to a contractor, a farmer, or anybody."
In Young's operation, a typical billing rate is $35 an hour. This means that if he saves about 40 hours of time, his plasma cutter has paid for itself.
Return on investment also comes in the form of customer satisfaction, when projects are completed by deadline.
For example, Continental Equipment Corp., Milwaukee, specializes in demolishing old industrial wash systems and erecting new ones. In two weeks the company had to completely remove an old system that prepared sheet metal for painting and install a new one.
The old wash system measured 110 feet long, 14 ft. high, and 14 ft. wide and consisted of 10-gauge to 1/4-in. mild steel plate.
Continental used a combination of five plasma cutters to cut approximately 1,000 ft. on the old washer system. That's somewhere around 50,000 to 60,000 lbs. of metal cut and handled, said Todd Becker, the company's plant manager. He estimates the plasma cutters saved at least a day and a half.
To cut a straight line, follow a straight edge. Plasma cutting allows this because it does not create the wide heat-affected zone (HAZ) that can melt or burn a metal, wood, or cardboard edge.
"It's good when you can cut plate to where it looks like it was sheared," said Bill Baxley, owner of Baxley Welding, Auburn, Calif. "I don't have a shear--I do a lot of field work--so I use my plasma cutter running off my welding generator's auxiliary power."
For cutting shapes, such as plates used to repair excavator booms, Baxley first makes a cardboard template of the desired shape. He places the template on a steel plate, traces its outline with soapstone, and then uses a cutting circle to cut a radius or a straight edge for a straight line.
For shapes you cut regularly, use a permanent metal template. For example, artist Eddie Dean, owner of Texas Silhouette, Midland, Texas, often starts the creative process with a digital picture. Once he has the digital image, he loads it into his computer and prints out a paper copy. He then projects that image on a wall to blow it up.
Using a special type of board for artwork (image poster board with metal on the back of it), Dean traces the projected image and adds last-minute details. Using a razor blade, he cuts out the pattern. Finally he lays the pattern on a sheet of 1/8-in.-thick mild steel and uses soapstone to trace the pattern and all its intricate details.
For fine detail, Dean holds the tip of the torch a fraction of an inch from the workpiece.
"The closer you hold the torch to the metal, the finer the cut," he said. "If you raise the tip up, it makes a wider cut. Under normal circumstances, my cut width is 0.040 to 0.050 in." It's important to note, however, that not all machines can cut this precisely.
Plasma cutters also can relieve physical stress. For example, U.S. Plumbing and Heating fabricator Layton Dilley used to cut pipe fittings with offset snips.
"Because I had to grip the snips so hard to cut the metal, I'd have to take regular breaks to relieve fatigue," he said. "With a plasma cutter, I can zip right through the cutting without stopping."
Generally, plasma cutting produces a small HAZ and cut width. This can lower the heat input into the metal, eliminating or minimizing warping.
Young noticed that thin and hardened steels didn't warp with plasma cutting. For example, the paddles in an asphalt drier are made from a Tri-Braze® steel with a 400 Brinell hardness. They need to be cut to specific sizes and have slots cut in them for mounting.
"When we cut the paddles with a torch, we noticed warping," he said. "We wanted a flat surface for easy fit-up and bolting, so we shifted to plasma cutting. We also get a cleaner cut with less grinding, and we can cut holes or slots with square corners."
Good fit-up also can benefit pipe fabricators.
"When you're coping and fitting pipe, you want a clean, even cut," said Eric Syring, shop foreman at U.S. Plumbing and Heating. "The plasma cutter allows us to cut...evenly and without distortion."