Every day, we are around plasma in TVs, fluorescent lamps, neon signs, and plasma arc cutters. A plasma arc torch is a great torch for working close to a patient because of low heat transfer and its ability to fit in tight spaces.
It is for use on thinner metals that are capable of conducting electricity, including stainless steel, ferrous, and many nonferrous metals.
OPERATION
The cutting action of a plasma arc torch is in the form of an electrical arc in combination with a high-velocity gas. For us, this gas can be room air from an air compressor or a self-contained breathing apparatus (SCBA) bottle. The compressed air flows into the tip that contains a plasma electrode and a plasma cutting tip. This electrically conductive air pushes through the pressurized chamber via a small hole in the cutting tip, taking the energy of the arc with it. The heat of the plasma arc melts the metal to be cut, while the force of the compressed air blows it away, creating a kerf. The temperature of the plasma arc, depending on torch model and settings, is 36,000°F to 50,000°F. Your plasma arc torch manual will have a table, like a “Torch Tip Chart,” indicating amperage, cutting speed, and air pressure recommendations based on the size and type of metal.
Using a 120-VAC 20-amp outlet, about the most you are going to cut is ½-inch-thick metal. To increase that capability, the simplest way is to get a 220-VAC powered machine. With this, you can get through 11⁄2 inches. Check your generator manual as to its ratings. Make sure your electrical extension cords are no more than 100 feet for 12-gauge or 150 feet using 10-gauge to prevent excessive voltage drop while running the cutter (see “Extension Cords: One of the Most Misused Tools on the Fireground,” Fire Apparatus & Emergency Equipment, April 2023).
Keep in mind the total power requirements. If you use an air compressor, it will take another 120-VAC/20-amp outlet. To power both a 120-VAC plasma arc cutter and air compressor sized to support maximum cutting capability, you will need a minimum 5-kW generator to cut through ½ inch. To reduce the power demand, use SCBA bottles as the air source. Compromises on source voltage affect the torch performance including shortening the duty cycle (see “Know Your Generator,” Fire Apparatus & Emergency Equipment, March 2022).
Establish a clean connection for the torch grounding clamp as close to the cut area as possible. You may need to grind off any coatings, paint, or rust. The plasma arc process produces a high voltage to cut. This electric energy can cause severe or fatal shock to the operator or others in the workplace. It is not recommended to use on complex machines like cars. In addition to high voltage, the plasma arc process produces very bright ultraviolet and infrared light. These arc rays will damage your eyes and burn your skin if you are not properly protected. To protect your eyes/ skin, always wear a torch jacket, welding helmet/shield, hearing protection, and leather gloves. Shade 7-8 lenses are suitable for most portable machines.
Because the material must be electrically conductive to react to the ionized gas coming from the torch, nonconductive materials like wood, glass, and plastics or poorly conductive metals like manganese, lead, tungsten, and tin cannot be cut with the plasma arc. Plasma can cut painted, dirty, or even rusted metal. However, as stated, the ground clamp connection needs to be clean for maximum performance. The arc is created when the arc cutter tip and the work piece are touched together and then separated by a small distance, typically no more than 1⁄16 inch. It can cut through small air gaps, ¼ inch or so, and multiple layers. This is comparable to coupling distance with flame cutting torches. It may be useful to make “test cuts” on the work piece to make sure your ground connection and cutt