Plasma Cutting - Cont.

The only drawback was that the plasma cutter had to be manually adjusted to match available voltage, and that often proved to be a time-consuming task. Additionally, the plasma cutter's electronics are susceptible to catastrophic damage if the voltage is configured improperly.

To eliminate voltage compatibility issues, advanced electronic circuitry allows the plasma cutter to sense incoming power and links to it automatically while providing the correct configuration. This eliminates the need to open the plasma cutter and link wires manually.

Some advanced plasma cutters are designed to operate at any location, and in any country. These plasma cutters automatically sense and adjust their connections internally to match any primary power level from 208 to 575 VAC on single or three-phase circuits operating at 60 Hz. Many systems even will work on the predominately European frequency of 50 Hz. An added benefit of such technology is the ability to handle fluctuations in the utility power supply, ensuring consistent cutting output.

It is also possible to run plasma cutters from the auxiliary power of an engine driven welder/generator.

Reliability

Plasma cutters traditionally work in dirty environments in which airborne dirt and other contaminants are commonplace. Dirt buildup can lead to overheating, and metal filings and salt deposits can cause the control board to short circuit. To combat this, some systems combine air channels built into the centers of the plasma cutters with fans that automatically blow air through the channels to cool the cutters’ internal components. Critical components are located on the outside of the channels where there is less opportunity for contaminants to collect.

Typically, aluminum heat sinks positioned inside the air channels dissipate the heat generated by the system's electronics. Meanwhile, the cutters are equipped with variable resistors that sense component temperatures. When temperatures reach a preset level, the resistors active central circuits to start fans that cool the components. After temperatures drop, the fans automatically shut off, minimizing the potential for airborne contaminants to be pulled inside the machines, and conserving energy.

Gouging

The traditional method of gouging metals uses the carbon arc gouging method. Carbon arc gouging equipment comprises a power source, a hollow carbon rod and a compressed air source. The power source is similar to a welding machine, but welding machines operate at low voltage and high current. For carbon arc gouging, a high output power source is needed to provide the adequate voltage required for quality gouging.

A plasma arc cutter, on the other hand, can be used as a practical gouging tool.

The plasma arc process is effective because it uses an extremely concentrated high arc-stream velocity. When gouging, a special plasma arc tip reduces constricts the plasma arc to a specified level. Less constriction produces lower arc-stream velocity. At the same time, the tip's wider-diameter orifice transforms the narrow cutting arc into a relatively wide and highly effective gouging arc.

To gouge, the operator holds the torch at an angle of 40 degrees to the workpiece and presses the trigger. Unlike the carbon arc process, there is no need to push the carbon rod into the workpiece to gouge. There also is no need for the operator to adjust the distance of his hand to the workpiece as the carbon rod is consumed or to stop working to replace the rods. Instead, operators are able to continue gouging by maintaining the necessary distance between the arc and the workpiece and adjusting for travel speed.

Plasma improvements

Two technological improvements to plasma arc cutters are torch-shield drag technology and the elimination of high-frequency (HF) starts.

Besides its high arc-stream velocity, a plasma arc can produce temperatures as high as 72,032-degrees F. These properties are the reasons that plasma cutters slice through metals so quickly and easily.

However, care must be taken with plasma arc cutters: If an operator cuts or pierces a material too quickly, the plasma arc can blow back and damage the cutting tip.

To minimize the potential for tip damage, electrically insulated copper drag shields are used to isolate tips from workpieces. This significantly increases tip life and allows the operator to drag the torch across a workpiece, increasing productivity.

Many plasma arc cutters use a high-frequency start to initiate a plasma arc. However, high frequencies can interfere with nearby electronically controlled equipment and computers. To avoid that problem, many plasma arc cutters use a contact start that allows the machine to start without high frequency, yet deliver the same performance.

Plasma Cutting Home