Farmers who experience the benefits of a handheld air plasma arc cutting machine rarely want to return to oxyacetylene cutting or mechanical cutting processes such as saws, cut-off wheels, shears or snips. Plasma cutting makes the seemingly difficult job of cutting stainless steel, aluminum or other metals effortless.
How it works
Plasma is the fourth and most highly energized state of matter: solid, liquid, gas and then plasma. In fact, plasma looks and behaves like a high-temperature gas, but with an important difference — it conducts electricity. The plasma arc results from electrically heating a gas (typically air) to a high temperature. This ionizes gas atoms and enables them to conduct electricity. A fluorescent light is an example of plasma in action.
A plasma arc torch spins a gas around an electrode. The gas is heated in the chamber between the electrode and torch tip, ionizing the gas and creating plasma. This causes the plasma gas to expand in volume and pressure.
The small, narrow opening of the torch tip constricts the plasma and accelerates it toward the work piece at high speeds (20,000 ft./sec.) and temperatures (up to 30,000°F). The force of the high-intensity plasma jet pushes through the work piece and removes the molten metal. This jet easily cuts through metals with poor heat conductivity (stainless steel) or excellent conductivity (aluminum). The flame created by an oxy-fuel torch lacks plasma's concentration and cuts stainless steel or aluminum so poorly (with excess warping or metal waste) that welding professionals don't bother to use it; they consider plasma arc cutting the standard process for these metals.
Plasma cuts faster, doesn't require a preheat cycle, minimizes the heat-affected zone and yields a cut with a small width. Plasma units also gouge, pierce, bevel, cut holes and trace shapes. In fact, the most difficult aspect of plasma cutting is selecting a machine that best matches the application.
Many people erroneously judge a plasma machine solely by amperage. Although this is important, the total output power (in watts) equals amperage times voltage. This is one reason why the cutting capacity of a particular “size” plasma machine varies greatly by manufacturer.
How to use
Here are a few tips for getting the most out of plasma cutting:
Follow proper safety procedures and wear personal safety equipment.
Inspect the torch tip, electrode and shield cup.
Check gas/air pressure at the compressor or bottle gauge.
Set the amperage control (generally to maximum), and check the air pressure.
Grind off rust or paint where you plan to secure the ground clamp.
Place the ground clamp as close to the cut as possible and place the clamp on the work piece itself when possible.
Relax; don't hold the torch too tightly.
When hand cutting, move the torch smoothly; try not to jerk the torch.
Selecting the appropriate plasma cutter and servicing it properly will bring years of trouble-free performance. In fact, most problems with plasma cutting relate to other systems (air, consumables), not the machine itself. Virtually every person who cuts with a plasma machine gets hooked on the technology and couldn't be paid to go back to other cutting methods.
David Anderson is manager of retail sales for Hobart Welders, Appleton, WI.