Transcript Plasma Arc Cutting

NCCER Unit 3
 Plasma arc cutting uses a jet of plasma to pierce, cut, and gouge metal.
 Plasma is produced by superheating gas in an electric arc.
 Temp is hot enough to melt any metal.
 Is faster and more efficient than any other cutting method.
 Always wear protective shaded glasses.
 Wear flame retardant clothing as well as gloves
 8” or taller boots
 Ear plugs to protect from sparks
 Always obtain a hot work permit
 Always make sure fire extinguishers are in working order.
 Do not ever cut near batteries. A spark could cause a hydrogen explosion which
would then cause battery acid to be blown everywhere.
 2 types of plasma arc cutting:
 Transferred arc and nontransfered arc
 Transferred arc is most common and is used to cut materials that are electrically conductive.
 Nontransfered arc is less common and is used to cut materials that are not conductive…such as
ceramic and concrete.
 In the transferred arc process, the workpiece is part of the electrical circuit as in
other arc processes.
 The arc is established between the electrode and the work area via an arc transfer
process.
 When the torch is near the workpiece, a high voltage arc is established between
the torch and the work via the plasma.
 For the transferred arc process to work, the metal to be cut must be grounded.
 Plasma cutting is performed with direct current. Power sources are specially
designed for plasma cutting and come in many different sizes.
 Simple units are made for cutting thin steel and sheet metal. Maximum cutting
amps is 14 to 30 amps and their duty cycle is in the 35 percent range. The simplest
units use compressed air for plasma and cutting gas.
 Larger industrial units are used for heavy duty cutting, they can cut steel up to 3
inches thick. These machines use dual flow gas to operate (2 types of gas). One gas
is used to cut and the other is used to shield around the cutting area.
 The most common plasma arc cutting torch uses a pilot arc and transferred arc
process.
 Typically contains a retaining cup, a copper electrode with a hafnium tungsten
insert, a gas swirl ring, and a nozzle tip.
 The torch can be handheld (most common) or machine mounted for more perfect
cuts.
 The two most common parts that are changed in a torch are the electrode and the
nozzle.
 All plasma cutters require one or more types of gas in order to operate.
 This can include air, nitrogen, oxygen, argon, hydrogen, and carbon dioxide.
 The simplest units use clean compressed air for plasma and cooling gas.
 If compressed air is used make sure it is free of oil and dry. The air pressure
regulator and filter/dryer on the power source will maintain the correct pressure
and flow rate for the system.
 Stop and start flow control to the torch is usually controlled by a solenoid valve that
electrically opens and closes a gas valve.
 Solenoid valves are mounted inside the unit and are controlled by pushbuttons on
the torch.
 Cutting amps depends on the type of equipment being used, the thickness of the
metal, and the type of gas being used.
 Light gauge steel may require as low as 7 amps, while 2” aluminum plate may
require 250 amps.
 Using the wrong amps will result in a poor quality cut, and if amps are to high it can
cause damage to the torch.
 Always be extra careful when handing fuel gas cylinders, keep them in the upright
position and keep the cylinder cap on the bottle until time to hook it up.
 Never use a pipe wrench or pliers to tighten the regulators connections. This can
cause damage to the delicate threads.
 When time to swap cylinders, always immediately reinstall the safety cap over the
cylinder valve once the regulator has been removed.
 To pierce very thin metal, hold the torch directly over the point to be pierced at a 0
degree work angle, and press the arc button.
 If piercing thicker metals, hold the torch at a 10 degree work angle.
 A major issue when using the plasma cutter is moisture entering through the air
line.
 This will cause the torch to hiss or sputter.
 If this happens, the filter needs to be cleaned.