120101j Plasma Arc Cutting and Gouging Flashcards
What is plasma?
Plasma is a gas that has been heated to an extremely high temperature by an electric
arc. This causes the gas to ionize, making it electrically conductive.
In plasma arc cutting, plasma is the:
a) tungsten electrode.
b) electrons travelling across the arc.
c) ionized gas.
d) outer shielding gas.
c) ionized gas.
The plasma arc cutting process:
a) can be used only on materials 6.4 mm (1/4”) thick or less.
b) can be used only on mild steel and stainless steel.
c) is used on metals that are electrically conductive
d) is used mainly to clean up foundry spills.
c) is used on metals that are electrically conductive
List five (5) safety hazards associated with plasma arc cutting.
a) electric shock (120V - 400V)
b) fumes (carcinogenic, ozone)
c) noise (100 dBA - 100 dBA)
d) radiation (visible, ultra-violet and infra-red light rays)
e) gases (compressed cylinders and hydrogen)
Any available welding power source may be used for PAC.
a) true
b) false
b) false; Power supplies designed for PAC are DCSP rectifier or inverter-type constant current machines with open circuit voltages ranging from 120 to 400 volts. They contain special circuits to produce a pilot arc that shuts off when the main arc initiates.
What are the functions of the plasma cutting torch?
The plasma cutting torch functions are to transfer current to an electrode, supply a flow of orifice gas to the constricting nozzle and supply a flow of secondary shielding gas. The torch transfers current to a fixed, non-consumable electrode and directs the flow of plasma and shielding gases.
Compressed air is generally used for PAC on which materials?
a) carbon steels
b) copper alloys
c) magnesium
d) titanium
a) carbon steels
What effect does improper PAC standoff distances have?
Improper PAC standoff distances results in poor quality cuts, excessive nozzle wear
and slow cutting speeds.
In the plasma arc process, what is dross?
a) a slag-like non-metallic by product
b) re-solidified oxidized molten metal
c) re-solidified non-metallic material
d) none of the above
b) re-solidified oxidized molten metal
What happens once the trigger lock is raised and the trigger is pressed?
a) Gas starts flowing through the torch.
b) The high frequency unit starts ionic bombardment.
c) Short circuit metal transfer begins.
d) The pilot arc starts immediately.
d) The pilot arc starts immediately.
What is the minimum welding shade recommended when using the PAC process at
250 amperes?
a) 5
b) 8
c) 10
d) 14
b) 8
PAC cutting produces no significant respiratory hazards.
a) true
b) false
b) false; Plasma arc cutting presents the same safety hazards as other arc welding and cutting processes. The fume particles generated from PAC are much smaller than those generated from OAC and create a greater health risk.
Stainless steels and aluminum require the PAC process and many of the fumes from these metals are carcinogenic or can lead to other other health risks.
The heat-affected zone of a plasma arc cut is extremely wide.
a) true
b) false
b) false; As a result of high temperatures and fast cutting speeds, PAC produces a very narrow heat-affected zone (HAZ) along the kerf.
CAC-A may be used to cut most ferrous and non-ferrous metals.
a) true
b) false
a) true
List three (3) safety considerations when using CAC-A
Any three (3) of the following are correct.
a) proper protective clothing
b) proper eye protection
c) adequate hearing protection
d) adequate ventilation
What type of power source is required for CAC-A?
a) AC only
b) DC only
c) AC rectifiers only
d) either AC or DC
d) either AC or DC
What is the purpose of compressed air with CAC-A?
a) to remove molten metal
b) to improve cut visibility
c) to cool the workpiece
d) to heat the workpiece
a) to remove molten metal
List three (3) metals that give off toxic fumes when cut with the CAC-A process
a) beryllium
b) cadmium
c) lead
Name the major components of the manual CAC-A electrode holder.
The electrode holder components are the power cable, the means to grip the electrode
and the air passages and orifices to direct the air stream.
Electrodes for CAC-A are usually made of:
a) cast iron.
b) aluminum.
c) carbon steel.
d) graphite and carbon.
d) graphite and carbon.
What is the maximum length that a CAC-A electrode should extend from the holder to the workpiece when gouging carbon steels?
a) 180 mm (7”)
b) 200 mm (8”)
c) 250 mm (10”)
d) 300 mm (12”)
a) 180 mm (7”)
What is the range of air pressure normally used for CAC-A?
The range of air pressure for CAC-A is 550 kPa to 700 kPa (80 psi to 100 psi).
How are the air jets positioned when air carbon arc gouging in the flat position?
a) toward the operator
b) toward the work, above the electrode
c) toward the work, below the electrode
d) in any position because it has no effect on the metal removal
c) toward the work, below the electrode
How can you reduce carbon deposits on the joint surface when using CAC-A?
Use the proper air velocity and electrode movement. Maintain a short arc without
touching the electrode to the work without an air supply.
When is surface hardening a problem when using CAC-A?
a) when working on high carbon steels and cast irons
b) when air pressures are inadequate
c) when using AC current
d) when gouging nickel alloys
a) when working on high carbon steels and cast irons
With CAC-A, when excessive slag adheres to the edges of the cut, what is the likely cause?
a) incorrect polarity
b) electrode angle is too shallow
c) air pressure is too low
d) travel speed is too fast
c) air pressure is too low
