120101j Plasma Arc Cutting and Gouging

Question 1

What is plasma?

Answer 1

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.

Question 2

In plasma arc cutting, plasma is the:
a) tungsten electrode.
b) electrons travelling across the arc.
c) ionized gas.
d) outer shielding gas.

Answer 2

c) ionized gas.

Question 3

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.

Answer 3

c) is used on metals that are electrically conductive

Question 4

List five (5) safety hazards associated with plasma arc cutting.

Answer 4

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)

Question 5

Any available welding power source may be used for PAC.
a) true
b) false

Answer 5

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.

Question 6

What are the functions of the plasma cutting torch?

Answer 6

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.

Question 7

Compressed air is generally used for PAC on which materials?
a) carbon steels
b) copper alloys
c) magnesium
d) titanium

Answer 7

a) carbon steels

Question 8

What effect does improper PAC standoff distances have?

Answer 8

Improper PAC standoff distances results in poor quality cuts, excessive nozzle wear
and slow cutting speeds.

Question 9

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

Answer 9

b) re-solidified oxidized molten metal

Question 10

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.

Answer 10

d) The pilot arc starts immediately.

Question 11

What is the minimum welding shade recommended when using the PAC process at
250 amperes?
a) 5
b) 8
c) 10
d) 14

Answer 11

b) 8

Question 12

PAC cutting produces no significant respiratory hazards.
a) true
b) false

Answer 12

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.

Question 13

The heat-affected zone of a plasma arc cut is extremely wide.
a) true
b) false

Answer 13

b) false; As a result of high temperatures and fast cutting speeds, PAC produces a very narrow heat-affected zone (HAZ) along the kerf.

Question 14

CAC-A may be used to cut most ferrous and non-ferrous metals.
a) true
b) false

Answer 14

a) true

Question 15

List three (3) safety considerations when using CAC-A

Answer 15

Any three (3) of the following are correct.
a) proper protective clothing
b) proper eye protection
c) adequate hearing protection
d) adequate ventilation

Question 16

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

Answer 16

d) either AC or DC

Question 17

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

Answer 17

a) to remove molten metal

Question 18

List three (3) metals that give off toxic fumes when cut with the CAC-A process

Answer 18

a) beryllium
b) cadmium
c) lead

Question 19

Name the major components of the manual CAC-A electrode holder.

Answer 19

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.

Question 20

Electrodes for CAC-A are usually made of:
a) cast iron.
b) aluminum.
c) carbon steel.
d) graphite and carbon.

Answer 20

d) graphite and carbon.

Question 21

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”)

Answer 21

a) 180 mm (7”)

Question 22

What is the range of air pressure normally used for CAC-A?

Answer 22

The range of air pressure for CAC-A is 550 kPa to 700 kPa (80 psi to 100 psi).

Question 23

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

Answer 23

c) toward the work, below the electrode

Question 24

How can you reduce carbon deposits on the joint surface when using CAC-A?

Answer 24

Use the proper air velocity and electrode movement. Maintain a short arc without
touching the electrode to the work without an air supply.

Question 25

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

Answer 25

a) when working on high carbon steels and cast irons

Question 26

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

Answer 26

c) air pressure is too low