Module 10 plasma, ark, 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 ionized making it electrically conductive.

Question 2

In plasma ark 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 art cutting process
A) can be used on materials 1/4” inch 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 safety hazards associated with plasma arc cutting

Answer 4

1. Electric shock
2. Fumes
3. Noise
   4.radiation
4. Compressed gasses

Question 5

Any available welding power source may be used for PAC (plasma ark cutting)
True or false

Answer 5

False
Power supplies designed for PC 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 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 shield and gas. The torch transfers current to fixed non-consumable electrode and directs the flow of plasma and shield and 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

Results in poor quality cuts, excessive nozzle wear and slow cutting speeds

Question 9

In the PAC process, what is dross?
A) a slag like non-metallic byproduct
B) resolidified oxidized molten metal
C) solidified non-metallic material
D) none of the above

Answer 9

B) resolidified 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) the pilot arc starts immediately

Answer 10

C) the pilot arc starts immediately

Question 11

What is the minimum welding shade recommended when using the PAC process at 250 Amps
A)5
B) 8
C) 10
D) 14

Answer 11

B) 8

Question 12

PAC cutting produces no significant respiratory hazards
True or false

Answer 12

False PAC process produces particles much smaller than that created from OAC and create a greater health risk. Many of the fumes from these metals are carcinogenic and can lead to other health risks.

Question 13

The heat affected zone of a plasma arc cut is extremely wide
True or false

Answer 13

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 maybe used to cut most ferrous and non-Ferris metals
True or false

Answer 14

True

Question 15

List three safety considerations when using CAC – A

Answer 15

1. Proper protective clothing.
2. Proper eye protection.
3. Adequate hearing protection.
4. 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 visibility
C) to cool the workpiece
D) to heat the workpiece

Answer 17

A) to remove molten metal

Question 18

List three metals that give off toxic fumes when cut with the CAC – a process

Answer 18

1. Beryllium.
2. Cadmium.
3. Lead.

Question 19

Name the major components of the manual CAC – a electrode holder

Answer 19

Power cable, the means to grip the electrode and the air passages and orifices to direct the 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 – an electrode should extend from the holder to the workpiece when gouging carbon steals?
A) 180mm or 7”
B) 200mm or 8”
C) 250mm or 10”
D) 300mm or 12”

Answer 21

A) 180mm or 7”

Question 22

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

Answer 22

550kPa to 700kPa or 80-100psi

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 working on high carbon steals and cast irons
B) air pressures are inadequate
C) when using AC current
D) when gouging nickel alloys

Answer 25

A) when working working on high carbon steals and cast irons

Question 26

With CAC – A when excessive slag adheres to the edges of the cut what is likely the 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