Chapter 8 - Plasma Arc Cutting

Question 1

What is the unique ability of Plasma Arc Cutting?

Answer 1

To cut metal without making it very hot.

This means there is less heat damage or distortion.

Question 2

What can be used to power a plasma cutter and an air compressor?

Answer 2

A portable welding machine.

Question 3

What type of metal can plasma machines cut?

Answer 3

Any type of metal, including stainless steel, aluminum, and cast iron.

Question 4

Plasma is highly _________?

Answer 4

Conductive.

Question 5

What can control and shape plasma?

Answer 5

Magnetic field.

Question 6

Define arc plasma.

Answer 6

Arc plasma is a gas that has been heated until it is a partially ionized condition, enabling it to conduct an electric current.

Question 7

What is the difference between a plasma welding torch and a plasma cutting torch?

Answer 7

Plasma welding torches produce a low-velocity plasma and cutting torches produce a high-velocity plasma.

Question 8

What does plasma produce?

Answer 8

Both high temperature and intense light.

Question 9

Approximately what is the temperature of a concentrated arc plasma?

Answer 9

43,000°F (23,900°C).

Question 10

How does a plasma torch work?

Answer 10

By constricting the arc into a small gap between the electrode and the nozzle, creating a high energy state gas that converts to plasma.

Question 11

What is a manual plasma torch body made of?

Answer 11

Special plastic that is resistant to high temperatures, ultraviolet light, and mechanical impact.

Question 12

What is the torch body referred to on a machine torch?

Answer 12

The torch body on a machine torch is often called a barrel. The rack is used to manually adjust the torch standoff distance.

Question 13

What are the main components in a plasma torch head?

Answer 13

Swirl ring, Electrode, Nozzle, Retaining Cap, Shield.

Question 14

What angles are most popular for a torch head in manual plasma arc cutting?

Answer 14

75° and 90°.

Question 15

What angle is a torch head usually used in machine cutting?

Answer 15

180°.

Question 16

What is used to cool a torch head?

Answer 16

Low power torches use air or water; higher power torches must be liquid-cooled.

Question 17

What are the commonly serviced parts of a plasma torch?

Answer 17

The consumable parts of a plasma torch are the shield, retaining cap, nozzle, electrode, and swirl ring. Together they are referred to as a stack.

Question 18

What is an air start and why should it be avoided?

Answer 18

An air start is starting the torch before you are ready to make the cut. It is harder on the torch to start it than it is to cut, thus air strikes should be avoided to prevent damage to the stack.

Question 19

What base metal is used for the electrode?

Answer 19

Copper because it has low electrical resistance so it does not heat up.

Question 20

What gases can a tungsten tipped electrode use?

Answer 20

Nonoxidizing gases like nitrogen or argon.

Question 21

What is an electrode setback?

Answer 21

The space between the electrode tip and the nozzle tip.

Question 22

What happens in the nozzle insulator?

Answer 22

Provides the space for the electric current to form plasma.

Question 23

To cut thicker metals with a plasma arc torch, what needs to be changed?

Answer 23

The nozzle tip.

Question 24

What is a shield or nozzle often called?

Answer 24

Cup or deflector.

Question 25

What is a water shroud nozzle attachment?

Answer 25

A specific attachment for cooling the plasma cutting process.

Question 26

How often should hoses and cables be inspected?

Answer 26

Once a week

Question 27

When should a nozzle tip be replaced?

Answer 27

The center hole is worn and lacks roundness.

Question 28

What lubricant should be used when an o-ring has become dry?

Answer 28

Silicone lubricant

Question 29

An electrode tip that is worn or has a pit depth of 1/16 or greater should be what?

Answer 29

Replaced.

Question 30

How are gas hoses sized?

Answer 30

They are sized to carry a specific gas flow rate

Question 31

What does a plasma torch coupling system consist of?

Answer 31

A water pump, coolant reservoir and hoses to carry the coolant to and from the torch.

Question 32

What water should be used as a coolant?

Answer 32

Distilled water

Question 33

What is used on compressed air plasma arc cutting torches?

Answer 33

A filter dryer - prevents contaminants like oil dirt or moisture from entering the plasma torch

Question 34

Where is the manufacturer's recommended cutting speed located?

Answer 34

Cutting chart provided by the manufacturer

Question 35

What can be done to nonconductive material so that it can be cut by a plasma torch?

Answer 35

Nonconductive material can be coated with a conductive material to be cut by a plasma torch

Question 36

What is the torch standoff distance?

Answer 36

The distance between the nozzle and the workpiece

Question 37

What can be used on a hand torch to ensure proper stand off distance?

Answer 37

Drag shield

Question 38

What terms are used to describe the squareness of a cut?

Answer 38

Kerf angle or Angular deflection

Question 39

What causes kerf angle to increase?

Answer 39

Increasing standoff distance

Question 40

Define dross and where is it found?

Answer 40

Dross is a metal compound that resolidifies and attaches itself to the bottom of a cut.

Question 41

Carbon steel, copper, and nickel-copper alloys are much more difficult to what?

Answer 41

Cut dross free

Question 42

What is stack cutting?

Answer 42

Numerous sheets held together with a C-clamp can be cut at once called stack cutting

Question 43

What is a water table used for?

Answer 43

Reduce noise level, control the plasma light, trap the sparks, eliminate most of the fuze hazard, and reduce distortion.

Question 44

Why must you never cut in the presence of combustible materials?

Answer 44

Sparks from the PAC process can be thrown away from the immediate work area

Question 45

What are the 3 ways of piercing a plate with a PAC

Answer 45

Raising the torch, running start, angling the torch

Question 46

What is plasma arc gouging used for?

Answer 46

Remove weld defects, prepare grooves on plates, remove slag

Question 47

What can a welder use when gouging with a plasma arc torch?

Answer 47

Heat shield

Question 48

What gas needs to be used on cuts on 3"-6" thick plate

Answer 48

Argon

Question 49

What is a pilot arc?

Answer 49

The initial arc created when a gas becomes iodized before leaving the torch

Question 50

When does a pilot arc become a plasma arc?

Answer 50

Whennthe arc touches the work piece

Question 51

What is kerf?

Answer 51

Kerf is the space left in the workpiece as the metal is removed during a cut

Question 52

What are 4 variations of plasma arc cutting?

Answer 52

1. Dual gas plasma cutting 2. Water injected plasma cutting 3. Water shielding plasma cutting 4. Precision plasma cutting

Question 53

What gas is used for low-power plasma cutting?

Answer 53

Compressed air

Question 54

What is a drawback of using compressed air?

Answer 54

Can leave surfaces with a layer of oxidation and nitration

Question 55

What metals are commonly cut with compressed air plasma cutting?

Answer 55

Mild steel, stainless steel and aluminum

Question 56

What gas produces the fastest and cleanest cuts on mild steel?

Answer 56

Oxygen

Question 57

What gas is used as a shielding gas when oxygen is being used for plasma cutting?

Answer 57

Air

Question 58

What mixture of gas produces the hottest and cleanest cuts on stainless steel and aluminum

Answer 58

65% argon and 35% hydrogen

Question 59

What are some of the special safety concerns for the PAC process?

Answer 59

Electrical shock Moisture Noise Light Fumes Gases Sparks