Chapter 8 - Plasma Arc Cutting Flashcards
What is the unique ability of Plasma Arc Cutting?
To cut metal without making it very hot.
This means there is less heat damage or distortion.
What can be used to power a plasma cutter and an air compressor?
A portable welding machine.
What type of metal can plasma machines cut?
Any type of metal, including stainless steel, aluminum, and cast iron.
Plasma is highly _________?
Conductive.
What can control and shape plasma?
Magnetic field.
Define arc plasma.
Arc plasma is a gas that has been heated until it is a partially ionized condition, enabling it to conduct an electric current.
What is the difference between a plasma welding torch and a plasma cutting torch?
Plasma welding torches produce a low-velocity plasma and cutting torches produce a high-velocity plasma.
What does plasma produce?
Both high temperature and intense light.
Approximately what is the temperature of a concentrated arc plasma?
43,000°F (23,900°C).
How does a plasma torch work?
By constricting the arc into a small gap between the electrode and the nozzle, creating a high energy state gas that converts to plasma.
What is a manual plasma torch body made of?
Special plastic that is resistant to high temperatures, ultraviolet light, and mechanical impact.
What is the torch body referred to on a machine torch?
The torch body on a machine torch is often called a barrel. The rack is used to manually adjust the torch standoff distance.
What are the main components in a plasma torch head?
Swirl ring, Electrode, Nozzle, Retaining Cap, Shield.
What angles are most popular for a torch head in manual plasma arc cutting?
75° and 90°.
What angle is a torch head usually used in machine cutting?
180°.
What is used to cool a torch head?
Low power torches use air or water; higher power torches must be liquid-cooled.
What are the commonly serviced parts of a plasma torch?
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.
What is an air start and why should it be avoided?
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.
What base metal is used for the electrode?
Copper because it has low electrical resistance so it does not heat up.
What gases can a tungsten tipped electrode use?
Nonoxidizing gases like nitrogen or argon.
What is an electrode setback?
The space between the electrode tip and the nozzle tip.
What happens in the nozzle insulator?
Provides the space for the electric current to form plasma.
To cut thicker metals with a plasma arc torch, what needs to be changed?
The nozzle tip.
What is a shield or nozzle often called?
Cup or deflector.
What is a water shroud nozzle attachment?
A specific attachment for cooling the plasma cutting process.
How often should hoses and cables be inspected?
Once a week
When should a nozzle tip be replaced?
The center hole is worn and lacks roundness.
What lubricant should be used when an o-ring has become dry?
Silicone lubricant
An electrode tip that is worn or has a pit depth of 1/16 or greater should be what?
Replaced.
How are gas hoses sized?
They are sized to carry a specific gas flow rate
What does a plasma torch coupling system consist of?
A water pump, coolant reservoir and hoses to carry the coolant to and from the torch.
What water should be used as a coolant?
Distilled water
What is used on compressed air plasma arc cutting torches?
A filter dryer - prevents contaminants like oil dirt or moisture from entering the plasma torch
Where is the manufacturer’s recommended cutting speed located?
Cutting chart provided by the manufacturer
What can be done to nonconductive material so that it can be cut by a plasma torch?
Nonconductive material can be coated with a conductive material to be cut by a plasma torch
What is the torch standoff distance?
The distance between the nozzle and the workpiece
What can be used on a hand torch to ensure proper stand off distance?
Drag shield
What terms are used to describe the squareness of a cut?
Kerf angle or Angular deflection
What causes kerf angle to increase?
Increasing standoff distance
Define dross and where is it found?
Dross is a metal compound that resolidifies and attaches itself to the bottom of a cut.
Carbon steel, copper, and nickel-copper alloys are much more difficult to what?
Cut dross free
What is stack cutting?
Numerous sheets held together with a C-clamp can be cut at once called stack cutting
What is a water table used for?
Reduce noise level, control the plasma light, trap the sparks, eliminate most of the fuze hazard, and reduce distortion.
Why must you never cut in the presence of combustible materials?
Sparks from the PAC process can be thrown away from the immediate work area
What are the 3 ways of piercing a plate with a PAC
Raising the torch, running start, angling the torch
What is plasma arc gouging used for?
Remove weld defects, prepare grooves on plates, remove slag
What can a welder use when gouging with a plasma arc torch?
Heat shield
What gas needs to be used on cuts on 3”-6” thick plate
Argon
What is a pilot arc?
The initial arc created when a gas becomes iodized before leaving the torch
When does a pilot arc become a plasma arc?
Whennthe arc touches the work piece
What is kerf?
Kerf is the space left in the workpiece as the metal is removed during a cut
What are 4 variations of plasma arc cutting?
- Dual gas plasma cutting
- Water injected plasma cutting
- Water shielding plasma cutting
- Precision plasma cutting
What gas is used for low-power plasma cutting?
Compressed air
What is a drawback of using compressed air?
Can leave surfaces with a layer of oxidation and nitration
What metals are commonly cut with compressed air plasma cutting?
Mild steel, stainless steel and aluminum
What gas produces the fastest and cleanest cuts on mild steel?
Oxygen
What gas is used as a shielding gas when oxygen is being used for plasma cutting?
Air
What mixture of gas produces the hottest and cleanest cuts on stainless steel and aluminum
65% argon and 35% hydrogen
What are some of the special safety concerns for the PAC process?
Electrical shock
Moisture
Noise
Light
Fumes
Gases
Sparks
