Plasma Flashcards
The earliest gas tungsten arc welding process used ____.
helium
The plasma created by an arc ____.
is an ionized gas that contains both electrons and positive ions
The temperature of an unrestricted arc is about ____ degrees Fahrenheit.
11,000
The temperature created when the arc is concentrated to form a plasma is about ____degrees Fahrenheit.
43,000
The ____ is made of a special plastic that is resistant to high temperatures, ultraviolet light, and impact.
torch body
The ____ may be a foot control or located on the panel for machine-type equipment.
power switch
The ____ is often made of copper with an imbedded tungsten tip.
electrode tip
The ____ has a small, cone-shaped, constricting orifice in the center.
nozzle tip
The ____ surrounding the nozzle tip is used to control the potential hazards of light, fumes, noise, and other pollutants.
water
The nozzle of a plasma torch is made of ____.
ceramic
Failure to use deionized water in a torch that requires it ____.
will result in the torch arcing out internally
The production of the plasma requires a(n) ____ power supply.
direct current
In PAC the ____ is higher and the ____ is lower than most other welding processes.
voltage, amperage
High-powered plasma cutting machines have amperages as high as ____ amps, and some very large automated cutting machines may have 1000-ampere capacities.
200
The voltage required for plasma arc processes range from ____ open circuit.
150 to 400 volts
When a flat piece of metal is heated, it bends ____ the heat, and as it cools it bends ____ the heat.
away from, towards
The PAC cutting speed can be as much as ____ feet per minute.
25
The width of a PAC kerf is ____ an oxyfuel cut.
often wider than
Keeping the diameter of the nozzle orifice ____ will keep the kerf ____.
as small as possible, smaller
On some torches the gas is directed in a circular motion around the ____ before it enters the ____.
electrode, nozzle tip orifice
In stacked cutting of sheets using the PAC process, sheets are held together using ____.
C-clamps
____ are easily cut dross free, whereas ____ are much more difficult to cut dross free.
Stainless steel and aluminum, carbon steel and copper
Manual plasma arc cutting is ____.
limited to low-power machines
In plasma arc gouging, the torch is held at approximately a ____ degree angle to the metal surface.
30
____ are good metals to gouge because there is almost no cleanup.
Stainless steel and aluminum
The ____________________ created by an arc is an ionized gas.
plasma
The spacing between the electrode tip and the nozzle tip is called the ____________________.
electrode setback
The nozzle is sometimes called the ____________________.
cup
____________________ are units of measure for electrical power.
Watts
The ____________________ distance is the distance from the nozzle tip to the work.
standoff
Any material that is ____________________ can be cut using the PAC process.
electrically conductive
The most common method to establish a current path through the gas uses a high-frequency ____________________ current carried through the conductor, the electrode, and back from the nozzle tip.
alternating
Sheets can be stacked in the PAC process because PAC does not rely on the ____________________ between stacked parts.
thermal conductivity
____________________ is the metal compound that resolidifies and attaches itself to the bottom of a cut.
Dross
A(n) ____________________ is used to reduce the noise level, control the plasma light, trap the sparks, eliminate most of the fume hazard, and reduce distortion.
water table
Describe the history of the development of plasma arc cutting.
The plasma process was originally developed in the mid-1950s as an attempt to create an arc, using argon, that would be as hot as the arc created when using helium gas. The early gas tungsten arc welding process used helium gas and was called “heliarc.” This early GTA welding process worked well with helium, but helium was expensive. The gas manufacturing companies had argon as a by-product from the production of oxygen. There was no good commercial market for this waste argon gas, but gas manufacturers believed there would be a good market if they could find a way to make argon weld similar to helium.
Early experiments found that by restricting the arc in a fast-flowing column of argon a plasma was formed. The plasma was hot enough to rapidly melt any metal. The problem was that the fast-moving gas blew the molten metal away. They could not find a way to control this scattering of the molten metal, so they decided to introduce this as a cutting process, not a welding process.
Explain Ohm’s Law, and use Ohm’s Law to calculate the number of watts used for an electrode operating at 18 volts and 90 amps.
Ohm’s Law states that the watts used in a circuit are determined by multiplying the voltage times the amperage. For example, a 1/8-in.-diameter E6011 electrode will operate at 18 volts and 90 amperes. The total watts used would be
W = V ´ A
W = 18 ´ 90
W = 1620 watts of power
Explain how metal becomes distorted during the welding process.
Anytime metal is heated in a localized zone or spot it expands in that area and, after the metal cools, it is no longer straight or flat. If a piece of metal is cut, there will be localized heating along the edge of the cut, and, unless special care is taken, the part will not be usable as a result of its distortion. This distortion is a much greater problem with thin metals. By using a plasma cutter, an auto body worker can cut the thin, low-alloy sheet metal of a damaged car with little problem from distortion.
Explain what happens when standoff distance increases.
This distance is very critical to producing quality plasma arc cuts. As the distance increases, the arc force is diminished and tends to spread out. This causes the kerf to be wider, the top edge of the plate to become rounded, and the formation of more dross on the bottom edge of the plate. However, if this distance becomes too close, the working life of the nozzle tip will be reduced. In some cases an arc can form between the nozzle tip and the metal that instantly destroys the tip.
Explain how high-frequency alternating current and a pilot arc can be used to start a plasma arc torch.
The most common starting method uses a high-frequency alternating current carried through the conductor, the electrode,electrode, and back from the nozzle tip. This high-frequency current will ionize the gas and allow it to carry the initial current to establish a pilot arc. After the pilot arc has been started, the high-frequency starting circuit can be stopped. A pilot arc is an arc between the electrode tip and the nozzle tip within the torch head. This is a nontransfer arc, so the workpiece is not part of the current path. The low current of the pilot arc, although it is inside the torch, does not create enough heat to damage the torch parts. When the torch is brought close enough to the work, the primary arc will follow the pilot arc across the gap, to the work, and the main plasma is started. Once the main plasma is started, the pilot arc power can be shut off.
A plasma is present in any
electrical discharge.
The plating of copper parts helps them
remain free of spatter longer.
Some low-powered PAC torches will operate with as low as
10 amps of current flow.
PAC produces a large quantity of fumes that are
potentially hazardous.
Stainless steel is a good metal to gouge because
there is almost no cleanup.
