To begin, I would like to mention why I chose Plasma Arc Welding as my research subject, and that is because I am a fan of the "Star Trek" genre. How that relates is : In " Star Trek: The Next Generation " as well as the related series, they mention certain processes relating to the "warp engines" which power their ships and make them capable of doing some of the things they are able to do( chiefly being faster- than -light travel through space). Specifically, I am referring to terms such as "warp plasma", "warp plasma injectors" , or simply " plasma injectors".
Now, I do understand that the whole concept of faster - than -light travel and an engine that can create this condition in space is all theory at best, but I do have a basic understanding of internal combustion engines, especially as they are manufactured today, so I correlate "plasma Injectors" (this made up fuel for this theorized engine) with what a fuel injection system does for the cars we drive nowadays.
Also, I have heard of plasma , as it relates to blood, as well as in science class, but I have still wondered", "What exactly is plasma, and what can it be used for? Could it perform as a fuel of some kind?"
Then I was assigned this task and it appeared to me that by me researching this process in particular, some of my questions might be answered. The following information, I must say, has given me some insight into what plasma really is and what it is used for; therefore, I offer the following:
As stated in the reference material "Welding Technology Today" pages 179-180, the basic states of matter are solids, liquids, and gases. Plasma however, is considered the fourth state of matter, because it is a gas that is being ionized or is conducting electricity. Ionization occurs when electrical voltage frees an electron from an atom, turning it into an ion.
In plasma arc welding, we are ionizing the gases in the arc with electricity and therefore creating a plasma gas. This theory gives us the basis for the process of plasma arc welding. This process, as explained in the reference material "The Welding Handbook" states that PAW (which was invented and developed by the Linde Company) is facilitated with an electrode which is located within a torch nozzle. This nozzle has an arc- restricting orifice. Inert gas, usually argon or nitrogen, is fed through the nozzle where it is heated as high as 50,000 degrees F(27,760 C), the plasma temperature range. The plasma arc emerging from this orifice is hot enough to melt any metal. In welding operations, a shielding gas is simultaneously introduced through a concentric passage of the torch, which protects the weld puddle from contamination from the atmosphere, similar to a TIG welding torch.
There are several advantages of using PAW as explained in "Welding Technology Today", page178: "By controlling the orifice gas flow rate, PAW can actually control the amount of penetration. High orifice gas pressure will produce a stiff arc and deep penetration; low orifice gas pressure will produce a soft arc and less penetration. This gives welders a controllability they have not experienced with other processes."
As I attempt to imagine using this process, I can see the possibilities of usefulness of this flexibility where I might be seeking a deeper penetrating weld with thicker metals. All I would have to do Is adjust the gas pressure accordingly
It is also mentioned that penetration can be narrow and deeper than Gas Tungsten Arc Welding (the process from which (PAW stems...) because of the plasma gas being denser. This also results in a lower heat affected zone which is definitely a desirable feature in my opinion, because the work metal would be less likely to distort from overheating.
As mentioned in "Welding Technology Today" pages 180-181, There are 2 basic types of gases used with PAW: The primary plasma gas ( also known as the orifice gas) and the secondary shielding gas.
The primary plasma gas is, of course, what actually conducts electricity and creates the heat for welding. Pure argon is almost always used as the plasma gas for PAW. The secondary (shielding) gas produces an additional outer shielded zone, which keeps any foreign gases away from the plasma gas and weld. If any foreign gases were to mix with the plasma gas, it would cause it to become erratic and turbulent (affecting the cleanliness and effectiveness of the weld) in addition to contaminating the weld puddle. The secondary gas is usually argon, but other gases such as CO2 and mixtures, can be used. For example, hydrogen or helium can be added to the secondary gas to increase fluidity for nickel-steel plasma arc welding. The key to PAW is its unique torch. It uses the same constant- Current power source as GTAW but it has a special plasma control unit and torch which is a bit bulkier than a GTAW torch because it contains additional parts, such as the gas distributor and tip. These parts are responsible for directing the plasma gas. Because of the heat generated inside the torch, they are almost always water-cooled. Also, 2% thoriated tungsten (EWTH2- red color code) is the best tungsten for PAW. It should be sharpened to a point with a vertex angle of 20 degrees to 60 degrees. Tungsten must also be gauged- - -adjusted to how far it is to extend out into the orifice tip. There is a special PAW tip gauge to assist in this process. As for the PAW machine, there are 2 main parts to this: The constant-current power source and the plasma control panel. The plasma control panel consists of: 1. Plasma Flow 1: This adjusts low flow rates in the primary plasma gas; these adjustments range from 0 to 10 cubic feet per hour (cfh) and are set for standard bead welding. 2. Plasma Flow 2: This adjusts high flow rates, and is activated for keyhole technique welding. Its range is between 0 and 5 cfh. 3. Shielding Flow: Sets the rate of shielding gas flow. It is usually set between 20 and 30 cfh, with the range usually being between 0 and 60 cfh. 4. High/Low Plasma Switch: This 2 position switch sets either plasma flow 1 or 1 and 2 simultaneously. Plasma flow 1 position is for standard bead welding, and the 1 and 2 setting is for keyhole welding. Pilot Control Switch: The pilot arc is a high frequency, low current arc that takes place in the tip. It helps to start the arc, much as the high frequency does with GTAW.
As I mentioned earlier, this project has broadened my understanding of the concept of plasma. It has also given me a better understanding of plasma welding, plasma cutting, and welding in general.
