Non Consumable Electrode
Because the GTAW En is a Inert gas with an ionization potential of 15.7 volts, the EP GTAW electrode cannot handle the electron bombardment therefore it vaporizes.
Argon Thermal conductivity, 9.69 at 32F
Ionization Potential 15.7 volts
Pure argon, when used as a shielding gas has mild thermal conductivity, and produces an arc which has two zones: a narrow hot core and a considerably cooler outer zone. As a result, the
penetration profile of a typical weld fusion area is characterized by a narrow “finger” at the root and a wider top. ( Cited Praxair Shielding Gas Handbook)
Consumable Electrode
The SMAW EP is an Active gas with an ionization potential upwards of 23.8 volts The consumable electrode can handle the electron bombardment of either polarity producing either a shallow or a deep penetrating characteristic.
C02 Thermal Conductivity 8.62 at 32F
Ionization potential 14.4 volts
A gas with high thermal conductivity conducts more of the heat outward from the arc core. This results in a broader, hotter arc. This type of heat distribution, which occurs with helium, argon/hydrogen, and argon/carbon dioxide mixtures is more uniform and produces a generally wider profile throughout the fusion zone. (Cited Praxair Shielding Gas Handbook)
When heated to the high temperatures present in the arc plasma (12-15,000 F), these gases break down, or dissociate into their separate atoms. They are then at least partially ionized,
producing free electrons and improved current flow. As the dissociated gas comes in contact with the relatively cool work surface, the atoms recombine, and it releases energy to
the base material in the form of heat. This process does not occur with gases such as argon, which consists of a single atom. Therefore, for the same arc temperature, the heat
generated at the work surface can be greater with gases such as carbon dioxide, hydrogen, and oxygen. ( Cited Praxair Shielding Gas Handbook)
Here is the next problem, we are trying to compare a Argon Atmosphere with a C02 or Carbon Monoxide Oxygen atmosphere, coupled with other flux agents creating i have no idea what.
When i stated current density and i stand behind it, you simply cannot produce the same type of weld with GTAW on EP as you can on SMAW EP due to the fact carrying 200 amps would require a electrode 1/2" in Dia. It all has to do with many more variables than simply saying its cause of the polarity, or cause of the atmosphere, or cause of the current, or cause of the burn off rate, or cause ones consumable and ones not, Here is the problem i have come to realize i am in wrong in comparison of the two during lecture and may need to change some materials because of it. They simply should not be compared in such a way.
Lawrence,
I think you hit something square on with that statement: "We sharpen our minds when we comapre them".
I went to the
Welding Handbook Volumne 1: Welding Science and Technology and found some interesting information in chapter 2.
In my opinion there are way too many variables to compare on any scale: How the Argon shielded plasma stream affects the arc plasma stream vs. the shielding from the consumed flux, width of the arc path from a sharpened tungsten vs the width of SMAW electrode arc paths, frequency of the current from the power source for SMAW vs the frequency from The GTAW power source, etc, etc. Is the arc voltage the same for both in order to do a proper comparison? Is the Volt/Amp ratio the same? Is the base metal being used for this experiment/comparison the same? Is the size of the tungsten the same as the electrode diameter for SMAW (at least puts it in the same ballpark)?
If we are to examine all features and do a proper comparison of depth of fusion with as many of the variables as possible brought into equality we may find it isn't as different as one would think when studying the textbook that says one is deeper than the other with DCEN while the other is deeper with DCEP. Textbook descriptions can be over simplified so as to not confuse the beginner student with too much technical information that they are not ready to digest. Truth be known, I think we are generally talking about such insignificant differences that it can be measured in 1000ths of an inch. But, they felt it was worth mentioning just for the sake of giving the student a comparison of the process variables.
So, the next question I have in our apples to oranges discussion is this: are they Granny Smith, Gala, or Red Delicious apples??
Just my two tin pennies worth.
Have a Great Day, Brent