tungsten red hot?

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Why does the tungsten get red hot? What is the cause of this?  Just curious.  Thanks
Reply:Because the arc temperature is somewhere around 3000 to 6000 degrees.  The tungsten is a refractory metal and I believe it melting point is around 10,000 F.  Hope this answers your question.
Reply:Actually, the inverse is true.  The arc temperature is above 10,000F and the melting point of pure tungsten is 6192F or thereabouts.  Thorium (or Lanthanum, Zirconium, etc.) is alloyed with the tungsten to give it a higher melting point.-Heath
Reply:what halbritt said and the gas and collet help pull heat out of the tungsten to keep it from melting most of the time unless you got the machine set wrong or have a lead foot  chuck
Reply:It makes sense to me that the tungsten is being heated in part from the energy in the arc, but I think the primary heating is electrical resistance heating, like a light bulb filament or electric stove element.  As you increase the distance that the tungsten sticks out beyond the copper collet, resistance increases, and the tungsten heats up more.  With enough current it will melt in two. The electrode will fail (melt off) mid-way between the tip and the collet.  This occurs because the tip of the electrode is actually cooled by the "refrigerating" action of the electrons leaving it's surface, and at the other end, of course the collet it providing cooling.Another interesting point (at least to me), if you measure the voltage across (+) and (-) at the power supply while welding, you will find that voltage increases as you add resistance in the torch lead, tungsten stickout, ground connection, etc.  This happens because, the power supply puts out higher voltage (pressure) to maintain constant current (flow of electrons) through a higher resistance (constricted pipe).However, if you measure the arc voltage, directly between the tungsten electrode and the workpiece, it will remain constant with these other resistance changes, it will change primarily based on the arc gap, current setting, and gas composition.
Reply:Great info guys, thanks, lots of stuff i just learned from those replys.  The reason i asked was a friend of mine told me that the tungsten shouldn't be red hot when you are tiggin.  Is this true or does it really matter if it is not changing the shape of the point?  Because i am trying to learn and am new to tig i am just curious if i am doing something wrong? Seems sometimes the tungsten is red and sometimes its not.I really enjoy posting a question before i go to sleep at night then coming home from work and seeing all the great answers.  This is a great forum with great members.  Thanks again
Reply:I guess that the redness of the tungsten could be used as an indicator of the balance between electrode diameter and current level.  I suppose for very critical and expensive product (space shuttle stuff) you would not want to risk running an overheated tungsten (really red) that might spit tungsten into the weld, or worst case just melt off and fall in.  Otherwise what might be the concern?  These sites have a bit of tungsten data including the recommended current capacity for a given tungsten diameter, http://www.pro-fusiononline.com/tungsten/diameter.htm   or   http://www.diamondground.com/Guidebook0105.pdf
Reply:ty pulser
Reply:Half the reason that many tig machines have a postflow setting is to shield the tungsten as it cools down.  In other words, it can be red hot, and if you have it shielded until it cools, it will remain clean for the next startup.  If the gas cuts off and the tungsten is red hot, it will get very dark and contaminated.
Reply:Originally Posted by halbrittActually, the inverse is true.  The arc temperature is above 10,000F and the melting point of pure tungsten is 6192F or thereabouts.  Thorium (or Lanthanum, Zirconium, etc.) is alloyed with the tungsten to give it a higher melting point.