Tig tungsten size.

[gordon stephenson]

As per title, Being a purely mechanical sort of person and a bit of an electrical buffoon on anything more than basic stuff, What is the reason to change tungsten diameters for varying amps etc?,And why does my machine want to know what size i'm using?,Must have something to do with the resistance of the electrode affecting the welding parameters, Otherwise why not just use a large tungsten as it's ground to a point anyway,
Let this be my little bit of education for the day.

 

[provenrad]

I believe you are at least partly right about the resistance - the electrode needs to be hot enough to work properly; hence at low currents a smaller diameter is required.

In addition, I think that electrode diameter and resistance affects the electromagnetic field around the tip, which in turn helps determine the arc shape (diameter) and penetration. The field is pinched at the very tip of the electrode, and the shape of the plasma (arc) is governed by the strength of the surrounding field and electron flow rate.

I studied level 3 Welding and Fabrication, and this is just what info I can recall from hardcore books in the college library... If anyone has a better understanding I would also be very interested to learn more about it.

 

[gordon stephenson]

Thanks Provenrad,
Is there anybody else can add to this explanation or is the above the complete answer?

 

[hotrodder]

http://www.mig-welding.co.uk/forum/showpost.php?p=279604&postcount=10 The Diamondground link goes into all sorts of detail about electron work function and oxide migration rates and their effect on performance

I'm guessing your machine probably wants to know what size you're using to optimise arc starting. Smaller, sharper tungstens start more easily than big blunt ones so optimise the start parameters for a big un and the tip of a tiny tungsten won't last as long. With AC some kit will vary the EP current for a few fractions of a second during arc initialization to round off/ball the tip according size or the parameters set.

 

[gordon stephenson]

Thanks Hotrodder,
I'v downloaded the pdf and will study it at leisure, Looks like the real deal where tungstens are concerned,
Much appreciated.
Gordon,