Re: Tungsten vs. Tungsten Carbide

To: tesla-at-pupman-dot-com
Subject: Re: Tungsten vs. Tungsten Carbide
From: "Robert W. Stephens" <rwstephens-at-ptbo.igs-dot-net>
Date: Mon, 25 Nov 1996 05:43:25 -0500
>>From mycrump-at-concentric-dot-netSat Nov 23 20:07:58 1996
>Date: Sat, 23 Nov 1996 20:10:01 -0500 (EST)
>From: "Daryl P. Dacko" <mycrump-at-concentric-dot-net>
>To: tesla-at-pupman-dot-com
>Subject: Tungsten vs. Tungsten Carbide

>I spent several hours today playing around with my arc lamp
>power supply and some tungsten rod and a tungsten carbide lathe
>insert to see which faired better in a torture test.

<snip>

>These carbide tips look better all the time !

>Has anyone else tryed carbide tips in a rotary ?

>Daryl

Daryl, All,

I employ tungsten carbide tips brazed to 1/4 inch steel mounting 
shafts as the stationary electrodes in the rotary gap for my MTC 
system.  The pad surfaces are about 3/8ths inch square each and 
radiussed to best fit the travel of the 1/8th inch thoriated tungsten 
rods that fly by on the disk.  I employ a 6.5 amp Lamb vacuum cleaner 
blower with a nozzle directed at each pad to assist in cooling the 
pads below the melting point of the brazing and also for improved 
quenching.  This system works faultlessly at 7 kVa.  The exact same 
system previously has had high carbon steel, and also brass stationary 
electrodes and would literally eat them in just three minutes of run 
time.  I have perhaps 15 minutes run time on the new setup and see no 
detectable wear yet on either the flying tig tunsten electrodes, or 
the thoriated tungsten pads.  It seems apparent that part of the 
trick to extending contact surface life, even with tungsten, is to keep them cool.

As a further note.  I employ the side of the flying tungsten rods, 
not the end tips, as my contact surface.  This trick reduces the 
current density of the arc and spreads out the wear for longer 
electrode life.  If it is increasing the gap resistance a bit by 
lowering the temperature of the plasma it hasn't hurt performance so 
that I'd notice.  This sytem consitently delivers hot, white, 12 foot 
streamers on just 7 kVa.  Note also that I  _ do not_  employ any 
power robbing stationary series quench gaps in the MTC system.
The mini pig voltage is 12 kV RMS.  Cap size is 0.125 mfd.  The 
peak primary current being switched by this rotary is indeed very high.
System energy is something like 17 Joules.

rwstephens