Re: Tungsten vs. Tungsten

To: TESLA-at-pupman-dot-com
Subject: Re: Tungsten vs. Tungsten
From: richard.craven-at-mkbbs.co.uk
Date: Wed, 27 Nov 96 20:11 +0000

Daryl and everyone

[Daryl said:

   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.]

Thanks for taking the trouble to look into the idea of using tungsten 
carbide. As we can see, it is not an insulator, but different grades 
have differing conductivities. A piece that I measured at work using a 
DVM was short circuit ( it was an uncoated tooling bit about half an 
inch long by 1/4 inch thick, lozenge shaped).

[From Brent:

   Used the round disks that I silver-brazed onto brass
   studs. In all honesty, they ablated (wore) away very quickly. I had
   used 3/8" round tips. I now use 3/16" pure tungsten rod, which is
   smaller, and ablates a bit more slowly. From what I understand, if
   you can cool the electrodes down a bit, they last longer. I plan to
   put a high-velocity blower nozzle on my gap to cool things down.]

My intention is to use tungsten carbide rods, 5mm diameter by 10mm long, 
inserted into my s-s electrodes. The electrodes on the disk will be 
cooled by virtue of 3000rpm speed, and the 4 stator electrodes are sunk 
in turn by large aluminium blocks (2 inch tall by 2 inch diameter 
cylindrical blocks). Air could be blown at the gap channels but I hope 
not to need to do this.

My interest in using tungsten carbide is because it is more available 
for me than the tig welding electrodes. I expect them to be a viable 
alternative as long as their conductivity is checked. I am having my 
rods made by a local company. The cost works out the same as buying 
machine inserts. The material is usually tungsten carbide and ditungsten 
carbide ( made by heating metallic tungsten with a small amount of 
cobalt as a catalyst) which is sintered at a low temp (900 deg C) and 
then machined. It is then high temperature sintered (1300 deg C) at 
pressures of several tens of kg per mm sq. Cobalt  is added here as well 
to help with the sintering. Co dissolves 30 or 40 per cent by weight of 
W and thus helps the mixing and sintering process. Other matls can be 
added (ceramic fillers) which will account for differing conductivities.
I will be using the rods end on probably. If I go for disks or other 
shapes, edgeways on as RWS suggests is an excellent idea.


Richard Craven, Malvern, England
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 CMPQwk #1.42 UNREGISTERED EVALUATION COPY