Re: [TCML] G-10 blistering

[drieben@xxxxxxxxxxx (David Rieben)]

Hi Bart,

I have 8 flying electrodes on my disc. Each of these flying
electrodes is a 3/8" x 1.5" long solid tungsten rod. Of course
since my rotary gap is an ARSG, I can easily vary the speed 
and break rate. I had been running the GM in the 300 to 350
bps range but I was probably running closer to 400 bps
during the last firing (I set the speed control variac to 85
on the dial instead of the typical 75). Doubling the number
of  flying electrodes and actually installing them is a bit more 
than I would want to try to tackle, so I'll just keep the power/
break rates down to more sane levels in the future ;^)

--
David Rieben

-------------- Original message -------------- 
From: bartb <bartb@xxxxxxxxxxxxxxxx> 

> Hi David, 
> 
> Looks like the Green monster is doing great as always! Sounds like the 
> flying electrodes are getting pretty hot. I have caused carbon tracks 
> across about an inch of G10 before (once). I've not had what your seeing 
> now. It is concerning. Additional air flow might help, but it sounds 
> like the current through the electrodes is just getting too high for 
> thermal heat dissipation of the electrodes. Probably any material you 
> use as an insulated disc will see similar affects. 
> 
> I don't remember off hand how many electrodes you have around the disk, 
> but you might be able to offset some of this heat by doubling up on the 
> rotating electrodes and halving the rpm (keeping bps the same). This was 
> about 340 bps? 
> 
> Take care, 
> Bart 
> 

I couldn't figure out 
> > exactly what was causing the odor at that time but a closer 
> > examination a couple of weeks later revealed that the G-10 
> > disc had actually scorched and blistered a bit around each 
> > of the (8) 3/8" x 1.5" long solid tungsten flying electrodes. 
> > I supposed that sustained 90 amp runs are just taxing the 
> > thermal dissipational characteristics of my ARSG componenets 
> > to their limits? Also, I believe the addition of the extra pair of 
> > stationary electrodes has increased the thermal load 
> > on the flying electrodes since they are now "sparking" twice with 
> > each disc revolution instead of once. BTW, the (4) stationary 
> > electrodes are each 1/2" x 3" long solid tungsten rods set in 
> > 1.25" x 2.5" long brass square stock. I suppose I'll have to up- 
> > grade to more massive flying electrodes if I wish to run at 90 
> > amp long runs on a regular basis. Other than the excessive flying 
> > electrode heat, which are whirling at over 3000 RPM, the coil 
> > is running great ;^)) Here is short video clip of it 
> > running BEFORE the ARSG modifications: 
> > http://youtube.com/watch?v=eWZD3M-nye8 
> > It runs notably smoother now without any racing sparks 
> > and at even higher power levels than I was able to run 
> > for this clip. Will the flying eledtrodes eventually burn their 
> > way out of the G-10 disc since they actually got hot enough 
> > to scorch the epoxy bonding agent of the G-10? Comments 
> > from others with high powered coil experience is welcomed.... :^) 
> > 
> > David Rieben 
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> > 
> > 
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