Re: [TCML] Rotary Disc Material

[DC Cox <resonance@xxxxxxxxxxxx>]

If you are running a .04 uF or larger cap size, especially with a pole xmfr,
then avoid the LE (linen-based) or CE (cloth based) phenolic.  This will
soften with heat.  Best to use the G-10 glass laminate grade of phenolic.
I've used both types and the LE or CE grade will work fine for small RSGs
and synchro RSGs, but with high power the glass G-10 grade is safer.

Dr. Resonance





On Wed, Apr 22, 2009 at 4:24 PM, Quarkster <quarkster@xxxxxxx> wrote:

> Andrew -
>
> I forgot to mention that McMaster-Carr (www.mcmaster-carr.com) sells 12"
> squares of G9, G10 and LE phenolic in various thicknesses. A 12" X 12" X
> 3/8" slab of G10 is priced at ~$47, with LE phenolic priced at ~$35. This is
> not unreasonable if you are going to make a reliable, well-designed, safe
> RSG.
>
> Herr Zapp
>
> --- On Wed, 4/22/09, Quarkster <quarkster@xxxxxxx> wrote:
> From: Quarkster <quarkster@xxxxxxx>
> Subject: Re: [TCML] Rotary Disc Material
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Date: Wednesday, April 22, 2009, 10:31 AM
>
> Andrew -
>
> Any polyethylene material is completely unsuitable for use as rotor
> material in
> a Tesla coil rotary spark gap. Polyethylene (even UHMW material) is
> extremely
> soft and has very low tensile and shear strength. Even worse, the
> heat-deflection temperature is extremely low, so the material will begin to
> distort at very low loads at even moderate temperatures.
>
> An RSG disk mounted on a high-speed motor is subjected to very high
> mechanical
> loads, and needs to be carefully designed and constructed so as not to be a
> potential bomb. The  structural failure of an RSG disk at full speed can
> release a tremendous amount of energy, and electrodes can "leave the
> scene" at very high velocity.
>
> There are several materials that are much better candidates than PE for RSG
> rotor material, but they still have temperature limits and stress limits
> that
> must not be exceeded:
>
> 1. Fiberglass fabric reinforced epoxy laminate (Grades G10 or G11);
> 2. Fiberglass fabric reinforced melamine laminate (Grades G5 or G9);
> 3. Canvas or linen fabric reinforced phenolic laminate (Grades CE or LE).
>
> The fiberglass-reinforced materials are strongest, and have the best
> high-temperature characteristics, but are difficult to machine and require
> carbide or diamond cutting tools to get decent surface finishes and tool
> life.
> All of these materials have good electrical characteristics (resistance to
> arc
> tracking, etc)
>
> The phenolic laminates are much easier to machine, and work well IF the
> electrode temperature can be maintained within the material's temperature
> limits. If the temperature limits are exceeded, the resin binder will begin
> to
> decompose, causing loss of strength of the material, loss of dimensional
> stability, shift in electrode position, etc.
>
> The G9 and G10 materials are good for ~285 deg. F; G11 is good for ~300
> deg. F,
> while the phenolic-based materials are good for ~265 deg. F.
>
> Regards,
> Herr Zapp
>
>
>
> --- On Wed, 4/22/09, Andrew Robinson <teslamad@xxxxxxx> wrote:
> From: Andrew Robinson <teslamad@xxxxxxx>
> Subject: [TCML] Rotary Disc Material
> To: tesla@xxxxxxxxxx
> Date: Wednesday, April 22, 2009, 4:54 AM
>
> Check out this image of my old SRSG:
>
> http://host.atomiklan.com/tesla/UHMW.jpg
>
> The disc used UHMWPE (Ultra high molecular weight polyethylene) as its base
> plastic. Ignoring the burned areas, what im really concerned about is the
> melting... I know all this looks bad, bear with with me a min.
>
> (Side note: UHMWPE has a melting point around 144 to 152 degrees C)_
> <http://en.wikipedia.org/wiki/Celsius>_
>
> This gap ran a 10KVA pig driven coil hence the crazyness. Those steel
> electrodes got so hot that they melted into the plastic. The washers that
> used
> to be there are now completely gone... vanished... MIA. lol
>
> Anywaz, the new gap is going to use tungsten electrodes that space out
> farther
> from the disc to prevent the burning , the the new electrode material
> should
> help with the heating up problem, but as an extra measure, im looking for a
> new
> material to machine the disc out of. I've seen alot of people out there
> that
> made the disc out of what looks like a brown brittle material. What can I
> use
> that will chock it up to the heat and be an excellent insulator?
>
> Thanks,
> Andrew Robinson
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