Re: Garolite (G9, G10, G11) questions.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "BunnyKiller by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bigfoo39-at-telocity-dot-com>

Hi Sam...

hows things going...   good to see you in here  :)

comments intersperced in your original letter...

Tesla list wrote:

>Original poster: "Sam Barros by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<list-at-powerlabs-dot-org>
>
> Greetings,
>
> This question concerns materials choice for a rotary spark gap. 
>Obviously we want the rotor disk to be as light as possible so that 
>a smaller motor can be utilized and the spin up time becomes shorter.
>

smaller discs offer problems in design as far as "insulation" values 
from the motor shaft to electrode distance. Plus... do you plan to start 
the disc spin-up as soon as you start the T coil? Most of us have the 
disc running well before we apply power to the coil..

>
>In order for a light disk to withstand the centrifugal forces encountered 
>in rotary spark gap duty it would make sense to use the strongest 
>material possible (within some price restrictions obviously). I notice 
>that G-10 grade Garolite seems to be the most often used material,
>and with a tensile strenght of 40000PSI and an impact strenght of 
>7ft/lbs/in it is definitely a good choice. I also see some designs 
>using polycarbonate but at 9000PSI tensile strenght, 12ft/lbs/in 
>impact strenght I would definitely go for G-10.
> However, why doesn't anyone use grade G-9 Garolite? With a tensile 
>strength of 66,700PSI lenghtwise and 51,900PSI crosswise, and an 
>impact strength of 14.5ft/lbs lenghtwise and 11,2 crosswise, it would 
>make a much better material choice for a lighter, stronger rotary 
>spark gap disk, no? 
>

availability of G-9 is the problem...  G-10 is much easier to find....

>The price is also virtually the same as G-10 
>($29 for a 1/4in thick, 1'x1' sheet). Also, what about other grades 
>of Garolite (G-11, G-30)? They seem to be weaker and more expensive,
>is there any advantage to them? Is there any plastic/composite material 
>that is NON CONDUCTIVE and stronger than G-9?
>

Glass fillled Teflon has really great insulative values, better heat 
capacities than most plastics but the price is higher than titainium 
nitrided tungsten  :)


>
> Finally, how stiff is G-9? Does it buckle under force or does it 
>tend to fracture in a brittle fashion (I am deducing from the relatively 
>low impact strength that it will shatter, but I couldn't find its 
>modulus of elasticity anywhere)?
> Any answers to these questions would be greatly appreciated.
>

it really doesnt fracture   it delaminates....  the differences in the G 
values is the material used as the base "fabric". there are glass 
fabrics, glass fiber, linen fiber, etc blended in the epoxy ( whatever 
binder) to make the material stiff and more heat resistant. The glass 
fiber matrix ( long fiber or fabric) of the higher end G materials can 
be a real pain to machine ...  you will need tungsten carbide or better 
tooling to work on this stuff..

>
>Sam Barros
>ME/EE Major at Michigan Tech.
>http://www.powerlabs-dot-org/
>
>
Scot D

aka BunnyKiller