[Amps] insulation

[John T. M. Lyles]

G10 will melt down into an awful stinkin' and 
burnin' mess when heated in high Rf fields. I 
rarely use it anymore, except for PW 
applications. It is certainly a big step above 
Delrin acetals or nylons. Have settled on several 
wonder materials like:
Rexolite (crosslinked polystyrene) rod and sheet
Polyetherimide (ULTEM* 2300) with 30% glass, also known as Tempalux*
Polysulfone (UDEL*), also known as Thermalux*
G7  (silicone resin reinforced glass)

All more expensive, but if you want the highest Q 
and no heating, they are worth it. These are all 
high temperature engineered plastics. If you are 
concentrating E field flux in the dielectric, 
even with a kW, G10 will heat up. Good old UHMW 
(ulta high molecular weight) polypropylene and 
polyethyline made good insulators but have low 
glass transisition temperatures and will soften 
and dimensionally change with heat.

Your local plastics supplier has them. Pricewise, 
the first two are about $1000 for a square foot 
of 1 inch thick material! The rod stock is much 
cheaper, and for smaller coils it is more so. The 
G7 is more difficult to machine or turn on a 
lathe than G10 due to the lamination layers. But 
it is excellent material structurally as well as 
RF'ly.

Cheers
John
K5PRO

Rich AG6K said:
>  I bought 50-lbs of porcelain clay and I tried making porcelain
>pottery.  The shrinkage factor is about double ordinary stoneware clay,
>and porcelain clay is hellish to work with.  My advice is use G-10
>fiberglass-epoxy for insulating.  It's good around RF, strong, and easily
>drilled/machined. 
>
>>My YL has a ceramics business, and I started thinking about trying to
>  >manufacture my own ceramic (porcelain) insulators. Has anyone tried this?