Re: General Questions

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

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-uswest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
> 
> Original poster: "Dr. Duncan Cadd by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com>

> I can understand nylon being very poor, as it will typically take up
> 2-3% water, and especially in the all-important surface layer.  This I
> can get my head round easily, as nylon is chock full of polar
> polyamide groups, but epoxy is pretty well devoid of anything polar.

I think that this is the problem. I observed that an insulator
freshly turned in the lathe is a good insulator, but after a month
or two the resistivity starts to decline, and I didn't find a way
to restore it.

> The only other thing which occurs as a possible cause is the hardener
> used, but as these are generally amines (they smell "fishy") and as I
> have used amines as additives in styrene/acrylate copolymers for use
> in photocopier toners, specifically because they hold a good
> electrostatic charge (!) I don't feel that's the answer.

A chemist said me that the hardener is probably the source of the
problem. I imagine that an additive to toners would be just to
add some conductivity to the material. A good insulator doesn't
get much electrostatic charge by conduction.
 
> Interesting to me as a polymer chemist, but probably dead boring and
> irritating to you!

Interesting for me, because I am searching for a epoxy-type glue that
hardens to a good insulator. Those types that harden with UV light
appear to be adequate, but are difficult to find here.
 
> This leaves the question of which plastics are good.  Polyethylene,
> polypropylene, polystyrene, polytetrafluoroethylene ($$$) are all
> first rate for rf high voltage as mentioned on this list many times by
> many people; polyacrylates, polyacetals, polycarbonates, polyesters
> nearly as good for many low frequency high voltage purposes (but not
> rf) and I think I'd give the rest a miss if I had a choice in the
> matter.

I agree with your list.
 
> My personal favourite for lf ht would be polyacetals, as not only do
> they have good ht performance, but excellent machining properties, and
> if you have a lathe and some sharp tools you can turn insulators and
> what-have-you very easily.  "Delrin" is one brand I've had good fun
> with, as always YMMV.

Here I can find easily, in rods of several sizes, Nylon (bad), 
acrylic (good), and Teflon (very good).
The order is as listed for insulation and machining properties, and 
inverted for price.

Antonio Carlos M. de Queiroz