Insulator material recommendations?

[K1JJ]

Hi All,

I've been doing some research on modern insulator materials for
ham use. Teflon seems to be the best, except for its high price.

I need some 1"-2" diameter round rod or 2"X 3/4" rectangular stock to
make up about 50 stand-off insulators for some 6M Yagis. I've
decided to float my parasitic elements and avoid the element to
boom plate influences and calculation guesses.

Anyway, after looking at McMaster-Carr's catalog I see that a
product called "MDS-Filled Cast Nylon 6" has similar charactoristics
to Teflon. It is UV resistant, has excellent insulator properties, high
tensile strength [better than Teflon] and can handle 250F temps, less
than Teflon, but OK. And, it's about 5 times cheaper.

Anyone have suggestions for a better and/or cheaper insulator
material? Lexan looks OK, but is more expensive.

BTW, anyone with some of this Nylon 6, Teflon, Lexan, etc material in
the "rough" sizes mentioned above or pieces that can be cut ?... I
would be interested in buying some before placing an order for new.

73,
Tom, K1JJ

[Rob K2CU]

HI Tom,

Just a couple of suggestions:

Be wary of "cold flow" with plastic type materials.  Material will deform away from stress, such as screws in tapped holes, and loosen.

Also check on materials dielectric loss tangent or dissipation factor.  This will probably not be an issue if you are using these at the electric neutral of the element anyway.  

Rob  - K2CU

[WA1GFZ]

Tom Vu,
I went through all the same stuff building my log. You want a material with glass fiber for strength. The material we got from Frank is still the best I have found.  All that other material will not hang in there. Teflon
is one of the worst, Delrin also won't last. I worked with the mechanical guys at work and they set me straight.

[K1JJ]

Tom Vu,
I went through all the same stuff building my log. You want a
material with glass fiber for strength. The material we got from
Frank is still the best I have found.  All that other material will
not hang in there. Teflon
is one of the worst, Delrin also won't last. I worked with the
mechanical guys at work and they set me straight.

Yeah, maybe you're right, Frank.  I have some fiberglass sheet
left over that I can use. Maybe using small aluminum "L" brackets
I can stand them up and bolt on the eles. I was looking for a tiny
footprint and this might do it.

Yes, Bob, Chuck warned me about cold flow and the instability
of some plastics. He said that many manufacturers are using
carbon filled nylon   for insulators and spacers in traps.

So, we'll see how the fiberglass sheet works out.

73,
T

[WA1GFZ]

Gee tom,
Maybe it is time to pay Frank a visit and check his scrap pile. I just drove by his exit a 1/2 hour ago coming back from our Farmington facility. Traffic was getting crazy and wanted to get north of hartford before rush hour.
mechanical guys told me you need some sort of fber in the material
to make it strong. fc

[N9NEO]

There are specific % fill you can get with nylon in order to reduce cold flow.  One 'expert' I had worked with many years ago used straight nylon to set the height of some spring steel used to clamp some TO-247 down.  They cold flow and we lost many good soldiers.

There is a company (or at least a product) called Glastic that I have used before.  Glass filled nylon standoffs with I think steel inserts in each end to thread a screw into.  Slick stuff, but as I recall there was a minimum order.  Good for high voltages

73
NEO

[N9NEO]

www.glastic.com

Just say NEO!

[W1GFH]

Pyrex.

[John K5PRO]

This topic has been discussed at length on the AMPS mailing list over the years. My own experience has been with high power RF, where it is critical to minimize loss (from burning it up).

Teflon is definitely great for lowest loss. But mechanically it is no go, esp under tension or compression. Crosslinked polystyrene (Rexolite) is next best, used a lot for radomes and high power coil form supports. It can be gotten from C-LEC plastics in NJ, also through distributors. It is also used as spacers in large coaxial transmission lines. It is rugged, but tough to machine. If it ever arcs, it will not survive like Teflon will. They sell it in flat sheets, and rods, $$. Nylon is somewhat hydroscopic, takes on moisture so that the loss increases from the data sheet values. The specs are not that good either, if you subject it to high voltage at high frequency, pssssttt..... It is an order of magnitude worse in loss tangent.

Mixtures of glass reinforced nylon may be better in rf and for strength. Glastic and other epoxy/glass laminates are pretty good in RF, but they sort of fade and eventually fall apart in heavy sunlight out here. If they are subjected to high fields, eventually the epoxy resin will boil out and burn. A new material which I found to be excellent is polyetherimide, or Ultem. There is a glass reinforced version also. I use it to support tube anodes on a very high power 2.8 MHz rf system I built at work. It is as good as G7 silicone/glass for RF, but a lot stronger. For ham use, depending on the voltage (from standing waves and also resonance in tank circuits) G10 isn't too bad. G7 is best, but hard to machine and also $$. Despite that some manufacturers have used it for coil forms, Delrin is not a good material for high electric field applications.

I bought a WT LaRose Thermall RF preheater, used from the semicon industry, years ago at a junk yard. It uses a single triode, running roughly 500W at 90 MHz, with a pair of plates under the lid. It can generate 15 kV of RF across plastic pieces, hoses, etc. Much better than using a microwave oven, it will heat up most plastics and soften them, giving a true feel for what works in RF fields. Some of the materials mentioned above have lasted about 5 minutes in the heater before bursting into flames or melting into goo.  

The book Dielectric Materials and Applications by A. Von Hipple (MIT 1954) is the best source of information on dielectric properties and it has been reprinted by Artech House in 1995 in paperback.

[K1JJ]

Tnx for the detailed info, John.

Yes, the plasdick products seem to have their problems.

I ended up using 3/16" thick fiberglass sheet to make up the 50
stand off insulators. I used small alum L brackets to stand the
2"X 4" pieces straight up and drilled a  3/4" hole thru to hold
each element. Two per ele balanced in the center.  Works FB mechanically.

I used this same fiberglass sheet for the ele insulators to build
a coupla of HF 13-30 mhz logs and for 5 years now has held up.
So, as Frank says, some fiber in the insulator diet is a good thing.

BTW, I'm cornvinced that using insulated eles for VHF/UHF is the way
to go. For a sharply tuned Yagi, those metal center mounting plates
with grounded eles can really ruin a pattern unless you are real lucky
and estimate their effects well. On HF it's no problem since the
plate becomes a tiny % of the ele size.  I can proceed with
confidence now that an untapered element suspended 3" above
the boom, floating, will work as the modeling says it will.

73,
T

[flintstone mop]

Sorry Tom
I  forgot what your post is all about.............I'm trying to decode the breastesess and the message there.
A very cute Asian lady by the way
G'day

[K1JJ]

Sorry Tom
I  forgot what your post is all about.............I'm trying to decode the breastesess and the message there.
A very cute Asian lady by the way
G'day

I haven't seen her drop it yet so guess no one's decoded it...

The answer: She's sending " R - R -  R -  R" over and over.   ie, no
matter what you want, she says "yes - yes - yes -yes".

However, if you look at it another way, it's: "N - N - N - N " -
you struck out.

T

[W2VW]

You numbal 10.

[wa1knx]

haaha,
        My gals daughter is having friends over Tom, a guy and gal.
and the gal is a petite cute little asian beauty. and so I'm in here reading
this post with your avatar swinging away and they come in
to introduce her to me! she starts glancing over to the screen
and I shrunk the screen like asap!!! tom you'd a popped a tent over this
gal ;;

[Bow/KD5KZN]

haaha,
        My gals daughter is having friends over Tom, a guy and gal.
and the gal is a petite cute little asian beauty. and so I'm in here reading
this post with your avatar swinging away and they come in
to introduce her to me! she starts glancing over to the screen
and I shrunk the screen like asap!!! tom you'd a popped a tent over this
gal ;;

Ahhhh yes... the Asian Persausion...

My "better half" XYL is 100% Japanese...

I know... I imported her...  

[wa1knx]

turning japanise I really think I'm really turning japanise I really think so;;

loved that song :_)

[VE1IDX]

Has anyone used UHMW,ultra high molecular weight,plastics in a high voltage situation?I know it will not heat in a microwave so it should be fine for RF but what about stand offs in a high voltage situation.I know ceramic would be best it's getting hard to find at a decent price and the UHMW is readily available for not too bad a price.It cuts and machines really well and would make nice insulators if it will stand up to a few KV's.