[Amps] RE : dielectrics for PAs TSPA
Will Matney
craxd1 at verizon.net
Fri Apr 14 17:58:40 EDT 2006
Jos,
Here's the link to it. They call it fiberoid fish paper.
http://www.oselectronics.com/ose_p147.htm
Best,
Will
*********** REPLY SEPARATOR ***********
On 4/14/06 at 5:51 PM Will Matney wrote:
>Jos,
>
>No this isn't transparent. It's a type of paper they make and use clay
>somehow with the fibers. It is used for transformer layer insulation, and
>in the slots of motor stators. It comes in different thicknesses from
>around 5 mil up to thick card stock like about 60 mil. Its voltage rating
>is probably around 100 volts+ per mil, or is what we use as a rule of
>thumb. It could actually be more than that though. 20 mil is used between
>the full coils, and the 5 mil between each layer of a coil. 20 mil will
>also work as a bobbin but I like it a little thicker, around 30 mils at
>least. Peter Dahl did have a photo of a transformer using it on his
>website. It was a large one they had not dipped yet. You can see though
>from the photo that he still uses the same stuff everyone else does. He
>started using a black dye in his varnish. Then you had to add it to the
>varnish, but now you can buy it with it in it. The black color supposed to
>help with heat transfer. Now how good it is for that, I couldn't say as
>I've never used it. I'm pretty sure I seen that paper for sell at
>Oceanstate Electronics. Below is a link to their website.
>
>http://www.oselectronics.com/
>
>Best,
>
>Will
>
>
>*********** REPLY SEPARATOR ***********
>
>On 4/14/06 at 10:27 PM hermans wrote:
>
>>Will,
>>
>>The bleu shining stuff you'r talking about, could that be what we called '
>>TRIAFOLL '.Shiny on one side, matt on yhr opther . We used that bleu
>nearly
>>transparant isolating layers in transformers. Its kinda mica, and it holds
>>very high voltages AC and DC as well. I still hold a roll of 26 x 0.2 mmm
>>might be more then 100M.
>>
>>Jos on4kj
>>
>>
>>-----Message d'origine-----
>>De : amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] De
>la
>>part de Will Matney
>>Envoyé : vendredi 14 avril 2006 21:35
>>À : amps at contesting.com
>>Objet : Re: [Amps] dielectrics for PAs TSPA
>>
>>
>>John,
>>
>>Thanks, that was very educational and a very good read. I have an old book
>>here that might be a good read for some on varnished cloths. It's titled
>>"Varnished Cloths For Electrical Insulation", by H. W. Chatfield Ph.D.,
>and
>>J. H. Wredden. The book is copyrighted 1947 by the Chemical Publishing Co.
>>There's no ISBN number. It gets into glass, cotten, etc including Micarda.
>>This is still used in the transformer industry in sheets and tape. It
>>explains a lot about how they should be used, etc. I know I learned a lot
>>from it. I'll try to locate a copy of the book you mentioned as it would
>be
>>a good reference.
>>
>>Best,
>>
>>Will
>>
>>*********** REPLY SEPARATOR ***********
>>
>>On 4/14/06 at 2:01 PM John T. M. Lyles wrote:
>>
>>>Will asked, and the floodgate opens:
>>>
>>>>What did you find good for use in the plastics
>>>>as I'm interested about that myself?
>>>>
>>>
>>>Thin Teflon sheet stock would make excellent
>>>chimney, easy to make. Also, others have stated
>>>that RTV silicone sheet does. Actually PET may be
>>>a decent insulator in thin sheets. You can get
>>>Mylar or even pop bottles and try them. Problem
>>>there is the low melting point, but the anode of
>>>a tube should not be 200 deg C!
>>>
>>>Here is a posting I made Jan 24, 2000 from the
>>>archives of AMPS at contesting.com about dielectrics
>>>for coil forms. G10 is probably OK for chimneys
>>>when the voltage is reasonable, although my
>>>experiences with it using 15,000 volts and higher
>>>at 27 MHz were disasterous.
>>>
>>>>Subject: [AMPS] dielectric losses
>>>>From: jtml at lanl.gov (John T. M. Lyles)
>>>>Date: Mon, 24 Jan 2000 09:26:51 -0700
>>>>
>>>>I've been meaning to get back to the dielectric materials topic with
>>>>some suggested alternate materials:
>>>>
>>>>At 11:50 PM -0500 1/15/00, owner-amps-digest at contesting.com (RF
>>>>Amplifier Discussion Dige wrote:
>>>>>I have been advised NOT to use Teflon, Delryn, and a few other
>>>>>insulating materials for an RF choke. Instead only use ceramic. It
>>>>>was then stated the "D" factor was the reason.
>>>>>
>>>>>OK, but why as I could not find info on this subject in the ARRL
>>>>>Handbook. Any help to point me in the direction of knowledge on this
>>>>>subject would be appreciated. May as well learn something while
>>>>>building my amp. And I want to do it RIGHT.
>>>>
>>>>The following reply is correct, thanks Dave for inserting facts into
>>>>that discussion.
>>>>
>>>>>Teflon is a (fluorocarbon resin) or (flourine plastic) and has the
>>>>>same structure as polyethylene, in which the hydrogen is replaced by
>>>(flourine).
>>>>>OR a part may be replaced by (chlorine), in which case it is called
>>>>>a (fluorohalocarbon resin).
>>>>>
>>>>>Polymerized (tetrafluoro ethylene), aka PTFE, which carries the E.I.
>>>>>du
>>>Pont
>>>>>trade name of Teflon, formula (CF2*CF2)n is probably the most
>>>>>common solid form used for insulating materials, bearings, gaskets,
>>>>>insulating tapes, wire insulation, etc. This is a white waxy solid
>>>>>with specific gravity of up to 2.3, typical tensil strengths of up to
>>>>>3500 psi,
>>>elongation
>>>>>of 250-350%, dielectric strength of 1000 v/mil and melting point of
>>>594*F.
>>>>>
>>>>>Another commonly encountered material in electronic use and sometimes
>>>>>referred to generally as "Teflon", is Teflon FEP, which is a
>>>>>fluorinated (ethylene-propylene). In thin films (typically down to
>>>>>0.0005"), it is
>>>most
>>>>>frequently found as insulation in capacitors. Typical tensil
>>>>>strength is 3000 psi, elongation 250%, and dielectric strength 3200
>>>>>V/mil.
>>>>>
>>>>>Neither PTFE or Teflon FEP emit phosgene upon decompositon at
>>>>>elevated temps.
>>>>>
>>>>>However, fluorothene plastic (which may be what Rich's info was
>>>referenced
>>>>>to) has the formula (CF2*CFCL)n and differ from (Teflon) in having
>>>>>one chlorine atom on every unit of the polymer chain, replacing the
>>>>>4th fluorine atom. This is a (transparent) material with a specific
>>>>>gravity
>>>of
>>>>>~2.1, has tensil strengths of up to 9400 psi, but has a lower
>>>withstanding
>>>>>temp (as related to Teflon) of around 300*F. This material is
>>>>>sometimes called "Teflon" due to its similarity in chemical and
>>>>>polymer-structure make-up, and will emit phosgene upon decomposition
>>>>>at elevated temps.
>>>>>
>>>>>73, Dave, K1FK
>>>>
>>>>
>>>>I worked for E. I. DuPont in RF reseach in the late 1980s. We made a
>>>>LOT of dielectric measurements up to 3 GHz. We used Teflon* as a base
>>>>material (a substrate or boat) in a lot of heating experiments in high
>>>>power RF. It is one of the best materials to use. Even when there is a
>>>>direct arc, unless it burns deep into the material, it can be reused
>>>>without repeat arcing. Teflon* is also rather inert, so it does not
>>>>readily combine with other chemicals in experiments. Surface
>>>>arc-resistance of pure Teflon* PTFE (* DuPont trademark) is excellent,
>>>>and carbonized arc paths do not easily form on the surface. As others
>>>>have already mentioned, the dielectric losses are among the best for
>>>>polymeric materials (or even natural materials besides gases like air
>>>>and vacuum). It is often used in radomes and in microwave windows. But
>>>>it cold flows very easily, so if clamped or mechanically held, it will
>>>>eventually deform. So it is rarely used where mechancal strength is
>>>>needed. Coil forms should be no problem, for smaller coils wound with
>>>>magnet wire, however.
>>>>
>>>>There is a sickness called the Teflon* flu. Machinists can get it when
>>>>working the material at higher temperatures near the smoking point.
>>>>This is to be avoided. It was not phosgene gas, but a fluorine
>>>>byproduct I think. I don't know how harmful it is, but sounds like
>>>>Rich's friend succumbed to an extreme case, or something else.
>>>>
>>>>The following Teflon* safety information came from E. I. du Pont de
>>>>Nemours and Company website: "Before using Teflon®, read the Material
>>>>Safety Data Sheet and the detailed information in the "Guide to the
>>>>Safe Handling of Fluoropolymer Resins, Latest Edition," published by
>>>>the Fluoropolymers Division of The Society of the Plastics
>>>>Industry-available from DuPont.
>>>> Open and use containers only in well-ventilated
>>>>areas using local exhaust ventilation (LEV). Vapors and fumes
>>>>liberated during hot processing, or from smoking tobacco or
>>>>cigarettes contaminated with Teflon® or Tefzel® fluoropolymer resins,
>>>>may cause flu-like symptoms (chills, fever, sore throat) that may not
>>>>occur until several hours after exposure and that typically pass
>>>>within about 36 to 48 hours. Vapors and fumes liberated during hot
>>>>processing should be exhausted completely from the work area;
>>>>contamination of tobacco with polymers should be avoided. Mixtures
>>>>with some finely divided metals, such as magnesium or aluminum, can
>>>>be flammable or explosive under some conditions. "
>>>>
>>>>
>>>>A lot of flexible conveyor belts for RF heating systems in industry,
>>>>use glass-reinforced Teflon* FEP polymers with silicone rubber. They
>>>>don't get very hot in the intense RF fields used to heat polymers.
>>>>
>>>>To circumvent the weak mechanical properties, microwave industry uses
>>>>crosslinked polystyrene, such as Rexolite, Polymer Q200.5, and maybe a
>>>>few other tradenames. This stuff is the hard brittle plastic that is
>>>>translucent, although it can be polished to be like glass. We use it
>>>>to carry 3 Megawatts of RF, as the spider in our 14 inch coaxial lines
>>>>in my present work. We buy it in 4 foot sheets, and cut and turn the
>>>>discs. We have a special polishing wheel that looks like a phonograph.
>>>>Rexolite does leave a carbon track when arced, and it can really melt
>>>>into a goo if ignited. But the dielectric properties are only slightly
>>>>inferior to Teflon*. K is 2.55 instead of 2.05-2.1. Loss tangent is
>>>>still 0.000x range. Its good mechanically. By the way, 3 Megawatts is
>>>>about 12 kV RMS, assuming perfect match in the coax line. It is worse
>>>>than this, because of the high VSWR during off tune (Q of our load is
>>>>60,000).
>>>>
>>>>Another material used a lot is ultra high molecular weight
>>>>polyethylene or polypropylene -also called UHMWPE. This stuff is soft
>>>>like Teflon*, a lot cheaper, and has good low loss, if you are careful
>>>>in what you spec and buy. However, it is very easy to get the wrong
>>>>material, so a dielectric test is really needed before designing with
>>>>a piece. This stuff is used for waveguide windows sometimes.
>>>>
>>>>Amateur applications of lower RF voltage and frequency can get by with
>>>>materials such as PVC, G10, maybe even Delrin (very questionable to me
>>>>though). In high voltage RF service, in the VHF region, none of these
>>>>can be used, due to excessive losses. Believe me, I have tried them
>>>>all. I have a standard test i perform, in a 90 MHz dielectric heater,
>>>>putting about 15 kV peak RF across a small block. In a few minutes,
>>>>most of those materials will either burst in flames, or will begin to
>>>>smoke and stink, as they are internally cooked.
>>>>
>>>>If you want to use fiberglass materials, G7 has lower loss than G10 or
>>>>G11, due to the use of silicone instead of the more lossy epoxy resins
>>>>in the other. It is harder to machine and cannot be turned for coil
>>>>forms, we tried it 2 years ago and it just delaminated and fell apart.
>>>>For the RF choke in the 100 kW 2.8 MHz amplifier, where the coil is
>>>>exposed to the E field alternating at the plate of the tube, I chose
>>>>polysulfone rod. It is easier to machine than Rexolite (crosslinked
>>>>Polystyrene), and has fairly good dielectric properties. It is sold
>>>>under one tradename UDEL* or Thermalux*. We are now using this same
>>>>material for HV insulator posts for a 90 kV klystron power supply (not
>>>>AC dielectric problem, only DC standoff).
>>>>
>>>>Another interesting new material is polyetherimide. This is
>>>>trademarked as ULTEM* by GE and Westlake Polymers and Hydex* by
>>>>Polypenco/DSM Polymers, I think. It can be had in glass reinforced
>>>>sheets, and has good RF properties. It is expensive but very strong
>>>>for mechanic support, such has holding an 80 pound tetrode so that it
>>>>does not crash into the finger stock at the bottom of the filament
>>>>connector in the socket.
>>>>
>>>>There are numerous other materials that are good, mostly more
>>>>expensive, like polyimides Torlon* and Vespel* with incredible
>>>>strength due to glass loading, etc. These are really beyond the range
>>>>of most of us. They should be considered in cases where the ionizing
>>>>radiation (gamma, Xrays) is high, and temperatures are high.
>>>>
>>>>The BEST reference book on dielectrics is still one of A. Von Hipple's
>>>>books "Dielectric Properties and Materials", MIT. Long out of print,
>>>>but I heard that they got reprinted not too long ago. Of course, these
>>>>texts don't have all the modern miracle polymers that I refer to
>>>>above.....
>>>>
>>>>If it works for you, then use it. But be aware that it may smoke now,
>>>>or later, when moisture is absorbed in your material. Pick something
>>>>that is not very hydroscopic if you live in a more humid climate than
>>>>I do in New Mexico.
>>>>
>>>>73
>>>>John
>>>>K5PRO
>>>>
>>>
>>>
>>>
>>>Here is another posting is from the March 24, 2004 archive:
>>>>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.
>>>
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>>
>>
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