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Author Topic: Dielectric tape  (Read 16562 times)
N4NYY
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« on: April 07, 2011, 08:35:57 AM »

I am looking to see if I can find some dielectric tape, to replace some brittle fish paper that needs to be replaced. I used to work with this stuff, and it is basically a thick and wider version of electrical tape. Ebay has nothing, and Google shopping shows crap like electrical tape.

I am insulating the exterior base of an RCA bakelite radio that is metal (brass), and the chassis is hot.
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KB4QAA
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« Reply #1 on: April 07, 2011, 11:16:23 AM »

Antique Electronic Supply has fish paper and insulating cambric cloth.
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KA0HCP, ex-KB4QAA Relocated to Ks. April 2019.
WB2WIK
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« Reply #2 on: April 07, 2011, 03:03:58 PM »

Kapton tape is very good for this. 

I use it all the time, even in very high voltage insulating systems.  Way higher dielectric withstanding voltage than "electrical" (PVC) tape, takes very high temperatures (500C) and will go through wave solder processes without damage.

You can get small rolls of it from places like this: http://www.all-spec.com/search?keywords=polyimide%20tape&x=25&i=1&f=f&gclid=CIzUn-6zi6gCFRphgwod33KhBg

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N4NYY
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« Reply #3 on: April 07, 2011, 03:06:28 PM »

WB2WIK,

That is exactly the stuff I used to use like circa 1988. I never knew what it was called. Thanks !
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AC5UP
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« Reply #4 on: April 07, 2011, 04:13:03 PM »

Wow! What a coincidence!

I threw out a whole case of that last week. Didn't know what it was. My bad.  Roll Eyes
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N4NYY
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« Reply #5 on: April 07, 2011, 07:03:06 PM »

Damn 5UP, not your fault. You were not supposed to know, and I did not know what the hell to call it. I finished recapping and new resiitors. No smoke, and picked up the Orioles game (in the basement no less). So, now onto power cord polarization, then cosmetics.
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N4NYY
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« Reply #6 on: April 07, 2011, 07:05:30 PM »

Found some guy on ebay that has a 1" roll (36 yards). He said it is 1 mil thick. How thick is that with respect to standard electrical tape? Is it sufficient to replace fish paper?
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AC5UP
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« Reply #7 on: April 07, 2011, 07:25:50 PM »

I have a couple of rolls of PVC tape in front of me complete with original labels... Scotch 700 "commercial grade" tape is .18mm thick which I think is another way of saying 1.8 mils. Scotch 35 is .177mm thick and that's so close to .18mm for all practical purposes I'd say they're the same.

As for the other question, ask the fish...........................
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KE3WD
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« Reply #8 on: April 08, 2011, 05:53:11 AM »

mm (millimeters) and mils do not mix well.  (Since this is the internet, someone will likely soon come along and try to show off by saying that mils can be converted to millimeters, true, but they likely have never encountered the sticky wicket known as "metric creep," where conversion can put things in the ballpark but not actually nail the measurement.  Unlikely in this case as it is only one mil, but...)

mils = thousandths of an inch

one mil =  0.001 inch or 0.001" using the standard abbreviation for inch.


In order to find out the dielectric strength of a kapton tape that is spec'd at one mil thickness, more information is needed, mainly the dielectric constant per inch of the substance, which should be found either in mfr's spec sheets or perhaps in a physics or other reference book that lists such for kapton. 


73
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KA5N
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« Reply #9 on: April 08, 2011, 07:29:21 AM »

.18 mm is a bit more than 7 mils.  Since there are 25.4 mm in one inch it is just simple arithmetic.  1 milimeter is almost 40 times as thick as 1 mil.  Of course I can't chide anyone since NASA also gets screwed up converting one system to another.  Remember crashed mars probe.  Use one system or the other and don't mix them.  " Feet and inches not "plopper wolve" for metric units"  (veiled reference to engine coolie's survey of the engine  in "The Sand Pebbles.")

Hi Ho

Allen
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AC5UP
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« Reply #10 on: April 08, 2011, 10:05:29 AM »

D'oh!

I sure did get the metric and English measurements co-mingled, and the hell of it is I should know better.

To revise a previous statement: The Scotch 700 PVC tape I have is labeled with a thickness of .007 inches. The Scotch 35 PVC tape also shows .007 inches... Even though the metric thicknesses are .18 and .177 respectively. On one hand that looks like an error, on the other there is the concept of rounding to the nearest hundredth.

Gotta' Love It!
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AD6KA
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« Reply #11 on: April 08, 2011, 10:19:35 AM »

Quote
I threw out a whole case of that last week. Didn't know what it was. My bad

Wow. Kapton Tape is quite expensive, or least it used to be
many years ago when I worked for a firm that fabricated items
with it using rotary dies presses. About $60/roll retail for 2" x 36 yards.
I imagine it has come down quite a lot since then.
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KE3WD
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« Reply #12 on: April 08, 2011, 03:32:19 PM »

D'oh!

I sure did get the metric and English measurements co-mingled, and the hell of it is I should know better.

To revise a previous statement: The Scotch 700 PVC tape I have is labeled with a thickness of .007 inches. The Scotch 35 PVC tape also shows .007 inches... Even though the metric thicknesses are .18 and .177 respectively. On one hand that looks like an error, on the other there is the concept of rounding to the nearest hundredth.

Gotta' Love It!


Typically the engineer needs to know the thickness of the actual dielectric, which is often given minus whatever thickness that an added adhesive would add. 

The polyimide (brand name is Kapton) I've got on shelf here lists it like this in the specsheet:

"0.0025" thick tape has a 0.001" thick film. 0.0035" thick tape has a 0.002" thick film"

The difference between what is called the tape and the actual Kapton substance itself. 

It is unlikely that the adhesives used would add very much if at all to the great dielectric properties of the Kapton.  But I've got one type that states a silicone adhesive and another which calls its adhesive, "acrylic".  The silicone generally touts a higher temperature rating IIRC.


73
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N4NYY
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« Reply #13 on: April 08, 2011, 03:56:26 PM »

Quote
Wow. Kapton Tape is quite expensive, or least it used to be
many years ago when I worked for a firm that fabricated items
with it using rotary dies presses. About $60/roll retail for 2" x 36 yards.
I imagine it has come down quite a lot since then.

5UP has quite a collection of stuff he has been discarding because he is cleaning house. We may have to pay him a visit, because he throw all the good stuff away !
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AD6KA
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« Reply #14 on: April 12, 2011, 08:16:07 PM »

Quote
It is unlikely that the adhesives used would add very much if at all to the great dielectric properties of the Kapton.  But I've got one type that states a silicone adhesive and another which calls its adhesive, "acrylic".  The silicone generally touts a higher temperature rating IIRC.


Correct, especially when it's laminated to Nomex.

And FYI you can tell the acrylic adhesive backed Kapton tape
from the silicone adhesive backing by smelling it. Silicone
adhesive has very little or no odor. The acrylic adhesive odor
is quite distinctive, unless it is really, really old. In that case
the adhesive is no longer "aggressive". (Tape-Speak for "not sticky anymore!")  Grin

How's that for useless trivia?
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