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-   -   PTFE tape for transformer insulation (https://www.vintage-radio.net/forum/showthread.php?t=153925)

TowerRadio 11th Feb 2019 11:22 am

PTFE tape for transformer insulation
 
Is plumbers PTFE tape any good for insulation between transformer windings? I am not talking about EHT,mainly low voltage AC and heater windings.Les

The Philpott 11th Feb 2019 11:35 am

Re: PTFE tape for transformer insulation
 
I don't know but...if PTFE overheats dramatically, it gives off toxic fumes. Summat to bear in mind.
Dave

G4_Pete 11th Feb 2019 11:35 am

Re: PTFE tape for transformer insulation
 
Hi , I have always used it for small transformers as it self binds without being sticky and keeps things from unravelling but for thicker wires you would need a large number of turns to get the mechanical strength as the pressure from thicker heater type wires will cut it through.
pete

P.S. Posts crossed. Just read the one above and looked up the health risks - nasty stuff it seems but it is used on frying pans!

Argus25 11th Feb 2019 12:02 pm

Re: PTFE tape for transformer insulation
 
Quote:

Originally Posted by TowerRadio (Post 1119442)
Is plumbers PTFE tape any good for insulation between transformer windings? I am not talking about EHT,mainly low voltage AC and heater windings.Les

I have seen it used, but it is very soft and pressure thins it significantly.

I have found that the better tape for transformers, between layers or groups of windings is Polyamide, otherwise known as Kapton tape. An example here:

https://www.ebay.com/itm/Kapton-Tape...ql3u:rk:1:pf:0

It is temperature resistant and strong.

For the outer bobbin layer I have come to use Scotch 27 tape as it is also temperature and burn resistant. Both of these tapes are superior to the common yellow transformer tape. Here is an example:

https://www.ebay.com/itm/Electrical-...EZkp:rk:3:pf:0

kalee20 11th Feb 2019 1:48 pm

Re: PTFE tape for transformer insulation
 
I wouldn't use it, except on a very temporary job.

PTFE is super stuff in the right place, it withstands high temperatures (250C-plus) well; doesn't harden or go brittle at low temperatures (-55C and below); has very high insulation resistance; very low dielectric loss.

But, as G4_Pete says, it yields easily under pressure. No good when you have another winding on top, pressing down! And as Dave points out, at very high temperatures (300C or more, so fault conditions in a transformer) it gives off seriously nasty fumes. Google 'PTFE Flu.'

Agree with Argus - Kapton is much better. Or Nomex. (The yellow polyester tape, eg Scotch type 57 is much cheaper and although rated to only 130C has a better adhesive.)

John_BS 11th Feb 2019 3:12 pm

Re: PTFE tape for transformer insulation
 
Large range of tapes from 3M!!


http://adhesive-tape-converting.mbkt...-PET-Film-.pdf


John

emeritus 11th Feb 2019 3:13 pm

Re: PTFE tape for transformer insulation
 
I first came across Kapton in the mid-1970's when metallised Kapton film started being used as a screen for individual twisted pairs in multi-pair cables. In the course of a conversation with a technical specialist it was mentioned that (at the time ) no-one had been able to find a way of bonding Kapton to itself or anything else using adhesives or solvents. NASA had tried in vain, and the problem was eventually solved by a Frenchman (AFAIR one Jean Vessy Lac) who found that by overlapping two sheets and running a high speed rubber friction wheel along them using the right speed and pressure, the sheets would hermetically bond together.

TowerRadio 11th Feb 2019 3:33 pm

Re: PTFE tape for transformer insulation
 
Thanks for the information but Kalee20 has hit the nail on the head,it would only be for temporary/experimental purposes where the fact that is non-stick would be an advantage.I should have made this clear at the beginning.Is anyone still using Empire tape by the way? Les.

John_BS 11th Feb 2019 5:42 pm

Re: PTFE tape for transformer insulation
 
Les: If you buy ptfe tape labelled for gas work it's much thicker.



John

Bazz4CQJ 11th Feb 2019 6:10 pm

Re: PTFE tape for transformer insulation
 
Some years ago, my company's Health and Safety Manager told me of an incident he'd been involved with where a fitter had lost a finger, apparently after coming in contact with traces of hydrofluoric acid which had been produced when PTFE tape had been over-heated. The acid passes through human tissue quickly and then reacts with calcium in bones.

That may well be an unusual case, but I've never wanted to be another example to add to the database!

B

kalee20 11th Feb 2019 6:25 pm

Re: PTFE tape for transformer insulation
 
A former colleague of mine said he heard of a case where an engineer used to smoke his pipe in the workplace and annoy his co-workers. They thought they'd play a trick on him, and bury some bits of PTFE insulation in the tobacco in his pipe when he wasn't looking.

He died.

It's great stuff, it has made the world a better place, I love it, and continue to use PTFE-insulated wire; PTFE-bushed stand-off solder terminals; PTFE coil formers; but just beware of its limitations and drawbacks.

emeritus 11th Feb 2019 7:56 pm

Re: PTFE tape for transformer insulation
 
Make sure you get the wide PTFE tape: very narrow PTFE tape is now available that is wound within the grooves of the pipe thread rather than across several of them. The plumber used some when fitting a new radiator for us a couple of months ago.

The drums of PTFE-insulated wire that I have, bear prominent warnings about the danger of exposing them to excessively-high temperatures. I have never seen corresponding warnings on pipe thread tape, presumably because the pipe tape would not expected to be subjected to dangerously-high temperatures.

turretslug 11th Feb 2019 8:02 pm

Re: PTFE tape for transformer insulation
 
Like PTFE, synthetic rubbers like Viton can decompose to form hydrofluoric acid under extreme heat- I was warned not to handle components from fire-damaged vehicles as things like door seals and engine component gaskets could produce HF residues, with similarly grim bone-eating consequences as outlined above.

Kalee20's account reminded me that (whilst not a smoker myself), we were warned not to smoke whilst using halogen-containing cleaners, such as trichloromethane ("trike") and quite a few others, as the vapour could be decomposed by contact with hot ash into phosgene (carbonyl chloride).

Bazz4CQJ 11th Feb 2019 8:39 pm

Re: PTFE tape for transformer insulation
 
Quote:

Originally Posted by emeritus (Post 1119603)
The drums of PTFE-insulated wire that I have, bear prominent warnings about the danger of exposing them to excessively-high temperatures. I have never seen corresponding warnings on pipe thread tape, presumably because the pipe tape would not expected to be subjected to dangerously-high temperatures.

I think you might get pressurised water or super-heated steam at dangerously high temperatures for PTFE. My conversation with the Safety Manager was in 1986 when he found out that we (chemists/materials people) were intending to use PTFE tape on connections to an autoclave which would hold water at 325'C. None of us were aware of the problem then. I think that most people in industry have picked up on the risks of PTFE by now.

B

Diabolical Artificer 12th Feb 2019 7:27 am

Re: PTFE tape for transformer insulation
 
I use Kapton tape off ebay, I'll send you the link.

Andy.

Nickthedentist 12th Feb 2019 9:05 am

Re: PTFE tape for transformer insulation
 
Quote:

Originally Posted by Bazz4CQJ (Post 1119628)
I think you might get pressurised water or super-heated steam at dangerously high temperatures for PTFE. My conversation with the Safety Manager was in 1986 when he found out that we (chemists/materials people) were intending to use PTFE tape on connections to an autoclave which would hold water at 325'C. None of us were aware of the problem then. I think that most people in industry have picked up on the risks of PTFE by now.

Our autoclave at work definitely has PTFE tape on some of the threaded pipe joints. :shrug:

TonyDuell 12th Feb 2019 11:25 am

Re: PTFE tape for transformer insulation
 
I thought solder sucker tips were PTFE. Mine regularly gets heated (albeit briefly) to 400C and I would hope it's not puting HF or similar onto my PCBs.

I did once use the back end of an old solder sucker tip as an insulating sleeve which had to withstand about 100C. Of course there was no problem with that.

Bazz4CQJ 12th Feb 2019 5:31 pm

Re: PTFE tape for transformer insulation
 
Quote:

Originally Posted by Nickthedentist (Post 1119753)
Our autoclave at work definitely has PTFE tape on some of the threaded pipe joints.

Tell me if I'm wrong, but don't steam sterilisers work at around 120-130'C? If so, that is well within the limit of ~260'C that's typically quoted for PTFE, whereas the work I referred to above was at well over 300'C.

As for de-soldering tools at ~400'C, I guess that's just the brevity of operation, compared with stuff that's running 24/7 for months on end.

The safe use of PTFE is one of those subjects that comes up on the forum every so often, and the conversation is always much the same. I see that RS now has a page on it's website devoted to PTFE tape, which you can now get with particles of nickel embedded in it to stop galling on stainless steel fittings :o. Wow, young people today....

B

Jon_G4MDC 12th Feb 2019 7:48 pm

Re: PTFE tape for transformer insulation
 
Hot wire strippers were often used on coax having PTFE dielectric - especially the twisted pair stuff called wireline. It was almost impossible to strip any other way.

Don't strip it that way without good ventilation!

Sean Williams 12th Feb 2019 9:18 pm

Re: PTFE tape for transformer insulation
 
Quote:

Originally Posted by Nickthedentist (Post 1119753)
Our autoclave at work definitely has PTFE tape on some of the threaded pipe joints.

Hi Nick,

I think, from my admittedly small exposure to Dental Autoclaves, that you have nothing to worry about - 121 deg C and 136 Deg C spring to mind in your application - Forum Member Onewatt is a bit of an expert in these matters


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