Glue for thermocouple wires is bad?

[grizedale]

Hello

I have always used loctite
superglue to glue ptfe clad thermocouple wires to pcbs as the thermocouple end which has been glued to the fet is setting.

GLUE:
Buy Superglues Liquid superglue,3gm tube Loctite 853188 online from RS for next day delivery.

However, i have just noticed in the glue datasheet that its not recomended for PTFE

(I also use activator spray)

Anyway, since its not recomended for ptfe, could you recomend a glue for glueing thermocouple wires to pcbs.........and preferably a glue with an activator product aswell so i dont have to hold it for ages while the glue sets

 

[KMoffett]

Since PTFE is a low surface-energy plastic, you will not likely find a glue that will stick to it. Maybe with a surface prep agent...check Loctite'e or Master Bond's web pages. I would just use epoxy, and mechanically imbed the wire in it.

Ken

 

[chuckey]

Err, do your thermocouples fall off? Are you supporting a house roof with your PTFE thermocouples? It would appear that you are happy with the glue's performance. Nuff said.
Frank

 

[FvM]

You're sticking the welded thermocouple joint, not the PTFE isolation. In so far, there's no PTFE bonding problem involved.

P.S.: I assume, the thermocouple tip looks like below. Then the superglue, epoxy or whatsoever 1. fixes to the metal surface and 2. embeds the PTFE

 

[jpanhalt]

Couple of additions:
1) Super glues ("CA glue") and PTFE have such vastly different maximum operating temps, if the CA glue is OK, then you could use some more easily bondable insulator with a lower temperature rating than PTFE.
2) PTFE can be bonded with CA glues or other adhesives, if it is first surface treated with an appropriate etchant. A common one is simply sodium metal dissolved in a non-protic solvent (e.g, sodium dissolved in naphthalene plus an ether). Obviously, such surface prep solutions are very sensitive to water, but the PTFE, once treated, is not.

John

 

[grizedale]

thanks All,

FvM....yes that picture is it , but i have the two exposed metal wires soldered together to ensure they are in contact with each other..

...i wasnt worried about whether or not i can fix the ptfe clad wire in place, your own kind threads tell of ways round that....but more i was worried that the cyanoacrylate glue will corrode the ptfe wire.

You see, these wires are massively expensive and we wish to re-use them and we cannot do that if we have to keep trimming them back to get rid of corroded bits.

 

[FvM]

but more i was worried that the cyanoacrylate glue will corrode the ptfe wire.

Absolutely unsubstantiated. PTFE is one of the most chemically inert plastics.

The welded joint is what you get with retail thermocouples. Soft soldered thermocouples are O.K. for low temperatures and can be attached with "superglue" as well.

 

[rohwmart]

You can use 3M Scotchweld DP 100. It can bond PTFE without primers or activators and sets within 4 minutes.