expanded ptfe 1

[RNDguy]

I have an application where an edge trim in expanded PTFE (if such an edge trim exists) would be desirable. Is any edge trim manufactured in expanded PTFE of a shape similar to commonly available bulb-type extruded elastomer sections? I really do not know the technological limitations of making seals in expanded PTFE, but something like this would be a desirable addition to the repertoire of available extruded shapes. My application is high temperature (575 degrees F +), stationary, aggressive chemicals like bleach, detergents, tartaric acid, salt etc. while providing an atmospheric pressure water tight seal. Thanks in advance.

 

[tothepoint]

575F is pretty high for expanded PTFE (ePTFE). A company called Inertech, Inc. in California makes ePTFE and advertises various custom shaped/sized profiles. You may want to find them on the internet and contact them. They'll probably have a minimum run requirement however.
Be aware that unlike elastomers, ePTFE is a rather "dead" material in that it takes a set and does not rebound. This is not a problem in a bolted, flanged connection however if you're not maintaining a load on the ePTFE it will not provide a very good seal.

 

[RNDguy]

Thanks. I was already in touch with Inertech, but they seem to offer the sealant cord and 1/8" thick self-adhesive seal-maker, I think that's what they call it. But if I can find edge trim in ePTFE, that may be of greater use to me. By the way, would you know if this is extruded?
Thanks again.

 

[longeron]

Yeah-- 575 F is awful high for PTFE. About that point it starts outgassing and decomposing... Hydrofluoric acid is one of the chemicals given off about this point... not something I'd want to be around.

 

[tothepoint]

I guess I'm confused with your description as "edge trim". If you're looking for a tadpole cross section ePTFE, I know another company called Darco Southern in Virginia that makes a folded/stiched tadpole tape from ePTFE. The ePTFE tape is extruded and expanded, and then it is formed around a woven ceramic rope, and stitched to form the tadpole cross section. Is this what you're looking for?

 

[RNDguy]

If you see, e.g. McMaster's catalog, there are many rubber/elastomer estrusions, some of which are edge trims, meaning they are U-shaped or some other bulb shape etc. attached to the U-shape. They can thus be pushed over a sheet metal edge and made to follow this edge all around. The sealing is effected on the side of the U- or bulb. The tadpole you refer to, if it had a split tail so it could be pushed on the edge, and if the inside of this split tail could take 600 F plus, then this may be a good trim. Oh one other thing, the seal we are looking for should form not just an air seal like in furnace doors, but should be a good water seal as well (at atmospheric pressure only). Thanks very much for your help and interest, I did go the web-site of Darco Southern, but now I need to talk to them also. Do you, or any one else, know of any edge trim to do a duty like this. Ideally, if this were a composite material, like some high temperature fibre inside and an elastomer outside, but does any one make it?

 

[tothepoint]

There are no elastomers that can withstand 600F for very long. Chemraz(R) #615 is a perfluoroelastomer that is rated for 600F, however it is VERY expensive. Also, it won't maintain it's elastic properties for very long at this temperature. Call Darco Southern- their ePTFE tadpole tape is probably your best shot.