Design for PFA or other fluoropolymer welding - need tips

[dcbloemer]

Hello, fellows! I am designing a plastic housing for a magnetic coupling. I have decided to use transparent injection-molded PFA (or possibly ETFE), due to its optical clarity, impact resistance, chemical resistance, and 'easy-to-clean' properties.

Here is a jpg of the coupling, showing the magnet, flux channel, and PFA housing assembly:

http://files.engineering.com/getfil...1a4c-4b29-af49-2f21a81cbb54&file=eng_tips.JPG

It's basically just a magnet and iron channel inside of a 'bowl-shaped' housing, with a fluid channel through the middle in the axial direction, and a cap fastened to the top of the bowl to contain the magnet and iron.

I want to weld the PFA cap to the PFA housing. The weld must produce a hermetic seal to protect the iron from oxidation (aqueous environment). I have no experience with joining fluoropolymers. I have considered sonic welding, hot plate welding, and laser welding, but am leaning towards hot plate welding as PFA has a very low friction coeffiecient, and is transparent.

Does anyone have experience in joining fluoropolymers, specifically PFA? If so, I would appreciate advice as to which welding method might work the best for this project. I would also appreciate specific design advice, if you have any, as far as features to add to the design for the specified weld method - i.e., energy directors for sonic weld, etc. I should specify that I am not looking for general design guidelines for plastics welding, as I am familiar with these; rather, I am looking for tips specific to fluoropolymer welds.

Thanks a TON in advance, will check back frequently.

-David Bloemer

 

[Pud]

If it's only an aqueous environment, may I ask why flouropolymer? Seems a bit of an overkill imho.
Have you considered Nylon 12? Good for most stuff, including hydrocarbons? Not cheap especially, but the "in position" cost will be a lot less.

H

http://www.tynevalleyplastics.co.uk

It seems to me you have confused a safe drinking limit with what I like to call "lunch"

 

[dcbloemer]

Pud - environment is mostly aqueous, but also some organic pollutants, tars, and combustion products. I don't want these contaminants building up on the walls of the device (including some very hard-to-reach internal chambers which were not included in the jpg).

The factors I had to consider when choosing a material were biocompatibility, clarity, impact resistance, chemical resistance, and the 'easy to clean' factor. I was indeed reluctant to use fluoropolymers because of the cost; however, the only other material family I could find that ended up meeting all of the criteria were some copolyesters, e.g. Eastman Tritan.

 

[coatingengineer]

Hello. My experience is coating-related. PFA, being melt-processable, monolithic, lends itself well to "joining" through heat. But, like other fluoropolymers, ETFE included, be sure to weld in a well ventilated area. In fact, DuPont will even recommend a self-contained breathing apparatus. There will be air-borne carcinogens, aldehyde or ketones.



William Gunnar

http://www.IndustrialCoatingsWorld.com