PTFE seal hardness testing

[swolsky]

Hello I need to hardness test a PTFE rotary seal to compare to the version we have received from a supplier. The issue is the PTFE seal is 1mm thick and I am struggling to find a hardness scale that can accurately depict the hardness of the OE compared to our production sample.

Does anyone have any recommendations as to which hardness scale i need to use to grab some accurate data given the gasket is so thin.

Thank You!

 

[GregLocock]

I'd be inclined to measure the compressive stiffness of the seal clamped between two plates. Alternatively stack 6 of them together and measure the durometer.

 

[TugboatEng]

Shore D is what I see used for PTFE o-rings.

If you want to get deep into the woods, why does hardness matter for a rotary seal? PTFE products die by creep. If you're not using the OEM seal supplier you need to work with your current seal supplier to find their properties that work for their specific product.

 

[Doug Hunter]

You can try ASTM D 1710, ASTM D 882 or ASTM D 4745 to see if they offer any useful information. Do you know if the PTFE has any glass fill? I don't recall any hardness checks or requirements in the PTFE seals I've worked with.

 

[swolsky]

You can try ASTM D 1710, ASTM D 882 or ASTM D 4745 to see if they offer any useful information. Do you know if the PTFE has any glass fill? I don't recall any hardness checks or requirements in the PTFE seals I've worked with.

No i have not material tested the two seals yet to determine what fillers are used. I was trying to determine which hardness scale I want the facility to use so i could get both tests conducted at the same time. I think i am just going to ask what the testing facility thinks we need to use.

 

[3DDave]

I think I have never heard of hardness applied to plastics like this. The amount (percentage) and kind of filler set the properties. The PTFE itself is not hardenable. PTFE itself is very soft and will cold flow under pressure over time.

This brochure describes a variant of PTFE that is modified to resist cold flow. It does not mention hardness as a characteristic.

https://multimedia.3m.com/mws/media/802318O/3m-dyneon-tfm-modified-ptfe-brochure.pdf

This brochure does mention hardness of pure PTFE from Du Pont - it has ratings for Teflon® PTFE:
Rockwell R Scale
Durometer D Scale
Durometer A Scale

Hardness and FrictionHardness
Table 14 lists the hardness of Teflon® PTFE resins as determined by various tests. Fillers elevate the hardness of Teflon® PTFE resins by 10 to 15% and much of the improvement is retained over a wide temperature range.In general, the greater the filler loading, the harder the compound. Spherical or flake fillers impart the best hardness.

http://www.rjchase.com/ptfe_handbook.pdf

 

[Doug Hunter]

Swolsky, I just found this on-line:

https://www.standard-ptfe.com/pdf/data-sheet-of-ptfe.pdf

It looks like Tugboat was spot on with Shore D, even over a range of glass-fills.