Hardness scales...

[Externet]

Was trying to find hardness figures for nylon, delrin, ABS, teflon,  poliethylenes ...  and got lost in too many scales Shore, Brinnell flavors, Vickers, Rockwell, and metric and not metric,  

Is so much variety needed ?  No consensus ?  Very nasty to see so many and looking for the proper conversion.  😱

[TheVat]

I only know the one geologists use, the Mohs.   Though named for a German fellow, his surname also provides the perfect mnemonic (in English) for recalling it....MOHS, measure of hardness scale.

[studiot]

16 hours ago, Externet said:

Was trying to find hardness figures for nylon, delrin, ABS, teflon,  poliethylenes ...  and got lost in too many scales Shore, Brinnell flavors, Vickers, Rockwell, and metric and not metric,  

Is so much variety needed ?  No consensus ?  Very nasty to see so many and looking for the proper conversion.  😱

That may be because hardness is a much less well defined concept, especially for ductile materials and even more especially for very ductile materials such as plastics.

Is the required information for machine workability ?

[Externet]

Thanks. 

Yes, I need a part made and wanted to have a sense of which material would be convenient.  I do not know if hardness is what I have to look for. 

'Deformability' plus 'resiliency' to act as a seal/gasket between surfaces would make more sense 🤔   Gathering several different materials to evaluate how they perform under 5000 psi after CNC machined.

[StringJunky]

Have a look at Vespel, but it's very expensive.

https://en.wikipedia.org/wiki/Vespel#:~:text=Vespel is mostly used in,hostile and extreme environmental conditions.

[studiot]

11 hours ago, Externet said:

Thanks. 

Yes, I need a part made and wanted to have a sense of which material would be convenient.  I do not know if hardness is what I have to look for. 

'Deformability' plus 'resiliency' to act as a seal/gasket between surfaces would make more sense 🤔   Gathering several different materials to evaluate how they perform under 5000 psi after CNC machined.

Deformability is not a very well defined concept either.

You listed a some 'plastics' materials.

Plastics as a collective term are renowned for their long term deformability. Continued unrecoverable deformation over time is called plastic behaviour and the result is called creep.
A seal that slowly squashes is of no long term use.
Soft copper for instance squashes once and stays that way.
It also has a higher upper and lower temperature working range.

 

But if this is critical you really need expert advice.

Edited May 21, 2022 by studiot

[John Cuthber]

I have used PEEK fittings at 5000 PSI and above.