Additive to reduce sticktion of Viton GF600S...

[quizzical1]

Hi All,

Is anyone aware of an additive to Viton GF600S that can help reduce or eliminate sticktion / break away friction?
We have an application where a molded plug part is compressed into a brass tube and tends to stick when trying to move after sitting idle for months.

TIA

~Q

 

[Compositepro]

A coating of solid lubricant like graphite or boron nitride powder might work.

 

[Latexman]

Wrap the plug with Teflon® tape before insertion?

Is an "expandable plug" an option?

Good Luck,
Latexman

 

[quizzical1]

thanks guys....what about powdered teflon?

 

[EdStainless]

We used to mill BN into some elastomers.
We were just looking for an inert filler so we never measured the friction.
Various Teflon powders are sometimes added also.
One thing that you need to do is look at your contact geometry.
You should have a lip or ridge making the seal and not a large surface area.

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P.E. Metallurgy, consulting work welcomed

 

[Compositepro]

You can also try simply baking the Viton plug in an oven for a dozen hours at,or above, your highest use temperature. Elastomer parts are often not fully cured during production because that takes too long. Also, volatile components created by the curing reaction in closed molds must be removed by post curing in the open in an oven.

https://www.viton.com/en/-/media/fi...595f956&hash=46BD72D3A1AD4E6CEB1792BBE4B2ED64

https://www.chemours.cn/-/media/files/viton/viton-post-curing.pdf

 

[quizzical1]

thanks guys!

Sorry, forgot to mention it must see temps at 32F and our compounder said the Viton would become much harder (durometer-wise) if we added any teflon or caranuba waxes to it.
Was thinking of leaving the plug alone and coating the bore with Krytox or NiCoTef.

Thoughts?

 

[EdStainless]

I can't see Teflon changing the durometer, it isn't bonded into the structure (no crosslinking) and it's hardness doesn't change much with temp.
But that said using an 'hourglass' shaped plug and coating the bore sounds like a better route.

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P.E. Metallurgy, consulting work welcomed

 

[3DDave]

Graphite is at least a molecular level lubricant; teflon powder is going to be relatively huge and potentially excluded or form a leak path.

Sticktion is tricky - the Viton may be simply conforming to the microscopic asperities over time and, at the same time, the contact pressure is pushing lubricants out of the interface.

Carnuba wax is not a great choice - it's used because it forms a good adhesive bond. If one is looking at a water barrier, that's a good trait; I saw a great video of carnuba wax in tiny proportion in other release waxes bonding silicone rubber beyond the tear strength of the silicone.

I tend to like bee's wax, but it too may form a mechanical bond with the tiny irregularities in the parts over a lengthy static period.

It might be possible to change the design so that whatever is moving the plug tends to stretch it if the shear force is too high in a way that the diameter is decreased. As soon as the sticktion is overcome then the stretching stops and it goes back to whatever was originally intended. If one is pushing on the faces of the plug that would make the situation worse.

 

[quizzical1]

Thanks guys!

ES - thanks, the NiCoTef was my next choice

3DDave - We actually added 1% Carnuba wax in a smaller Viton Plug (.125" dia x .25" lg) as a release agent during molding and it seems to work well (was tearing upon release prior to this).

So, the graphite would out perform the teflon? any recommendations or is this ok?

https://www.amazon.com/Blaster-8-GS...28510&sprefix=graphite+powder,aps,118&sr=8-23

 

[3DDave]

Was the mold still hot?

 

[quizzical1]

Can’t say, that’s what our molding vendor told us

 

[quizzical1]

Would the graphite powder react with the brass tube if water were introduced?