Plug Seal interference

[dbrlogan]

I need to checks interference fit specs for a polypro plug seal into a glass bottle. I currently have a .0177 interference at MMC but that is too high to function properly. Before just loosening the fit I would like to go over reccommended interference specs for this fit, however I have not found anything on a web search.

Machinery's Handbook has interference fit specs that I will be researching but it does not take into account the polypro elasticity.

Does anyone have recommended interference fits for a polypro plug seal into a fixed (glass) cylinder?

This is for a problem that has just exploded onto my desk and that I have to answer quickly so thank you for any help.

 

[MikeHalloran]

If the plug is solid, it might work okay with a looser nominal fit and circumferential fins.

However, I don't recall ever seeing a solid PP plug; it seems customary to relieve the center or otherwise make them hollow.



Mike Halloran
Pembroke Pines, FL, USA

 

[dbrlogan]

Correct. This plug seal is in a pump-spray bottle assmebly. It is how the pump-spray is sealed into the glass container. However our interference is too great and puts too much pressure on the assembly as we secure the pump-spray into the bottle. I want to reduce the interference but I want to base that reduction on recommendations rather than a 'guess'. I may have to resort to the Handbook specs if I can't find anything that gives me an allowance for the elasticity of the polypro in this situation.

Thanks

 

[MikeHalloran]

What do you mean by "too much pressure"?

Is the plug fracturing the bottle necks?

Is it too hard for the assembly tooling to push in?

Just for fun, what's the nominal diameter?



Mike Halloran
Pembroke Pines, FL, USA

 

[dimjim]

You are compressing the material, isn't elasticity a function of stretching or putting the part in tension?
I would think the compression factor would or might be
one third of the elastic or tension factor. It might
make sense to use a tapered id or tapered hole on this
part.

 

[dimjim]

http://www.chemraz.com/85256D3C0038D8DA/vwContentByKey/N25S7NQJ541ELETEN

This url is for o-ring compression rates and may give you
some ideas. I saw this on another post.

 

[dbrlogan]

Thanks for your help. The plug is tapered and was subjectivly tight with manual insertion.

We went ahead and used standard FN1 interference tolerances on the plug (the hole was set because of method of manufacture)

thanks for all your assistance.