Interference fit of HDPE into HDPE

[lurks]

I am trying to design a part that requires an interference fit of an extruded HDPE pipe .79" OD and .55" ID into a base of the same material. What is the rule of thumb for diameters and tolerances for an interference of plastic into plastic. I have formulas that would work for metals, but do not really apply for plastic. The elongation of HDPE is over 100%. Can anybody help me?

Thanks in advance,

lurks

 

[Pud]

The rule of thumb is really that whatever inteference fit you have, giving a particular strain, the stress will drop off with time due to creep. HDPE is poor for creep. Your best bet is for max interference commensurate with easy assembly and cross your fingers!

Note the stress will not drop off completely, but may be less than your design requires.

If the PE is cross linked, you will be a bit better off.

Cheers

Harry

http://www.tynevalleyplastics.co.uk

 

[tbuelna]

lurks,

You may also lose your original interference fit over time due to the effects of creep/cold flow.

Good luck.
Terry

 

[MikeHalloran]

Note also that to assemble parts with any useful interference, you have to grip the HDPE pipe and push it, hard. Which is harder than it sounds because the stuff is kind of rubbery, and will want to collapse where you grip it, and/or buckle in the space between the grip and the base.

You might want to take a look at thermal welding, e.g. with an embedded heating wire.



Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

I forgot to mention that HDPE is also slippery, so gripping it is not trivial.



Mike Halloran
Pembroke Pines, FL, USA