Ertalyte PETP

[eski1]

Hi

I have machined some parts in Ertalyte PETP , approx size 300 x 120 x 20 thick .
In places they have been machined down to 4mm thick . The original parts were injection moulded from PolyPropylene but because of moulding costs we have had to veir away from these.
We tried to machine some replacement parts from PP but ran into problems with the materials moving and difficulty holding tolerance on the 4mm thick section.

Our problem is we were advised to use Ertalyte PETP as it wouldn't move about , which it didn't but it is very brittle , in as much as when you drop it from 3ft it shatters (not out normal test but 1 off them accidentally fell on the floor which set alarm bells ringing)

So what i really would like to know is :-
a) Can we salvage the parts that have been machined by either annealing them or some other process , i suppose we could do with getting close to being as non - brittle ( technical term ) as the PP.
b) if we were to make them again what ( if you can from the limited info i have given you ) would you suggest we use .

They are under little stress but would be subject to knocks and bumps , basically they are end plates that go on a large water screening conveyor chain .

Cheers in advance for any help
chris

 

[patprimmer]

PET becomes particularly brittle when differential shrinkage causes frozen in stress.

Annealing can reduce this stress, but may also cause warpage. You could try annealing under various conditions, including restrained and unrestrained.

If you had to make it again I would consider nylon or acetal. Both have their individual pros and cons.

Regards
Pat
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