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I need the shrink factor..

I need the shrink factor..

I need the shrink factor..

We are bidding on a project that calls for :

Polyethylene, ASTM D4976 Group 1 (branched), Class 2 (medium density, grade 5 (flow rate to 0.4) containing
2.50+ .05% carbon by weight, approx. 5.27" OD X 2.79" high,
approx. 6 oz.

Could anyone please tell me the shrink factor of this?
The molded part will resemble a bowl and the wall thickness will be about .187.


RE: I need the shrink factor..

.187 is awfully thick for a part this size. Consider reducing it to .06-.04.

Shrink is affected by the added carbon. Check with manufacturers or compounders. LNP has a web site.

RE: I need the shrink factor..

Good morning,
I aggree that .187 is a thick wall, however the part dictates this..

RE: I need the shrink factor..

considering the bowl shape  & wall thickness i guess the gating u will consider for this part will be direct kind i.e. either cold sprue(normal) or hot sprue type(with PE this will pose difficulty need to check for flow of 0.4)

One noticeable point in this regard : if the part geometry is in the form of revolved section the difference in shrinkage along & across flow will cause little deformation on shrinkage but any deviation from revolved geometry will show itself in the form of deformation.

RE: I need the shrink factor..

Hi I would check with the molder of the end mold as to what it should be.  If they can't tell you ask which resen they will use and go to the resin company. They will use a specific supplyer and a specific brand.  The Shrinkage will very from Supplyer to supplyer and brand.  The plastic supplyers have a abundance of knowledge of there plastics and will give it to you free.  That has been good for me in the past.


Rick Marmei - Tool Designer

RE: I need the shrink factor..

Don't just use resin suppliers basic data sheet quoted shrinkage. Get their detailed lists with indications of variations in shrinkage due to:-
 section thickness
 mould tempreature
 injection pressure
 hold up time
Variations in pigments used for colour will also effect shrinkage.


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