we have a product that made of HDPE, but the part size is tool large after cooling. we have tried many different HDPE with shrinkage from 0.15%-0.21%. but the problem is still there. it would be highly appreciated if anyone can provide a solution for it? thank you.

hi
i believe that there no hdpe that shrink 0.21% it supposed to be around 1%-3.5% shrinkage.

maybe your tool has wrong dimensions if not try to eject the part as hot as posible ( no deformations) from mold, this will increase the shrinkage.

there is plausibility that you are not using hdpe, check and double check!

p.s. hdpe shrink for about 24 hours
good luck

Hi Dimitry,

sorry it should be 2.1%. yes, we used the HDPE.

we have tried many way to adjust the process, like you said, but still not get good parts.

we can get the correct part in size, but there will be deformation on the surface. we can also get non-deformation part, but it is oversize(5mm).

do you know any HDPE that has higher shrinkage? like 3.5%?

Hi thanks for you all.

the shrinkage should be 2.1%(type error), it is provided by resin supplier. the resin we have tried is 1.8%, 2.1% in shrinkage. but the result is not good.

PS. the part is 37.8" in size, a large part.

contact your material supplier, let him find best match.

lower you holding pressure to the minimum possible.(no sucking marks, no deformation) probably around 400 bar absolute

if you like send me you processing/conditions sheet, may be me and my colleges would be able to help.

besides the material grade the temperatures will call the shots in 80% of your difficulty.

check your part geometry the mould might be preventing the part from shrinking depending on the thickness of the wall. i.e. a form of stretch moulding. Eject quickly at maximum practical ejection temperature and put on a cooling jig to keep flat if necessary that allows the part to shrink.

Thank you ken and Dimitry. i have forward your comments to my engjineers to try.