I need the shrink factor please..

[smokehouse]

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.

Thanks!

 

[yanish]

I have never used it, but RTP has a carbon fiber reinforced HDPE that has a shrink rate of .002" to .004" inch per inch. This is the closest I was able to find to the material callout you are looking for. This is an unbranched version, so you may see more shrink in yours. Your best bet would be to call RTP, GE, or some other supplier of reinforced materials and get their thoughts. Although, they will not be willing to give you more than an estimate as tool design can make a large difference in the shrink rate of any material. Good luck.

 

[1chris]

Material suppliers give shrinkage values based on standard test pieces produced under ideal conditions (of course_. PE, however, varies so much depending on all the usual factors (orientation, part geometry, processing conditions (tool temp, melt temp, pressure) that values quoted have to be viewed with suspicion. eg Lupolen 1800S shrinks between 1.6-1% depending on orientation & follow-up pressure alone. Good luck. ps fibre reinforcent (RTP - related answer) will further confuse the issue.

Chris Newman
Technical Service Engineer (Raw material Supplier - UK)
Ultra Polymers