×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

I need the shrink factor..

I need the shrink factor..

I need the shrink factor..

(OP)
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!

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..

(OP)
Good morning,
I aggree that .187 is a thick wall, however the part dictates this..
Thanks!

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.

Regards

Rick Marmei - Tool Designer
http://axis-design.org

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
 orientation
 mould tempreature
 injection pressure
 hold up time
Variations in pigments used for colour will also effect shrinkage.

Regards
pat

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources