molding polypropylene

[KJS]

This is off topic but I thought you guys might have some advice. We're in the process of making a mold to mold a 3 inch by 4 inch by 1/8 thick polypropylene part. We usually don't use this material so I was wondering if anyone is familiar with it's shrinkage or warpage during molding. Any other tips or advice would also be helpful. Thank You!

[Scott Reiner]

Shrink should be between 1.018" to 1.022". If there are any fillar's the shrink generally will drop, as well as the shrink will change based on where the part is gated if there are fillars. PP is a very forgiving plastic to mould. If you have really tight tolerances on a specific area, leave material in the tool, mould some samples and then adjust the tool to suit the tolerance and shrink.

 

HTH

 

Scott

[KJS]

Thanks for your help. How hard is it to get the part to come out scratch free? Will polishing it to an almost mirror finish do the trick?

[Scott Reiner]

Polish in the line of draw, as smooth as possible, 300+ stone finish. Mirror finish only if you have to, ie Clear Part(probably not applicable to a PP part). Have at least 1/2 degree of draft so that you don't get any drag marks.

 

Scott

[McRae]

Good technical advise ambass, are you a mold engineer or something??

[Scott Reiner]

No, I never claimed any Engineering title that I made up, just a lowly Mould Maker.

[Trevor Bailey]

Blow over it with a torch.

[KJS]

Thans again for your help Scott. Very useful advice.