Page 366 - Injection Molding Advanced Troubleshooting Guide

362 37 Pin Push

application. During development it is worth evaluating if the enhanced release
material is allowed for the application and determining if it processes better.
If a masterbatch additive containing release agent (such as zinc stearate) is added
to the material make sure that it has been added at the appropriate level. Verify
that the letdown ratio is correct and thorough mixing is occurring. Do not take it
for granted that the appropriate letdown ratio was used, especially if sticking and
pin push start to occur “out of nowhere”.

37.3.4.2„ Material: Moisture Content
When hygroscopic materials are molded with excess moisture they often times
tend to become stickier. This increased stickiness can lead to pin push due to the
higher level of force required to eject the molded part.

See Chapter 9 on drying for more details.

37.3.4.3„ Material: Fillers
The addition of fillers will have two positive effects on pin push:
1. Nucleating effect
The nucleation impact on a semi-crystalline material will result in a part that
has a more solidified wall stock, thus reducing the risk of pin push.
2. Stiffness of the part
The addition of fillers will tend to provide a stiffer wall that is more resistant to
pin push defects.