Page 286 - Injection Molding Advanced Troubleshooting Guide

29.3 Flaking Troubleshooting 279

29.3.2.1„ Mold: Lifter, Pins, or Slides
One of the typical sources of flaking is flash that can occur around mold compo-
nents such as lifters, ejector pins, or slides. When there is flash around any mold
component the movement of the component during ejection can peel off the flash
and leave behind a flake of plastic.
Another area of concern with mold components is when there is an undercut on a
slide or lifter that can be peeled off during ejection. These areas of concern on a
part will be highlighted by a scrape on the part. Where a part is scraped during
ejection, plastic flaking can occur.
Any spots on the mold that are flashing must be corrected. If mismatch on a lifter
or slide is causing the flaking the component must be spotted to eliminate the un-
dercut.

29.3.2.2„ Mold: Gates
Gates are another key area where plastic flaking occurs. When a sub gate or ca-
shew gate breaks away from the parts, flaking from an unclean break can be a
problem. The gate can break in a fashion that leaves behind a flake at the separa-
tion point; see Figure 29.2 for a magnified picture of a sub gate with flaking.

Figure 29.2 Magnified photo of sub gate with flaking

Often times a sub gate or cashew gate will have to have the break point sharpened
to help provide a cleaner break. There will be situations where due to part quality
constraints a sub gate or cashew gate will not be the best choice for gating due to
risk of flaking.

A runner can have flash that can separate during ejection and leave behind flakes.
Figure 29.3 shows a runner with excessive flash that led to flaking defects. Utilize