Page 296 - Injection Molding Advanced Troubleshooting Guide

30.3 Flash Troubleshooting 289

Always inspect the surface of the mold for any potential trapped plastic. It only
takes a small piece of plastic to prevent proper shut off. Many times if there is
trapped plastic on the parting line the machine will alarm due to mold safety
preventing lockup. Unfortunately, it can be very time consuming to remove all of
the plastic that can become trapped after severely flashing a mold. Prevention is
the best solution to this problem, and make sure that people start up processes
running a fill only shot to help prevent flashing the mold.

30.3.2.4„ Mold: Support

When a mold is built there must be steel that provides structure to allow the
machine tonnage to apply force from the platen through the mold. Support pillars
must be added when mold areas are cleared out. The two common areas that are
cleared out and need additional support added are:
1. Ejector box
The space where the ejector plate travels within the mold must have support
pillars added to ensure that the mold does not deflect from cavity pressure (see
Figure 30.6; the smaller inner circular shapes are support pillars).

2. Hot runner manifold
The space in the hot half that is occupied by the hot runner manifold needs to be
cleared for locating the manifold. Due to the clearance of the steel around the
hot runner manifold support must be added to avoid mold deflection.

Figure 30.6 Support pillars

If a mold is not adequately supported it will experience plate deflection that will
lead to flash. The internal mold deflection will not be measurable from the exterior
of the mold like platen deflection is. An internal deflection sensor can be installed
in the mold to determine if the mold is actually deflecting.