Page 332 - Injection Molding Advanced Troubleshooting Guide

33.3 Gloss Variation Troubleshooting 327

sult can be variation in gloss levels on the molded part. Efficient cooling of a mold
is critical to final part quality and must be focused on during mold design.
If gloss differential is occurring in specific areas on the part, review the mold
design to determine if there is adequate cooling in this location. Thermal images of
the parts will help to highlight areas of poor cooling. Surface probes can also be
used to determine the actual mold steel temperature and look for heat concen-
trations.
If an area on a mold is hotter than the rest of the mold verify why; it may be due to
a lack of water near the area, a plugged water line, or a mold that was incorrectly
watered. An important part of molding setup is ensuring that the cooling for the
mold is consistent every run. Water diagrams must be recorded for every mold.
These water diagrams may be sketches of the layout or may even be photos of the
water layout, but a consistent technique must be established and followed for every
mold set. Also on the water setup sheet the in and out temperature of the water
should be documented, as well as flow rates and steel temperatures. With all of the
above data, troubleshooting a cooling issue versus the baseline process becomes
much easier.

33.3.2.4„ Mold: Venting
A lack of venting will lead to areas in the mold that may not fill as easily as others.
Because these areas do not fill as well the plastic may not be in contact with the
mold surface as well as other locations in the mold. Also restricted venting can in-
fluence the ability of the part to be packed out against the mold surface.
Verify that the mold is clean and the vents are open. Additional venting in locations
with poor gloss consistency may improve the appearance of the part. Lack of venting
can create buildup on the mold surface that impacts the gloss levels of the part.
See Chapter 7 for more details on venting.

33.3.3„ Gloss Variation Troubleshooting Machine Issues

Gloss issues relating to the machine are usually an issue with machine perfor-
mance (see Chapter 8).

33.3.4„ Gloss Variation Troubleshooting Material Issues

Some specific material-related issues that will lead to gloss are:
ƒ Material type
ƒ Additives