Page 202 - Injection Molding Advanced Troubleshooting Guide

192 21 Cloudiness

„ „21.2„ Cloudiness Troubleshooting Chart

Table 21.1 shows the cloudiness troubleshooting chart.

Table 21.1 Cloudiness Troubleshooting Chart
Molding Process Mold Machine Material
low melt temperature water leak hang up areas contamination
improper material change surface of mold semicrystalline nucleation
low mold temperature hang up areas moisture content

„ „21.3„ Cloudiness Troubleshooting

Cloudiness is most typically an issue with the material, specifically with contami-
nation of the material.

21.3.1„ Cloudiness Troubleshooting Molding Process Issues

The key items to verify cloudiness in the process are:

ƒ Melt temperature
ƒ Improper material change
ƒ Mold temperature

21.3.1.1„ Molding Process: Melt Temperature

Verify that the melt temperature of the material is appropriate according to the
material supplier’s recommendations. An actual melt temperature should be mea-
sured either with a melt probe or with an IR gun. Actual melt temperature is im-
pacted by a variety of factors including barrel temperatures, back pressure, screw
rotation speed, residence time, and screw geometry.
If the melt temperature is running low it can lead to a cloudy appearance. Try rais-
ing the melt temperature to see if the cloudy appearance improves.
Sometimes low melt or mold temperatures can lead to a jetting defect that actually
produces a cloudy appearance, as shown in Figure 21.2. In this example the jetting
is obvious; however, there are times when the jetting effect is the root cause but it
is not apparent that jetting is occurring until short shots are run.