Page 246 - Injection Molding Advanced Troubleshooting Guide

25.3 Delamination Troubleshooting 237

Keep in mind that even though the throughput through the barrel is good, hang up
areas will change the game for residence time.

25.3.4„ Delamination Troubleshooting Material Issues

The reasons for delamination defects attributed to material issues usually fall into
a couple of main categories:
ƒ Contamination of material
ƒ Incompatible color concentrate

25.3.4.1„ Material: Contamination
If a material is contaminated with a foreign material there is a good chance that
delamination will occur. This will obviously be more prevalent if the contaminating
material is incompatible with the base resin; for example, if ABS and polypropyl-
ene are mixed you will have a problem, but on the other hand mixing polypropyl-
ene and polyethylene is not problematic.
It is key during all material handling to ensure that materials are kept clean and
separated. There are many ways that materials can be contaminated including:
ƒ Uncovered containers. If a box, barrel, bin, hopper, or gaylord is left uncovered
there is an opportunity for foreign debris or material to get into the container.
Something as simple as someone using an air hose to blow out a hopper on the
next machine could lead to contamination in uncovered containers.
ƒ Lack of verification. Sometimes people will dump a material into another con-
tainer based on the color or appearance of the pellets without verifying that the
materials are the same. This can also be an issue if someone switches over a feed
line without verifying that the correct material is being sent to the correct loca-
tion. It is therefore critical to clearly label all materials including regrind. Make
sure that anyone that handles material understands the importance of getting
the correct material into the correct containers. Also make sure that everyone
who grinds runners or parts understands the correct grinder to use. Also when
a silo is to be loaded make sure that someone has verified that the tanker is hook-
ing up to the correct silo (this can be set up with different fittings as a poka-yoke).

Case Study: Material Contamination Causing Delamination

This particular case was at a molding shop that used mostly precolored
material. There was one job that ran with natural base resin and a color con-
centrate. During an off shift the color concentrate ran out so the material
handler went looking for more concentrate. They looked high and low and
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