Thin wall IML defects

[Horeki]

Hi, everyone.

I’m having some trouble with some defects after long production runs.

Production starts normally without an almos 0% rejection rates, but after 12 hours the rejection rate gradually keeps increasing from 1% (acceptable) to 5% (really bad) and I don’t know why.
Tried reducing the temp, increase back pressure, adjusting injection speed, injection force, rpm, increasing cooling time and it stays the same.

Process and settings details:

-Thin wall IML cup
-Temp: Front 250, Middle 240, Middle 240, Back 237, Hoper OFF
-Material PP MFR 35, with 1% titanium oxide
-Injection speed: 210mm/s
-Cooling 1.5s >mold temp 18C
-Shot 71mm ø50mm
-Hot runner temp: 250C
-14KGF back pressure
-1450KGF injection force
-160ton clamping force
-Filling time 0.86s
-Hold time 1s
-Cycle time 10.8s

Photos of the defect:
366
366

[iautry1973]

I am not sure from the pictures exactly what the defect is you are having, but looks like a burn mark on the edge? If that is correct could it be that the vents on the mold are getting plugged? Do you have a set process on how often the mold is cleaned during production. If you clean the mold do the defects get better?

[daniele_66]

Hi,
it's single cavity or multi cavities mold... where is the split line? I'm agree that seems e burn mark, so if there are propewr venting you can try to reduce clamping force. If you share more information, may be we can help you better.

[rickbatey]

I’m not really getting a good feel for defect from the pictures you put up. Can you add some more and then perhaps the root cause will be clearer.
Rick

[Horeki]

It recently came back from maintenance with and external provider and it’s the doing the same.

[Horeki]

Hi,
it's single cavity or multi cavities mold... where is the split line? I'm agree that seems e burn mark, so if there are propewr venting you can try to reduce clamping force. If you share more information, may be we can help you better.

-2 cavity arranged vertically ( I don’t like the arrangement but the EOA came like that).
-Split line located at the cup rim.
-Reduced clamping force and it just got a really bad flash.
-Reduced injection force and cavity It’s not filling.

[Horeki]

I’m not really getting a good feel for defect from the pictures you put up. Can you add some more and then perhaps the root cause will be clearer.
Rick

https://imgur.com/sXu3fdK
https://m.imgur.com/a/gCGHOn0

The label is destroyed at the rim, some times the label pases tru the rim.

[rickbatey]

Great pics and I totally understand the issue. I’ve seen a similar problem when back molding textiles onto plastic substrates. You need to reduce the peak pressure or length of time the label sees high injection pressure in the cavity. You may even have a problem with certain cavities that points to wall thickness variations, pressure variations or core shift.
Slightly higher barrel or maybe mold water temperatures could reduce or eliminate the defect.
Rick.