Page 245 - Injection Molding Advanced Troubleshooting Guide

236 25 Delamination

rial is degraded it can show a number of defects including delamination, splay,
black specks, and brown streaking.
Also, if there is a mismatch between the sprue bushing and the nozzle orifice,
material may become trapped, hang up, and degrade. For cold sprues nozzle tips
should be 1/32 in under-sized to the sprue orifice size, and if running a hot runner
the tip and sprue orifice should be 1 to 1 in size. Dead spots between components
must be avoided to eliminate any potential material hang up areas.

25.3.2.2„ Mold: Lubricant Contamination
If grease or oil from a mold is allowed to get into the cavity the result could be a
delamination-type appearance. The lubricant will contaminate the material and
potentially leave a blistered delaminating surface where the contamination is in
the plastic.
Watch for hydraulic cylinders that are leaking as they can leak into the cavity. Also
beware that over-lubricating mold components can result in contamination of the
cavity with the lubricant. Many times when a mold comes back from being ser-
viced the tool shop will have taken the approach of “if a little grease is good a lot is
better”, and this can lead to hours of defective product being run due to the
contamination of the lubricant.

25.3.3„ Delamination Troubleshooting Machine Issues

The machine itself can lead to delamination problems; the most common reasons
are:
ƒ Machine performance
ƒ Hang up areas

25.3.3.1„ Machine: Machine Performance
See Chapter 8 on machine performance.

25.3.3.2„ Machine: Hang Up Areas

The main potential machine cause for delamination is due to areas of hang up such
as between the end cap and the nozzle. If there are any steps in the steel as one
component transitions to the next one there will be risk of trapping material. When
material is trapped in the barrel or barrel components it will be dragged into the
melt over time. This could lead to contamination with the previous material, which
could be incompatible with the current material. Another effect of trapping mate-
rial can be degradation of the material, which in turn can lead to delamination-type
defects on the part surface.