Page 61 - Injection Molding Advanced Troubleshooting Guide
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44 5 Mold Hydraulics
5.4 Hydraulic Cores or Slides
When using hydraulics for core pulls that have shut-offs on the cavity, the shut-off
should not be the positive stop that takes all the impact of the hydraulic pressure
in the set position. It is best to have a step or ledge on your component that bottoms
out at the same time as the shut-off to protect it. Furthermore, at times these shut-
offs need to be vented and without the added protection they will just hobb shut
over time.
Hydraulics are also used with slides that require excessive travel when the stan-
dard mechanical horn pin cannot provide the amount of travel needed. In many
cases the slides will have a lock angle with the stationary half locking it in place
against the plastic pressure where the hydraulic pressure is not needed to with-
hold cavity pressure.
With hydraulic driven slides extra caution is needed when there are low draft shut-
offs between the slide and the stationary half. This can contribute to galling on the
shut-off with the slide being locked forward with hydraulic pressure. In these situ-
ations when adequate draft cannot be added there is a simple device you can add
to protect your component on the set position if there is a lock angle on the station-
ary half of the mold that locks your component forward. If you use a T-slot coupler
you can create extra travel in the machined slot and add a spring to hold it in the
back position. Normally this will be set up where the component is 0.030–0.060 in
from the home position when the cylinder is bottomed out. When the mold closes
the lock angle on the stationary half will push it in the home position while col-
lapsing the spring. This will protect the shut-offs from galling. This method can
also be used when the component has critical shut-offs of the moving half to pro-
tect them with set speeds and pressures.
5.5 Multiple Sequences
When hydraulics are used on a tool there is a good chance that the tool will have a
suicide/crash condition that can be costly to repair if this occurs. Also when using
multiple core/hydraulic sequences this situation is typically a risk. When using
multiple hydraulic sequences, it is important to label them, color code them, or
better yet use different size fittings for each sequence so they cannot be set up im-
properly in the press. Using male and female connections for set and pull can help
distinguish them at setup. It is also important to have a core sequence plaque on
the mold to show the sequence of the cores to assist with machine setup [2].
