Page 141 - Injection Molding Advanced Troubleshooting Guide
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128 14 Mold Cooling
Mold steel temperature. The actual surface temperature of the mold steel should
be checked after running the mold on cycle. The cycle should be stopped and the
mold temperatures quickly checked with a surface pyrometer. On a sketch or
picture of the mold make a note of the locations where the temperature was
checked. Avoid scratching class “A” surfaces with the contact probe, because it is
usually a better idea to check just outside the cavity rather than risking damage
of the cavity surface.
Part ejection temperature. Check the part temperature after it has been ejected
from the mold. This can be done with a surface probe, an IR temperature gun, or
even better an IR thermal imaging camera. The part ejection temperature will
provide a roadmap for where the hot spots are on the part. If the hot spots have
changed over time it may indicate reduced cooling capacity. In some cases, the
thermal checks will indicate very clearly that a water line is plugged leading to a
line of decreased cooling across the mold.
Size of TCU. By documenting the size of the TCU used on the mold it will be easy
to verify that the correct unit is being used during future troubleshooting.
14.4 Tooling Techniques
Mold materials can have a large impact on cooling ability. Steel or alloy materials
can be considered relative to cooling ability and wear resistance. Copper-based al-
loys can transfer heat much faster than steels but must have a protective coating
when using glass-filled materials. Also, hardened steels are less conductive than
steels such as P-20. Hardened H-13 is 15–20% less conductive than P-20 so the
material must be a consideration when designing a mold. The material being
molded often drives the steel choice due to wear resistance but cooling should also
be factored in.
When it comes to cores and inserts the material is also important. Remember if
you are able to get a cooling channel into the detail alloys are often not necessary.
Bubblers are a very effective component to get cooling into tight areas. Bubblers
are an often-overlooked cooling solution when space is restricted. There is also a
time and place for ISO pipes but they are not as effective as getting flowing water
into an area. Keep in mind with small bubblers that plugging can become a prob-
lem if the plant water is not being properly conditioned. If plugging is becoming an
issue it is important to understand that all of the mold is being affected by the
buildup of mineral deposits and the cycle time of the mold may be compromised.
When water issues occur dig into the root cause of the issue and deal with the
plant’s water treatment.
