Page 140 - Injection Molding Advanced Troubleshooting Guide
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14.3 Documentation 127
save them from manually calculating the results. Higher flow rates improve cool-
ing capability but there is a point of diminishing returns where the extra heat re-
moved is not worth the energy to generate the higher flow. One interesting thing to
note on this equation is that cooler water temperatures require higher flow rates to
achieve turbulence. Another important thing to consider is that adding antifreeze
to the water will require nearly twice the water flow to ensure turbulent flow. There
are cases where people are trying to reduce the water temperature and end up
losing turbulent flow, which in turn restricts the cooling capability of the mold.
Re =(3160 ×Q / )( × ) n (14.1)
D
where:
Re = Reynolds number
Q = flow rate (GPM)
D = diameter of water line
n = kinematic viscosity of cooling medium
Re should be higher than 5000 to achieve turbulent flow.
14.3 Documentation
To provide a repeatable cooling process in injection molding it is important to doc-
ument the following items:
Water line layout. The water lines must always be connected in the same manner
for every mold run, or otherwise the cooling capabilities of the mold may be im-
pacted. Water line layouts must be clearly documented with in/outs, as well as
location and number of jumper loops. Hard plumbing all of the jumper loops on a
mold is a good way to provide consistent water hookup.
Water flow. The return flow should be documented for all cooling circuits on the
mold. Note that flow should be checked with all circuits open, not just the circuit
being evaluated. In some cases, people will check flow through an isolated cool-
ing line without opening the rest of the lines being fed from the TCU in question,
and the result is a much higher value because all water flow is diverted through
the one open line.
Water temperature in and out. The water temperature should be checked at the
inlet of each circuit as well as the outlet of each circuit. The industry standard as
taught by experts including RJG Inc and John Bozzelli is a maximum of 4 °F tem-
perature rise between the incoming and outgoing water. If the temperature rise
is higher than this the circuit should be reduced in length by breaking the circuit
into multiple circuits.
