20
4–3 Heat-Cool Control
A
n injection mold is required to be controlled at 120°C to ensure
a consistent quality for the parts. An oil pipe is buried in the mold.
Since plastics are injected at a higher temperature (e.g., 250°C),
the circulation oil needs to be cooled as its temperature rises.
Here is an example:
The PID heat-cool is used for the example at left. To
achieve this, set the following parameters in the setup
menu:
INPT=PT.DN
UNIT=°C
DP= 1-DP
OUT1=REVR
O1TY=RELY
CYC1=18.0 (sec.)
O1FT=0.0
OUT2=COOL
O2TY=4–20
O2FT=BPLS
Set SV at 120.0°C, CPB at 125(%) and DB at -4.0(%).
Apply auto-tuning at 120°C for a new system to get
optimal PID values. See section 3-11.
Adjustment of CPB is related to the cooling medium
used. If water is used as the cooling medium instead
of oil, the CPB should be set at 250(%). If air is used
as the cooling medium instead of oil, the CPB should
be set at 100(%).
The adjustment of DB is dependent on the system
requirements. A higher positive value of DB will pre-
vent unwanted cooling action, but will increase the
temperature overshoot, while a lower negative value
of DB will result in less temperature overshoot, but
will increase unwanted cooling action.
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