PROCESS CONTROL EXAMPLE
Four IMRs are used to control a Plastic Injection Molding
Process. The raw material
(Thermo-Plastic Resin)
is contained
in a bulk storage bin and is removed and prepared for mold
injection by a screw feed. While the material is in the screw feed,
band heaters, placed around the screw barrel and controlled by
IMR RTD indicators, gradually melt the material. The
temperature of the material must be brought up to injection
temperature in three stages, 300, 400, and finally, 500 degrees.
Using the controlled relay outputs of three IMRs, the various
temperatures of the bands are controlled precisely. After the
material is injected into the mold, the mold temperature must fall
below 250 degrees before the mold can be opened and the part
removed. A fourth IMR is used to control actuators which open
the mold and eject the part and restart the molding cycle when the
mold temperature falls below the temperature threshold. After
the process is set-up and running properly, the indicators can be
programmed into the
“quick programming”
mode to allow
modification to setpoints and deadband only, if desired.
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