Aftercooler: Inside each DMZ there is an aftercooler for the process air. The
aftercooler serves several purposes. First and foremost, it protects the desiccant
rotor by catching any small fines that may get past the process filter and build up
in the rotor. It also condenses any gases that may be given off during the heating
of the plastic pellets. The Aftercooler begins to cool the moist process air before
it goes through the desiccant rotor, to help the air “give up” the moisture to the
desiccant. Inadequate water flow to the aftercooler may result in a higher dew
point and poor drying conditions. In addition, it cools down the hot air moving
through the process blower, which will help increase the life-span of bearings,
motor, etc.
Thermocouple: The thermocouple, simply stated acts like a thermometer and
senses the temperature of the air flowing through either the regeneration heater,
or the process heater. The thermocouple reports the temperature to the unit
controller. If the Process temp is set for 200° F, and the thermocouple is either
misadjusted or broken, two results can occur: First, if the temperature in the
hopper is too low, moisture will not be removed from the plastic pellets. Likewise,
if the temperature is too high, a melt down inside the hopper can occur. A
properly adjusted thermocouple is important to insure proper drying.
Magnetic Contactors: magnetic contactors are the “switches” that turn the
heaters and blowers on and off, following the commands of the temperature
controller. These contactors are generally good for 1 million on / off cycles. This
means if a dryer is running 24 hours 7 days a week, the heater contactors will
last about 9 months. The blower contactors last considerably longer, as once the
blower is on, the contactor is not cycling on and off. The constant on / off action
is what wears out a contactor. Watching the heater contactors is especially
important because if one or more legs of the contactors burn out, eventually, the
corresponding heater will burn out. Contactors are cheaper than heaters.
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