Page 100 - Injection Molding Advanced Troubleshooting Guide
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9.2 Keys to Drying 85
An inactive desiccant should be replaced in the dryer because it will not ob-
tain an adequate dew point with a bad desiccant.
9.2.3 Air Flow
Poor air flow can come from the following issues:
Plugged filters restricting the air flow:
All dryer filters must be kept clean. Do not run dryers without filters or the des-
iccant bed will become contaminated and not be capable of achieving adequate
dew points.
Feed hoses can become crushed, which restricts the air flow. Verify that all hoses
are free of crushed areas and holes.
Too small of a dryer for the drying hopper:
Dryers are measured in cubic feet per minute (CFM) of airflow. If the dryer is
undersized relative to the hopper there will not be enough air movement in the
hopper to effectively reach much of the material.
A burned-out blower will result in no air flow. Check that the blower is running
and has not burned out. Verify that the dryer is not wired with reverse polarity
or the blower will run backwards.
Most modern dryers will alarm if the airflow is inadequate. Do not make a habit
out of silencing alarms on equipment: It is ringing to tell you something.
9.2.4 Time
Lack of drying time typically comes from the following:
Simply starting up the machine prior to the required amount of drying time:
This is a plant discipline issue, and processors must know that the material has
had adequate residence before starting the press.
Allowing hoppers to run down before filling them:
If they run too low you will have material that has not dried long enough. This is
also a plant discipline issue. Material handlers cannot be allowed to let hopper
volumes run down.
Material flow:
Molding expert John Bozzelli has conducted studies that show that some dryer
designs will tend to have a “rat hole” flow where the center pellets travel much
faster than the outer pellets in the hopper [1]. This is a hopper design problem
