6.Determine the desired additive feeder setpoint (% of extruder (master) screw RPM). To determine this, you must know:
•Total extruder feedrate (lbs./hr.).
•The RPM of the extruder screw at that feedrate.
•The letdown ratio of the additive (% or :).
•The additive feedrate required at that letdown ratio (total feedrate X letdown ratio).
•The additive feedrate RPM needed to achieve this feedrate (as determined by the calibration procedure).
Extruder Tracking Equation:
Set Point = (rpm of feeder / rpm of extruder) x 100
Example:
Total extruder feedrate = 500 pounds per hour Extruder screw rpm for 500 lbs/hr = 50 rpm Additive letdown percentage = 7% Additive feedrate = 500 X 0.07 = 35 lbs./hr.
Feeder auger rpm needed for 35 lbs./hr. = 44 rpm (as the calibration procedure has shown)
Assuming this, set point = 44 rpm/50 rpm x 100 = 88 or 88% of the extruder screw speed.
Additive Feeders | Chapter 4: Operation | 27 of 50 |
