Screw speed buys output and spends element life. The trick is knowing where the trade turns against you.
Tip speed rises with rpm. A faster flight drags more filler across the barrel wall, and the wall and the tip both wear faster.
The wear rate does not climb in a straight line. Below a certain tip speed, wear stays modest. Above it, wear climbs quickly, because the filler stays in the gap longer and cuts deeper.
Pick three speeds and run each for a fixed number of hours. Measure tip clearance before and after each run. Plot the loss against the hours.
Most lines show a knee in that curve. Below the knee you gain output cheaply. Above it you pay in elements and in barrel life.
A higher screw speed adds shear heat. When the melt temperature reaches the limit of the polymer, the extra speed buys output you cannot sell.
Check the melt temperature at the die, not at the barrel zone display. The die reading tells you what the product actually sees.
Look at the motor current against the rated value. A screw that runs near the limit has no room for a cold start or a filler change.
Leave margin for the worst day, not the best one.
A screw that outruns the downstream equipment creates a new problem. Check the pelletizer, the screen changer and the cooling line before you raise the setpoint.
Output that backs up at the die costs more than the speed gained.
Add the element cost to the power cost and divide by the tonnes produced. That number compares two running points honestly.
Many lines find their best point below the maximum speed. The extra tonnes cost more than they earn.
Keep a simple table: date, hours, speed, output, melt temperature, clearance. Six months of that table beats any simulation.
The gearbox sets a hard limit that no screw design changes. Check the service factor and the oil temperature before you run at a higher speed for a full campaign.
Oil that runs hot tells you the box works near its limit. Slow down and fix the cooling before you chase output.
The wear curve moves when the filler changes. A line that ran talc for years will wear differently on glass, and the curve you measured no longer applies.
Re-measure after a product change. Two data points are enough to see whether the knee moved.
A running point that works in winter can fail in a humid summer, when the polymer carries more moisture and the torque climbs.
Leave margin for the worst month. The best running point is the one you can hold all year.
We size elements for the speed range you actually run. Send the range and the filler, and we will pick a grade that holds up at the top of it.
We size elements for the running point you describe. Tell us the speed range, the filler and the target output, and we will suggest a grade and a geometry that hold up across that range.
