A clean barrel protects the screw, the next product and your schedule. A careless purge does the opposite.
Polymer left in the barrel cools, shrinks and grips the flights. On the next start the screw works against that grip, and the torque climbs before the melt even forms.
Purge compound carries the old melt out and leaves an oily film on the steel. That film stops the next polymer from sticking to the flight tips.
Use a purge that matches your process temperature. A purge rated below your barrel temperature will not melt, and it will block the screw worse than the polymer did.
For glass-filled jobs, choose a purge with a mild abrasive filler. It lifts deposits off the flight lands. For clean polymers, a simple purging resin does the job.
Ask your supplier for the temperature window and the recommended dwell time. Follow both, because a short dwell leaves the dead spots untouched.
Keep the screw running at low speed. Raise the temperature a little above the normal setpoint, so the purge flows easily. Open the die area, so the material leaves without building pressure.
Feed the purge in slugs, not in one dump. A slug pushes the old melt ahead of it. A dump coats the screw and leaves the old melt in the gaps.
Look at the strand. When the colour and the surface stay even, the barrel runs clean. When you see streaks or gels, run another slug.
Do not judge by the clock. Judge by the strand.
A small slug cleans the screw and leaves the barrel wall untouched. Use enough purge to fill the channel twice over.
Weight is a better guide than volume. Check the barrel volume in the machine manual, then feed a little more than that in total.
Do not chase the purge with a high screw speed. Speed throws material through the barrel before it can lift the old film.
Keep the screw slow and the barrel hot. Let the compound sit in the mixing zone for a few minutes, then push it out.
The die holds more residue than the screw does on many lines. Pull the die and clean it by hand while the barrel purges.
Look at the flight tips once the barrel cools. A clean tip shows bare steel. A coated tip shows a film that will bake on during the next run.
Clean that film with a brass scraper, not with a grinder.
On a long stop, leave the barrel full of purge, not of production polymer. Purge releases from the steel far more easily than a filled compound does.
Turn the screw by hand before the next start. If it moves freely, the barrel stayed clean.
Write the purge grade, the temperature and the number of slugs in the shift log. After a few months you know which routine keeps your elements clean at the lowest cost.
A line that purges well uses fewer elements over a year. The saving hides in the parts budget, and the maintenance team rarely gets credit for it.
We supply elements that tolerate normal purging practice. Tell us the polymer and the purge grade you use, and we will match the surface finish and the grade to your routine.
