I was recently in a plant technically supporting a chemical purge trial in a very large sheet extrusion system. The system had two extruders, breaker plate, screen packs, extensive downstream plumbing, static mixer, melt pump, and an adapter with a 60” die.
They were struggling with contamination issues. The line had not been torn down and cleaned in some time. Degraded, carbonized polymer was consistent throughout the line. We decided to try a chemical purge to eliminate the contamination then begin a preventative maintenance program to maintain it.
Chemical purges are heat activated. More heat = increased chemical activity = better cleaning. We were conducting the purge at 545F. Procedures can differ between purge manufacturers but for the most part, you can run the purge at normal processing speed until it emerges uniformly from the die reaching the outer edges. The RPM’s on the extruder are then minimized to a safe controllable level reducing the amount of purge compound necessary for cleaning. That starts the clock on a soak cycle which can last from 10-30 minutes.
We noticed at normal processing speed there was a great deal of chemical activity from the purge when leaving the die. After slowing it down, the reaction decreased. The distance from the extruders to the die was extensive. The increased dwell or residence time was using up the chemical activity of the purge material.
Once we increased the RPM’s on the extruders to where we had consistent chemical activity again, we soaked for 20 minutes and cleaned the system effectively.
Ready to reduce your production downtime to protect your profits? Learn more about how purging compounds and process efficiency work in tandem.