I recently visited a prospect who produces cast films from 0.003” to 0.025” in various resins and colors including R-PVC, PMMA & PC from a 34” hangar die and a 3.5” diameter screw. They called me with a problem. It takes several hours to tear the extruder apart and then split the die to remove the previous color, carbon and resin.
This is a laborious task to say the least, which requires a technician to loosen several large bolts while the die temperature is still at 400-500ºf. Once all the bolts are removed, he has to turn the die and split it to clean out said material. Then he reverses the process and get the die ready for the next run. This blog will hopefully help those having similar issues to simplify their process.
- 1) Choose the proper purge compound for the resin being processed. In this case I chose Asaclean NCT as the R-PVC resin had a durometer of 84.
- 2) The R-PVC was running 400ºf. Flush out the R-PVC with a flush resin HDP.
- 3) Raise the heats on all equipment from the end of the extruder through to the die to 500º. This temperature will help with carbon removal as well).
- 4) Start extruding the NCT through the system at a fast rate in order to fill out the hangar all the way to the ends of the die
- 5) When you are extruding a fairly uniform sheet of purge, reduce RPMs to 5-8 RPMs and allow the purge to soak with the screw slowly turning for 20-30 minutes.
- 6) Once the soak time is complete, run out the remainder of purge
- 7) Raise or lower your heats to the next production resin and flush the remainder of the purge from your system
Once you complete step 7, the machine and die are now clean and there is no need to split the die to clean it.
This prospect (turned customer) has saved a tremendous amount of time and money not having to split the dies anymore for cleaning and now has more up time to produce salable product. That is not even including reducing the wear and tear on the machine. If you are struggling in cast film, consider this approach and learn how to make your life easier.
Learn about the importance of implementing proper purging procedures by downloading this free industry guide.