Flow lines are one of the most common processing issues faced by blown film extruders. There are many possible causes, but these are the four "usual suspects":
1) Color Changes
If going from a dark color to light or clear, color can hang up in negative flow areas.
2) Material Changes
If performing a resin change from one polymer to another a difference in viscosity can cause flow lines or gels.
3) Poor Preventative Maintenance
Over time polymer will degrade creating carbon (black specks). This carbon will hang up in areas and is difficult to remove.
4) Extended Shutdowns
Shutting down the line for extended periods of time will create carbon or contamination due to residence time and the cool down and heat up process.
Purging compounds help you address all of these causes and can dramatically improve your efficiency overnight.
Chemical purge compounds are heat activated. More heat = increased chemical activity = better cleaning. Chemical purge’s foam, creates steam and carbon dioxide. These reactions generate an internal turbulence that gets into negative flow areas and dead spots effectively. That combined with mild abrasives can effectively clean the system without the need to manually clean. When purging, it’s only necessary to raise heats in the areas where the problems are, commonly in the die. The rest of the system can be run at normal production temperatures.
The purge process has two components. The purge has to clean the machine and be easily removed. This is accomplished by matching viscosity of the carrier resin of the purge and production material being displaced.
Ready to reduce your production downtime to protect your profits? Learn more about how purging compounds and process efficiency work in tandem.
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