As companies cut costs, the ability to quickly shutdown or startup a line becomes more and more significant. In response to shifts in demand and general pressure to cut labor, many traditionally 24/7 extruders are now shutting down parts or all of their production over weekends. Most thermoplastic resins, when left in the barrel for even a short period of time, are likely to degrade and cause product contamination. Running engineering grades raises the likelihood of this occurring. Degradation will even occur if resin is left in the barrel when the heats are shut off – there is simply no effective way to cool that resin down quickly enough to avoid degradation (see ABS example below). To prevent contamination or deposit formation over a weekend or any extended shutdown (maintenance, lack of orders, etc...), use a purging compound to clean and seal your extruders.
To seal an extruder with a purging agent, first purge out the production resin. Increase die temperatures, while staying within the safe operating range. Wipe out the hopper and remove the screen pack if using a glass filled grade. Using a thermally stable purge compound, purge the extruder (per the instructions above) until the purge pile is free of contamination and previous resin. Once clean, slow the screw down to make sure the flights are as full as possible. Then, shut the heats off. When ready to start back up, turn the heats on and purge the purging agent out with the next production resin.