A manufacturing engineer from an extrusion blow molding plant reached out to me to help him work on a project. His goal was to speed up their shutdown process on a specific machine. He felt it was taking way too long for how frequent this line was shutdown.
He told me they had experimented with commercial purge compounds over the years. Unfortunately, these compounds were unproductive and delivered no benefit. Based on these past experiences, there was a lot of skepticism regarding purging compounds at this particular plant. They decided that the most fruitful and useful method was to use a cheap, thermally stable resin. This was not the best choice.
To obtain a clearer understanding as to why their shutdown process was drawn-out and how to make them swifter, we collaborated with each other in depth over numerous months and thoroughly investigated what their processing, purging, and shutdown conditions were. We considered factors such as production/purge material melt indices and normal processing/purge temperatures for both the barrel/screw and accumulator head, just to mention a couple.
To help this engineer facilitate faster shutdowns, I recommended four simple, yet effective, steps:
- 1.) Use a heat-activated, chemical purge compound to displace the production material from the machine faster.
- 2.) Elevate the processing temperatures to between 500Fº to 550Fº in all heat profiles zones, to optimize the chemical and foaming activity of the purge.
- 3.) Contain the purge in the entire system (barrel/screw and accumulator head) with the screw turning at slow RPM for a heat soak of 30 minutes, so that growth of it would occur and enable it to get into low-pressure areas.
- 4.) Completely empty the purge from the system, kill the heats and then go home for the weekend.
The engineer reported that the shutdown process went well after the preliminary trial run. These modest changed reduced shutdown time by 25%. It seems as though their shutdown process advanced to some extent. I have high confidence, with a little more practice, overtime it will get even faster for him.
Learn more about improving your purging process with proper procedures.
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