posted June 06, 2001 09:05 PM            

quote:

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Originally posted by wiseguynj:
Running a 4/2" 32:1 DS with RRVC powder have material coming out of the vent, it has never happened before, have any idea what is going on?

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The simple answer is a higher pressure in the discharge section of the screw. The complicated answer depends on what you find caused that!

posted July 01, 2001 06:32 PM               

A few more thoughts to throw "in the hopper"
In running RPVC, depending on die opening (i.e thin or thick walled pipe), and orifice opening in adapter,I'd first want to know my exit melt temperature.If it's on the high side of 400F, NEXT string-up would call for a larger orifice insert. I would first play with screw oil temp.--increasing to equal or slightly above metering zone temp., to try to reduce melt viscosity and lower front end and head pressures, allowing faster flow through head and die, which should relieve vent flow.
You may have to lower crammer speed some while these adjustments are going on, then you can increase crammer to just below vent flow to maximize output rates.
Having said all of this, I'm assuming your formulation is well balanced to your extruder (lube balance,process aid, etc.?)
Also, if this "never happened before", were any blending room mistakes sent to your silo?? I highly recommend a Brabender fusion/stability curve be run--not on EVERY batch out of the mixer, but at least six or eight times during an eight hour shift!

Regards,
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