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  double venting extruder.

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Author Topic:   double venting extruder.
Guy S
Member

Posts: 2
From:Israel
Registered: Feb 2005

posted February 14, 2005 02:47 PM     Click Here to See the Profile for Guy S   Click Here to Email Guy S     Edit/Delete Message   Reply w/Quote
I produce optical quality PMMA and PC sheet.
To reach this high quality we are not applying any pre-drying to avoid contamination coming from the dryer (even filtered).
This limits our capacity by the efficiency of the vacuum venting. (We are getting 550-600 kg/h from 150mm extruder).
I’m looking for a new extruder now, and in order to increase capacity, again without pre-drying, I was advised to look for a double venting extruder.
What is your opinion about it, any comments or ideas?

Thanks, Guy

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Tom C
Moderator

Posts: 460
From:Brodheadsville, PA USA
Registered: Jun 2001

posted February 14, 2005 02:51 PM     Click Here to See the Profile for Tom C   Click Here to Email Tom C     Edit/Delete Message   Reply w/Quote
Guy,

What is happening when you exceed the vent's capacity?

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Best Regards,

Tom Cunningham

Extrusion Technical Services

www.ExtrusionTechnicalServices.com

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Guy S
Member

Posts: 2
From:Israel
Registered: Feb 2005

posted February 14, 2005 02:59 PM     Click Here to See the Profile for Guy S   Click Here to Email Guy S     Edit/Delete Message   Reply w/Quote

Hi Tom, thanks for your fast replay.
Normally if I will exceed this capacity, bubbles will appear in the melt.

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Tom C
Moderator

Posts: 460
From:Brodheadsville, PA USA
Registered: Jun 2001

posted February 14, 2005 04:50 PM     Click Here to See the Profile for Tom C   Click Here to Email Tom C     Edit/Delete Message   Reply w/Quote
Guy,

Without knowing the screw design involved, it is a safe bet that an additional vent will help. However given that you are processing viscous resins I would not expect a great deal more output from your extruder before you begin to expereience problems with excessive melt temperature. Additonally another vent will lengthen the extruder using up power and further heating the melt.

If you are not already using a vacuum vent setup, that would be a good thing to try first.

Another issue with vents is buildup on the screw in those area due to the lack of scrubbing forces. With two vent you are twice as likely to expereince sudden bursts of yellow and burned material.

------------------
Best Regards,

Tom Cunningham

Extrusion Technical Services

www.ExtrusionTechnicalServices.com

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