Posts: 4
From:
Registered: May 2002

posted May 30, 2002 06:50 PM               

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We produce vertical blinds using rigid PVC in powder and aren't pretty sure to use the convenient screw type. We have 3 1/2" (90mm) and 2 1/2" extruders with L/D 24:1.Just for the record: four months ago we were using PVC in pellet but due to a cost reduction strategy we decided to use "made in home" powder. Any help or comments will be higly appreciate.

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Posts: 111
From:Silver City, NM, USA
Registered: Jun 2001

posted June 04, 2002 04:02 PM               

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When going from pellets to powder blend, you
really need a vented barrel in order to pull a good vacuum---along with a two-stage screw
comprising these zones: feed,compression before the vent,
decompression at the vent, and metering with a 3:1 compression ratio. Also, a vertical crammer feeder in the hopper to assure uniform pressure on the feed zone to maintain good output rates.

Skip

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Posts: 4
From:
Registered: May 2002

posted June 05, 2002 11:33 AM               

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Thanks for your response. I think that we have a bigger issue than it looks like. We have only single screw barrier design extruders with non vented barrel. Do you think that a two-stage screw is our best option? What can we do if our barrels donīt have the vent?

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Posts: 386
From:Christchurch,New Zealand
Registered: Jun 2001

posted June 05, 2002 03:12 PM               

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Hi Beto

You are faced with a number of problems.

A vented barrel is normally 28:1 LD (or longer), with a 24:1 Barrel, I don't think you're going to get a two stage screw to work acceptably. You could get a new barrel and screw made (28:1)- but you would also need new heater bands/cooling fins cast up.

A cheaper option would be to hunt up a good second hand vented extruder.

Steve H

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Posts: 4
From:
Registered: May 2002

posted June 05, 2002 04:45 PM               

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Thank you for your time Steve. I have some questions related with this: Do you think that we really need a 28:1 L/D extruder to process succesfully PVC rigid(powder)? or Can we use our 24:1 L/D non vented extruders to do that along with another screw design? At this moment we have barrier screws with maddock mixing section.

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Posts: 386
From:Christchurch,New Zealand
Registered: Jun 2001

posted June 06, 2002 04:27 AM               

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Hi Beto

Skip is the guru on PVC extrusion- Another problem with powder, is that it is corrosive.

I don't think you're going to be able to satisfactorily extrude it on a 24LD machine, without a vent. What has your material supplier recommended?

Steve H

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Posts: 4
From:
Registered: May 2002

posted June 06, 2002 11:26 AM               

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Hi Steve

In fact, we supply the material to ourselves. Let me explain this: Besides the vertical blinds, we produce custom profiles (windows, forniture, folding doors, etc.)and RBS constructing system. We handle a huge quantity of rigid PVC powder to produce them and because of this, we decided to install a compound plant in our facilities 4 years ago(we use twin screw Amut extruders to process powder). And as you can see, this year we decided to use powder instead of pellet in our vertical blind production. That's the reason why we are looking around for help, information or suggestions.

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Posts: 386
From:Christchurch,New Zealand
Registered: Jun 2001

posted June 07, 2002 04:11 AM               

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Hi Beto

Posibily you might get powder working if you
could enclose the feed hopper and pull a vacuum on it- It would be pretty messy though.

You'd have to ensure the screw shank was sealed- I'd look at getting a vented extruder if the volume of work makes it worthwhile.

Good luck and let us know how you get on.

Steve h

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