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Computer simulation of twin screw design.

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Topic: Computer simulation of twin screw design.

malikengg
Senior Member

Posts: 15
From:Mumbai, Maharashtra, India
Registered: Jul 2001

posted February 21, 2004 02:18 PM

I have designed contra-rotating twin screws 75mm size 28/1 L/D for LDPE foam extrusion.

I want to check the design for actual performance and output, etc. Can anyone help me out on this aspect?

Regards

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Tom C
Moderator

Posts: 293
From:Brodheadsville, PA USA
Registered: Jun 2001

posted February 21, 2004 10:29 PM

I am deeply involved in computer simulation of extrusion. To date I have not seen any software that deals with counter-rotating twin screws. There are some references in books on determining the carrying capacity of the trapped C shapped channels. Usually these extruders are processing PVC where the viscosity is very high, wall slip is present, and calendering is occuring in the gaps. Add to this the idea that PVC is more fused together rather creating a fluid melt and most find simulation a huge challange.

The 4 requests a year that I get for simulation on this type of extruder is not much of an incentive for anyone to create anything.

As a best guess from an outside observer the rules for design of these screws seems to be:

1) Volumetric compression from solid to melt of a little greater than bulk to melt density.
2) Thick strong flights.
3) The higher the viscosity, the more generous the gaps.
4) Restrict the flow if there is not enough melting.
5) Cut slots in flight tops if there is too much pressure, power consumption, or wear in a certain area.
6) Wide channels and long pitch under vents.
7) Wide flights and medium pitch for pumping.
8) Narrower flights and short pitch for melting.

All in all I wish you luck.

Tom C

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