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Screw extruder

Posted by rammstein737 
Screw extruder
September 03, 2010 06:23AM
Hi all,

I have a screw extruder that's being used to make bone scaffolds. The nozzle that I have fixed to the bore at the outlet is of diameter 100 microns. I plan to replace it with one having 50 microns diameter. The material being used for extrusion is polycaprolactone (pcl). Should I have any problems like back flow due to the pressure exerted? If there are any problems, would a tapered screw extruder or a step screw extruder be better? Is it possible to show using finite element analysis or cfd, the possibilities of flow patterns in the extruder. What software should I use for this?

Thanks a lot! smiling smiley
VDX
Re: Screw extruder
September 03, 2010 07:42AM
... maybe 50 microns is to small to extrude confused smiley

I had difficulties with a nozzle with 60 ID and a paste with nearly the same viscosity like water eye rolling smiley

You need a really short tube (the 'friction' in the tube grows nearly exponentially with smaller diameters and length) and you will need much higher pressures than with 100 microns, so backflow could be a serious problem ...


Viktor
--------
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Call for the project "garbage-free seas" - [reprap.org]
Re: Screw extruder
September 03, 2010 09:49AM
hmm....yeah 50 micron is too small for the nozzle but then thats what i want. Since you're saying that back flow is a serious problem, would back flow reduce if i used a tapered screw extruder or a step screw extruder? Are there any other alternatives or use screw extruders of a different design?
VDX
Re: Screw extruder
September 03, 2010 03:48PM
... i estimate, that for extruding through a 50micron-nozzle you need more than 1000 bar pressure - some small comercial extruders apply until 1000bar for extruding ABS through nozzles down to 0.2mm eye popping smiley


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
Re: Screw extruder
September 05, 2010 02:43PM
oh..thats awesome! ....is it possible for you to share a website giving info about the above said extruder? or any pics? Thanks a ton!
VDX
Re: Screw extruder
September 05, 2010 04:21PM
... here is a link to a hand-extruder: [www.orbi-tech.de]

... used for hand-injection-moulding too: [www.orbi-tech.de]

Some other types were development in progress and i don't have links or further information ...


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
Re: Screw extruder
December 29, 2010 03:07PM
Bone scafolds? Out of shapelock material? I had no idea that was biocompatible
VDX
Re: Screw extruder
December 29, 2010 05:56PM
... with high pressures you can use arboform-materials or other biocompatible materials too ...

With SLS you can use lignin or ceramic dust - lignin is bio-degradable, ceramics for static inserts ... but with lime you can print/sinter bio-degradable ceramics too ...


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
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