Screw extruder

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!

... maybe 50 microns is to small to extrude

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

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 ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

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?

... 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

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

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!

... 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 ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Bone scafolds? Out of shapelock material? I had no idea that was biocompatible

... 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 ...

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Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]