Alternate Extruders
Posted by pbreed
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Alternate Extruders March 02, 2012 07:01PM |
Registered: 12 years ago Posts: 4 |
I was wondering about some alternate extruder designs...
Can the plastics used (ABS and PFA) stay molten for a long time?
IE can one melt a bunch of cheap plastic pellets and then extrude with a positive displacment pump rather than a filiment?
In the present extruder designs is the plastic fully molten or is it just soft when extruded?
Does the software running the nozzle PID loop take any feed forward information on the amount of fiber being extruded to add the energy for the plastic heat of fusion to the nozzle? (I think this would give better temp control)
Has anyone ever built a functioning pellet extruder?
Has anyone ever put a needle valve in the tip of the extruder to positivly shut off the flow for no strings?
Can the plastics used (ABS and PFA) stay molten for a long time?
IE can one melt a bunch of cheap plastic pellets and then extrude with a positive displacment pump rather than a filiment?
In the present extruder designs is the plastic fully molten or is it just soft when extruded?
Does the software running the nozzle PID loop take any feed forward information on the amount of fiber being extruded to add the energy for the plastic heat of fusion to the nozzle? (I think this would give better temp control)
Has anyone ever built a functioning pellet extruder?
Has anyone ever put a needle valve in the tip of the extruder to positivly shut off the flow for no strings?
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Re: Alternate Extruders March 02, 2012 08:08PM |
Admin Registered: 17 years ago Posts: 7,879 |
pbreed Wrote:
-------------------------------------------------------
> I was wondering about some alternate extruder
> designs...
>
>
> Can the plastics used (ABS and PFA) stay molten
> for a long time?
No it starts to degrade at the temperatures we use if you leave it molten for minutes rather than seconds. For example it will start to go brown.
> IE can one melt a bunch of cheap plastic pellets
> and then extrude with a positive displacment pump
> rather than a filiment?
Pellets can be extruded with an Archimedes screw pump.
>
> In the present extruder designs is the plastic
> fully molten or is it just soft when extruded?
They are viscous, paste like substances at the temperatures we use. PLA can become syrup like a little hotter but that does not produce good objects because it doesn't hold its shape.
>
> Does the software running the nozzle PID loop take
> any feed forward information on the amount of
> fiber being extruded to add the energy for the
> plastic heat of fusion to the nozzle? (I think
> this would give better temp control)
No but temperature control of the heater is not a problem as long as the heater is powerful enough for the flow rate. The plastic will come out cooler as flow increases though because it doesn't have as much time to heat up as it passes through. The feedback loop controls the temperature of the walls of the melt chamber, rather than the plastic exiting the nozzle.
>
> Has anyone ever built a functioning pellet
> extruder?
Yes someone in the German forums has made one. It was relatively big and heavy compared to filament extruders.
>
> Has anyone ever put a needle valve in the tip of
> the extruder to positivly shut off the flow for no
> strings?
Yes one was made with Piano wire and a solenoid. It was later found to be not necessary as simply reversing the feed a millimetre or two stops strings.
Edited 1 time(s). Last edit at 03/02/2012 08:11PM by nophead.
[www.hydraraptor.blogspot.com]
-------------------------------------------------------
> I was wondering about some alternate extruder
> designs...
>
>
> Can the plastics used (ABS and PFA) stay molten
> for a long time?
No it starts to degrade at the temperatures we use if you leave it molten for minutes rather than seconds. For example it will start to go brown.
> IE can one melt a bunch of cheap plastic pellets
> and then extrude with a positive displacment pump
> rather than a filiment?
Pellets can be extruded with an Archimedes screw pump.
>
> In the present extruder designs is the plastic
> fully molten or is it just soft when extruded?
They are viscous, paste like substances at the temperatures we use. PLA can become syrup like a little hotter but that does not produce good objects because it doesn't hold its shape.
>
> Does the software running the nozzle PID loop take
> any feed forward information on the amount of
> fiber being extruded to add the energy for the
> plastic heat of fusion to the nozzle? (I think
> this would give better temp control)
No but temperature control of the heater is not a problem as long as the heater is powerful enough for the flow rate. The plastic will come out cooler as flow increases though because it doesn't have as much time to heat up as it passes through. The feedback loop controls the temperature of the walls of the melt chamber, rather than the plastic exiting the nozzle.
>
> Has anyone ever built a functioning pellet
> extruder?
Yes someone in the German forums has made one. It was relatively big and heavy compared to filament extruders.
>
> Has anyone ever put a needle valve in the tip of
> the extruder to positivly shut off the flow for no
> strings?
Yes one was made with Piano wire and a solenoid. It was later found to be not necessary as simply reversing the feed a millimetre or two stops strings.
Edited 1 time(s). Last edit at 03/02/2012 08:11PM by nophead.
[www.hydraraptor.blogspot.com]
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