1 Topic by lorenzo.chiodi

  • lorenzo.chiodi
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Topic: Optimizing PCL and PVP Extrusion

Hello this is my first post but hopefully I can find some help with a project I am working on. So I am currently extruding PCL with my filastruder and had a few questions which someone can hopefully direct me to some solutions.

So I started a new internship and project which is pretty new to me on 3D printing which I am in charge of looking into extruding customized filaments which can be 3D printed using a rep-rap requiring a 1.75mm filament. I successfully got the filastruder built and working but am still working on putting together the filawinder. The filawinder I read is pivotal to getting the correct diameter filament but wanted to make sure that I can optimize the system for other plastics/materials as well. I purchased the PCL separately in pellet form and it extrudes but not the best quality. I have not tried the PVP yet but I know it will definitely vary greatly in melt temp since it is in a powder form.

What is the best/easiest way to measure the 'dead volume' or waste of the materials in the filustruder?

PCL
PCL supposedly has a melt temp of 58-60C which I can confirm with the use of a digital infrared thermometer that reads just about the same temp when aimed at the nozzle.
My concerns:
1.) The filament extruded looks to be under a high amount of stress (I can see and feel the ridges and grains) but I am not sure if it is because of the leadscrew's rpm or if caused by the general material props. of PCL associated with shrinkage.
2.) PCL has a very high limit on its melting point (I believe around 220C) but I have set the temperature value on the PID to 120-140C.
3.) If I change the current(staying under 2.6A) to provide higher rpms and a faster flow rate, should I change my set temp to accommodate the change in feed speed?
4.) I have not successfully extruded 1.75 filament yet due to the filawinder not finished but will I have an issue with diameter size if my filament is already experiencing what looks like shrink?
5.) Is there a way to wire the filawinder directly to the filastruder so they can work together and send information back and forth?
6.) The temperature of the resin coming from the extruder tip is around 100C which when hanging and spooling onto the ground seems to cause the PCL to stretch/move under the tensional stress of its own weight under gravity so is this a clear indicator that the temp is too high?
7.) The set temp was 140C, the temp measured on the nozzle was varying from 50-61C, but the PID temp display was reading around 28C when I turned the motor on. I do not have the thermocouple attached (although I am planning on using Kapton tape) but resting in its recess which is I would say situated at 11 o'clock relative to the face of the nozzle. The temp now has been bouncing a bit on the PID reading and I'm realizing how sensitive it really is by the difference when moving the insulation further around the nozzle. Is this variance in the PID temp reading and measured nozzle temp detrimental to continual testing?

PVP
7.) What precautions should I take when switching from the PCL pellets to the PVP powder? Aside from the lower melting point and adjustment to the set temp, do I have to disassemble the extruder from the housing and rinse it with acetone or is there a much simpler and quicker process?

Lastly, the thermocouple supplied only fits halfway down into the recess hole on the nozzle so it clearly is being disrupted by ambient temp. Is it alright just to install another thermocouple such as one from another rep-rap I had? Also, with the issue of PCL sometimes having an issue melting soon enough in the barrel, would adding a layer of thermo conductive material between the barrel and insulation help that much? Could I just install another heater in the beginning zone closer to the hopper so as to provide evenly distributed heat throughout the barrel?

This is a good amount of questions but seeing or in this case not seeing an abundant amount of similar material being tested is why I am posting here to helpfully provide others extruding PCL or PVP. Thanks everyone.

2 Reply by elmoret

  • elmoret
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Re: Optimizing PCL and PVP Extrusion

One of our customers extruded PCL and had this to say:

.I was able extrude PCl (with a good finish) after many iterations with regards to the optimum temperature required. The ideal temperature is 85 DegC.
 
Do not let the filament fall a great height just after extrusion as shown in one of the testimonials with ABS ( Its own weight turns out enough to reduce the diameter of the filament; PCL having a really low yielding point).In my case it reduced to 1.4mm(with a die of 1.75mm).

As for your questions:

1.) Are you sure the polymer is properly dried/dehydrated? How was it dried?
3.) 2.6A is already too high. Perhaps you meant 1.6A?
4.) You can drill out the nozzle size if experiencing too small of an average diameter.
5.) They already "share information", in that the laser sensor tracks how fast the extrusion is and adjusts the uptake spool in order to keep the loop height constant. What other information are you looking to exchange?
6.) Yes. Most people extruder PCL at more like 85C.
7.) Yes, the variance is detrimental. The thermocouple should secured with Kapton tape as described in the instructions.

7.) Disassembly should not be needed, just run until empty, add new pellets, run again. During the purging time, the temperature should be set to the higher of the two materials extrusion temperatures

The thermocouple hole should only be a quarter of the diameter of the nozzle face, so it is normal not to go all the way in. But you are welcome to post a photo if you like and I can comment about it.

Filastruder - the robust, inexpensive filament extruder
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3 Reply by lorenzo.chiodi

  • lorenzo.chiodi
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Re: Optimizing PCL and PVP Extrusion

Hello elmoster, thanks for the quick response.

1.) I am not sure that it was even dried properly when it was sent over but definitely not since it was received. What is the best way to dehydrate/dry the pellets and how would you do so on the powder PVP?
3.) Yes you are right I meant 1.6A but it brings me to my next question of, if the current is ramped up therefore producing more force and heavier shear through the lead screw, would the particle size/particle conglomerates be lessened with the increase of shear force?
4.) Alright but that is a last resort sort of thing.
5.) Not sure if any other information would help except for filament diameter.
6.) Tested 85 works but still unsure because of the lack of Kapton which when the main power is on the system heats to around 60 and immediately when I turn the motor on the temperature readout it bounces around jumping to 160+. Which obviously is caused not only by the lack of insulation of the thermocouple but also assuming that the original auto calibration was done with a faulty/imperfect thermocouple placement.
7.) I will secure the thermocouple, I noticed some burn resin on the face of the nozzle though and some build-up around it which im afraid might give further inaccurate readings if the 'crud' made its way into the thermocouple recess.

Further arising questions:
1.) The dead volume inside the chamber should be the same for all material? as long as the materials are extruded at their respective flow temps?

4 Reply by elmoret

  • elmoret
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Re: Optimizing PCL and PVP Extrusion

1.) Most people use a food dehydrator. Moisture in the polymer will make quality extrusion difficult.
3.) I'm not sure what you mean about lessening particle size? The current draw of the motor is a function of how much load there is on the motor, not the particle size.
5.) The Filawinder can't measure filament diameter and even if it could, what action would the Filastruder take? By the time the diameter is measured, it is too late to change anything at the extruder. An extruder, even in an industrial process, is run at a constant speed in order to produce relatively constant melt pressure. Attempting to change speed or temperature on the fly is not a good control scheme for tightening filament diameter tolerance.
6.) The temperature measurement shouldn't bounce around. I'd recommend checking the thermocouple cable for damage, or for a bad connection.

If you're referring to the space between the tip of the auger and the internal face of the nozzle, yes, generally that is left constant. It might be possible to realize some benefits by tweaking to the material but it is not worth the effort in my experience.

Filastruder - the robust, inexpensive filament extruder
E3Dv6 All Metal Hotend - the premier 3D printing hotend

5 Reply by lorenzo.chiodi

  • lorenzo.chiodi
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Re: Optimizing PCL and PVP Extrusion

What I meant by lessening the particle size is say I introduce a secondary polymer to the batch which is much smaller particle size than that of the first polymer you would see conglomerates of the second polymer surrounding particles made of the first polymer's. Pretty much just breaking down the polymer and intermolecular connections that bind them together. My thought process was that if the current can be set with the dial on the back of the stall protection board then in turn the load on the motor can be changed. Changing the load on the motor should change the speed or also the force of the lead screw on the resin which would increase the friction between the screw hence further breaking down the material inside the extruder's barrel. But I could very well be 100% wrong too lol.

6 Reply by elmoret

  • elmoret
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Re: Optimizing PCL and PVP Extrusion

It sounds like you're talking about mixing. The Filastruder does an OK, not great job of mixing owing to its feedscrew being an auger bit. A custom feedscrew can have better mixing characteristics but would cost more $500+.

Changing the current limit doesn't change the motor load.

Think of the current limit like a weight limit for employees in a factory. They can lift boxes up until 50 pounds, for example. If a box s 5 pounds or 50 pounds, the employee will lift it.

If you tell the employees not to lift anything over 25lbs, that doesn't change the weight of the boxes.

The stall protection board is just like a factory supervisor that says not to try to lift anything with more than 50 pounds of force (or in this case, about 12 N-m of torque)

Filastruder - the robust, inexpensive filament extruder
E3Dv6 All Metal Hotend - the premier 3D printing hotend