What are the steps in the production process that factories that produce filament have to take to get from pellets to a full spool of filament.
Which of these steps are critical for quality (thickness, roundness, long shelf life,..) ?
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$\begingroup$ You are asking for a full description of the entire process from pellet to filament and including another question on top of that. I am voting to close this question as "too broad". (And note that whether it is on-topic is questionable; "at home" filament production would be on-topic, but should professional plastic processing be on topic as well?) $\endgroup$– Tom van der ZandenApr 3, 2016 at 6:58
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$\begingroup$ I think it is interesting for "at home" filament production to know how the factory is doing it. That might explain differences in quality and might give ideas of how to improve the "at home" process. The "on top" question is just saying that I want more than "Heat up pellets until they melt. Then push the molten plastic through a nozzle and let the result cool, then wind it on a spool". If you feel that you can't describe the whole process then only describe the steps that you know. Others might now the other steps. I don't see a way to split this question to narrow it down. $\endgroup$– Lars PötterApr 3, 2016 at 15:56
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$\begingroup$ I noticed that your question has not had much activity lately, are you still looking for an answer to this question? How might we be able to close some gaps? $\endgroup$– tbm0115Jul 3, 2016 at 20:21
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$\begingroup$ Yes I'm sill interested in the details of the process. Do you have Ideas of how we could improve the situation? $\endgroup$– Lars PötterJul 5, 2016 at 17:54
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$\begingroup$ @LarsPötter Sorry for the delay, I never received a notification of your response. It's tough to say what you can improve in your question, except to maybe highlight how the current answers do not fully answer your question. (If you ping me with '@[UserName]' I'll get a notification when you respond) $\endgroup$– tbm0115Feb 27, 2017 at 16:04
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3 Answers
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Some general comments about the process used (plastic extrusion):
The plastic extrusion process is not simple- many textbooks dense with equations have been written about it. The lowest cost industrial extrusion processes do not use pellets at all- because pellets have already gone through an extrusion process so they are more expensive than powder resin. There is typically a 'compounding' stage where colors etc. are added before extrusion.
Significant heat is generated by the screw (which often has a complex geometry) via shear action that is itself temperature and pressure sensitive, and the heat is added to by external heaters in various zones (or subtracted by water cooling and chillers in larger extruders). In some cases we were able to operate an extruder adiabatically- the heat created by the screw motor matched the heat loss as the product left the die and no heating or cooling was needed once the process was stabilized.
The end result is that you want to plasticize (melt) the plastic and achieve a certain pressure at the die. The plastic is deteriorating the higher the temperature and the longer the time so you want to limit the residence time at high temperature. There is some trial-and-error and a lot of previous experience in the setup person's task. Once the parameters are determined they are recorded and are used the next time that material is run.
The size of an extrusion is typically determined exactly by downstream equipment rather than controlling the conditions at the die. It is essentially stretched as it comes out of the die and the heat is removed in a cooling trough.
Here you can see a factory environment with a very typical extrusion setup, used in this case for 3D printing filament (but the setup would look almost the same if they were making slats for Venetian blinds). Notice that there are cooling fans as well as band heaters on the extruder barrel. They control the diameter by adjusting the take-off capstan RPM once the extruder is running well. This extruder looks like it has 4 heat/cool barrel zones and two (heat-only) nozzle zones (6 temperatures total).
https://www.youtube.com/watch?v=40HOAsUnSQ8
Extruders are categorized by the barrel bore diameter in inches or mm. A very small extruder might be 25mm. An extruder used for pipe production might be 6" (150mm) or more. Some machines use multiple screws.
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I do my own filaments and its pretty simple. The real key for quality is stability of everything. The temperature, the movement of the air around cooling part, the extrusion force, both internal and external. It is funny to watch how I have several atm pressure inside my extruder, yet the gust of wind outside the room changes the outside pressure enough to affect filament.
Yet I manage to keep my tolerances +- 0.05 mm which is enough for everything but miniature printing.
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$\begingroup$ Can you clarify what you mean by miniature printing? Do you mean printing miniature objects (what qualifies as miniature)? Or do you mean printing miniatures (as in table-top minis for gaming)? $\endgroup$ Jan 26, 2017 at 16:43
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Each step is critical for quality. It's refined plastic mass. And in oil-based-products, every step is crucial for quality.
In this vieo, everything is explained.
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$\begingroup$ I don't think that it explains everything! In the video he explains that is was hard to figure out the right temperatures for the 4 different temperature zones in his Filament making machine. Why 4 temperature zones? What are the right temperatures? $\endgroup$ Apr 16, 2016 at 14:38
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$\begingroup$ @JosipIvic it is typically best-practice to provide additional details related to the content within the links you provide. This is recommended to avoid issues with "link rot" $\endgroup$– tbm0115Sep 28, 2016 at 14:03