BBL PA-CF is ferrous?

Bambu Filament and Accesories Filament
21

Wait, so this happened with both samples of PA-CF from eSun and Bambu?

TF is going on?!

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Have you tried it with fresh filament still on the spool?

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I hadn’t, but I did. It is a very weak attraction. pic taken from underneath as it won’t hold if there is any shear force.

IMG_20230531_204347
IMG_20230531_2043471480×1110 130 KB

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See? You all thought I was crazy.:slight_smile:

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25

Super interesting! I have some Bambu PA-CF and Polymaker PA6-CF on hand, neither the raw filament nor the printed parts show any sign of ferromagnetism

26

OK…I came into this thinking that the OP was full of it (sorry). But what the hell? I just tried with a printed piece and a 4" stack of neodymium magnets (read: strong magnetic field) and the attraction is strong enough that the piece will jump about .5" off of the table to the magnets and hold there. I can also feel the attraction on the raw filament (on the spool), though it seems a bit weaker.

Not static - the pieces I was testing with have been around for a while, so any static build up from printing is long since discharged.

Only thing I can think of is the carbon fibers. While they’re not magnetic in nature, due to their conductive nature there may be an interaction between them and strong magnetic fields.

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While they’re not magnetic in nature, due to their conductive nature there may be an interaction between them and strong magnetic fields.

Magnetism doesn’t work that way. Yes, if there’s a changing magnetic field, that will induce a current in a conductor exposed to that field. If this was the effect causing the observed behavior, the magnet wouldn’t stay attached once it stopped moving.

Not to mention, I have tons (well, not “tons”) of Carbon Fiber plate in varying thicknesses and none of them are magnetic. And if it was CF, then PLA-CF should do it too.

CF doesn’t explain it. Nylon doesn’t explain it. The only explanation I can think of is that the filament is doped with Iron, making the only question (for me, at least) “why?”. :slight_smile:

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I don’t think it can be explained through iron/ferromagnetic material inclusion – that would need to be at a sufficiently high density that it would be immediately noticeable by weight of the material. For those that have printed with bronzefil and similar, you know the weight difference I’m talking about.

I’d be curious on a couple of tests:

  1. Print a cube (calibration cube or whatever) in PA-CF. Does it exhibit magnetic attraction along all axes, or only aligned with the print direction/layer lines?

  2. Test PA12 to see if there are somehow similar properties. I doubt it will, but then I wouldn’t have believed PA-CF would either.

We know that PLA-CF doesn’t exhibit the same behavior, so I don’t think it’s the CF on its own…and I doubt that it’s the PA12 on its own. My best hypothesis at this point is that the longer chain of the PA12 is forcing the CF into partial alignment. While a static magnetic field will not induce a current, the introduction of the magnet creates a changing field…which could induce a current in those fibers that are properly aligned…which when the current changes (as the magnetic field stabilizes) could create a magnetic field in the fibers of different alignment…interacting with the magnetic field of the neodymium magnet. Something like the coil in a vintage car. Lather, rinse, repeat…wipe hands on pant.

There are a LOT of holes in that hypothesis - it’s an off the cuff idea that I can immediately see issues with, but may point in the right direction.

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The object I printed when I discovered this property was a Poop Collector (Septic Tank?). It extends across the back of the printer and wraps around the side so I can scoop the poop from the front. Probably close to 180 square inches of surface area. All of it only 4 layers thick/wide. The print is uniformly magnetic everywhere. As is the roll of filament it came from. Either polarity of the magnet appears to attract equally, which demonstrates that the plastic itself has no intrinsic field of its own. A quick test with a compass (just now) confirmed this. The compass’s indication of North doesn’t change if I put it inside the print.

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Did you try to measure if it is current conductive ?

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Just as a point of reference for folks that haven’t seen this. The piece in question is a solid print of BL PA-CF (a stamp for leatherwork). Nothing done to it after printing…and it was printed about 2 weeks ago.

IMG_2831

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32

An interresting test would be to try to heat it up with a coil using alternative current :slight_smile:

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33

Well, I took a 5cm long piece of unmelted PA-CF (Bambulab) filament and it is absolutly not conductive, I may try induction tomorrow, if it contain ferrous it should heat up.

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Nobody even remotely thought that, you are just being silly now :laughing:

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#3 definitely did not happen. OP is imagining a material property change at the atomic level. That won’t happen in uncontrolled conditions like a 3D printer. We’re only applying relatively low heat here, nothing else. I’m no rocket doctor but if this transition were possible it would have been well documented a long time ago.

36

Will this filament show signs of rust if it is wetted?

Are there other filaments that are attracted by magnets? This could be a useful property for some prints.

37

Err, not sure how you can predict every variable of manufacturing technique to make such a definitive statement, but that’s a handy diviner skill you have. Besides that was clearly a theoretical exercise of exhaustive postulating, the thing you do when you are forming a hypothesis, not a definitive statement such as you have made.

I hope you realize that the material you are feeding into your extruder was also extruded at the factory level, and the preprocessing of such materials through recycling, sourcing pelletizing, chemically treating, the machines they were stored in, the environment they were subjected to et cetera et cetera.

It’s amazing we have to get to such a pedantic level of minutia just from a listed possibility.

While I don’t disagree with your statement, it’s not out of the realm of possibility to discover something new, that’s just another day for science. Happens all the time.

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Not Ferrous. Here is your answer, from ScienceDirect website, via Google.

“Until very recently, polymers were generally considered to be unaffected by magnetic fields. However, it is now known that they are weakly magnetized because they are diamagnetic materials, and therefore do respond to magnetic fields.”

“The main ways in which polymer composites are magnetised are by melting the polymers or placing them in a liquid suspension to break up the cross-links, so that when the magnetic field is applied, the fibres within the polymer composites realign.”

The BBL print bed is a magnetic field, and is almost certainly the source of the magnetic field needed to align fibers.

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39

Thank you for sharing this information, as it does make sense that crystalizing anything from a molten state has any number of variables, akin to pouring water out of a tap, the molecules are going to do something.

While I don’t really think the bed’s magnetic field could align the structures itself, this observation just reinforces some of my statements and theoretical explanations.

The sheer amount of “no” and “I’m a subject matter expert” in this thread is downright unprofessional.

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That was my first post here on the forum, and I’m certainly no expert either… well maybe at 3D printing after 18 years of experience, but not with composites or polymers. My excerpts are certainly inadequate at providing an meaningful synopsis of the research described in the article. Search up “ScienceDirect Magnetic field assisted 3D printing of short carbon fibre-reinforced polymer composites” in your Google machine and have a read since no links can be posted. I found it fascinating. My curiosity has been piqued!