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Abrasive

Polycarbonate clear vs. black & white

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I'm curious as to why the clear polycarbonate is so brittle compared to the black and white?  I print the same part with 90% infill, all Cura settings the same, and then hit it with a hammer to test the durability.  The clear PC immediately catastrophically fails and explodes into a ton of pieces.  The black and white I can hit 30+ times and it won't break.

 

I'm not sure if this is a material issue or if the clear should have its own temp profiles because it has different needs?

 

That being said I really love this material as it prints so consistently well on my UM3 and is super strong.  For the time being I've just been using the clear to test fit and weight and then print the real part in black or white.

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Hi Abrasive,

 

An interesting question you asked. Poly-carbonate is a real strong thermoplastic, however everything has issues that's may/change their properties dramatically.

So, there is many variants of Poly-carbonate out there using different brand names as,

Lexan -the name GE (General Electric) is using for their own version of Poly-carbonate for some products.

 

So, we know that some types of filament will be fast hardening and become very brittle when exposed to UV radiation. Normally transparent Poly-carbonate just become kind of yellow over time, however, this is very dependent of the brand of Poly-carbonate you're using.

As a transparent object made of (in this case) P-carbonate, will be transparent for UV radiation as well as might reflected by the mirror effect inside your printed object that's really increase the effect of this kind of radiation. So, darker colored filament absorb UV and black is best.

 

Then, a few of the fast'es aircraft made have their windows made of Poly-carbonate (but not using any kind of this thermoplastic). The modern bowling balls made today have the cover stock made of (yes) Poly-carbonate and they last as long you want to use them.. :)

 

Lastly, there is some stuff (we all knows very well) that Poly-carbonate should never be in contact with; normal car fuel of mogas type and "acetic acid" (as some silicone "glue" with this kind of smell). If you need to clean away grease or fingerprints use alcohol.

Car fuel will over some time lead to tiny micro cracks. Silicone glue containing acetic acid will lead to catastrophic reaction and will crack up overnight. So do not use this stuff to glue together parts made of Poly-carbonate.

 

So, what kind of Poly-carbonate filament brand are you printing with? 

 

Thanks

Regards

Torgeir.   

 

 

 

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Thanks Torgeir,

That's the most long-winded and informative post I was never expecting that also lead to one single direct question?  In my case I was using all Ultimaker polycarbonate filaments in the varieties of clear, black and white.  I would just print the part and attempt to break it with a hammer after it had cooled to room temperature.  There was no time for UV radiation to have an effect.  No chemicals touched them other than skin oil.

I'm building a combat robot so this was a litmus test for "can this take a forceful hit?".

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My guess would be that the opaque PC does have some modifiers (plasticizers etc.) in it that make it much less brittle, and that those modifiers can't be used in the clear PC because they would affect the transparency negatively.

Edited by P3D

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There are many physical properties of materials but the most important one is strength and the second most important is modulus aka stiffness.  transparent is both stronger and stiffer.  Stiffer is not always better - it also means it is more brittle.  If you drop a rubber ball versus a glass ball - the rubber which has a low modulus will stretch and spread out the load over time (only 100 milliseconds versus the glass which shatters in under 1 millisecond) and not break.  Even though glass is stronger than rubber.

 

Impact strength and brittleness and modulus are extremely closely related.  Knowing the modulus and strength you can predict the impact strength (somewhat).

 

I post these properties of both types of UM PC and glass and many other filaments here in this graph:

http://gr5.org/mat/

 

The third most interesting property is working temperature which I try to capture in the second graph in the above web page.  You can zoom into the graph and hover over any material for more details.  It's log scale in both axes so read carefully.

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On 8/30/2018 at 6:20 AM, Abrasive said:

Thanks Torgeir,

That's the most long-winded and informative post I was never expecting that also lead to one single direct question?  In my case I was using all Ultimaker polycarbonate filaments in the varieties of clear, black and white.  I would just print the part and attempt to break it with a hammer after it had cooled to room temperature.  There was no time for UV radiation to have an effect.  No chemicals touched them other than skin oil.

I'm building a combat robot so this was a litmus test for "can this take a forceful hit?".

 

Hi Abrasive,

 

Thanks..  This material really can change due to our treatment of it.. 

 

Torgeir.

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If you want good impact strength then you want it to be somewhat flexible.  Nylon is pretty amazing for impact strength.  If you need it to be strong - say a link in a chain then strength is much more important than flexibility.  If you are making a quadcopter arm or typical structural element then nylon is too flexible.  If you are making a gear you don't want the teeth to be very flexible at all - it needs to be stiff and strong.  So it depends what you are making and how it is used.

 

It's easy to get materials that are more or less flexible.  It's hard to get materials that are stronger. Everyone wants stronger.  Steel is pretty amazing for stiff and strong.  No plastics come close.

 

If it's flexible enough it's indestructable (you can twist it into a knot and it won't break) but many applications don't want something that flexible.

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I used polycarbonate for a weapon adapter for the combat robot and it held up.  The weapon blade screws into the bottom of the adapter and the brushless outrunner presses into the top.  CAD models shown in the attached pictures.  I could't use flexible filament as it needs a fair amount of rigidity. I was skeptical that it would work as it is spinning at a few thousand RPM.  I thought the screws would split it under the torque during impact, or it would just explode.

 

The adapter I made is on Cubey's Revenge, the taller tube robot with big blue wheels. This is one of the more violent fights and it didn't break.

I'm going to iterate on the adapter some more and experiment with 3D printed wheels that can hopefully survive horizontal spinners.  Flexible filament might work well for the wheels, I just need to keep them under 14g or so.

Weapon mount bottom.png

Weapon mount top.png

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Nylon is stiff.  It's just flexible enough to be very tough.  I think it's really hard to explain in words unless you've tried a few *slightly* flexible materials.   Hmm.  Like wood. But without the grain.  People don't tend to think of wood as flexible but compared to aluminum it's quite flexible.  Nylon is too flexible for gears but this above application looks perfect for Nylon.  There's no way it would ever crack -- tear maybe -- but it will stretch 10% before tearing.  There is an "elongation at break" or "elongation at yield" specification for most materials that tells you how much it will stretch before it breaks.

 

All filaments - well 99% of filaments - have a materials specification sheet of some sort.  Just google the material and "modulus" and it should have lots of temperature and physical characteristics like this.  That's where I got the data for my graph.

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