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I came across a new Steel infused PLA from Colorfabb. On the store page someone had asked, what happens if it was exposed to water, would it rust. I am actually, not sure what would happen. I am interested what the effects of leaving in the elements a 3D printed object made of the 2 most common type of fused materials.

  1. Wood Infill
  2. Metal Infill (not stainless steel)

Would it be preserved by the PLA coating it, or would, over time, rust and dissolve? Would the wood last forever, or will the print get discolored and become mulch?

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  • $\begingroup$ I would expect the wood to be subject to fungal attack, but I have nothing to substantiate that. $\endgroup$ – Andrew Morton Aug 2 at 17:21
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If you use filaments filled with metal particles, some particles will be exposed to the environment. Depending on the corrosion resistance of those metals, yes the environmental conditions will weather the print object. So if it contains iron (and does not contain elements that prevent oxidation like used in stainless steel) and it is subjected to water and oxides, the print will rust.

This is e.g. also valid for copper filled filament, which you can polish to get a gold shine surface (removing the copper oxides), or bronze filled filament, that if correctly subjected to weathering environments, will give the looks of a very old statue. In both cases this implies that the metal particles have undergone a(n) (de-)oxidation process.

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The particles on the outmost part of the print which are exposed to air will rust. The ones inside will still be protected somewhat by the PLA. The rust color/effect is part of the idea, since it give certain prints an old look.

ProtoPasta Iron-Filled Metal Composite PLA

https://www.proto-pasta.com/products/magnetic-iron-pla

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  • $\begingroup$ As the rust takes up a greater volume than the steel, would that cause additional damage to the structure? (Like how rust flakes off old car chassis.) $\endgroup$ – Andrew Morton Aug 2 at 17:20
  • $\begingroup$ No, because only the ones exposed to air could fall out. The internal particles are surrounded. $\endgroup$ – user77232 Aug 2 at 17:39
  • $\begingroup$ I thought that maybe the expanding rust on the outside of the print might push against the PLA, distorting and breaking it and letting moisture further into the structure where more rust would form, in turn expanding and perhaps pushing off outer pieces of PLA. I suspect that if someone wanted a durable part for outdoors, rustable PLA wouldn't be the material of choice. $\endgroup$ – Andrew Morton Aug 2 at 17:58

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