Casting Nylon to Silicon Mold

[Ghadeer 0]

Hello all,

 

This is away from 3D printing but I was wondering, will it be possible to melt the Ultimaker Nylon filament onto a bowl and cast it into a mold made out of silicon? I have seen videos of people making molds out of silicon and pour epoxy or urethane as a cast to make a part or a jewellery... So will molten Nylon work too since it hardens at room temperature? 

 

 

[ahoeben 1,948]

Casting with molten materials is quite different from casting with materials that cure chemically such as epoxy or urethane. The molten material will tend to solidify quite quickly when touching a cold mold, thus blocking any further molten material from flowing into the molded cavity. I don't think this will work very well.

[geert_2 557]

Most silicones I have seen can withstand 200°C, and up to 260°C for a very short while. But molten nylon is likely to be too viscous at this temperature: more like thick sirup instead of water. You would have to inject it at very high pressures and speeds (which would deform or damage the silicone). It will also be very difficult to get entrapped air out. And indeed, it will cool quickly upon touching the mould walls, making it difficult to fill the mould.

 

You would need liquids that chemically cure, like ahoeben said. But then still make sure they are not too exotherm, as this may damage the mould, or the epoxy/PU may catch fire. Also, saturate the silicone mould with silicone oil prior to casting. Otherwise the vapors of the epoxy will penetrate the mould and make it fail brittle and fail very soon, after a few castings. Silicone is water-tight, but not oiltight and not solvent-tight. Although I haven't used it, I read that PU exists in tough flexible versions similar to nylon (they use that to protect car undersides and trunks).

 

Edit: there is a reason why plastic injection moulding machines require heavy metal moulds, and clamping forces up to some tonnes, depending on the model...

 

Edited March 5, 2019 by geert_2

[Ghadeer 0]

alright. Thanks guys!

[Brulti 177]

As a side note, one of my customers had me make a mold in PVA to make something in silicon. The PVA held the molten silicon without a hitch and then he dissolved it in water.

[geert_2 557]

1 hour ago, Brulti said:

As a side note, one of my customers had me make a mold in PVA to make something in silicon. The PVA held the molten silicon without a hitch and then he dissolved it in water.

 

This could be an interesting method indeed for mould making. Did you try to smooth the PVA with water to remove layer lines and artifacts? And if so, did that work well?

 

[Brulti 177]

I sent the mold in PVA directly to the customer, with no post-treatment. He did not try to smooth it, and the layer lines did appear on his silicon object, but it was only for a proof of concept I believe, so he did not need it to be smooth.

 

The PVA held remarkably well, according to the customer, when he poured the liquid silicon through the holes into the mold, and it was tight enough that there was no leak; the mold was in two parts that assembled together.

 

I sent it with a silicon packet because I was afraid it would get soft due to humidity during transport, but it did not.