Oxygen Absorber at 200-350 deg F For Curing Photopolymer

[EricM81]

Basic Question:

I am trying to heat cure a photopolymer for a couple of hours at 350 deg F in an anoxic atmosphere. My idea was to seal the part in aluminum foil with charcoal to absorb the oxygen, but was not sure that the carbon and oxygen would react at that temperature.

Extra Background Info For The Extra Curious:

I'm working with a 3D printer that uses a light cured polymer (B9 Creator). 3D models are sliced into layers and projected one at a time into a vat of photopolymer. It starts the reaction and cures the model just enough to make it solid. Any more and the light would bleed into the next layer. Once a part is printed, it's washed with IPA to remove liquid polymer and then fully cured. The cured model is placed in a gypsum based investment and the polymer is burned out of the mold for casting.

Problem:

The polymer is reacting with the investment. Gypsum based investment utilizes a complex chemical reaction. Normally, water is mixed with the powder and a slurry is poured into the mold. The water and binder harden the slurry into a solid. The next reaction completes the hardening. If you heat the model at a specific rate, water is expelled and the cristobalite expands at a rate that maintains dimensional stability.

One way that the polymer interferes with the investment is through thermal expansion. If you fully cure the polymer with a UV light box, the model will undergo thermal expansion. Thicker cross sections will break down the investment just as the cristobalite begins to expand.

The other way it interferes is if you opt to heat cure the model. Heat will complete the reaction initiated by light and allow the model to undergo thermal expansion prior to being in the investment. However, heat cured models will interfere with the investment's chemical reaction leaving a rough surface finish.

Recently, someone tried curing the models by heating submersed models in baby oil (microwave). The results are reportedly perfected. My theory is that the heat plus anoxic environment are making the model thermally and chemically inert. I would like to test this by sealing them with aluminium foil and oven curing them in an anoxic atmosphere.

 

[EricM81]

Thanks Greg. To phrase as simple as possible, at what temperature does carbon react with and absorb oxygen?

 

[mfb]

I don't know about the carbon, but that would not be my first approach. A reaction would also heat up the carbon, with the risk of starting a fire.

If oxygen is the problem: do you have access to nitrogen, dry ice or something else you can use to flush your heat chamber?

However, heat cured models will interfere with the investment's chemical reaction leaving a rough surface finish.

What about some special treatment of the surface after curing?

 

[EricM81]

At higher temps to prevent oxidation, we use a kind of steel foil with charcoal to absorb oxygen, which is why it was my first thought for doing it at 350 def F with aluminium foil.

Fire is not a problem. This is in a commercial burnout oven that's made to allow airflow and burn out all of the carbon in the chamber.

I can bathe it in argon while I seal the foil. That will give me a near oxygenless environment for testing, but if successful it's not a great long term solution.

Surface treatments have varying levels of success. Plus they're hard to apply in a thin layer evenly without pooling. You tend to lose detail, sub 1mm holes get filled in, etc. If only you could electroplate a polymer.