Heat pressure casting, potentially insane idea - vac in a press pot in an oven?

[punkonjunk]

So, efficiency is a big deal. I'm still working on a sprueless idea, and I think this workflow might be awesome, but I'm not crazy familiar with heat and pressure.

I have found reports that 175-200 have worked well with pressure pots, or wrapping them in heated blankets, other types of things, so that's cool, I anticipate that working well.

so what I'm wondering about experimentally, is getting a vac can that'll fit inside my pressure vessel. So, I make my molds, put them in the vac, vacuum the resin in the mold to clear the bubbles on out and smooth it out. Then I place the vacuumed resin directly into the pressure vessel inside the vac can, pressurize, and place the whole thing into my oven at 175, and let it go with very, very little effort. Assuming all parts are heat safe, this should work out just fine, right?

I have an idea for making sure resin flows where I want it, without sprues, but if I can make this work, it'll hugely simplify that process.

Has anyone attempted anything similar to this with success? Any suggestions or feedback? I'm hoping to give this a shot this weekend.

[donutcat]

I would not suggest doing this. Like, this sounds all sorts of wiggity, especially putting a pressure pot into an oven. They make heat pads explicitly for pressure pots and vacuum chambers, so I would look into that instead of the oven. And I'm also not especially knowledgeable in casting processes yet, but it feels a whole lot like you're trying to cut a whole lot of corners in this process you're describing, and cutting that many corners is only good if you're in the lawn care service. Otherwise it's almost always better to stick to the proper processes and methods, especially in the presence of pressure differentials. 

[sinusoid]

Has anyone attempted anything similar to this with success?

Yes, it's called an autoclave:
https://en.wikipedia.org/wiki/Autoclave_(industrial)

Just to make sure, never put a vacuumed container in hi pressure environment (unless it's specifically made for that purpose). It's gonna collapse. Violently. And the impact may puncture the pressurized container, sending the lid in your face, or worse...
I think you're not trying to do that, but you skipped the 'open vacuum chamber' part, so making sure.

Adding heat, you'll be dealing with a lot more shrinkage from the resin. Usually you let resin sit around 25°C ambient for a few hours until it pre-sets, then condition it in 60-80 for specified amount of time. Check the spec sheet for curing parameters. Some have multiple scenarios for heat treatment, including a fast setting heat treatment.
You normally don't want to depressurize a heated container, because the resin may still be soft from the heat (depends on kind of resin), and air bubbles may expand back.

If you want to speed up the process, why not just get more molds and more pressure vessels? Get enough of them, and you can work continuously, without waiting times. 



edit: fixed link parsing

[punkonjunk]

I would not suggest doing this. Like, this sounds all sorts of wiggity, especially putting a pressure pot into an oven. They make heat pads explicitly for pressure pots and vacuum chambers, so I would look into that instead of the oven. And I'm also not especially knowledgeable in casting processes yet, but it feels a whole lot like you're trying to cut a whole lot of corners in this process you're describing, and cutting that many corners is only good if you're in the lawn care service. Otherwise it's almost always better to stick to the proper processes and methods, especially in the presence of pressure differentials.

I appreciate it, I'm going to look into hot pads. A couple folks on a model making forum posted success with both - I just felt like, 200ish oven (it goes down to 170, so I'd start way low) would give me a little extra insulation if something goes wrong.
I wouldn't want to cram it in there much hotter - although it's all metal and should be fine, if it isn't fine, it's a bomb.
And I did already rig up a remote pressure release on a pulley, in case something gets weird.

Yes, it's called an autoclave:
https://en.wikipedia.org/wiki/Autoclave_(industrial)

Just to make sure, never put a vacuumed container in hi pressure environment (unless it's specifically made for that purpose). It's gonna collapse. Violently. And the impact may puncture the pressurized container, sending the lid in your face, or worse...
I think you're not trying to do that, but you skipped the 'open vacuum chamber' part, so making sure.

Adding heat, you'll be dealing with a lot more shrinkage from the resin. Usually you let resin sit around 25°C ambient for a few hours until it pre-sets, then condition it in 60-80 for specified amount of time. Check the spec sheet for curing parameters. Some have multiple scenarios for heat treatment, including a fast setting heat treatment.
You normally don't want to depressurize a heated container, because the resin may still be soft from the heat (depends on kind of resin), and air bubbles may expand back.

If you want to speed up the process, why not just get more molds and more pressure vessels? Get enough of them, and you can work continuously, without waiting times. 



edit: fixed link parsing

Oh my god, I thought autoclaves always used steam - I am familiar with them from my work with dentists, piercers and metal casting, but never gave it a second thought because I thought steam was somehow integral to the heat and pressure elements in an autoclave. After some more research that is absolutely not the case, and I am unclear how I got that idea in my head.

And of course, I intended to release the vacuum, then pressurize, all in the same chamber. I would never but a vac'd container under pressure, althought I imagine it would be fun to watch in a safe environment, my basement lab is NOT that environment.

Your suggestions are pretty good, too - 3 pressure pots and a series of molds would work equally well, and depending on my heat source (pig blanket, heat pads) I could build around that rather than try to scale up too fast. And now I know my endgame, if my crap sells well, will be an industrial autoclave/ dry heat pressure sterilizer.

[Dodgy]

I would recommend against doing this. Putting a pressure pot in an oven sounds like a bad idea, and is completely unnecessary. I'd recommend against mixing any of your resin casting materials and tools with any of your food preparation facilities. Also I would definitely not do this if your oven is gas lit.

Please note, you don't want to vac resin while it's in the mold, and you don't need to. Your resin will foam all over the place and overflow, and also probably push your mold pieces apart and shift them. You want to vac resin before you pour to remove any suspended air, then pressurize after pouring to force resin into any spaces that the poured resin traps into the mold.

My question is, what's so hard about transferring the mold from the vac chamber to a pressure pot and putting the pot ontop of an electrical heating blanket? Why this Russian nesting doll type of workflow?