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mkawa:
the ASME standard for building pressure vessels is a process certification that signifies that the manufacturer followed best practices in welds, material sourcing (EXTREMELY IMPORTANT), rolling or forming, and of course, that the design was certified by the standards body.
the sum total of this is that the asme certified pressure vessel construction is the absolute minimum that an engineer designing a critical pressure/vacuum system will require in production. here is why: when a pressure vessel explodes, people die.
SO! there are plenty of tanks out there that invite you to fill them with pressurized gases or fluids. many of them are ok on their first few uses, or ok for the first month after production, but after repeated cycles of expansion and contraction, and potentially oxidization at weak points in the vessel, they will eventually let go. if you're lucky (for example, a contractor's compressor tank), the vessel will pop a few leaks and the end result will just be the compressor's motor locking up from overwork.
if you're unlucky, the vessel will basically become a grenade; it will explode and high velocity steel shrapnel will fire off in all directions. you will probably not see any evidence that the unlucky case is going to happen. often, this will happen while the vessel is pressurized (and not during a release or pressurization cycle). once a large enough piece of tank fires off, the resulting stress on the hull will disintegrate it.
so anyway, my rule of thumb is that for typical cast and mold applications with the materials that people here use, a 40-50psi cure pressure is pretty standard. to hold 40-60psi for the duration of a cast (30-60mins), i source at least 100psi asme rated pots. also, because these pots tend to sit at pressure for long periods of time, i only source stainless pots. finally, i don't source anything that could even possibly have chinese "steel" in it (the chinese metal market is an absolute mess).
finally, all seals, gaskets, and fittings are fluorinated, period. silicone cures give offgas caustic nasty stuff. a seal failing will have a similar effect to the catastrophic explosion above (possibly worse, actually).
so that's the pot! a lot of people ask about compressors and hosing (OH MY GOD SO IMPORTANT) as well. but yes, the pot? don't screw around. your life is not worth the hundred or so dollars separating a high quality certified pot from something that has a non-trivial chance of killing you.
oh, i should mention that vacuum pots are not things you should be screwing around with either. i have seen far too many acrylic topped soup pots that i can to recall. hey remember pressure pots turn into small grenades when they explode? turns out that vacuum pots do the same thing when they implode!
Binge:
--- Quote from: mkawa on Mon, 18 May 2015, 20:30:35 ---the ASME standard for building pressure vessels is a process certification that signifies that the manufacturer followed best practices in welds, material sourcing (EXTREMELY IMPORTANT), rolling or forming, and of course, that the design was certified by the standards body.
the sum total of this is that the asme certified pressure vessel construction is the absolute minimum that an engineer designing a critical pressure/vacuum system will require in production. here is why: when a pressure vessel explodes, people die.
SO! there are plenty of tanks out there that invite you to fill them with pressurized gases or fluids. many of them are ok on their first few uses, or ok for the first month after production, but after repeated cycles of expansion and contraction, and potentially oxidization at weak points in the vessel, they will eventually let go. if you're lucky (for example, a contractor's compressor tank), the vessel will pop a few leaks and the end result will just be the compressor's motor locking up from overwork.
if you're unlucky, the vessel will basically become a grenade; it will explode and high velocity steel shrapnel will fire off in all directions. you will probably not see any evidence that the unlucky case is going to happen. often, this will happen while the vessel is pressurized (and not during a release or pressurization cycle). once a large enough piece of tank fires off, the resulting stress on the hull will disintegrate it.
so anyway, my rule of thumb is that for typical cast and mold applications with the materials that people here use, a 40-50psi cure pressure is pretty standard. to hold 40-60psi for the duration of a cast (30-60mins), i source at least 100psi asme rated pots. also, because these pots tend to sit at pressure for long periods of time, i only source stainless pots. finally, i don't source anything that could even possibly have chinese "steel" in it (the chinese metal market is an absolute mess).
finally, all seals, gaskets, and fittings are fluorinated, period. silicone cures give offgas caustic nasty stuff. a seal failing will have a similar effect to the catastrophic explosion above (possibly worse, actually).
so that's the pot! a lot of people ask about compressors and hosing (OH MY GOD SO IMPORTANT) as well. but yes, the pot? don't screw around. your life is not worth the hundred or so dollars separating a high quality certified pot from something that has a non-trivial chance of killing you.
oh, i should mention that vacuum pots are not things you should be screwing around with either. i have seen far too many acrylic topped soup pots that i can to recall. hey remember pressure pots turn into small grenades when they explode? turns out that vacuum pots do the same thing when they implode!
--- End quote ---
This was a focus of my presentation at keycon regarding casting methodology. The technology used is pretty intense.
Condensing this information into some, "prerequisite equipment features for casting safety," would be a useful reference.
bcredbottle:
--- Quote from: mkawa on Mon, 18 May 2015, 20:30:35 ---
so that's the pot! a lot of people ask about compressors and hosing (OH MY GOD SO IMPORTANT) as well. but yes, the pot? don't screw around. your life is not worth the hundred or so dollars separating a high quality certified pot from something that has a non-trivial chance of killing you.
--- End quote ---
mkawa's post is right on the money but I think this needs to be emphasized. A pressure chamber is only a few steps away from a bomb.
Binge:
--- Quote from: bcredbottle on Thu, 08 October 2015, 12:26:45 ---
--- Quote from: mkawa on Mon, 18 May 2015, 20:30:35 ---
so that's the pot! a lot of people ask about compressors and hosing (OH MY GOD SO IMPORTANT) as well. but yes, the pot? don't screw around. your life is not worth the hundred or so dollars separating a high quality certified pot from something that has a non-trivial chance of killing you.
--- End quote ---
mkawa's post is right on the money but I think this needs to be emphasized. A pressure chamber is only a few steps away from a bomb.
--- End quote ---
Right indeed.
Found this post on reddit https://www.reddit.com/r/ResinCasting/comments/3mpyhx/is_a_pressure_chamber_necessary/
I'm noticing a lot of fledgling artisans trying to find some sort of buried treasure in this craft that simply does not exist and will never exist with the effort/resources they are trying to employ. I think if there were not so many strict warnings about safety around geekhack many of these folks would not even understand the danger of pressure casting associated with cheap tools.
If anyone out there is trying to cut costs please re-adjust your mentality and WAIT on the craft. There is no harm in spending a little extra time to save the right amount of money to get started. There are so many other ways you could improve what you offer in your art. Sculpting, mold creation, and color theory to name a few.
With how often I had been approached because this craft and how often I see guides referenced by new artisans and then the outcomes of their efforts vs the efforts of the artisans who have created the guides or have provided the advice... I am deeply discouraged.
Staying on topic- safety awareness is super important! Remember that respecting your chemicals is extremely important! I was approached about what materials I use to sculpt. Many of them are toxic and should not be in reach of pets/children. While I understand the need to try new things I am reminded every time I make a mistake that it is not worth the risk to do things without adequate research. Had I been any less careful with my ammonia gas baths I probably would have caused permanent damage to my lungs.
mkawa:
Yes seriously there are tons of toxic gases involved in pressure casting or casting in general and not to mention the amount of stored energy in a pressure or vacuum container. The key here is that these things can kill you. I repeat, these things can kill you and cause irreparable harm to your body.
I'm not saying this to scare you off. I'm not saying this because I feel I have a magic bullet that will keep you safe. I say this so that you go into this hobby with your eyes wide open
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