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Hanaldo
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I wouldn't trust a jar to hold full vacuum. I've collapsed steel cylinders before, and only managed about half vacuum before they let go. They need to be pretty robust things to handle the vacuum well.
In all honesty, it probably wouldn't be that dangerous - but I'd still take cover. There's a chance that the thing would implode, the energy of which would send shards flying. It's much more likely that it develops a crack first that destroys the vacuum and nothing else happens, but flying glass isn't something I'd be taking chances with.
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Lester Populaire
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I wouldn't recommend a jar as if it goes wrong it probably send glass flying everywhere. that being said - i have done it plenty of times without issue...
I think the better solution is to use a section of thick walled PE plumbing tube with a thick plywood lid. soak the lid in epoxy to get them airtight. i made a seal for those with a silicone rope which worked really well.
The MTI hose works really well tho and improves process reliability by quite a bit for complex parts.
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oekmont
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The problem with jars is the workshop environment. There are infinite many scenarios what could happen to make the jar turn into a flying shard cloud. Why should they be designed to withstand full vacuum? I doubt the food industry applys full vacuum before sealing. Usually they will take full vacuum, but you never know for sure. And usually the underpressured gas area is very small, as the jar is filled with liquid. Applying vacuum to the whole jar increases the potential explosion energy a lot, as liquids don't need much energy to change their pressure, but gases do. So filled jars are under low pressure, but contain very little energy, which could be released in case of failure (except for the enormous energy stored in their mass of course (e=mc^2))
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quinn
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+xI wouldn't trust a jar to hold full vacuum. I've collapsed steel cylinders before, and only managed about half vacuum before they let go. They need to be pretty robust things to handle the vacuum well. In all honesty, it probably wouldn't be that dangerous - but I'd still take cover. There's a chance that the thing would implode, the energy of which would send shards flying. It's much more likely that it develops a crack first that destroys the vacuum and nothing else happens, but flying glass isn't something I'd be taking chances with. I could probably make it safe by wrapping in fiber tape or something, but ill find a safer way. A chunk of capped off pvc would definitely be safe. If it can handle over 100 psi inside, I'm sure it can handle 14.7 outside.
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Steve Broad
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+x+xI wouldn't trust a jar to hold full vacuum. I've collapsed steel cylinders before, and only managed about half vacuum before they let go. They need to be pretty robust things to handle the vacuum well. In all honesty, it probably wouldn't be that dangerous - but I'd still take cover. There's a chance that the thing would implode, the energy of which would send shards flying. It's much more likely that it develops a crack first that destroys the vacuum and nothing else happens, but flying glass isn't something I'd be taking chances with. Well they are definitely designed to handle vacuum since that's how you preserve food in them but I don't know for certain if they are 100% safe at full vacuum. I could probably make it safe by wrapping in fiber tape or something, but ill find a safer way. A chunk of capped off pvc would definitely be safe. If it can handle over 100 psi inside, I'm sure it can handle 14.7 outside. Maybe over the top, but interesting none the less :-) https://www.youtube.com/watch?v=2bWxgrtOKz8
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quinn
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Group: Forum Members
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+x+x+xI wouldn't trust a jar to hold full vacuum. I've collapsed steel cylinders before, and only managed about half vacuum before they let go. They need to be pretty robust things to handle the vacuum well. In all honesty, it probably wouldn't be that dangerous - but I'd still take cover. There's a chance that the thing would implode, the energy of which would send shards flying. It's much more likely that it develops a crack first that destroys the vacuum and nothing else happens, but flying glass isn't something I'd be taking chances with. Well they are definitely designed to handle vacuum since that's how you preserve food in them but I don't know for certain if they are 100% safe at full vacuum. I could probably make it safe by wrapping in fiber tape or something, but ill find a safer way. A chunk of capped off pvc would definitely be safe. If it can handle over 100 psi inside, I'm sure it can handle 14.7 outside. Maybe over the top, but interesting none the less :-) https://www.youtube.com/watch?v=2bWxgrtOKz8 Yeah pretty much, mine will just be an 8in long or so section with 2 caps, maybe 1 1/2 diameter. Drill 2 holes in one of the caps to silicone in some plastic barb fittings and just glue the caps on. Probably under 5 bucks for the whole thing, throw it away when I'm done.
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quinn
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Group: Forum Members
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Another question, after I'm done with the part and it's removed from the mold, how am I gonna want to finish it? I've heard pva can leave a less that perfect finish. Is a clear coat pretty much inevitable? Also am I gonna be able to sand the seam line from the split mold? I would imagine since I'm not laying any kind of gel coat first or anything like that, the fabric is gonna be right at the surface. Since I'm using infusion, I don't really have the option of building up a layer of epoxy at the joint before lay up right?
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Lester Populaire
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+xAnother question, after I'm done with the part and it's removed from the mold, how am I gonna want to finish it? I've heard pva can leave a less that perfect finish. Is a clear coat pretty much inevitable? Also am I gonna be able to sand the seam line from the split mold? I would imagine since I'm not laying any kind of gel coat first or anything like that, the fabric is gonna be right at the surface. Since I'm using infusion, I don't really have the option of building up a layer of epoxy at the joint before lay up right? I would use a chemical mold release. PVA does a really good job at releasing, but when working with spray tack you often time rip off the PVA film when repositioning the fabric which is no bueno. And as you said the surface finish of your part is only as good as the application of the PVA, so realistically you will have brush marks. If your molds line up perfectly then you don't need any gel coat or anything. Just sand the Burr with the same grid sandpaper as the mold, or a little finer, and you will hardly see it.
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quinn
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Group: Forum Members
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+x+xAnother question, after I'm done with the part and it's removed from the mold, how am I gonna want to finish it? I've heard pva can leave a less that perfect finish. Is a clear coat pretty much inevitable? Also am I gonna be able to sand the seam line from the split mold? I would imagine since I'm not laying any kind of gel coat first or anything like that, the fabric is gonna be right at the surface. Since I'm using infusion, I don't really have the option of building up a layer of epoxy at the joint before lay up right? I would use a chemical mold release. PVA does a really good job at releasing, but when working with spray tack you often time rip off the PVA film when repositioning the fabric which is no bueno. And as you said the surface finish of your part is only as good as the application of the PVA, so realistically you will have brush marks. If your molds line up perfectly then you don't need any gel coat or anything. Just sand the Burr with the same grid sandpaper as the mold, or a little finer, and you will hardly see it. Ok, what would you recommend as a chemical release? Preferably something affordable in very small quantity. The canopy surface is about square 0.2 meter and I'll only do a couple so no need to spend a bunch of money on expensive release that will expire. I imagine maybe I want to season my mold with a few runs using pva? I could just do a few single layer lay ups with fiberglass cloth just to help deactivate the mold surface before doing a canopy with no pva if that would help.
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Steve Broad
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Group: Forum Members
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+x+x+xAnother question, after I'm done with the part and it's removed from the mold, how am I gonna want to finish it? I've heard pva can leave a less that perfect finish. Is a clear coat pretty much inevitable? Also am I gonna be able to sand the seam line from the split mold? I would imagine since I'm not laying any kind of gel coat first or anything like that, the fabric is gonna be right at the surface. Since I'm using infusion, I don't really have the option of building up a layer of epoxy at the joint before lay up right? I would use a chemical mold release. PVA does a really good job at releasing, but when working with spray tack you often time rip off the PVA film when repositioning the fabric which is no bueno. And as you said the surface finish of your part is only as good as the application of the PVA, so realistically you will have brush marks. If your molds line up perfectly then you don't need any gel coat or anything. Just sand the Burr with the same grid sandpaper as the mold, or a little finer, and you will hardly see it. Ok, what would you recommend as a chemical release? Preferably something affordable in very small quantity. The canopy surface is about square 0.2 meter and I'll only do a couple so no need to spend a bunch of money on expensive release that will expire. I imagine maybe I want to season my mold with a few runs using pva? I could just do a few single layer lay ups with fiberglass cloth just to help deactivate the mold surface before doing a canopy with no pva if that would help. EasyComposites offers Easy-Lease at £6.80 for 100ml
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