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quinn
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+xIf your item is, say, 24 inches long and 4 inches in circumference, then 100psi is around 5 tonnes of pressure. That's equivalent to over 4 Ford Fiestas!. Talking to my carbon supplier, they suggested that 2BAR (approx 44psi) was more than enough when making a carbon/aramid hockey stick using the bladder process, so 7BAR is a massive overkill! It sounds like a lot, but think about a much larger, much thinner walled aluminum scuba tank holding 3000 psi. My mold is held together with 12 m6 bolts with enough thread depth that the bolt snapping is definitely the failure point. A single m6 bolt can hold 2 tons, so theoretically, if one side of my mold was fixed to something, you could hang about 20 ford fiestas from it before shearing the bolts. Not to say 100psi isn't overkill, but I'm pretty confident it would be well within the safe range. I'll try much lower pressure if you guys think 100psi is far more than what's useful. Also, when applying any pressure at all, I'll test it in a safe place with a long hose and go quite a bit higher than I will when pressurizing near myself just to make sure its safe. I'm sure things also change when heated, so I'll stay away from the oven while cooking and be mindful of what direction aluminum is gonna fly lol.
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Lester Populaire
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+xIf your item is, say, 24 inches long and 4 inches in circumference, then 100psi is around 5 tonnes of pressure. That's equivalent to over 4 Ford Fiestas!. Talking to my carbon supplier, they suggested that 2BAR (approx 44psi) was more than enough when making a carbon/aramid hockey stick using the bladder process, so 7BAR is a massive overkill! Yeah i agree fir everything other than a thick walled small diameter tube you do not need more than 2 to 3 bar of pressure.
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Steve Broad
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If your item is, say, 24 inches long and 4 inches in circumference, then 100psi is around 5 tonnes of pressure. That's equivalent to over 4 Ford Fiestas!.
Talking to my carbon supplier, they suggested that 2BAR (approx 44psi) was more than enough when making a carbon/aramid hockey stick using the bladder process, so 7BAR is a massive overkill!
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Lester Populaire
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+x+x+xLooks pretty good from a couple feet away, but there's some pinholes. Hoping the higher pressure of bladder will fix that. One thing I'm trying to wrap my head around though, with vacuum bagging, any tiny voids in the laminate are at full vacuum so as the resin heats and starts flowing, the voids should mostly collapse on themselves and dissapear. How does this work with bladder molding? The bladder pushes on the laminate with a lot more pressure, but any tiny voids in the laminate will be at atmospheric pressure, so won't they just stay there? How do they work their way out? With an autoclave, the voids have vacuum on them and the positive pressure assists with extra pressure so that makes sense, but I can't picture how this works with just positive pressure from bladder and no vacuum on the laminate. How do small pockets of air escape the laminate? I guess somehow it works since it's a common method, just trying to understand how You basically just increase pressure so bubbles become so small you cannot see them anymore. Furthermore air can still eacape through mold seams realistically. On moulds where i cannot apply too much pressure i usually pack the whole shabam into an envelope bag as well. Ok, that makes senss. A tiny void at atmospheric pressure will become almost nothing at all when compressed to much higher pressure. I imagine it also might be slightly beneficial to orient the mold so seams are vertical, one seam at top and one at bottom so bubbles moving around will have an escape at the high point. As for pressure, with this mold I imagine I could go as high as I wanted. Would probably take 1000 psi to split this mold apart. Although at some point the m6 bolts will start to stretch a bit and open the seam slightly. I'll probably go with 100psi or so. Is there any benefit to varying pressure throughout the cure? Like maybe lower pressure at first so bubbles can move around easier while resin is liquid, then ramp up the pressure right before going to final cure temp? Or just give it full pressure in the first place and keep it there? There probably is but i had good luck with full pressure from the start and never had to experiment with that.
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quinn
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Group: Forum Members
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+x+xLooks pretty good from a couple feet away, but there's some pinholes. Hoping the higher pressure of bladder will fix that. One thing I'm trying to wrap my head around though, with vacuum bagging, any tiny voids in the laminate are at full vacuum so as the resin heats and starts flowing, the voids should mostly collapse on themselves and dissapear. How does this work with bladder molding? The bladder pushes on the laminate with a lot more pressure, but any tiny voids in the laminate will be at atmospheric pressure, so won't they just stay there? How do they work their way out? With an autoclave, the voids have vacuum on them and the positive pressure assists with extra pressure so that makes sense, but I can't picture how this works with just positive pressure from bladder and no vacuum on the laminate. How do small pockets of air escape the laminate? I guess somehow it works since it's a common method, just trying to understand how You basically just increase pressure so bubbles become so small you cannot see them anymore. Furthermore air can still eacape through mold seams realistically. On moulds where i cannot apply too much pressure i usually pack the whole shabam into an envelope bag as well. Ok, that makes senss. A tiny void at atmospheric pressure will become almost nothing at all when compressed to much higher pressure. I imagine it also might be slightly beneficial to orient the mold so seams are vertical, one seam at top and one at bottom so bubbles moving around will have an escape at the high point. As for pressure, with this mold I imagine I could go as high as I wanted. Would probably take 1000 psi to split this mold apart. Although at some point the m6 bolts will start to stretch a bit and open the seam slightly. I'll probably go with 100psi or so. Is there any benefit to varying pressure throughout the cure? Like maybe lower pressure at first so bubbles can move around easier while resin is liquid, then ramp up the pressure right before going to final cure temp? Or just give it full pressure in the first place and keep it there?
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Lester Populaire
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Group: Forum Members
Posts: 311,
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+xLooks pretty good from a couple feet away, but there's some pinholes. Hoping the higher pressure of bladder will fix that. One thing I'm trying to wrap my head around though, with vacuum bagging, any tiny voids in the laminate are at full vacuum so as the resin heats and starts flowing, the voids should mostly collapse on themselves and dissapear. How does this work with bladder molding? The bladder pushes on the laminate with a lot more pressure, but any tiny voids in the laminate will be at atmospheric pressure, so won't they just stay there? How do they work their way out? With an autoclave, the voids have vacuum on them and the positive pressure assists with extra pressure so that makes sense, but I can't picture how this works with just positive pressure from bladder and no vacuum on the laminate. How do small pockets of air escape the laminate? I guess somehow it works since it's a common method, just trying to understand how You basically just increase pressure so bubbles become so small you cannot see them anymore. Furthermore air can still eacape through mold seams realistically. On moulds where i cannot apply too much pressure i usually pack the whole shabam into an envelope bag as well.
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quinn
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Group: Forum Members
Posts: 155,
Visits: 992
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Looks pretty good from a couple feet away, but there's some pinholes. Hoping the higher pressure of bladder will fix that. One thing I'm trying to wrap my head around though, with vacuum bagging, any tiny voids in the laminate are at full vacuum so as the resin heats and starts flowing, the voids should mostly collapse on themselves and dissapear. How does this work with bladder molding? The bladder pushes on the laminate with a lot more pressure, but any tiny voids in the laminate will be at atmospheric pressure, so won't they just stay there? How do they work their way out? With an autoclave, the voids have vacuum on them and the positive pressure assists with extra pressure so that makes sense, but I can't picture how this works with just positive pressure from bladder and no vacuum on the laminate. How do small pockets of air escape the laminate? I guess somehow it works since it's a common method, just trying to understand how
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Lester Populaire
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Group: Forum Members
Posts: 311,
Visits: 13K
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quinn
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Group: Forum Members
Posts: 155,
Visits: 992
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quinn
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Group: Forum Members
Posts: 155,
Visits: 992
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+x+x+xPhotographic evidence? :-) Here it is. The fan I got on Amazon for pretty cheap. It's a blower fan made for fireplaces so figured it's probably designed to handle some heat. Handled one cycle so far, we'll see if it holds up. Temp controller also on amazon for pretty cheap. I just had it set to a basic mode that holds one temp, but once I figure out the terrible chinglish manual, it can go through up to 12 difference temperature profiles with specific amounts of time. Should be great for a full ramp up, soak, ramp down cycle. The temp sensor on it is a bit slow to react though. That other little temp sensor I bought sitting next to the controller seems much better. I'll try moving the controllers sensor in front of fan air to see if it reads quicker. One thing that's bugging me a bit, the oven puts off a smell, not like burning, but I think it's from the mdf getting hot. Mdf combusts at like double my my max temp, so not worried about it, but hopefully the smell will get better after a couple cycles. Probably wouldn't notice it if I didn't open the door while running a cycle. Edit: running into a slight issue. My oven is too efficient lol. Ran another cycle this morning with my aluminum molds in it. Ramp up of mold temp was slower but not too bad, with probe placed inside a bored hole in the mold, it took a bit over an hour to go from 20c to 120c. Ramping down is the issue. This mold stores some serious energy. Without the mold in there, the oven would drop a couple degrees per minute with bulbs off, with mold in there, it has now been over an hour since bulbs turned off and it has only dropped to 108c. The mold is like a big heating element in the oven and doesn't want to ramp down with the insulation containing all the energy in the oven. Easy solution would be to just open the door, but I'd like to have a full cycle of ramp up/ramp down programmed without having to touch the oven. My temp controller does have an outlet for cooling, just need to figure out what to power with it. Somehow need to set it up to vent the oven without losing insulation during ramp up.   Looks very good. I wonder how long it will be before it is too small? :-) Had the same thought so I designed it much bigger than I had originally planned. Before i was only gonna make it big enough for the boom mold, but decided I might eventually do cf sheets or canopies. Interior is 950mm wide, 450mm deep, 500mm high (350mm from floor to bulbs). Plenty big for any future projects I would do.
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