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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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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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Group: Forum Members
Posts: 311,
Visits: 13K
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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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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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Steve Broad
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Group: Forum Members
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+x+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. I wasn't saying the bolts wouldn't cope with the pressure, just trying to show how much weight 7 BAR is equivalent to :-) I consider that 3BAR is more than enough and any extra pressure won't make any noticeable difference to the finished product but will add to the risk. However, as I will be nowhere near it's your call :-) Keep us informed as this will be interesting.
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quinn
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Group: Forum Members
Posts: 155,
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+x+x+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. I wasn't saying the bolts wouldn't cope with the pressure, just trying to show how much weight 7 BAR is equivalent to :-) I consider that 3BAR is more than enough and any extra pressure won't make any noticeable difference to the finished product but will add to the risk. However, as I will be nowhere near it's your call :-) Keep us informed as this will be interesting. I'll try 50psi or so. I'm sure there's a point of not much return. The resin ratio is set with prepreg, so as long as there's no voids with lower pressure, going higher isn't gonna make anything better
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Steve Broad
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Group: Forum Members
Posts: 408,
Visits: 4.1K
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+x+x+x+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. I wasn't saying the bolts wouldn't cope with the pressure, just trying to show how much weight 7 BAR is equivalent to :-) I consider that 3BAR is more than enough and any extra pressure won't make any noticeable difference to the finished product but will add to the risk. However, as I will be nowhere near it's your call :-) Keep us informed as this will be interesting. I'll try 50psi or so. I'm sure there's a point of not much return. The resin ratio is set with prepreg, so as long as there's no voids with lower pressure, going higher isn't gonna make anything better Correct, once the air is removed there is nothing left in the composite that is compressible.
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quinn
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Group: Forum Members
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Got some stuff in the mail to try for bladders. Some long balloons and a latex bike inner tube. I think the inner tube is gonna work well as a reusable bladder. It will be secured at both ends in the endcaps I'm going to mill. End caps will have a few small channels milled into the mating surface against the mold so air can escape as bladder fills. After thinking about it, it would be very easy to combine both vacuum and pressure with this setup. I can just envelope bag the whole thing with the ends of the bag sealed around the outside edge of the end caps. Really quick and easy to bag it this way. When pulling air out of the bag, air will be pulled out between bladder and mold wall through the milled channels. The bladder should basically inflate itself inside as air is pulled out, then I can add more positive pressure inside the bladder through a fitting in the endcap. Then it really will be just as good as an autoclave. I'll try with and without vacuum to see if there's much difference. If not, the process is a bit quicker without the bagging.
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quinn
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Group: Forum Members
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Been doing a little more reading and feeling a bit less confident about the latex bladder. Seems that latex isn't all that resistant to heat and deteriorates pretty quickly. I already have some wax sheets that I ordered a while ago when I was planning on making my own bladder, so I went ahead and ordered some silicone too so I'll also have that option.
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Steve Broad
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Group: Forum Members
Posts: 408,
Visits: 4.1K
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+xBeen doing a little more reading and feeling a bit less confident about the latex bladder. Seems that latex isn't all that resistant to heat and deteriorates pretty quickly. I already have some wax sheets that I ordered a while ago when I was planning on making my own bladder, so I went ahead and ordered some silicone too so I'll also have that option. The thick sausage type party balloons survived 120 deg C with no issues.
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