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quinn
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I'm about to start machining my mold but I have a few concerns. The composite part is an 800m long tapered tube. 46mm diameter at one end, 30mm at other end. The closed mold is 75mm square by 800mm long. This means the mold walls will be as thin as 15mm at one end and as thick as 22mm at other end. One concern is the time it takes for this big chunk of aluminum to heat up, the other concern is uneven heating, thinner walled end heating up first. How should I approach this with my ramp cycles? Just go slower in general? Hold temps longer? I'm really not sure what to expect for how long it's gonna take for it to heat up. If the varying wall thickness is gonna be a big problem, I can do some machining on the outside to even it out, but would rather not if it isn't needed. First few parts will be done with vacuum bag so the laminate will be exposed to the heated air but later on I'll be trying silicone expanding plug so I'm sure that will change things as far as heating. Any advice on how to approach this? Thanks
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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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+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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Group: Forum Members
Posts: 155,
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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
Posts: 408,
Visits: 4.1K
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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,
Visits: 992
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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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