Vacuum system on how long?
01-11-2005, 07:08 PM
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Vacuum system on how long?
Hi everybody,
Taking a cue from several glider builders whose work I've admired, I have been leaving vacuum applied to my molds for a full 12 hours. (using West Systems epoxy with slow hardener) Obviously, the epoxy has cured to the point where vacuum is no longer extracting epoxy from the layup after a few hours, depending on temperature.
I've assumed that the reason to leave the system on is to prevent the parts from pulling away from the mold when the system is turned off, although I haven't had that problem. So...
How long do you leave your vacuum system turned on, and why?
Taking a cue from several glider builders whose work I've admired, I have been leaving vacuum applied to my molds for a full 12 hours. (using West Systems epoxy with slow hardener) Obviously, the epoxy has cured to the point where vacuum is no longer extracting epoxy from the layup after a few hours, depending on temperature.
I've assumed that the reason to leave the system on is to prevent the parts from pulling away from the mold when the system is turned off, although I haven't had that problem. So...
How long do you leave your vacuum system turned on, and why?
01-11-2005, 09:15 PM
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RE: Vacuum system on how long?
Hi Mike,
I am using Axson 2015 epoxy, fully cures in 24 hours at 22 °C but I accelerate the curing using a hot box at 40°C it takes eight hours. Vacuum should be mainteined until a fairly advanced stage of cure has been reached. As a means of checking the state of cure, when laminating I take some small off cuts of the glass fabric used in the laminated component , wet them out in a piece of polythene, then laminate together the same number of plies as there are in the laminate and put this small sample on top of the mould. I cheked the sample from time to time when it has hardened turn off the vacuum pump but leave the mould untouched until the laminate is fully cured.
The cure time will depend on the resin type, the speed of the hardener and the conditions at the time of lamination.
Marco
I am using Axson 2015 epoxy, fully cures in 24 hours at 22 °C but I accelerate the curing using a hot box at 40°C it takes eight hours. Vacuum should be mainteined until a fairly advanced stage of cure has been reached. As a means of checking the state of cure, when laminating I take some small off cuts of the glass fabric used in the laminated component , wet them out in a piece of polythene, then laminate together the same number of plies as there are in the laminate and put this small sample on top of the mould. I cheked the sample from time to time when it has hardened turn off the vacuum pump but leave the mould untouched until the laminate is fully cured.
The cure time will depend on the resin type, the speed of the hardener and the conditions at the time of lamination.
Marco
01-12-2005, 12:48 PM
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RE: Vacuum system on how long?
With no leaks, I just leave the pump off. It's good for the pump. You should get a vacuum switch, that way the pump will only run if the vacuum falls below your preset level.
01-12-2005, 02:29 PM
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RE: Vacuum system on how long?
I should be more clear about the question...
I've been making molded parts for almost 15 years, so am not new to that, but am new to vacuum bagging. My question is, (regardless of whether the pump is actually running or not) How long do you leave your parts under full pressure? Until the resin has stopped moving, or until the parts are at their initial "full cure"? (say, 12 to 24 hours)
It seems to me that if you leave them under pressure until the epoxy has stopped moving through the peel-ply, but leave them bagged and untouched for approximately 16 to 24 hours, (using West Systems resin at room temperature) that should be sufficient.
I've been making molded parts for almost 15 years, so am not new to that, but am new to vacuum bagging. My question is, (regardless of whether the pump is actually running or not) How long do you leave your parts under full pressure? Until the resin has stopped moving, or until the parts are at their initial "full cure"? (say, 12 to 24 hours)
It seems to me that if you leave them under pressure until the epoxy has stopped moving through the peel-ply, but leave them bagged and untouched for approximately 16 to 24 hours, (using West Systems resin at room temperature) that should be sufficient.
01-12-2005, 11:45 PM
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RE: Vacuum system on how long?
Mike,
When I bag parts (and not using VARTM) I use a Gast diaphragm pump and let it run unregulated (24" Hg) until a full-ish initial cure is achieved. 16 hours should do it for West Systems 105/205 in a warmish (around 73 degrees) shop, but more time is better. I 'abused' my first diaphragm pump this way for ten years or so...it still works well but doesn't pull quite like it used to. Most diaphragm-type pumps are rated for continuous (or sustained) use.
A reservoir / vacuum switch is cheap and easy to construct. I have a rig like this on another diaphragm pump (the whole thing isn't that large so it's easy to move around the shop) but the vacuum switch will only take around 16" Hg. It only gets used for balsa / white EPS foam structures...not much use, but handy to have.
Either setup works well. The penalties for NOT using a reservoir / vacuum switch are reduced pump life (seals, etc.) and layup 'spring-back' if the power goes out...a reservoir can maintain adequate vacuum provided your sealing job was decent.
-Tom
When I bag parts (and not using VARTM) I use a Gast diaphragm pump and let it run unregulated (24" Hg) until a full-ish initial cure is achieved. 16 hours should do it for West Systems 105/205 in a warmish (around 73 degrees) shop, but more time is better. I 'abused' my first diaphragm pump this way for ten years or so...it still works well but doesn't pull quite like it used to. Most diaphragm-type pumps are rated for continuous (or sustained) use.
A reservoir / vacuum switch is cheap and easy to construct. I have a rig like this on another diaphragm pump (the whole thing isn't that large so it's easy to move around the shop) but the vacuum switch will only take around 16" Hg. It only gets used for balsa / white EPS foam structures...not much use, but handy to have.
Either setup works well. The penalties for NOT using a reservoir / vacuum switch are reduced pump life (seals, etc.) and layup 'spring-back' if the power goes out...a reservoir can maintain adequate vacuum provided your sealing job was decent.
-Tom
