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Henkka
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Hi,
Is it possible to cure prepregs that are supposed to be used in an autoclave using an oven? The manufacturer recommends 85 psi of autoclave pressure and 177 degrees C temperatures for curing and I'm wondering how critical the pressure is to achieve good results.
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Lester Populaire
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+xHi, Is it possible to cure prepregs that are supposed to be used in an autoclave using an oven? The manufacturer recommends 85 psi of autoclave pressure and 177 degrees C temperatures for curing and I'm wondering how critical the pressure is to achieve good results. It will result in a lot of porosity. i would recommend against it.
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ArturK
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If you do not have an autoclave, lets try some prepregs that are dedicated for OOA manufacturing (out of autoclave curing). Easy Composites have that products. You can have good results with OOA if the products do not have many curvatures.Complex products with many curvatures will need autoclaves. Here you can find some additional info: http://www.dexcraft.com/articles/carbon-fiber-composites/prepreg-autoclave/
Carbon fiber sheets and composites . www.dexcraft.com
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Steve Broad
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I bought some out of date autoclave (just approaching its best before date) carbon from a supplier at a very good price, it would have been rude not to. Their help desk said that it could be used OOA if the following procedure was followed. Lay up first two layers, using a roller to compress the layers firmly together, then vacuum bag for 8 hours. Unbag and add next layers and repeat until all the carbon is in the mould. Vacuum up and place in oven. Bring up to 80 deg C and dwell for 30 minutes, then continue to desired curing temp and dwell for prescribed time.
However, not all autoclave carbon is the same so I suggest that you check with your supplier to see if your stuff is suitable for OOA.
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Hanaldo
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+xI bought some out of date autoclave (just approaching its best before date) carbon from a supplier at a very good price, it would have been rude not to. Their help desk said that it could be used OOA if the following procedure was followed. Lay up first two layers, using a roller to compress the layers firmly together, then vacuum bag for 8 hours. Unbag and add next layers and repeat until all the carbon is in the mould. Vacuum up and place in oven. Bring up to 80 deg C and dwell for 30 minutes, then continue to desired curing temp and dwell for prescribed time. However, not all autoclave carbon is the same so I suggest that you check with your supplier to see if your stuff is suitable for OOA. Have you actually tried it though, did it work as described? I've tried samples of autoclave pre-preg from several different suppliers who all claim that it will work OOA. None of them gave good results in composite moulds, very bad porosity. Worked ok on glass and metal tools (not perfect but salvageable with some clear coating) so I feel this is what the manufacturers base their recommendations on.
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Steve Broad
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+x+xI bought some out of date autoclave (just approaching its best before date) carbon from a supplier at a very good price, it would have been rude not to. Their help desk said that it could be used OOA if the following procedure was followed. Lay up first two layers, using a roller to compress the layers firmly together, then vacuum bag for 8 hours. Unbag and add next layers and repeat until all the carbon is in the mould. Vacuum up and place in oven. Bring up to 80 deg C and dwell for 30 minutes, then continue to desired curing temp and dwell for prescribed time. However, not all autoclave carbon is the same so I suggest that you check with your supplier to see if your stuff is suitable for OOA. Have you actually tried it though, did it work as described? I've tried samples of autoclave pre-preg from several different suppliers who all claim that it will work OOA. None of them gave good results in composite moulds, very bad porosity. Worked ok on glass and metal tools (not perfect but salvageable with some clear coating) so I feel this is what the manufacturers base their recommendations on. I have no idea of porosity but there are very few pin holes. As I paint the carbon I am not interested in a mirror finish so my moulds aren't polished so can't speak for the quality of a shiny surface.   
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Chris Rogers
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I think Steve is on to something. The resin viscosity is temperature related, so if you can get to the right curing temperatures then you should be ok. Unless the resin is very high viscosity and needs the pressure (unlikely) then you should be fine. Debulking will be the most important factor in laminate porosity. Increasing the "dwell" at 80C to an hour or more (especially with a heavy tool or with core) will allow the resin to "flow" more before the curing process starts. If you have surface issues, try a "hot debulk" of the first two layers. Just bag them (I like to leave the backer on, spiky roll it, and cover with infusion flow-mesh) and heat under vacuum bag to 60C or so - enough to make the resin flow but not cure. You only need maybe half an hour of this debulking - not sure where the 8 hours they recommend came from. If you are making a part with many layers, try to repeat the debulking procedure every 1000g of material or so. Lack of debulking and slip joints are two areas where prepreg lamination can go off the rails. Mold finish also effects surface porosity a lot - which is why the same process in a polished aluminum mold will look better than in a composite mold sanded to 320 grit. Adhesive teflon is great for this for one-off molds because it has very low surface tension. Moisture can be a real problem especially if the prepreg is unwrapped cold and condensation forms on it. This is why is is always key to store prepreg in a sealed bag and to defrost it to room temperature while it is still in the sealed bag - the condensation forms on the bag, not the material.
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Steve Broad
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+xI think Steve is on to something. The resin viscosity is temperature related, so if you can get to the right curing temperatures then you should be ok. Unless the resin is very high viscosity and needs the pressure (unlikely) then you should be fine. Debulking will be the most important factor in laminate porosity. Increasing the "dwell" at 80C to an hour or more (especially with a heavy tool or with core) will allow the resin to "flow" more before the curing process starts. If you have surface issues, try a "hot debulk" of the first two layers. Just bag them (I like to leave the backer on, spiky roll it, and cover with infusion flow-mesh) and heat under vacuum bag to 60C or so - enough to make the resin flow but not cure. You only need maybe half an hour of this debulking - not sure where the 8 hours they recommend came from. If you are making a part with many layers, try to repeat the debulking procedure every 1000g of material or so. Lack of debulking and slip joints are two areas where prepreg lamination can go off the rails. Mold finish also effects surface porosity a lot - which is why the same process in a polished aluminum mold will look better than in a composite mold sanded to 320 grit. Adhesive teflon is great for this for one-off molds because it has very low surface tension. Moisture can be a real problem especially if the prepreg is unwrapped cold and condensation forms on it. This is why is is always key to store prepreg in a sealed bag and to defrost it to room temperature while it is still in the sealed bag - the condensation forms on the bag, not the material. The 8 hours is due to my failing memory. On checking my notes it is an hour :-)
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Mariusz
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Guys, im sorry for little off topic, but at the moment i don't have a facility to store large curing equipment at home. Is there any other way to work on prepreg without autoclave or oven ?
Also using same opportunity would like to ask if anyone heard about co-operation spaces to work on carbon fibre? I was thinking off to rent garage, but things like temperature or even access to the enough power is challanging. I am located in West Midlands - Tamworth
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Steve Broad
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Group: Forum Members
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+xGuys, im sorry for little off topic, but at the moment i don't have a facility to store large curing equipment at home. Is there any other way to work on prepreg without autoclave or oven ? Also using same opportunity would like to ask if anyone heard about co-operation spaces to work on carbon fibre? I was thinking off to rent garage, but things like temperature or even access to the enough power is challanging. I am located in West Midlands - Tamworth The definition of an oven is very loose. As long as you can sustain a temperature of around 100-120 deg C for around 4 hours (temp and time will vary depending on the resin used in the carbon but this will work with most) with the carbon under vacuum then you are good to go. Basically, all you need is heat and vacuum. With regard to power, all you need is access to a 13amp 220v supply. What size are the parts you are thinking of making?
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