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dilligaf76
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Hi, can anyone tell me what the required Vacuum pressure is required for wet laying Carbon Fibre?
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Steve Broad
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+xHi, can anyone tell me what the required Vacuum pressure is required for wet laying Carbon Fibre? As much as you can manage, IMO. The better the vacuum the better the compaction and carbon/resin ratio. Extreme vacuums are not essential when wet laying, again IMO, but if your vacuum pump can manage 99.95% that will be good.
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dilligaf76
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Group: Forum Members
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+x+xHi, can anyone tell me what the required Vacuum pressure is required for wet laying Carbon Fibre? As much as you can manage, IMO. The better the vacuum the better the compaction and carbon/resin ratio. Extreme vacuums are not essential when wet laying, again IMO, but if your vacuum pump can manage 99.95% that will be good. I've heard that could draw out to much resin and be too dry and cause pin holes etc...
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Steve Broad
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Group: Forum Members
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+x+x+xHi, can anyone tell me what the required Vacuum pressure is required for wet laying Carbon Fibre? As much as you can manage, IMO. The better the vacuum the better the compaction and carbon/resin ratio. Extreme vacuums are not essential when wet laying, again IMO, but if your vacuum pump can manage 99.95% that will be good. I've heard that could draw out to much resin and be too dry and cause pin holes etc... I used peel ply, perforated release film, two layers of breather cloth and the full vacuum capabilities of the EC pump (99.97%) and had no problems. By weight my carbon to resin ratio was between 100:45 and 100:50 with no visible dry patches, pin hoes or delamination. Image shows car floor under vacuum, showing the resin seeping into the breather cloth having been sucked through the peel ply and release film, 
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Chris Rogers
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I don't totally agree with Steve on the vacuum level - especially if you are doing thin-skinned parts or trying to do core in one shot. Its one of those things where there are lots of variables and one person's successful recipe of material and process won't translate if you change materials, resin viscosity or layup method. Mold surface and release system matter too when comparing surface finish outcomes. I have seen many cases of over-bleed or over-compaction with too much vacuum in wet-layup. If you are trying to make parts against a mold, 15-20 inHg or about 1/2 the potential vacuum should be fine. For secondary bonding or thicker parts (2mm+), full vacuum should be fine - and actually preferable. Make sure the mold you are vacuum-bagging to is fully air-tight or you will have problems. Envelope bagging is a good idea for small stuff. Also make sure there is enough resin in your surface layer if you are looking for a cosmetic finish. And rolling with a bubble-popper is a good idea. With core, the possibility of pulling resin out of the bottom skin if you are pulling too much vacuum is very real. Core edges should be well tapered too. For cosmetic parts (carbon) - doing a wet-preg method with wet-out on plastic can give very good results. Here's a simple example in a video I made: https://youtu.be/06-0Vxs_9nYThis method is extra helpful when you have patterns and slip-joints - which you should totally have for a more complex shape.
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dilligaf76
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+xI don't totally agree with Steve on the vacuum level - especially if you are doing thin-skinned parts or trying to do core in one shot. Its one of those things where there are lots of variables and one person's successful recipe of material and process won't translate if you change materials, resin viscosity or layup method. Mold surface and release system matter too when comparing surface finish outcomes. I have seen many cases of over-bleed or over-compaction with too much vacuum in wet-layup. If you are trying to make parts against a mold, 15-20 inHg or about 1/2 the potential vacuum should be fine. For secondary bonding or thicker parts (2mm+), full vacuum should be fine - and actually preferable. Make sure the mold you are vacuum-bagging to is fully air-tight or you will have problems. Envelope bagging is a good idea for small stuff. Also make sure there is enough resin in your surface layer if you are looking for a cosmetic finish. And rolling with a bubble-popper is a good idea. With core, the possibility of pulling resin out of the bottom skin if you are pulling too much vacuum is very real. Core edges should be well tapered too. For cosmetic parts (carbon) - doing a wet-preg method with wet-out on plastic can give very good results. Here's a simple example in a video I made: https://youtu.be/06-0Vxs_9nYThis method is extra helpful when you have patterns and slip-joints - which you should totally have for a more complex shape. Thank you Chris you seem to know what you're talking about and have educated me a little more than to what I already know, a massive help and appreciate all the comments on here from everyone...
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Steve Broad
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Group: Forum Members
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+x+xI don't totally agree with Steve on the vacuum level - especially if you are doing thin-skinned parts or trying to do core in one shot. Its one of those things where there are lots of variables and one person's successful recipe of material and process won't translate if you change materials, resin viscosity or layup method. Mold surface and release system matter too when comparing surface finish outcomes. I have seen many cases of over-bleed or over-compaction with too much vacuum in wet-layup. If you are trying to make parts against a mold, 15-20 inHg or about 1/2 the potential vacuum should be fine. For secondary bonding or thicker parts (2mm+), full vacuum should be fine - and actually preferable. Make sure the mold you are vacuum-bagging to is fully air-tight or you will have problems. Envelope bagging is a good idea for small stuff. Also make sure there is enough resin in your surface layer if you are looking for a cosmetic finish. And rolling with a bubble-popper is a good idea. With core, the possibility of pulling resin out of the bottom skin if you are pulling too much vacuum is very real. Core edges should be well tapered too. For cosmetic parts (carbon) - doing a wet-preg method with wet-out on plastic can give very good results. Here's a simple example in a video I made: https://youtu.be/06-0Vxs_9nYThis method is extra helpful when you have patterns and slip-joints - which you should totally have for a more complex shape. Thank you Chris you seem to know what you're talking about and have educated me a little more than to what I already know, a massive help and appreciate all the comments on here from everyone... As I mentioned twice, IMO :-) I can only comment on my experience and Chris is quite right that this is a movable feast :-) The only way to find out is to experiment with the method and materials you plan to use. my floor was two layers of carbon, 1/8" core and two more layers of carbon. Full vacuum worked fine for me on this job and many others. A lower vacuum will certainly reduce the risk of defects but will add weight and reduce compaction, but if these aren't a concern then not a problem using a lower vacuum. Only one way to find out..... :-)
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taimur
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Vacuum bagging is a technique employed to create mechanical pressure on a laminate during its cure cycle. Pressurizing a composite lamination serves several functions. First, it removes trapped air between layers. Second, it compacts the fiber layers for efficient force transmission among fiber bundles and prevents shifting of fiber orientation during cure. Third, it reduces humidity. Finally, and most important, the vacuum bagging technique optimizes the fiber-to-resin ratio in the composite part. These advantages have for years enabled aerospace and racing industries to maximize the physical properties of advanced composite materials such as carbon, aramid, and epoxy.
What is Fiber-To-Resin Maximization and Why Is It Important?
The reason that composites are used increasingly is the strength-to-weight advantages that they offer. The key to obtaining these advantages is maximizing the fiber-to-resin ratio. The reinforcement (fiberglass, aramid Kevlar®, carbon, etc. is not particularly strong in the textile state. Also, thermosetting resins such as polyester and epoxy are quite brittle if cured without reinforcement. If excess resin exists in the laminate, the laminate will have more of the properties of resin only. If too little resin exists, places where the reinforcement is dry will cause weak spots. To optimize the resin content, the entire reinforcement must be saturated with resin with as little excess as possible. The technique of "squeezing out" excess resin to obtain a maximized fiber-to-resin content is the theory of vacuum bagging.
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oekmont
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Theoretically this is 100% true. In most practical hobbyist applications vacuum is applied to keep the carbon cloth in the edges of the mould during cure and that's it. If if you apply 50% vacuum (wich I recommend) it will already remove almost all excess resin. The coth will be pressed together untill the vacuum force equals the force the cloth creates because of fibre stiffness (measure the cloth carefully with a caliper, then again, but press the caliper hard together. There will be a small difference). The resin itself can't create forces to withstand the vacuum while it's liquid, that is the physical definition of a liquid. 100% vacuum will only press the fibres a little bit more together, wich will result in a slightly higher fibre content.
There is nothing like sucking out to much resin. If there is already no pressure in the resin, there is no force wich will move the resin out of the laminate. What really happens is that you degas the resin inside your laminate if you apply too much vacuum. And since there is no movement in the resin, the air can't escape the laminate and will accumulate at the fibre crossings.
If you degas resin in a clear view chamber, you will see that almost nothing happens until you reach about 90% vacuum. But after that an air volume many times that of the resin will be released. Under vacuum pressure, but in case of vacuum bagging the resin will cure that way.
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Steve Broad
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Group: Forum Members
Posts: 408,
Visits: 4.1K
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+xTheoretically this is 100% true. In most practical hobbyist applications vacuum is applied to keep the carbon cloth in the edges of the mould during cure and that's it. If if you apply 50% vacuum (wich I recommend) it will already remove almost all excess resin. The coth will be pressed together untill the vacuum force equals the force the cloth creates because of fibre stiffness (measure the cloth carefully with a caliper, then again, but press the caliper hard together. There will be a small difference). The resin itself can't create forces to withstand the vacuum while it's liquid, that is the physical definition of a liquid. 100% vacuum will only press the fibres a little bit more together, wich will result in a slightly higher fibre content. There is nothing like sucking out to much resin. If there is already no pressure in the resin, there is no force wich will move the resin out of the laminate. What really happens is that you degas the resin inside your laminate if you apply too much vacuum. And since there is no movement in the resin, the air can't escape the laminate and will accumulate at the fibre crossings. If you degas resin in a clear view chamber, you will see that almost nothing happens until you reach about 90% vacuum. But after that an air volume many times that of the resin will be released. Under vacuum pressure, but in case of vacuum bagging the resin will cure that way. Then why do EC proclaim that their EC.4 pump reaches 99.98% vacuum and autoclaves add even more pressure, if this isn't that important?
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