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Help with Vacuum Bag
Help with Vacuum Bag
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vniebles
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vniebles
posted 5 Years Ago
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Hi everyone, I was wondering if you guys could help me troubleshoot. I had some issues vacuum-bagging a 4' x 2' sandwich core panel. We used 18 oz. of epoxy resin/hardener for 27 oz of plain weave carbon fiber to follow a 40/60 ratio of resin to carbon fiber. We had a laminate sequence of 0/180/core/180/0. We had issues pulling a vacuum but we managed to achieve a vacuum level of 23 in Hg. During the layup, the carbon fiber seemed saturated with resin but I found today that the resin did not fully wet out the carbon fiber. We also had issues with striations on the surface and strands of breather sticking to the top of the layup. I believe our issues are a combination of not using enough resin (by not accounting for the resin uptake of the Nidacore) and not pulling a high enough vacuum. However, I would really appreciate any insight into this. I have attached some pictures of the panel for reference. Thanks!
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Help with Vacuum Bag
vniebles
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5 Years Ago
If this is wet lay vacuum bagging then 23inhg is generally too much vacuum so could have made things worse by squeezing out more resin. Generally we tend to recommend around 6-7 inHg as a starting...
Warren (Staff)
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5 Years Ago
Interesting comment. Years ago I asked an Airtech support person some questions on vacuum bagging. He suggested pulling a full vacuum and after a short 'period of time' backing off to 10hg to let the...
ahender
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5 Years Ago
Are you sure you have this the right way round? I remember seeing an Airtech research paper on the vacuum bagging process, and in that paper they were talking about taking advantage of the resin...
Hanaldo
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5 Years Ago
Hi Warren, thanks for the reply! I definitely agree that 60/40 was unrealistic, I'll just try applying an equal weight of resin to carbon fiber next time, hopefully that should be sufficient for any....
vniebles
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5 Years Ago
We've always recommended 20% vacuum which is around 6-7inHg. Without testing, its hard to know the virtue of Airtechs method. But in theory it could help to get all the air out initially but it...
Warren (Staff)
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5 Years Ago
thats is an interesting info given by Warren. Just for stiffness testing tI did a 1/2 sqm panel with 5x 600gsm biaxial and the ridgidity was not impressive and it was thinner then expected. That is.....
torstenker
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5 Years Ago
Compressing and consolidating the fibres are different but linked. In some cases a bit of compression is useful to avoid voids and excessive resin content. Also in some woven cloths it can be...
Warren (Staff)
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5 Years Ago
I agree with Warren that less vacuum is usually best - I use 15inHg as a starting point but often 8 is plenty, especially with thin laminates... you just bleed off less resin. The key is that you nee...
explorecomposites
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5 Years Ago
Thank you Chris.
ahender
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5 Years Ago
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