Carbon Fiber Layup Problem

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rsmith98

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I recently started using a vacuum pump for my carbon fiber layups. Previously I used heat shrink which does the job but it's not ideal for outer tubes because it creates lumps in layup which take forever to sand out. My issue with the vacuum layups is the mylar. I want to wrap it around the mandrel so that it's loose enough to slide the layup off once it's finished, but not loose enough to where it creates wrinkles in the layup. It's just really difficult to get the mylar on there smoothly in the first place. It seems to wants to wrinkle up. I was wondering if there's an alternative to using mylar on the mandrel. I did some research and I was wondering if wrapping the mandrel in teflon sheets would help? Or maybe Partall Hi-Temp wax? Just something that the epoxy will not stick to and something that will make it so that I can slide the layup off of the tube relatively easily once the layup has dried. Does anyone have any ideas?
 

AeroAggie

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What is your mandrel made of? Polished aluminum with something like Frekote should work just fine. Frekote is semi-permanent, in that if you prep properly, you can pull multiple parts off a tool before having to reapply.
 

G_T

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You can get spray on low temp mold release wax. Spray on multiple layers to build up a coating of a little thickness. Lay up the part, vacuum, and let cure. DO NOT POST CURE! No elevated temps. Once initial cure is done, then put the part in a hot water bath - a bathtub will work - and this melts the wax. Then slide the part off.

Post cure the part afterwards at an elevated temperature.

Gerald

PS - Freekote, PVA, other alternatives, are not likely to release well given (1) carbon fiber is very stiff, and therefore (2) the release is in shear over a large area. Melted wax forms a lube of sorts, like a thick grease, and also provides the clearance for the part to slide.
 
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watheyak

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+1 on the Frekote! Tubes release nearly effortlessly after a chill.

I tried it with mylar a few times early on, but quickly abandoned it. Works great without any compression, but once you put the squeeze on it it makes it really difficult to remove the tube from the mandrel.

I now use a polished aluminum mandrel and Frekote 700. Works great. I also use it for elevated cure temperatures.
 
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mpitfield

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Although I have a few dozen CF layups under vacuum at this stage, including some complex 3D shapes I have yet to roll my own. However I have watched quite a few videos on YouTube on the subject. Here are a few links that may be informational for you.

I am pretty sure that tfish has a video on it, here is a link to his channel
https://www.youtube.com/user/tfish38/videos

Here is another one from a guy named Mark Joseph, which has some good tips
[video=youtube;TwfyvkGAPjQ]https://www.youtube.com/watch?v=TwfyvkGAPjQ[/video]

I am pretty sure I watched one from John Coker as well, but to be honest I can't recall I have watched so many of his how-to videos I may be getting him mixed up, still a great resource
https://www.youtube.com/user/JohnLCoker/videos

I do like the the simplicity of Gerald's method above, that one is new to me.
 

markjos

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Here is another one from a guy named Mark Joseph, which has some good tips
[video=youtube;TwfyvkGAPjQ]https://www.youtube.com/watch?v=TwfyvkGAPjQ[/video]
In all fairness, the presentation was by Steve Dramstad (SDramstad), who makes lots of his own composite tubes. I just shot the video.

Mark
 

amarillo_rocket

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What is the thickness of your mylar? I have used mylar exclusiverly for my CF airframes and never had an issue with wrinkling the mylar. It sounds like your mylar may be too thin. I normally use .005 to .007 mylar.
 

rsmith98

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For those that were wondering, I'm using a 6inch diameter aluminum mandrel
 
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