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Wrinkles, WTF

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Erinhdisc
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Wrinkles, WTF

Postby Erinhdisc » Fri Sep 04, 2020 8:23 pm

This is a sandwich construction XPS with 3mm divinycel top and bottom. This bottom layup is 2 layers of 6 oz carbon and 1 layer of 6oz uni. Applied them with wet layup technique on plastic sheet. Everything was very smooth no wrinkles or bubbles. Used perforated peel ply to wrap board then breather cloth. I payed special attention to smoothing bag material and pulling around wrapped rails so bag was smooth where carbon was. Used only 15 hg, partly because I am high altitude and partly because core is xps. Pulled it out of the bag and it is not good. Very wrinkled with what seems like lifted areas of cloth into the wrinkles. I felt I did everything right. Had never used this peel ply before and it was almost zero stretch and can't follow contours. The flat bottom of the board was as bad as anywhere though...I see my only option as sanding all ridges down and putting another layer over the top. Its pretty disappointing, especially since I don't know why I got such a poor result. Any insights?
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kitexpert
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Re: Wrinkles, WTF

Postby kitexpert » Sat Sep 05, 2020 1:32 am

What does 15 hg means? Some Hg pillar height pressure but who knows what.

In SI units normal air pressure is 1013mbar or 1.013bar of 1013hPa. If you have 50% vacuum then you have 50% atmospheric over pressure on your work piece, that is about 50 000Pa or 50kPa or 0.5bar. Then every cm2 has 5N (equals 0,5kg weight) of pressure which is usually enough. I've used 90% vacuum or more and never had any problems with pressing too hard, not even when using foam cores.

Working in high altitude need better vacuum if anything.

Wrinkles mean laminates have somehow creeped before epoxy has cured. Have to sand down of course

Erinhdisc
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Re: Wrinkles, WTF

Postby Erinhdisc » Sat Sep 05, 2020 4:53 am

Yes, 15 inches of mercury or .5 bar. New theory: the perforated ply was unable to let enough resin pass through it and the wrinkles are excess epoxy with nowhere to go. This, combined with not enough vacuum...also I am not sure of the maximum number of layers you can get away with while doing a single layup. This was 3 with patch over box channels. Maybe I had too much resin in the cloth and under vacuum pressure the resi. Needed to purge but couldn't. I sanded it down and it was nasty. I'm going to go with nylon peel ply for the save. Hoping for better luck on top layup and will use 20 hg, which is all I can pull at 6500' elevation. I still think that what happened with these wrinkles is very odd and I have never seen it before when vacuum bagging. Would be greatful for insights that would give my confidence back.

handy
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Re: Wrinkles, WTF

Postby handy » Sat Sep 05, 2020 6:30 am

Pretty sure it's excess resin that filled up the wrinkles in vour vac bag. Just sand em down and you will be fine

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Re: Wrinkles, WTF

Postby jaros » Sat Sep 05, 2020 7:28 am

Erinhdisc wrote:
Fri Sep 04, 2020 8:23 pm
This is a sandwich construction XPS with 3mm divinycel top and bottom. This bottom layup is 2 layers of 6 oz carbon and 1 layer of 6oz uni. Applied them with wet layup technique on plastic sheet. Everything was very smooth no wrinkles or bubbles. Used perforated peel ply to wrap board then breather cloth. I payed special attention to smoothing bag material and pulling around wrapped rails so bag was smooth where carbon was. Used only 15 hg, partly because I am high altitude and partly because core is xps. Pulled it out of the bag and it is not good. Very wrinkled with what seems like lifted areas of cloth into the wrinkles. I felt I did everything right. Had never used this peel ply before and it was almost zero stretch and can't follow contours. The flat bottom of the board was as bad as anywhere though...I see my only option as sanding all ridges down and putting another layer over the top. Its pretty disappointing, especially since I don't know why I got such a poor result. Any insights?
Did you do just one side of the board or top and bottom at the same time?

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Re: Wrinkles, WTF

Postby windmaker » Sat Sep 05, 2020 9:19 am

handy wrote:
Sat Sep 05, 2020 6:30 am
Pretty sure it's excess resin that filled up the wrinkles in vour vac bag. Just sand em down and you will be fine
:thumb:

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Re: Wrinkles, WTF

Postby merl » Sat Sep 05, 2020 4:20 pm

I guess when you say perforated peel ply what you mean is perforated release film. I suspect that if you had used real peel ply (a woven synthetic fabric) under the release film then you would have gotten a better finish.

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Re: Wrinkles, WTF

Postby TomW » Sat Sep 05, 2020 5:27 pm

it seems you did not use correct schedule of vacuum consumables.
1. Make sure you stretch out carbon fabric after you put in down on the blank using a squeegee.
2. Then woven peel ply. Use squeegee to pull i even.
3. Perforated film, then pull that around edges with masking tape .
4. Absorber.tape it in place
5. Put it in vbag and even out the bag, on bottom. pull up pressure, then release it , work bag around rails , ramp up pressure again.

Erinhdisc
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Re: Wrinkles, WTF

Postby Erinhdisc » Sat Sep 05, 2020 9:59 pm

Thanks builders. I think I failed by not using peel ply and thinking that perforated film did the same thing. While sanding the wrinkles down it was evident that I went through most of top twill layer and partially into the unidirectional in some spots. This leaves one fully intact base layer 3/4 of the uni and a 16" x 12" reinforcement patch over chinook boxes. All these layers are/were 6 oz cloth. Is a single 6oz layer over the top enough for a strong board. Top will be 2x 6 oz carbon twill with extra 12” wide uni running full length. Also is it a good idea to do all these layers in one bagging operation?

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Re: Wrinkles, WTF

Postby fluidity » Sun Sep 06, 2020 12:56 am

I feel for your pain, been there myself.
Peelply is a very tightly woven plastic. It will breath through the plastic but you also need another thicker breathing fabric over it to absorb the excess air and resin. Infusion mesh works really well for dispersing resin sideways and is of course used for resin infusion process as well.You could use stacked layers of paper towels over the peelply instead, so long as there are enough layers to easily absorb all the excess resin. In any case, it will give you a much better result.
And have to agree with the coment higher up, at a higher altitude, you are already at a very small partial vacume from being at a higher altitude, what you need is RELATIVE vacuum to your already lower pressure so you need an even lower pressure to acheive same result as those of us close to sea level would.

To describe the vacuum another way, you have air pressure all around you, when you vacuum out the air under the bag layer it's that air pressure pushing on the outside of the bag and forcing air and resin flow towards your vac tube. Higher altitude- less air pressure around that bag. And you need the flow from the far end of the bag to the vac tube, that's what the additional breather fabric is for.


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