Bubbling at the end of the degas


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Raf4C
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Dear all, I need again your precious advices. I started a couple of years ago to make composite laminates by using vacuum infusion with easycomposite equipment and materials. I am satisfied of the laminates that I obtain. However, last week I experienced a new problem. I was degasing the resin+hardener before the infusion (I use the EC20 pump with the big vacuum chamber), the bubbling phase was almost finished, and then, suddenly, the bubbling started again for few seconds. Afterwards, it started again and then stopped after few seconds. This was repeated few times before I stopped the process. It was the first time that this happened. However, I decided to make the infusion with that resin and the results is that I had some voids in the plate that I produced (of course the bag was super OK). Anyone of you can help me regarding this problem? Any Idea?
Hanaldo
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Likely to be some moisture in there. If the hardener is a bit old then that is the likely culprit, epoxy hardeners are hygroscopic and will absorb a bit of moisture from the atmosphere.

In any case, degassing isn't necessary for void-free results with infusion, so the fact you got some voids in your laminate isn't likely to be due to the fact the resin didn't degas.
Raf4C
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Hanaldo - 2/11/2021 11:56:45 PM
Likely to be some moisture in there. If the hardener is a bit old then that is the likely culprit, epoxy hardeners are hygroscopic and will absorb a bit of moisture from the atmosphere.

In any case, degassing isn't necessary for void-free results with infusion, so the fact you got some voids in your laminate isn't likely to be due to the fact the resin didn't degas.

Thanks a lot Hanaldo for your message. The hardener and the resin were new. I opened them few minutes before mixing. I could try a new infusion without degasing but I am not sure if this is the problem.

Hanaldo
Hanaldo
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Pinholes and voids with infusion tend to be related to other issues, rather than degassing. The only time I have ever found degassing to help, is when you have bridging or areas of fine detail that you can't get fibres into (which is essentially still bridging), as these areas are where the air bubbles will accumulate and hold. So if you had those issues and you didn't degas, there's a good chance they will end up either looking cloudy because they have a million tiny bubbles. 

But if you have a really good layup with no bridging anywhere, then the air bubbles and other potential volatiles that are in the resin dont tend to show up as voids or pinholes. On inspection with an electronic microscope you may be able to detect a higher void content in the matrix, but there certainly shouldn't be any visible defects or porosity at all. If its visible, it is likely another problem. If your vacuum is solid, I would be looking at infusion speed (especially if your layup has any areas with staggered thickness), and resin content. Being a tiny bit too lean can have a big effect on surface finish and porosity level, which becomes especially noticeable if you are clear coating. So for cosmetic parts, its a good idea to lean on the slightly resin rich side and leave the resin feed open a touch longer - especially considering the actual weight difference this makes to the part once you have removed the consumables is very negligible. 
Raf4C
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Hanaldo - 2/12/2021 2:23:25 PM
Pinholes and voids with infusion tend to be related to other issues, rather than degassing. The only time I have ever found degassing to help, is when you have bridging or areas of fine detail that you can't get fibres into (which is essentially still bridging), as these areas are where the air bubbles will accumulate and hold. So if you had those issues and you didn't degas, there's a good chance they will end up either looking cloudy because they have a million tiny bubbles. 

But if you have a really good layup with no bridging anywhere, then the air bubbles and other potential volatiles that are in the resin dont tend to show up as voids or pinholes. On inspection with an electronic microscope you may be able to detect a higher void content in the matrix, but there certainly shouldn't be any visible defects or porosity at all. If its visible, it is likely another problem. If your vacuum is solid, I would be looking at infusion speed (especially if your layup has any areas with staggered thickness), and resin content. Being a tiny bit too lean can have a big effect on surface finish and porosity level, which becomes especially noticeable if you are clear coating. So for cosmetic parts, its a good idea to lean on the slightly resin rich side and leave the resin feed open a touch longer - especially considering the actual weight difference this makes to the part once you have removed the consumables is very negligible. 

Maybe you got the point, I used a new resin (very low viscosity) and the infusion was looked very quick. In your opinion, should I try to reduce the infusion speed? Thanks again. 

Hanaldo
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It depends. For small parts (less than 0.5sqm) I probably would limit the infusion speed to about 1" per minute. For anything bigger, it tends to regulate itself better and you dont have as much lag between the top of the laminate and the tool surface.
Chris Rogers
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I agree with Hanaldo on the slow it down thing.  Over-running trapped air, vapor or whatever can cause it to get trapped and make voids.  Was your material all very dry too?  You don't say what your laminate is but is there core?  When you're sure leaks aren't the problem I always look to vapor issues next... and sometimes its a thing.

I disagree with the whole Easy Composites method of turning off the vacuum after the part is filled. 

Documented in this post I did last year:  https://explorecomposites.com/articles/lamination/troubleshooting-vacuum-infusion/ 

It can clearly be done both ways so maybe I'm making too much of it but my opinion is that if you have any leak or trapped air issues this will make them worse.  Degassing is a good idea if you need perfect cosmetics and have the time.  In theory is shouldn't be that useful but it can make a big difference sometimes for reasons I'm not 100% on. There's something fishy about your mix still bubbling after you thought it should have stopped.  If there's gas or volatile stuff in there it will just keep coming.  The vapor pressure vs. vacuum level could be causing moisture to be released only after the vacuum level gets really high - after your normal trapped air bubbles boil off and the resin should be fine.  Shouldn't happen with new resin though! 

Check this out from Vacmobiles in NZ - excellent description of the vapor issue: https://www.vacmobiles.com/vapour_pressure.html

Good luck!




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