Bubbles rising back into resin cup


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Leon
Leon
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Hi..

Looking on your project, it was soo impresive. What you've done adapted from closed mould system generaly applied by RTM (resin transfer moulding),  yes for a moment  it's look simple but when I look inside it turns "The devil is always on the detail". first in closed mould system the resin flow under pressure from RTM infuser, its look like a pump push inject the resin, second the mould flanges are sealed with some kind like a sillicon ruber as a containment sealer, to keep the resin stay on the moud. And third is vacum assist are necessary to help  sealed the mould and maintaining low pressure then resin could be easisly spread all the area and focus on vacum line catchpot point. fourth, many manufacture using close mould made the upper moulding with transparant form so they can monitoring the resin flow. Gloss both side on the part would be nice 

Have a luck

Leon
Edited 13 Years Ago by Leon
fgayford
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Your tear drop looks really neat. As for the guy who said that you need the vacuum pump higher than the mold. It seems to me that what he is doing is by having the vacuum pump lets say 4 feet higher during infusion, excess resin coming out would have a harder time getting into the pump for it would have to travel UP 4 feet of line. If the pump was on the ground it would flow into the pump immediately. He was probably not using a catch pot. As far as vacuum goes, it doesen't matter where the pump is. 

Fred     
Warren
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be careful when heating the resins you dont warm them up too much.

Heat it too much and the resin will cure really quickly when its mixed up as it cures exothermically and you will build up a lot of heat in a pot.  Much over 30 degrees celsius and you might have issues with large quantities of resin.
fgayford
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I have a special valve on my large catch pot. It is very fine in its increments. So I adjust it to decrease my vacuum by letting air into my catch pot which my vacuum pump cannot overcome. I can set it to constant 15 HG all the way up to full vac.

Fred 
prairiecustomcomposites
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Thanks for all the advice guys. I have since pulled two more from that mould, and both turned out great. I think allowing it to FULLY de-gas has helped tremendously, and heating the resin and mould makes a world of difference too.

For these parts, I am using 31grams of mixed epoxy, and it takes about 5 minutes to fully de-gas. I am using infusion grade epoxy, and have degassed at full vacuum and it doesn't appear to boil off any solvents (as it still hardens at the end of the cure cycle). I definitely see this as a problem with other epoxies, so it is a good thing to be aware of, but it doesn't appear to affect the epoxy I am using.

The nice thing about my setup, is I can de-gas the epoxy right in the resin pot, and then remove the vacuum line and begin infusing right away. It eliminates the air that would normally be between the epoxy and the line clamp to begin the infusion. The picture below is the modified cup



The plastic cup I am using is actually from the local dollar store, and has a silicone seal for its lid. I just drill and tap a couple connectors on the top and bottom, and now it is really easy to see how fast the resin is being sucked into the part. This works nicely for testing new moulds where the exact amount of resin required is unknown. The cup is also double walled, so if I ever get fancy, I might include a water-jacket in between the two walls to help regulate heat inside the resin pot.

Anyway, here are two pictures of the new, untrimmed "teardrops" with no bubbles or imperfections.


Teardrop #2


Teardrop #3


Teardrop Mould

As a side note, I have found it very easy to place the fabric inside the mould even without using any spray-tac. I used the first teardrop mould as a buck (the one with bubbles and general nastiness) to press the fabric into place inside the mould. While I hold it there, I tape down the edges of the fabric to the flanged area on the mould. Now, when I pull the teardrop shape buck out, the fabric is well placed. Then, when I am setting the vacuum bag up, I begin by placing the vacuum bag around the teardrop shape buck and set it into the mould. This way, I know the vacuum bag will be able to reach the inside and not create any bridging. It has worked fantastically well, and while it may not work on every mould (especially ones with a really thick layup), it certainly worked here.


To summarize, here are the important steps I have learned from these tests.

1. Always fully de-gas the resin. It makes a huge difference in the amount of bubbles that travel through your part. Visually, once the resin reaches the vacuum port at the end of the part, there were noticeably less bubbles as compared to when I did not de-gas.

2. Heating the mould and heating the epoxy makes everything easier.
It allows the epoxy to flow much easier, it de-gases faster, its just a plain old  good idea when infusing to warm everything up. I want to get an infrared thermometer to measure how just how warm, "warm" should be.

3. Ensuring that there are no leaks is insanely crucial. I saw on another forum that some people will infuse as long the leakdown test does not drop more than 0.5inHg in an hour. I have had infusions that came out perfect with 0.5inHg leakage per hour, and have had infusions that have failed horribly with 0.5inHg leakage per hour. So I don't know where I stand yet on this, but I am certain through my tests above, that a leak is what caused the resin to climb back up the resin feed line on my original panel. I think NikCFC is right about the bubbles, so find those leaks! Regardless, check out Fred's post about sealing edges of infusion mesh and spiral tubing.

4. Think of how gravity/buoyancy will effect any air inside the mould.
This is still in the testing phase, and I am certain it is not necessary if you have a fully sealed bag, but on both successful infusions of the teardrop, I setup the mould so that the resin inlet was below the vacuum inlet. I did this because I noticed something very interesting about the first failed infusion of the teardrop. There were bubbles trapped in the part, but they clung to the carbon fiber, almost as if they were trying to rise to the top of the part (on the backside), but were blocked by the fabric. I figured I could avoid this in my next teardrops by letting gravity/buoyancy allow the bubble to rise up to the vacuum inlet, in hopes that they would get sucked up. Again, I doubt this has any relevance, especially if you have no leaks and have de-gassed properly, but it is something I will try to test and determine its effectiveness.


Overall I am pretty happy with my procedure now. And I do want to thank everyone who has pitched in some information. I hope to keep posting and updating with new tests and projects on this thread. Now what to do with all these random teardrops? Christmas ornaments? I should have designed a testing mould for something that was useful haha.



But onto my next question. I saw someone mention that you HAVE to have your vacuum pump operating at a higher location than your resin pot for a good infusion. I could not for the life of me think why that would be the case. I can't ask him as his post is a couple years old, and I don't think hes been active on that forum for a while. So fellow composites people, any ideas why?
Edited 13 Years Ago by prairiecustomcomposites
NikCFC
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Considering #3 you don't want to re-infuse the resin in the catch pot because it's full of air. As far as the bubbles rising back in the resin cup you have a leak near the resin inlet and air finds the closest way out.

Fgayford how do you keep constant 24HG pressure? do you allow a small amount of air entering the system so you can regulate the pressure? 
Edited 13 Years Ago by NikCFC
Warren
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degas the resin properly to start with.

Ive seen what looks like boiling when you apply vacuum initially but it is just gases from mixing coming out.  If you increase the vacuum slowly then it isnt so obvious. Also once degassed for a few minutes, bringing back to atmos then back to vac causes no bubbling because theres no gas present.
Kevin-Lee
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Hi,

Modern infusion grade epoxy (like the IN2 from EC) CAN NOT BOIL or OUT GAS!!! It is 100% solids and has NO solvents! But if your using polyester, or even non infusion epoxy then the chances are it will boil, hence the reason for only pulling at -25psi with those and not the full -30psi...

Kev.
fgayford
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Hear is one more thing to consider. When you degass you are exposing the epoxy to full 29.9 HG and what happens? It boils and out gases.

Now if we infuse with full vac 29.9 it stands to reason that it will expose the resin to full vac again and what's going to happen? It is going to boil in our part. So closest to the vacuum source is where you have your pin holes because it is exposed to full vac but the feed line side is no longer exposed.

So I have been in a habit of infusing at 24 HG where I know there will be no out gasing in the part.

What do you guys think of that?

Fred
Matthieu Libeert
Matthieu Libeert
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thanks for sharing that information!

Matthieu Libeert
Founder MAT2 Composites X Sports
website:
www.mat2composites.com




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