Infusion problem with strechlon

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#1

I infused a part last night with a funny shaped core in it, so I wanted to give strechlon a shot. The part is kevlar and glass with a divinycel core that I scored every 3/4". The stack after the part consisted of infusion peel ply, green flow media, and the strechlon. I wrapped the spiral wrap in peel ply because it usually allows the resin to get to the ends of the wrap before infusing through the part. I did a leak check on the part prior to the infusion and it held vacuum with the pump off. I did this twice, once with the vacuum source on my resin-source T-fitting with the other side blocked off with sealant tape, and once with all lines in place and the source line clamped off. The results were the same. The resin used was PTM-W PT2712 w/B hardener (60 minute geltime at 77F).

15 minutes, 1/2" drop
25 minutes, 1" drop

I figured I was good, so I started infusing. Immediately I’m getting air bubbles that I find to be the resin source T-fitting and fix it immediately. Why would that show up THEN and not during my 25 minute leak check? In either case, although I’m pulling 26" the bag is now bridging on all the radii, and every radius has about a 1/8" pocket full of resin and air that aren’t making their way to the vacuum source. Under the vacuum why would that not suck down? The resin/air combo seemed to fill all of the radii and just hang out there while the remainder of the part infuses air bubble free. All the bubbles seemed to work their way through the bag when I applied a heatgun to the radii of the bag. The bag was also slowly sucking itself into the radius, before I got the bag too hot in one area and suddenly lost all vacuum :). I popped the bag, but at that point I was just gathering data.

This was all done in my garage, not the shop, at 55degrees F. Sooooo here’s what differed from my conditions in the shop where I do awesome infusions. Let me know what you think it might be.

1)I used stretchlon (800), instead of my usual ear-extraveganza bagging material
2) It was 55 degrees F, and I did not get the resin up to 77F. Possibly it wasn’t viscous enough to really let the air bubbles escape? Once I heated the resin/bubble rich areas, I got back my compaction and the air bubbles slowly disappeared.
3) I was using a 2.5 cfm pump. Once I introduced air bubbles, maybe i didn’t have enough cfm to crank down the bag quickly enough?

Sorry for the wordy post.
Pics:
first debulk/leak check

Resin rich bag, with resin filling all the radii


Closeup of frothy resin rich area.

Any thoughts/ suggestions? I would like to be able to do some work in my garage for small personal projects.

#2

I would suggest going through the side of the bag/sealant rather than using those T-fittings for both vac and feed lines. They are highly unrerliable and completely unneccessary for that part.

#3

How would I connect the line to the spiral wrap without the t-fitting? Slide the tube into the spiral wrap, rather than inserting it perpendicular through its side?

Why would it not leak for 25 minutes, and then as soon as resin is pulled through, let in piles of air?
Do you think it was the initial leak that caused all of this?

#4

thats correct, slide the spiral over the tubing put a little tape around it. As for not picking up the leak, I have no idea, perhaps the selant got in contact with the resin and lost its seal? Regardless, you will be much happier not using the t-fittings in my opinion.

#5

Air is trapped between your clamp and the bottom of the line going into the resin cup. It may just be 3 or 4 inches of air in the line but it goes into the lay up.

 What he said... the resin somehow got under the bag sealant tape.  Make sure you do not wax the mold under the sealant tape.

You can also switch your lines going into the bag. Have your resin inlet line in the center of the part, then have a perimeter vacuum line made of spiral wrap. Airtech International sells non imprinting resin inlet cushions you can set them right on top of the flow medium, under the vacuum bag.

you may be resin rich in that one area if the flow medium or peel ply is bridging.

#6

I have had air pump through FROM the fitting area. trapped air as the resin flows through can break up the air around the fitting connections to break up. Almost like cavitation of resin :slight_smile:
I so sometimes have air trapped in the spiral, jus because it isn’t smooth, and has places for air to be trapped as it’s filled with resin.

Also, your bridging should be fixed with pleats!!! Not heating the bag to melt it!!! Make sure ALL layers are placed well in the radii. Fiber, peel ply, distro media, bagging. Else it’s a REAL good area for air to be trapped in a fast fill.
Remember, the fiber tows wet out slower than the gaps between the tows. If you infuse quickly, you still have trapped air in the middle of the tows. Sometimes that can leak out and cause voids.

#7

You just found out why I do not like stretchy bag. Besides being expensive, I feel the stretch and thus thinning of the bag will cause porosity, and when the pressure rises, the bag gets pulled out of the corners, causing (temporary) resin rich places, and race tracking.

Besides that, I feel your infusion medium is quite fast for such a small product. High speed is not always desirable. Quality is far more important. A slower infusion medium or even leaving it out will cause less issues with bubbles.

And indeed, bring the vacuum lines out of the bag in a pleat, not through a hole in the bag. Holes in bags are a big nono, unless there is no other solution. When I need a vacuum point somewhere in the middle, I just run a hose under the bag in a pleat to the desired location.

One other thing: I see you are using AT200Y tape. Try the Airseal 2 tape. Much more tack. You have to get used to it, but 90% of my customers do not want anything else. Costs less too.