Infusion Voids

General Composites Discussions Composites Talk
#1

Hi guys,
I believe I have read almost all possible threads on the topic but still having issues…

See picture for my voids issues…

Is this “Intra Tow” or “Inter Tow” voids? Voids or air pocket?

My process:
0. In mold Coating with Duratec, wait for 7h for no more (or barely) tack
1.Layup:
1.1 (3) layer of 3k 200gsm 2x2 twill carbon fiber, using some Airtech Spray adhesive but only between carbon layers where needed.
1.2 Peel-Ply (Econo stich) (I tried without and same results)
1.3 Infusion grade Perforated release film (I tried without and same results)
1.4 Flow media (sometimes using green flow, and some other time using a “nylon knitted version”)
1.5 Double vacuum bag to reduce perforation 28.5/ 29 inHg
2. Apply vacuum for 15min, ensure absolute no leak
3. Mix Adtech 820/823 (350cps)
4. Degaz for 10min the resine at 29inHG. “Air seeded” with Scotch Brite.
5. Let infuse the resine (using 3/8 spiral tube): I tried slow speed (1in/min) by restricting the resin inlet and fast (+5in/min). Same results. Note: The inlet resin reservoir is at same height as the mold.
6A. Close the vacuum first wait 30sec then close the inlet
6B. I also tried closing the Inlet first, wait 30 sec and then close the Vacuum… Same results.
Note: I do have a “Peel ply” “break zone” around 1-2in before the vacuum tube to slow down everything and let underlaying resin catch up.

Shop conditions:
Temp: 79F
% Hum: 32%

No matter which condition I seem to be using I cant get it without those voids… And since I am doing In Mold Coating, those voids can not be repaired as they are caught between clear and carbon fiber…

Any brilliant idea??

Is it something to do with Intra-tow Capilarity flow speed and inter-tow flow front speed?

Tks!!

#2

100% a speed issue.

I have this problem quite often on smaller parts because the resin flows so quickly. On larger parts it doesn’t tend to be a problem because the size accommodates for it, though on thinner parts it will still happen fairly regularly.

Slow your feed down a bit and see if it helps. I tend to aim for about an inch a minute if that helps. Good luck!

edit sorry, just read you have tried slowing it down. I will update my reply just now!

#3

Ok, sorry, should have read your whole post first. I am still confident that it will be a speed issue given how thin your laminate is. An inch a minute normally works for me, but generally the parts I make are at least 1.5mm thick. At only ~0.8mm thick I would still suggest trying it slower.

Failing that, the only other thing I might point out is that 28.5mm/Hg isn’t a good enough vacuum. But in my experience, that will present itself in a different way. These voids look 100% a speed issue to me.

#4

Thanks Hanaldo!

  • i will try max 1in by minute!
  • its ok to restrict/squeeze the resine inlet line to fine tweek the speed?
  • on your parts do you now have consistently no voids? or you still have those voids like on 1 on 4 parts? trying to see where ideally I can go in quality…

NOTE : i havent mentioned that during infusion there are multiple bubbles appearing in the 3inch behind the infusion front… its not leak! this “bubling” section progress as it follows the infusion. only on 3 inch behind. its like if those where air which was initially stock in the bags or laminate but which did not vacuumed during the 15 min prior to infusion. you get that on your side?
tks!

#5

Totally fine to restrict the feed line.

My parts are generally consistent, I only get voids if I make a mistake elsewhere, which happens from time to time on my prototype runs. For my production parts it’s generally very consistent.

The bubbling behind the flow front is totally normal, it’s the area of resin that is under full vacuum. The area behind it is at a reduced vacuum and so the bubbles shrink. Nothing to worry about there.

#6

Are you certain that these are voids?

It’s hard to tell from a pic but it kinda looks like mold release residue. Have you tried washing it off with warm water?

I can’t see how deep they go but have you tried a light wet sanding and / or some buffing?

A void, where the cf is not held in place against the mold surface with enough pressure, usually looks more serious as a problem on my parts.

Is this a new problem that is specific to one part?

#7

They are voids, but not from bridging. Without the coating on top, it would appear as dry sections between the fibres.

#8

I just did another Infusion tonight… Will see in 24h how it looks like!

  • 32% humidity
  • 68F
  • 28inHG
  • 5h “soak time” on vacuum before starting infusion (not intentional… had to interupt my work, but that should even help :slight_smile: )
  • Infusion speed: average 0.75in/min
  • 30min leak test, no pressure lost.
#9

I’m wondering if 68F will be too cool. That’s ten degrees cooler than your first post. 79F is the sweetspot and I think you might need a heat source for the epoxy to cure if it’s only 68F in your shop/garage. I just did this the other day at about the same ambient temp. The leftover epoxy in the mixing cup kicked at the usual time, but the epoxy in the laminate took hours to firm up so I placed a work light near the mold to heat it up to about 80F. Turned out fine. But I’m a newbie, as well so I’m still learning all of this.

#10

how did you get on mate?

#11

I don’t do infusion but for typical vacuum/oven parts heat makes a difference. Try heating your resin and seeing how that does for you.

#12

Hi, sorry for the delay!
The result was MUCH better! :slight_smile:
But I still have some places where the same issue is visible :frowning:

The thing is that it appeared that I had a really slow leak (only noticeable after a couple of hours) which I think might not have helped… I will try another time and report back :slight_smile: