Freq flyer I will try to answer any and all questions you have. Right now I’m freezing on a mountain snowboarding for the weekend. And typing on my phone is kinda harsh. I’ll answer all your questions specifically tonight when I get back to the cabin.
Dallasb84, I’m not bashing double bag, we do that often, not the way that the capri patent describes.
I think the point of this thread is to help freqflyer to fix the problems he currently has, and in my opinion, they don’t stem from single/double bag.
N
This is complete independent from our product. The double bag works well because you can be sure that your vacuum is stabil, and that is the most important thing! You can use hard pieces between the two baga in complex shapes, that allowes a better allocation of the pressure.
But double bagging does not effect a better laminate quality or higher fibre to volume ratio.
The two baga work as one bag on the laminate and the pressure is depending on the pressure difference between the ambient pressure and bag one.
Capri is an advanced form of double bag. Basically the same thing. And Nash no offense taken. I was responding to compound. I’m still trying to correlate double bag and bernoli… And… Having multiple pressures does not work in his model of incompressible fluids… But since you asked… Lol here you go. In today’s commercial aviation sector where aircraft are designed and built to last longer than 30 years… Here you go compound… Capri flies and single bag composite infusion doesn’t even come close. How much more bernoli do you want?
So, if you have a double bag and you put 29" Hg in the outer bag and 0" Hg in the inner bag how much pressure is against the laminate? If you put 29" Hg in the outer bag and 15 Hg in the inner bag how much pressure is against the laminate? If you put 29" in the inner and 15" in the outer how much pressure is against the laminate?
Adam
Who already knows the answers. 
I think you mean the vacuum and not absolute pressure, than
1=0
2=15
3=29
the second bag is complete irrelevant if it is not bridging over the first bag. If it is bridging it decreases the first bag, and that is contraproductiv.
Hi Adam,
We have applied for a patent for the process we use, thus, I cannot talk about it here till we get the patent in hand.
However the most referred work has been done by the boeing company on double bag infusion. In the link you can download and go through their patent and see what dallas was talking about. We have a major improvement over this process.
We use a process based on its needs, complexity, and the laminate performance the part is designed for. We’ll not do a double bag infusion for everything.
Oh, and I’m currently LEARNING hand layup for molds to reduce the cost of our tooling from epoxy to VE/PE and to have molds that can be refinished to a high luster after many pulls of the parts. So I’ll not eliminate any process, we choose what is best for the job at hand.
Hope that this answers some of your questions.
Exactly, I can’t see how the double bag could improve the Vf except for the increase in vacuum integrity. I see some people claiming a Vf of 70% with double bag infusion which has got to be total BS. I’ve even read in a trade journal where they recommend allowing the feed line to be open to atmospheric pressure after infusion with a double bag so excess resin can pushed out the feed line. This would actually remove all the pressure from the laminate and cause the debulked fiber to rebound.
Nash, I’ll have to read the Boeing patent to see if can understand the reasoning of the double bag except for vacuum integrity.
Lol wrong again… Sort of. Yes if you have your inner bag at 0 and pull vac in only the outer bag you’d still have zero and a big mess. But… That’s not a correct method at all.
Once you debulk and pull full vacuum in the inner bag. The second bag is then pulled to full vacuum or slightly less depending on vf values.
If you pull full vac on inner bag. And then pull full vac on outer… Even if you open inner bag to zero… 14.6 psi is still exerted to the laminate because the outer bag is still clamping. At this point the fabric is still clamped and resin infusion can be controlled by inner bag pressures.
After infusion you can allow the inner bag to vent but keep in mind you now have 14.6 psi at each tube pushing to get into the back… Usually there is vacuum applied albieght not near full vac.
If you never applied vac to the inner bag… To debulk … The second bag is useless. If however you apply full vac to inner bag & full vac to outer bag then vent inner bag to .1-29 hg the laminate still has 14.6 psi surface clamp load.
1 29hg
2 29hg
3 15hg
Assuming full vacuum debulk and infusion pressure does not change while infusion takes place.
Hope you will never build any safety relevant parts:eek:
Don’t worry I don’t hold ignorance against you.
I don’t have any more pics of the finished messed up part on this computer. I’ll try and get some more and post them.
What I do have is pics of the part being laid up and the first part of the infusion.
I used strips of coremat around the perimeter of the mold beyond the part as a resin break and several inches of coremat where the vacuum is applied. I didn’t have any resin getting sucked out of the part during or after the infusion. I do sometimes get resin coming out after parts are completely infused.
The last two pics are of the upper part of a cowl that we made without core. I don’t claim to be a wiz at this stuff, but I will say that’s a damn fine part.
I think resin traveled out of your part after infusion. Try to use a bigger brake zone out of peelply.
No resin left the part after the infusion. I took the part out of mold and saw the lines myself.
Was your resin degased?
No, but it was infused at a low enough vacuum that there was no out-gassing.
Freqflyer, nice photos of your cowling. Well I can think of three things that could help you address your issues:
- Try to have the resin front vertical (gravity will assist in filling the front more evenly). That is to say, either have the resin inlet on the bottom edge along the axis of symmetry of the cowling, and on both the sides on the top the vacuum port. Or you can simply hold your mold vertically (so that your inlet is at the bottom and the spinner side is at the top.
- Try to reduce your infusion speed to as low as you can safely go.
- try to keep the green flow away from the edges, by at least 1" and from the vaccum outlet by at least 1.5"
I’ll also use a ±45 deg on the inside, that will give you some torsional rigidity, in addition to solving your draping issues. You can analyze it using FEA or some other progs you may have. We have a full license of NASTRAN and an explicit solver (to simulate crash/impact).
Another thing: coremat cannot be used as a resin-barrier, you need peel ply for that, it will allow air to pass but will restrict resin. Coremat will just absorb resin. I also think that your flange area is insufficient for setting a decent infusion stack.
Hope this helps,
N
Here is my second attempt. Let me know if what I’m doing will work without the bridging problem. Also, is what I’m doing over kill to prevent the bridging.
I put in two layers of carbon like I did before. Then I put the core in. Then I put in the third layer of carbon. I cut a hole out of the third layer of carbon just a little bit bigger than the core. I place the core in the cutout. Then I layed 2" bias cut strips under the edge of the third layer going up on to the core. Then I trimmed the carbon left over from the cutoff so it’s just a bit smaller than the core. I laid it on the core and over the edge of the bias cut strip.
I think you might want to add doublers around the perimeter of the core with .50 overlap both sides.
I’m at work and cannot receive signal inside the vault much less have a phone. How late will you be up I will shoot you a text message and see if I can help you after work if you like.