Core Problem.

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#1

I did my first vacuum resin infusion part using a core. This is not my first resin infusion, just my first with core. I won’t say I’m a total pro at resin infusion, but without core I have made some very good parts.

Here are the particulars.

5.7 oz plain weave carbon
Endurance resin
1/8" thick Divinymat structural flow media. The grooved and scored kind.
mixture of plain peel ply and teflon peel ply.

The layup was 2c1 with the 1 being on the inside of the mold. The part was laid up and max vacuum was pulled for several hours.

The vacuum was reduced to 18" and infused. After the infusion was complete a second bag was placed on the part. 18" was maintained in the first bag and max vacuum was applied to the second bag. The part was tented and cured at approximately 100 degrees F. Vacuum was maintained until well past the green stage and probably until a full cure, 5 plus hours. Due to it being a Friday. The part stayed in the mold for over two days.

As you can see in the pictures the carbon “puckered” around the edges of the core. Even though the core was only 1/8" thick, I beveled the edges with a sanding block . What caused this and how can I prevent it?

#2

Shiney picture is mold side? That is normal. Try to bevel the core to a sharp edge. If the fibers can shift around, they will, EVEN tool side. If second picture is bag side, you had bridging bad due to peelply or bag issues. Which will cause the tool side to lift up as well.

#3

Don’t reduce the vacuum, and why using a second bag? If the girst bag is tight you do not need a second bag!!!

#4

I did bevel the edge of the foam to a sharp point. I know I have a bridging problem. Lol. I’m wondering why. Do you think the Peel ply is the problem? As for it being the bag. It could be but I’m leaning against that being the cause. I’m reasonably experienced and the bag was pulled down tightly and this was in a flat area and bags generally don’t bridge on flats. I will say the fabric was not attached to the mold in that area and the layers were not attached to each other. The core was spray tacked to the carbon.

As for reducing the vacuum before the infusion. You have to. The resin will out gas at 29". The first bag was fine. The second bag is used for compaction. It’s called double bag resin infusion. You can Google it. What is does is let you match the resin content of prepreg. I don’t want to say it’s a new process but it’s not widely used yet. I don’t know why it works.

Any advice on my core problem would be greatly appreciated.

#5

second bag will add no more compaction then whatever the first bag is. Second bag is good for vacuum integrity thats about it. As for your bridging proplem, it is probably from your flow medium. use your core as a template and cut the mesh so it wont bridge. Also using a rubber squeegie during light vacuum to push the bag and all materials in to corners will make a huge difference.

#6

I use the rubber squeegee trick all the time. The flow media bridging really makes sense. I used green flow 75. It’s not very stretchy. Should I switch to something like Enkamat?

Also, you say cut it out the shape of the core. My core is actually a flow media, so do I really need flow media on top of it? Also, don’t I need some sort of flow media right up to the edge of the core and touching it to get the reason to go through it?

#7

Hi Freqflyer,

I use the greenflow and the same type of core except, mine is not grooved. I never have compaction or problems at the bevels. For such a small part we never tac anything, its bad practice to use tac adhesive in anything that is aero-structure. Try to make a jig to place the core which you can remove after the core is nice and tight.

It seems from the top ply that its a UD, if that’s the case, your infusion strategy needs to be studied and whatever I’ve suggested below doesn’t count. You need to have darts (splits) on the bevel, since your reinforcement will not follow the junction properly. It also seems that you have BID at 0-90 on the peel ply side, thats a setup that will never drape properly over the bevel. Also have a bevel of at least 1:3 in thickness. If you have a beveled edge, try to have BID-twill at ±45deg to get a proper drape of the sheet. Can’t give you any educated suggestions without having details of your stack.

Your problem perhaps stems from the fact that you have grooves and perhaps you have square-splits. These are not good for infusion with epoxy, since most epoxies are thicker than VE or PE resins and once the reinforcement is wet from the outside (where the grooves are present), the tight structure of aero reinforcements doesn’t allow proper wetting of the core-reinforcement. That is perhaps one reason that you are infusing at 18". We infuse between 3-10 millibars of absolute pressure, that is extremely high vacuum and never have any wetting issues either. Another thing is that you need a resin break at the end of the stack. I’m presuming, due to lack of a picture of your stack, that you’d covered the bevel area’s with the greenflow. Thats not good. You need to have at least 20mm or so from the edges on the side and 30mm from the vacuum side of the stack. This covering of the greenflow could have also created race-tracking of the resin…

One last thing, if your core is very thick, and you are hellbent on covering the whole with greenflow, just make a split where it bends, and leave it like that. You can easily overlap that area if that split opens up too much to your liking.

Well, hope this helps, this is based on the little info you have shared and a healthy dose of presumptions on my part with a lot of ifs and buts.

N

#8

Your top layer shifted and crunched the bottom layer surrounding the core in the initial debulk. Another way that hasn’t been pointed out yet is to tailor a buffer ply between core and bottom laminate to allow movement if you do not dart the top layer.

Do you also apply vacuum to the resin cup?

Do you do a single debulk on initial compaction?

Are you filling and bleeding?

Double bagging does work and achieves much better performing composites than the traditional vac bag approach. I think you might need to study the layup and laminate orientations a bit to fix the core problem. Pun intended.

And hojo double bagging does indeed increase compaction and help achieve better vf than single bag so much so that infused laminates using double bag achieve vf and consistent thickness as and autoclaved part.

The science behind it is this…

Pre preg bag and autoclave offers an inert atmosphere for resin degassing and autoclave resolves pressure compaction.

Traditional vac infusion bag consolidates fiber with Atmosphere compacting bag. Compaction is lost as infusion begins.

Double bag utilizes a bag For infusion and a bag for compaction. You are also able to infuse at a constant
atmospheric pressure unlike a traditional setup. Also manipulating debulk cycles along with resin cup pressures and that ability to fill and drain the laminate from both feed and exit are superior in fine tuning a perfect out of autoclave advanced composite.

#9

Complete wrong! Double bag does not change anything else than the vacuum integrety! I wonder how many people work in composites that do not understand the physiks:eek:
We talked about in another thread, does anybody know which thread that was?
I found it
double bag

#10

Hey guys, I really appreciate your help and I want to keep it coming. I have done wet lay up for years, vacuum bagging for a long time, and infusion for about a year. I just haven’t used core in infusion until now.

I don’t want this thread to get into a double bag versus single bag pi**ing match. I appreciate everybody’s input, but unless you think the second bag is causing the problem let’s pretend I didn’t use one. I have done identical parts, weighing everything that went into it and compared that to the final part. There is a difference with double bagging.

Dallas, I would love to talk with you about double bagging in the future. I have some questions concerning it and the guy who developed the process and show me how to do infusion seems to be really busy. It takes days to get him to return my calls.

#11

You will not get good results if you do not understand the physik. If your second bag is not placed correct this could also cause your problem.

#12

Back to the problem.

  1. tailor a buffer ply between core and bottom laminate to allow movement if you do not dart the top layer. What do you mean?

  2. Do you also apply vacuum to the resin cup? No

  3. Do you do a single debulk on initial compaction? Explain please.

  4. Are you filling and bleeding? Explain please.

No Uni in the part. It’s all 5.7 oz plain weave. The lay is all 0/90 no 45s. Your right the fabric doesn’t cross the core on the bias. Since this in not a structural part, by the time we get a layup that has the surface properties we need, it’s more than strong enough. Therefore, the 0/90 layup saves material and still works well.

We have made this part in glass, carbon, and basalt without any problems. I was just trying to use core to see what I would come up with and save a layer of carbon.

I’m infusion at 18" because that what I was taught to do, to prevent out gassing of the resin.

I’m not hell bent on do anything a certain way. I just want a good part.

#13

Did you use a epoxy resin? If yes infuse at 0.6 inHg absolute. Use a brake zone or the MTI hose.
I think your resin traveld from the part to the evacuation hose and than you got the resin less area.
Be sure that your mould is tight, your resin degased, the absolute presure 0.6inHg abs and a brake zone or MTI hose. Than it should work.

#14

It is epoxy resin as I stated in the first post, it’s endurance resin.

What’s a break zone or MTI hose?

Also. There isn’t resin less area. The places where the “pucker” is are wetted out. In fact, resin puddled there in some places.

#15

For the MTI hose take a look at the products talk, there is a MTI thread. A brake zone means for example 2-3in peelply between the part and the evacuation hose. This brakes the resin flow.
With resin less I ment the corners around youre core. I think direct after infusion you had no problem. But while curing resin traveld to your evacuation hose and thats your problem.

#16

Hi Freqflyer, did you degass the resin? I would suggest to put the rear ply at a ±45 bias, that will lay properly on the core and you’ll not have gaps that could race track. I don’t think that double or single bag is the problem here.

A resin break/barrier/stopper or whatever, is that area where you don’t have resin-flow-media to enhance its flow front. That allows the resin to properly go through the thickness of the plies and travel forward at a slower speed. Try doing a search for a resin-break.

Is there a curve on the mold? Does the core sit flat on the mold as it should? Put up some more detailed photographs of the part, that would help in analyzing the issue.

Hope this helps you.

N

#17

Lol it was another thread where I left without it becoming an argument. Unfortunately it’s compound that’s completely wrong.

Lol the patented process is called Capri. It’s a fact that two bags are better than one… It’s simply physics!

Don’t bash something just cuz you haven’t seen the results.

Btw big lawsuits have been filed over Capri because it was used because of it’s performance.

#18

Oh and with double bag and vacuum on cup you don’t need resin breaks. You can control feed with vac on cup and vacuum at exit.

Ok initial debulk full vac on inner bag. Hold for 10 minutes. Then lower to infusion pressure. Lock outer bag full vac. Balance vac on feed cup. Lower vac on feed cup or increase exit vac to control stop or speed up infusion. At all times you will have constant atmosphere the whole time.

Now fill and drain goes like this. Once laminate is saturated full vacuum is applied both to feed and exit tubes. Depending on howmany you have.

#19

Ok, please write here the physiks, maybe you can use Bernoulli to show me that I am wrong:p

#20

I challenge you to research it smarty pants. If your too lazy to do it on your own then conversation is over. I don’t bash your process or accessory product Mti hose on the forum. Please be respectful.