Infusion dry spots - resin flows fast and then slows drastically

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#1

Hi,

MY SETUP

I have a vacuum infusion process set up with a medium-sized dual stage rotary vane pump. I’m infusing a wing that’s 1 meter long and 30 cm wide as a test.

The core is a styrofoam positive wing mold that will remain in the final product. Over that I place the fiberglass. Then the perforated film, breather fabric (http://www.fibermax.eu/shop/breather-fabric-vc014-p-175.html), flow fabric (http://www.fibermax.eu/shop/flow-fabric-vc017-p-176.html) and then the vacuum bag, sealed by vacuum tape.

Along the both of the longer sides of the wing, I place a spiral tube for vacuum and resin flow, approximately 2-15 cm away from the part edge with the flow media reaching the spiral.

My resin is a thin nicely flowing resin and a 2h hardner.

WHAT HAPPENS

When I turn on the vacuum pump, it pulls the resin nicely and evenly across the entire wing. Then about half way through it slows. Then it slows even more.

In the beginning the resin goes under the perforated film nicely, but then just some dots get through without connecting and then, in the worst cases, nothing.

Even if the resin has reached this stage and essentially is standing still, standing it on a side with the inadequate wetting on the bottom will help - gravity will do the rest and wet out the fabric. But only if there’s plenty of time and with plenty of experimentation.

THEORIES

  1. Not enough vacuum. Though my manometer shows 200 mbar between the pump and resin trap.
  2. Not enough flow. Perhaps the pumps small reservoir and resin traps holds some vacuum and that pulls the beginning faster. But that doesn’t sound very sensible - if the pump was able to pull the beginning nicely, why not the end.
  3. The flow media is pulled down so closely that it imprints itself into the styrofoam underneath and doesn’t allow the resin to flow. But in this case, why does gravity help and why isn’t there an imprint on the glass itself?!
  4. Other - help me out!

I’ve tried it on many-many parts of different sizes and the same thing nearly always happens.

Ideas will be much appreciated!

#2

Your layup is VERY wrong. Get rid of that release film!!! do this: Part, peel ply, flow media, bag. Breather will suck up resin, no reason for that. Perforated release film will not let resin get into your part!!!

#3

The setup and materials sounds more appropriate for a wet layup that’s vacuum bagged.
The perforated film can work with a long gel time resin. But the breather is totally wrong for infusion. It absorbs resin, and isn’t meant to flow much. That would definitely slow the infusion process.

#4

If you use a very big holey perf between the peel ply and transfer mesh it makes it easy to remove the mesh. This is good if you are going to waterjet cut or machine it. You do need a water like resin and a slow gel but it can work. I wouldn’t bother in most cases.

#5

As far as I can work out, the release film is not the issue. It’s providing the benefit of being much easier to remove from the part than peel ply and leaves an ok finish.

From my research it seems to be a very common practice for infusion. Even on top of the release film, I believe the flow stopped in the end, leading to the theories above.

#6

Good tip, I’ll try that. I believe I tried it in the beginning, but can’t remember the results.

#7

breather is never used in an infusion. it will suck the resin out of your laminate! the point of the process is to infuse the laminate, not the breather…

#8

no need for breather or release film in an infusion lay up.I have never seen anybody infuse this way.try a small test without them using the correct set up riff42 gave you in the post above .

#9

I am having a problem with my layup also. If I use the release fabric, I get a teeny tiny dry spot towards the end of my infusion if I do a end to end infusion and a dry spot in the centre if I do a line infusion for a cylinder. When I remove the release fabric (it also likes a breather for me), I get too much voids in my composite because of the air in it. Can you suggest any alternatives for the layup to work smoothly???
Besides, I get a very high thickness of the finished part. It is almost 2 mm thick for 4 layers of the glass fibres 0.5 mm. I think I can resolve this issue by using a double vacuum bag and partial pressure. Could someone tell me if there is any other solution to the above mentioned double vacuum bag???

#10

get rid of the release film, use a peelply that has release on it, do not use natural as it is very difficult to remove after. And as far as your resin flow, all infusion starts fast and gets slower the further it goes due to the more mass the resin must travel through impeading the flow.

#11

With single bag infusion the part will always be more resin rich at the start of the flow and more resin starved at the end . This is simply due fluid dynamics and total available energy.

Couple this with extremely lossy breather and barely permeable plastic film and you’re definitely going to have flow issues. It may be easier to remove but if your parts aren’t coming out correctly the justification fails there. Follow the above suggestions.

#12

Hi,

As suggested previously, I tried removing the release fabric and did the infusion with the perforated peel ply below the resin distribution medium. But it did not help me as I get more and more empty spaces with no reisn in them.

I will try once again but am not really hopeful about them working smoothly without the release fabric.

As regards thickness distribution, it does not help whether at the beginning or at the end as I do radial infusion around a cylinder where the flow front travels axially so it should be a tapered cylinder in regards with the above theory. However, I get a cylinder with varying radii along the length of the cylinder. Any suggestions are welcome.

Kind regards

#13

why not post some pics? Its hard to help when you cant see the setup. Im sure it something simple.

#14

Perforated film: use P, P1 or MP22. These will not disturb resin flow.

Bleader/breather: do not use it.

As for materials: please post a list of materials that you are using, and some pictures of the layup are helpful as well.

Are you using polyester or epoxy? If polyester, are you using a thin hand laminating resin, or an infusion resin? (not modified / thixotropic resin)

#15

Hi All,

I am using an Epoxy. It is slightly viscous but everything is fine now. I am continuing to use the release fabric and no perforated peel ply (mainly because once u cut off pressure supply,flow is too slow to go through the pores into the dry fabrics). My resin flow and distribution is good now.

However, I have come to a problem of demolding my part from the release fabric as it gets stuck and I have to use the knife to remove it which leaves cut marks on the samples outermost resin layer. I tried using acetoe but it does not help much too.

Secondly, I cannot remove the air completely from the fabrics as in the part I can see strands of fibres with naked eye, so I can estimate the impregnation to be really bad under careful study.

My layup is simple as follows

Polyurethane foam as mold, glass fibres (4 layers 0.5mm thick), release fabric, Resin Distribution mesh (Airtech supplied it) and the vacuum bag. Am I missing a breather (but I think release fabric can work as a breather too) and because of this I have the fibres in the lay up which can be seen under light with a naked eye???

Any help is good!!!

#16

1: sometimes it is hard to get off, depending on the thickness of your flow media, the resin you are using, and if you are using a good peelply or not. It should be release coated. The flow media, if thick, sometimes just pretends to be it’s own composite, and become very solid, and hard to peel off. Just keep at it, or use a lighter flow media.
2: your layup is fine.
3: not sure about the bare fibers. You are obviously not getting a good flow in the part. Where is the dry areas occurring? edges, middle, etc?

#17

Show us some pictures. I have had comments on some strands not impregnating, at a factory where they create large diameter tubes. My laminate was dark-green and transparent (19mm or 3/4" thick) and theirs was light green (same resin!) and opaque, from air bubbles and bad impregnation.
On every square foot or so you could find a fiber in my laminate which did not impregnate, and show up as a 2" long white stripe.

What do you call “perforated peelply” and what “release fabric”???

I guess you are mixing things up.

The thin film with perforations is “perforated film” or “release film” and the fabric, usually with red or black stripes, is “peelply”.

Peelply is worthless in removing your RI consumables. The only reason for being there is it gives a nice surface to do secondary bonding to, and it can be used in the RI process for connecting vacuum lines to a part. Air will go trough it, but as soon as resin reaches the peelply (there should be only peelply connecting a vacuum line, no laminate or flow media) the resin will dramatically reduce in speed, giving other areas the time to impregnate fully as well.

The perforated film is the stuff that makes removal of consumables easy. But for infusion, make sure you get the “P”, “P1” or “MP22” perforation style. This should not harm your infusion.

#18

+1000 never use breather.

Use just the following:

  1. Carbon fiber 1,2,3 layer
  2. Peel ply
  3. Resin flow

Nothing else

#19

Hi all,

Thanks for the advices,

@George Grat — I tried using the layup without the peel ply, I n such a scenario I get a problem of air pockets which are very obvious around the perforations of the release film. I tried it 4 times and it was failing. Besides, in my experience, it tends to retard the flow to quite an extent.

@Riff42 ---- The less impregnation is coming at areas where the resin is the last to flow. I guess this could be because of air not being completely sucked out of it. Hence, I tried repeated compaction of the preform to make sure of removal of the air and during infusion kept the vacuum line on for 1 hours. Lets hope it works. Also, Vacuum Infusion is fun definitely as you can see so many processes and systems together but really difficult to master it and make it work repeatedly. I only had all my material for infusion for 2 weeks so still am in the exciting phase.

Thanks for any suggestions which are yet welcome.

#20

There is couple of peel ply cloths in the market for nice smooth surface. :wink: