Resin starvation non-consolidation - I must be going mad

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#1

Hi everyone, I am looking for some advice with my layups.
I issue that I am having is porosity/insufficient consolidation of resin to tool face.
This is an intermittent issue, sometimes it comes out fine, sometimes it does not. I understand that there are many different factors that will affect this such as work environment, resin systems, process, vacuum etc, but I feel that my issue is something very specific.
I have tried many different variations of layups including IMCs (does not help because then bubbles will appear behind this surface coat), different vacuum levels, over saturating the fabric, pre impregnating the fabric etc.
This is my basic process sans IMC:
Resin system: Aeropoxy 2032 with 3663 hardener
Carbon fiber – have used a variety of weights from 5.8 – 7.2oz if I recall correctly
Schedule:
0/90
45
0/90

  1.   Surface coat – have done with and without

  2.   Layer 1, add resin, stipple with brush, resin rolled until full saturated

  3.   Layer 2 - As previous layer

  4.   Layer 3 - As previous layer, ensure full saturation

  5.   Peel ply – have done with and without

  6.   Perforated release film all over

  7.   Breather – have done with single layer, and multiple

  8.   Vacuum (max 24.5 from my Gast) – have done scenarios with max vacuum from the get go, have done with a bleeder and held at around 10inches (full layup)  and also done low vacuum until gel, then max. 

  9.   Bag has always been good, I do leak checks.

Some layups I have completely oversaturated the material to a point where my breather is fully saturated.
Other times I have tried to calculate exactly how much I need according to material used.

My results vary, and they does seem to coordinate with any changed I do. Ex, completely over saturating will come out the same as lower resin content etc.

I am stumped as to why I still have such a high failure rate. Especially when I see the same process done on videos, and in books and the parts come out with a smooth surface.
Some options that I am thinking of trying:
-Slightly oversaturated mix and solid release film

  • No breather – don’t really want to do this, I’m afraid the weave will distort
    Do you think it can be my resin system?
    Any ideas and test suggestions are much appreciated.
    I am honestly at a point where I feel that my issue is so small, that I just have to fine tune or change something in my process.
    Also don’t want to go the infusion route or non-vacuum bag for this piece due to design of mould/part.
    Thanks friends, all the best.

#2

Looks like a perfect case of trapped bubbles. It happening when you are rolling it , and then there is no way they can make it way or evacuate out into the breather cloth.
There are a few ways you can tackle this also the type of roller can make a huge difference.
IMO I find felt rollers work best for me… Foam rollers don’t give the compaction as I like.

First off , I’d practice your lay up on some sheets of glass with your off cuts. This way it’s very easy to see what is going on and what works for you. It very nice to roll or screed and see what’s happening to the face of the carbon.

Using a 15 or 20g veil cloth 1st ( woven) will defiantly help but most off all using the credit and technique to screed the resin along the fibre diffection will help push the bubble out.
And there is such a thing as too much working the resin , as you sometimes can induce bubbles no matter how much resin you have slopping around the moulds.

The glass it your freind… Gives you a great perspective of what you doing right and wrong.
Perfect your technique on that and your big job will be perfect every time.

Cheers

Tim

#3

I get the same results with vacuum bagging but much better results with infusion.

#4

Agree, this is why infusion is superior… Unless you have an autoclave of course. Alternatively, you could get a good out of autoclave prepreg which can get really nice results comparable to infusion

#5

I have a trick that works well for me. I tend to make more complex shapes with tight corners and curves etc, so keeping the cf firmly against the mold surface consistently is always a challenge.

If the issue is trapped air (as it sounds like it is), I apply the resin to the cf for the surface layers outside of the mold on a perfectly flat surface. Instead of using a brush, I spread the resin over the cf using a squeegee. I sandwich the cf between two smooth release films or one smooth and one perforated release film (for larger parts).

The type of resin is important for this too. I often use a fast cure or medium cure resin for this surface layer. Once the resin is applied and the cf is sandwiched between the two release films, I use my squeegee to remove all air bubbles. With the cf between two smooth release films, all trapped air bubbles will be visible and easy to smooth out. You just push all the excess resin and air to the edges.

Once all the excess air is removed, I wait until the resin has gelled and become tacky. Once it has gelled, it will be hard / impossible for new air bubbles to work their way into the resin. The cf will also be easy to cut neatly at this stage with straight lines (without fraying etc). I then carefully remove the release films and lay the cf into the mold.

Laying the first layer of cf using this method will be noticeably easier that a typical wet lay-up. The tacky CF will stick easily to the mold surface and the fabric won’t fall apart easily or leave loose ends everywhere. The lay-up experience will be more like using pre-preg. You won’t have to keep prodding and poking the CF to hold all the edges down like a game of wack-a-mole…

Once the surface layer is in the mold, the other layers can be added using your usual method but I still recommend applying resin on a flat surface with a squeegee. You can do it all in advance by using a slower hardener for the 2nd and 3rd layers. The less trapped air, the better. Excess resin is best removed ahead of time imo.

I also recommend using a template to cut the cf into the right shape before laying it in the mold if you have tight corners. If the cf is the wrong shape and is stretched over corners, you are more likely to get voids and air bubbles, even under a vacuum.

Also, think about the method you use to hold the cf firmly against the mold. If a vacuum bag alone is not doing the job, try adding some rigid or flexible mold inserts (at least for problem areas).

I prefer to use compression molding for problematic parts. Compressing the cf between and male and female mold (using the lay-up method described above) leaves far less room for the sort of problems you describe.

Good luck!

#6

Timbuck

I will try the glass layup method to see where I am going wrong. Also, when you say felt, are you referring to the bristle rollers, or an actual felt material on a roller?

Zebra,

I have tried the"pre-impregnating" method between two pieces of plastic, and it did not really make a difference. When you let the first layer gel and then lay it down onto the mould, you don’t find any air bubbles getting trapped underneath?

I will give that a shot as well.

Looks like I will have to experiment with different rollers and what know. I will update you guys with results once I have them.

Thanks

#7

Felt material on the roller. Quite short only about 5mm in length , allows you to get nice even compression when rolling.

Cheers
Tim