air bubbles?????

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#1

I got a couple of questions for the infusion experts here! Basically the problem is that I seem to be getting what appear to be air bubbles and resin build up in certain areas of my part that I am making. I am sparying the mold with clear gel coat mixed about 10% with Duratec high gloss additive. I set-up the infusion, pull vacuum and I get about 29" of vacuum and it will hold very well with 1-2" loss over 20 minutes. The resin I am using is very low viscosity (125cps) PER.

Here is what I get when I pull it from the mold.

The thing circled in red is a pit in the gel coat about 1/16" deep and the blue circle is excessive resin build up. The bag seems to sit flat in the mold before I introduce the resin. I have a few theories about my problems which are #1. Moisture in the gel coat. #2. My vacuum pump does no pull enough CFM to keep the bag flat after I let the resin in. I built a homemade vacuum pump with a fridge compressor. I am not sure if it is possible to have full vacuum but not enough CFM??? #3. Spraying the gel coat to thin.

I have had them come out of the mold with very little resin build up and no bubbles or pits and then other times it will look like the pic, but nothiong in my technique changes. This one has me stumped. Let me know what you guys think.

Thanks

#2

the cloth is bridging, you really need to make sure its tight against the gelcoated mold surface before putting the bag on.
Once the vac is applied the resin rushes in to fill that void created, thus leaving that solid chunk of cured resin.
I can see excess resin on the other raised section to the right of the circled one also.

#3

Thats my though also, but when I lay the carbon in the mold I am very careful to make sure it is down as flat as possible in all areas. I also get excess resin in some other areas that are almost 90 degree egdes. One thing I have noticed is that when I apply the vacuum the bag seems to be absolutly flat across the entire piece, then when I let the resin in it seems to raise these areas of the bag and these spots will seem squishy and I can see a bit of excess resin. If I push on these areas to try and kind of squeeze the resin way it won’t move.

#4

definately bridging,are you using pleats in the bag?? do a search for pleats as i did a post about this.

#5

Yes, I put pleats in the bag. I have 2 different kinds of bag, one is stretchlon 800 and the other is just regular bag and it does not matter which one i use.

#6

try an infusion with no gelcoat and see what happens.

#7

If you’re using gel coat, it’s tough to get all areas of the carbon to go down flat because it wants to stick in places where you don’t want it to go. Sometimes you can think the area is down flat but it’s really bridging. I don’t think there’s really an answer to solving your bridging problem besides taking more time in each little crevice of your mold.

If the air bubbles are in the resin, not the gel coat, try dying your resin black. Those tiny bubbles will “disappear”.

As for the small hole in the gel- How are you laying your gel coat? If you’re brushing it on, it could be an air bubble. I use an HVLP gun with a 2.0 tip to spray it on. It could have also been a peice of trash that was on the face of the mold, that transferred it’s impression into the gel.

#8

can you take a pic of your backside?

Take this pic above ^^^^^ This is what was the problem I had too at one point. I would lay the carbon down and it would seem perfectly fine. I would lay my other laminate and my peel ply. Then make my bag as normal. The pressure of the bag is going to want to lay flay. While it is doing it, it will add pressure to the laminate and want to add it flat as well. Most peel plys are not strechy at all! So when the bag trys to lay flay if you don’t have enough peel ply for the hole the pressure will flaten the peel ply and leave a gap there. when that happens it pushes the carbon too and flatening that out leaving the void. Now bout the resin it pools in the void. Resins are letting off a gass and also their is trapped micro air and also moisture in your laminate piece mostly the carbon. These gatther to become small air bubbles. The air will always try and find pockets or larger areas of resin, such as your void. That is why that area has a ton of air. Hope that all makes sense. That is the problem I had but without knowing your other materials I could be wrong

#9

As the rest of the guys have said this is a bridging problem. The most important part of any infusion is getting the laminate down into every part of the mold, if this is not done correctly everything you do after this is a waste of time.
Especially on my complicated parts i spend what seems like a ridiculous amount of time ensuring the carbon is into every corner, i use various tools to achieve this, mostly home made from bits around my workshop.

On this part pictured below it can take me best part of 30 mins to get the first layer in place.

Baz

#10

are you laying dry in the mold or on top of a gel coat surface?

#11

Here is what I do. PVA sprayed in, clear gel coat sprayed in, 2 layers of 5.7oz 2x2 twill carbon, 1 layer of porous peel ply, 1 layer of resin flow media and vacuum bag.I did another one today and it seems that maybe the resin flow is what is causing the bridging. It seems like everything is down fine, but as soon as I let the resin in it immediatly pools. Is the flow media needed for a part that is about 11"x7"?

#12

On top of Duratec, then a little 77 spray but just enough, not too much.

Baz

#13

The one I did today did not have any clear gel coat, just PVA and a very small bit of super 77 to hold the carbon in place.

#14

Are you infusing directly on the part? If so try moving to the flange. Even on small parts i`ll use a small amount of flow media.

Baz

#15

No, the infusion lines are on the flange. I will post a pic in a few minutes.

#16

Try as a test piece just one layer and make absolutely sure its down every where. What might be happening is subsequent layers of carbon and peel ply etc maybe lifting the carbon slightly off the surface. Try laying the subsequent layers of carbon in separate pieces.

Well get you there dont worry.

Baz

#17

Well here is what it looks like. This one has alot more resin build up than usual. I think I let alittle air in when I unclamped the feed hose.

This is the back side afterwards.

Now believe it or not this piece had no resin pools or air pockets, but what happened is that I pressed the carbon onto the edges enough that it broke through the pva and slightly stuck in a few spots.

#18

make your bag bigger, don’t be afraid to have wringles in your bag on the part. I don’t see any! That is why your bag is bridging and not pushing down!! I let the vacuum go then turn it off, fix my bag make sure I have enough roof for it to suck in edges or curvess. Vacuum again let it about 80% suck then turn it off. Push it in every place that it is bridging and watch the trouble areas. Hold down the trouble areas while it sucks down the rest.

#19

Ok, yeah, this is starting to make more sense now. Is there any adverse effect of using the clear gel coat in there?

#20

watch this, you can see that I made a bigger bag because this has a lot of angles and then made sure everything was pressed in. IF you leave yourself enough bag it wont lift when you add the resin

http://video.google.com/videoplay?docid=5323772851550698047&q=infusion