air bubble/voids ?

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#1

I am having trouble getting nice parts out of my mould… I’m making 24 foot racing canoes. they are carbon/kevlar with a foam core… my epoxy is 600 cps and we are using slow hardener… We are using 20oz since we have a ton of it around. To help with the large weave we are using a 3/4 veil first… Where the foam core is we don’t really have the any voids or air bubbles… around it we do… we are using a peel ply and breather/bleeder cloth inside the boat since we have to glue bulk head and seat brackets and stuff to the inside… we vac to about -15 hg and pull the vac about 2 hrs after we start mixing the first epoxy… it is not gelled yet of course but it is a bit thicker…

any advice on a process change to keep this from happening?

we thought about less vaccum to not pull epoxy away and then thought more to get rid of the bubbles… maybe pref ply or more ports (we use two. nose to first port is 8 feet and then 8 feet to the next port then 8 feet to the tail… ) or a heavier veil? not sure and don’t want to waste time and money on r/d if we might be able to get some helping ideas from so pros…

Thanks

#2

Wet lay or infusion ? infusion is the way to go and make sure you have a good seal on the bag and degas the resin.
Chris
www.carbonfibreworks.co.uk

#3

We are just doing regular wet layup and then vaccing
I know infusion is popular but we are not set up for it.

#4

15 Hg seems very low to me, pull a deeper vac and let the vac on longer. Also degassing the resin can / will help, even with normal wet/vac.

#5

If you just press the laminate by vacuum you do not need sich high vacuum. I would prefer 7-10 inHg relative vacuum, so not that much. Degassimg the resin is important and maybe not that much breather cloth so that you can not suck out that much resin.

#6

I know you say you are not set up for infusion but have you considered MTI hose ? no catch pot required and easy to use.
Chris
www.carbonfibreworks.co.uk

#7

right now we are laying one layer of bleeder down… its the just your standard 60" bleeder/breather… we weight everything before and after for resin ration and had a 1.2 to 1 ratio…

so now is when I get confused?? One person says less vac and one says more… why would less vac help or why would more help?? would I need to let the resin gel more or use perf ply in there…

we are just wetting out the cloth on a table and then transferring it to the mould… When we are working the epoxy into the cloth with the squeegees we get air in the epoxy from the squeegees being pulled over the cloth… That doesn’t cause the voids in the cloth between the veil and the carbon or the air bubbles since it’s not in the area of the core material on the bottom … It’s mainly the nose and tail the areas farther from the ports… There are some on the sides which are close to the ports but they are smaller…

would it help to work the cloth with rollers with a few pounds of pressure on it but not a big pull of vac?? or let the epoxy gel more or less before the vac??

#8

If I used less vac and less breather/bleeder what would be good to use in place of the breather/bleeder so a proper amount of vac would make it to the nose and sides easily?

I’m guessing there wouldn’t be even hg right away or trap the air… I’m just guessing now since I have only been doing this a few years and have not trouble shot a ton of things yet.

Thanks.

#9

Too much vacuum and breather can draw out so much resin that your end product can be dry, it is not easy to get a good cosmetic part using wet lay and vacuum bag. The item you are making is a performance part and the only way is infusion, it is not expensive to set up for infusion and you can create a quality part each time.
Chris
www.carbonfibreworks.co.uk

#10

From my point of view, the question is: are you watching voids or bubbles ?

If bubbles, you’ll need to avoid them (by degassing, lowering resin’s viscosity …) or extracting them by a strong vacuum.

If voids, you´ll need not to suck so much resin; maybe by a lower vacuum, choosing less holes on your perforated or higher resin’s viscosity when vacuuming and shorter sucking time.

Also try to determine WHERE the voids/bubbles are. Gel coat, surface glass, first carbon layer… ?
Once determined, you’ll have to act THERE.

I spent a good time making tests, analizing, determinng and thinking how to eliminate em by the means I had: viscosity, pressure, time, flow …

(Always from my perspective)

Good luck !

#11

The large bubble (picture 1) looks like a large air pocket. I doubt the part has seen any vacuum on that place. Or it might be bridging.

#12

yes, it looks so.

If the PVC has been vacuumed togethr with the outer carbon, probabily there was no exit for the air thorough that area (not enough holes on the foam)

#13

Somehow you seem to have a problem with our product, I don’t know why. You wrote things that are not comprehensible for me.
In this case I have not written anything about MTI if I am correct. The thread starter wrote that he does not want to got by infusion so I wrote what he can do to get better results.
If you have a problem with me or our product write me a pm.

Back to topic. Less vacuum because the air in the part will expand. Than more vacuum than bigger the air bubbles. You can go to maximum vacuum to suck out as much air as possible and than go to less vacuum to minimize the air bubbles.
Less breather because high vacuum and too much breather will suck out too much resin. If you use less breather you may get a more resin rich, but less porouse laminate.
If you want a light but nice laminate by wet bagging I would recomend to make the first layer without vacuum and when it is cured the following layers with higher vacuum and breather.

#14

I have stated many times that MTI hose is an excellent product, it is easy to use and on every occasion i have used it the component quality has been first class with no bubbles/voids. Like every other product it has its place but for me it is not cost effective to use on a commercial basis. I mentioned the MTI hose in this thread as you have no need for a catch pot when using the hose.
Regards Chris

#15

Sorry, for me it sounds in another way.

#16

we gave it another test last night. we got rid of the veil where the voids were between the veil and the carbon . Now we will just have to see if the weave from the cloth has the tiny air pockets between the cross sections of the weave… we vacced this part to 24 hg and added a tiny bit more resin to the carbon and then put the kevlar in… we leave our vac on over night since we pull vac around 9 p.m. and then we shut it off in the morning…

we also pulled vac 30 min after mixing epoxy this time with the 600 cps epoxy…

Should we be vaccing for less time?? or will letting a vac off before the epoxy has gelled good cause problems??

We can get thicker epoxy ( 900-1100 cps) and use less vac if that would help?

I know infusion might give more consistent results but then we need flow media perf ply and the tubing for infusion… so around $12 more per yard of boat… I could not find a good place in the US for the MTI hose you Talked about… plus our bottom mould needs a tube bag since the shape… There really isnt a flange to tape the bag to…

#17

just read the post above… I guess we should have backed off our vac to 5 or so after the first big pull… good idea.

since weight is a big deal doing a total hand layup on the first cloth would not work out to well since in some spots there is only one layer… but if I can’t get this figured out I might try it as a last resort… people just don’t like it when you say it was a hand layup, even if you control the resin and have it almost as light as a vacced part… ( on canoes since you don’t have tons of layers)

I will update on this part…

#18

Are you using one continuous piece of fabric around the vee of the nose and tail. Are the voids in the vee area?

#19

The nose and tail have its own small patch so the cloth can get pulled into those tight spots easier. Our last part from a few nights ago without the veil was better. But as I thought we have pockets of no epoxy in between the weave directions. Anyone have any input on thicker epoxy? Or we can back off the vac after the first big pull for another test. We are thinking about vaccing to glass to watch what is going on as well.

#20

I think a thicker resin is a good idea.
My aim was to decrease resin out-flow to avoid voids.

What I did on my last tests was increasing resin’s viscosity + reducing vacuuming time.

In order to increase viscosity I waited (after impregnating the cloth) till resin geled.
Then I did vacuum. Short time “sucking” = lower voids probability.

Another way to reduce resin outlet is by mean of the perforated. Smaller holes, less holes, two layers …