Hi all

I've been lurking on here for a while and have recently started making some parts for a project car.  I've started using resin infusion hoping to get a more uniform finish and like everybody (I guess) I occasionally get voids where I havent gotten my cloth in to the corners but I'm also getting surface voids along the edge of where I have used closed cell foam as a stiffener.





The above is 2 layers of 200g carbon, the stiffener then another 200g layer on the back, any advise on what I'm doing wrong would be appreciated.

Thanks

You could do the outer skin with a peel ply on the back, bond in the core then do the inner skin.  It would be a bit of a pain doing it in two passes but it'd stop this problem.

Hi,

I never used closed cell foam so I'll let experienced people develop on this.

But I know that voids can be due to pulling the vacuum for too long after the resin feed line is closed. If you're concerned only about strength, then its the way to go.

But if you want "cosmetic perfection", then you should shut off vacuum line first, then resin feed. Some people will even let resin feed opened a minute after the vacuum line is closed. That way you'll get "resin rich" laminate which is less prone to voids.

If I was to work with closed cell, I would do the way that FLD suggested: first the outer skin and then the rest.

Hope it helps.

 



 


    A $1000 electronic device will always protect a 10 cents fuse

you shouldnt need to do two passes to get a good finish with closed cell foam.

You need to prepare the foam before use.

Closed cell foam is impervious to resin. Therefore if you do nothing, you are just relying on a small vacuum head pulling the resin through the layers of cloth under the foam.  Normally the infusion mesh does this for you easily. As a result you can often end up with dry patches or pin holes.

The other problem you have is the edges leaving  the voids.  No matter how good your bagging, the 3mm or so thick foam edge will be hard for the bag to 100% conform so the carbon lying on the edge can lift slightly from the surface once its floating in the resin.  ie you will get slight bridging no matter what you try.

hence you get the line of voids around the foam core. Even if youd allowed more resin into the part and left it resin rich, you might loose the voids but you would still be able to see the imperfection in the carbon weave around the foam as its lifted from the surface.

To solve the pinholes and dry patch problem you need to drill holes all over the foam core. 2 or 3mm holes approx 15-20mm apart or so.  You can score the foam between the holes to aid resin flow if you want.  By having holes you allow the resin to flow under the core ensuring the carbon under the core wets out fully.

To solve the edge void/lifting issue you can do two things. If its a part where the foam goes almost to the edge, you can lay carbon tape around the foam to build upto the thickness of the foam. A bit like how EC laid tape around the soric in the bonnet video.  Alternatively you can sand the edge of the foam to a smoother edge so there is no right angle.  That way the bag can lay flat with no ridge around where the foam core is.

Thanks for the input guys.