Hy




I have a problem, which i do not know how to solve. For my application i need a thin sheet of carbon fiber that is perfect finish on both sides.




I am using one layer of deltapreg 200g prepreg and vacuumed between two glass panells and than baked in autoclau on 4bar. The problem is no matter what i try i get pinholes on both sides, which are not acceptable. I have also tried with drg carbon with resin and the result is similar.




What can i do to get rid of the pinholes on both sides and get a perfect finish?

There could be many issues causing problems.  Without having experience of your specific pre-preg, as its not one of our products, I can only give general advice.

You might be squeezing out too much resin so perhaps adjust the pressure slightly.  Also consider your gel and flow temperatures of your pre-preg.  You may need to allow it to dwell for a while so the resin can fully flow. 

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Are you making your carbon the same size as your glass panel ?,don't have any gap at the sides and flash tape all round the edge to stop any resin bleed

Hy the carbon fiber si twill 200g/m2, and the technical data sheet of the epoxy is here http://www.delta-tech.it/pdf/STE%20DT120-6.pdf




What i found is that nearer the edges there are less and less pinholes, to about 2cm from the edge there are no pinholes left.

The main focus is that we get rid of this pinholes on both sides and is not important structuraly.




And another thing that i found out is when i put the glass panel on just one side, the surface was perfect and pinhole free.

How would you recomend the autoclau cycle (pressure and temperatures) to give the best chance of getting what i want.

And also i am wondering what is causing the pinholes. Is it gas forming in the epoxy that can't escape, or is it epoxy bleeding out.




F1rob




Yes the carbon fiber sheet is the same size as the glass panels but i didn't flash tape around so I Will try that also, if the problem is resin bleed.




Regards

Well looking at the data sheet its a 42% resin material an a fairly standard cure (120,2 dag a minute ramp)

For a single ply you wouldn't need a dwell so straight to 120

but on glass you should be ok with 30psi to get the Finnish but still tape the edges off

Thanks Rob,




I taped the edges, and straight to 120C at 3 bar and the result is outstanding

no pinholes, really perfect glossy finish on both sides.

Hy




now that i have a pin hole free surface i have another question.




Although the surface is smooth there are still some stripes visible from the release agent i think. I am using a frekote 770-nc.

Is there a way to get ride of this stripes on carbon fibre. And how/can I get rid of this problem when applying the release agent. I have tried polishing it with a smooth cloth by hand after the release agent has dried, but it seems that is not enough.




Thanks

I found that is more of an application error. There's 3 main things that cause it:

Thanks for the tips




Yes i do use gloves, but i don't change the cloth for each coat. And i'm pretty sure i applied a too heavy coat as i just sprinkle it on the glass and then wipe down.

There's your problem, always apply to a cloth first then wipe onto the mould