Ok, I have had a good week and solved a lot of problems.

I already posted in the other thread how I finally get perfectly sealed bags now and what the problem was.

I now have made 3 pin hole free parts in a row. Before these, I never have gotten a  perfect part.

This is only my opinion, so here goes.

I believe the problem is viscosity. The infusion resin does say it is 300cps but I never thought about the actual temperature I was working under.

So this is what I did. I have a 5 ft wide oven that I built. (Its easy to make) and I then put my vacuum bagged mold and catch pot in the oven at 100F.

While the pump was running at full vac connected to the mold I then prepare my resin. I heat it to 90F and then mix in the hardener and degassed it in a chamber that I built. (it is also simple to build)

Once degassed I open the oven and infuse. It goes very quickly because the resin is like water.

Once the resin is coming out of the mold and into the catch pot I clamp off the vacuum line but leave the resin line open for about 15 seconds. Then I clamp it off and let the mold cook at 100F overnight. (Vacuum pump turned off) Bing !my first absolutely pin hole free perfect part.

As I though it was a fluke I did it 4 times and each time I got perfect parts!

So here is my take on whats happening. Imagine infusing resin as thick as molassis, do you really think it will wet out every fiber even if you get some coming out the vacuum line. Even though I heated the resin, I believe that because the mold was heated it would not allow the resin to cool down as it made its way through the carbon, so helping the resin along. Letting the resin continue into the mold after the vacuum line is clamped off seems to equalize the pressure in the bag so that no vacuum voids can build up between the weaves.

Thanks to Matt for showing us on the hood scoop video, the trick of clamping off the vacuum completely after the infusion.

Fred          

Hi,

I have been trying to make Carbon Fiber sheets using resin infusion process. I have given 9 tries till date and have not able to eliminate pinholes. Glass has been used as the mold surface. I use wax and PVA as release agents, have also tried 2 Mil MYLAR sheet as releasing agent, but has not been able to produce single sheet with out pinholes.

Size of sheet tried 20mm X 15mm. Mesh area of 25mm X 20mm. Resin Mixture 130 Grams for infusion. Fiber cloth 200 GSM Plain 6 Layers.
Resin has been completely Degassed before use. Vacuum Drop test is conducted and have verified full vacuum of -1 bar.

I have attached a sample photo can you please let me know where i am going wrong in the procedure

Thank you

+x

 

Madhu Gowda Bekka Prasad - 10/24/2019 8:19:37 AM

+x

 

Lester Populaire - 10/24/2019 6:51:36 AM

+x

 

Madhu Gowda Bekka Prasad - 10/24/2019 4:42:49 AM

Hi,

I have been trying to make Carbon Fiber sheets using resin infusion process. I have given 9 tries till date and have not able to eliminate pinholes. Glass has been used as the mold surface. I use wax and PVA as release agents, have also tried 2 Mil MYLAR sheet as releasing agent, but has not been able to produce single sheet with out pinholes.

Size of sheet tried 20mm X 15mm. Mesh area of 25mm X 20mm. Resin Mixture 130 Grams for infusion. Fiber cloth 200 GSM Plain 6 Layers.
Resin has been completely Degassed before use. Vacuum Drop test is conducted and have verified full vacuum of -1 bar.

I have attached a sample photo can you please let me know where i am going wrong in the procedure

Thank you

So the Flow Media is longer than the plate you are making if i understand correctly? Cut the flow media always 2cm or so shorter than the fabric to make sure the resin has to pass through it and can't skim across. Then use a strip of peel ply at the end to pull the vacuum from. We just had this a month ago with someone else. I'm sure you can find that thread somewhere 

Hi Lester Populaire,

Thanks for the reply, When you say flow media you mean the Mesh we apply over peel ply correct. So the mesh should always be lesser than fabric area correct? 

I think what lester meant (and this is how I set up) is hang your flow media and peel ply off the inlet side edge of the part but leave them both short of the vent side (and left and right) edge of the fabric so the incoming resin has to infuse down thru the last 2cm. Having said that, pin holes like you described, in my experience, are the the result of air infiltration during your cure. Trapped air as a result of poor flow management leads to discreet pockets or patches of dry fabric, not systemic pin holes. Does your flow media have little bubbles trapped in it when you come back after the cure? If so, that's air infiltration from a micro leak in your film or bag. It pushes in thru the flow media and down through the part, leaving pinholes everywhere(not to mention scrapping your part). If there's no bubbles in the media, it's possible your leaving it to cure under too high a vacuum. The resin effectively boils itself to swiss cheese as it cures and that can look like pin holes but there's generally a bunch of white frothy residue everywhere, and im not seeing that in the photo. You want to pull resin under full vac but drop it down below the vapor point of your resin before crimping off your lines. 
Good luck.
P