Thin sheet carbon caul plate infusion problems

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#1

Hey guys,

I want to infuse a single skin of 240gsm 3k carbon with a double sided gloss finish. I have tried many different ways, most failed badly, but the last ones seem to be close to a result.


I am getting a lot of pin holes (as the pictures will show) and it seems to be spread randomly across the whole sheet on both sides.

The sheet is 55cm x 35cm of 200gsm 3k twill. Resin is Gurit Prime 20 LV with an extra slow hardner(http://www.gurit.com/prime-20lv-1.aspx) Ambient temp is beteen 25-30’C.
I don’t have a vacuum chamber to degas the resin, but I let it stand for 10min after mixing, before infusion. Infusion takes about 2 hours. I cut off the inlet 10 min before I close the vacuum line, could this be the problem? I also don’t pull resin through into the trap, as the flow speed is very slow at the end of the infusion, even if I leave the inlet and vacuum open I doubt I will get resin up to the trap.

I udes the 200gsm CF instead of the 240gsm as it is cheaper to waste on tests, could it be that the loose spacing between the tow is causing the cavities?

I just got some Prime 20 ULV resin with a lower viscosity, I hope that this would at least help in reducing the pin holes.

What am I missing? What am I doing wrong. I am pretty new to caul plate infusions, so don’t be gentle.

Regards
Jacques

#2

the first problem is that you are pulling resin through the laminate that has bubbles. The bubbles themselves only move because the resin they are in is moving thus when you stop the flow the bubbles remain stationary despite vacuum still being present. The vacuum at this point is only pulling a very small fraction of the resin, essentially just debulking… so there really isn’t any motive force for the bubbles. They stay where they are until cure. lower visc resin makes degassing easier and less time consuming.

#3

Thanks for the reply.

I don’t see bubbles in the feed line or before the caul plate, I’m not sure what happens under the plate as it isn’t see-through. Could the resin be degassing under the plate?

#4

Could you have moisture in the stack or other solvents? These could be outgassing, I would doubt that it’s the resin, the gurit is top shelf from those that have more experience than I in the field.

Does the carbon have any treatment of surface coating? Ive heard of treated glass/carbon/kevlar that are intended for one type of resin system or the other…

When I had problems with bubbles it was either due to pinhole leaks, bubbles in the resin I was infsusing with or letting the resin front travel too fast across the part.

you are likely encountering difficulty as well because there is no flow media. The resin, although very thin is only travelling through very densely packed fibers…

#5

The air bubbles will expand under vacuum, so what may look like tiny little bubbles in your resin pot or vac line will actually become way bigger inside the cavity.

I think for what you are doing, degassing would be essential. With a normal infusion you’ve got your flow mesh and possibly even perf release film, both of which help with holding the air bubbles and preventing them from making it inside your part, so I don’t believe degassing to be necessary for regular infusions. But without them you’ve got nowhere else for the air to go, it will always end up in the part.

#6

Being from S. Africa use the Elon Musk approach and think from first principles. What causes bubbles? (outgassing, etc… look at your cure temp ramp rates, possible contamination from release agents, etc.) Once bubbles are formed then how do you get rid of them in the process? (edge bleed, perf film, etc.)

Basically you need to understand the chemistry and physics behind your process and what’s going on in your system and then reason from there to solve your challenge.

#7

^^thanks man.

I guess I was hoping my problem was more obvious as the other options involve trial and error.

I will start with degassing first, then move on from there.

I know this is very difficult to infuse,but being so close, I want to get it right.

#8

I can almost say for certain its air. I’ve had parts look like that before. Actually had a flat panel infused on glass that had only a few patches of those pin holes in a 28x18 inch part. My resin inlet came up and sucked in air for a split second.

But I degas my epoxy. Not exactly sure but like others have said start with degassing first.

#9

Don’t have air leaks in my bag. I test my bags for leaks by vacuuming down, then closing the vacuum line and leaving the bag for a few hours. I do this before every infusion.

I don’t let my resin feed line get close to the air, and my bucket and lines are fixed in place. So I doubt that was the cause, but I will double check everything just in case.

I also added some flow mesh before the caul plate in the hope of trapping some bubbles in it. Don’t know if it will make a difference, but it won’t hurt to try.

It is currently infusing as I type this, flow rate is extremely slow through the 240gsm 3k. So far it traveled 30cm in 3 hours.