Infusion Dry Spot Repair

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#1

I did an infusion tonight, and the result is some dry spots on the mold side of the core. My layup is:

2 plys carbon (5.9oz 2x2)
5 layers glass (8.8oz 2x2)
divinycell core (w/ holes drilled on 1.5" centers)
5 plys glass
2 plys carbon

I have never infused 14 plys before, and the end result was some dry spots on the mold side of the laminate. The part is a splitter for a race car. Aesthetics aren’t important, so I’m hoping to salvage this piece. I have attached a picture of the mold side for reference. My “mold” is a double pane sliding glass door panel, so I had the advantage of being able to see through before pulling the part from the mold.

How to repair this? I was thinking maybe pull it off the mold, then put bagging tape around the dry area on the mold side, and try to infuse it. Not sure if the resin would really wick into the dry areas though. Other thought was to use some resin and heat it up quite a bit to get the viscosity really low and just brush it in or roll it. Thoughts on how to salvage this layup?

Thanks!

#2

Infusing it would give you a better chance of completely wetting out all the fibres, as that is likely 7 plies of dry fabric in those areas. You could likely brush or roll resin into that, but its never great to try and push resin through 7 layers of fabric, you’ll get voids for sure. How much that matters is probably up for debate.

Infusing it would definitely wet out the dry areas, and it would do it quite well. You will have some excess resin to clean up, but you said it’s not cosmetic so shouldn’t be too big a deal. Biggest challenge may be getting it a 100% seal, as dry laminates have a habit of letting air in even when it seems totally impossible.

#3

When I have that happen, I usually bag the part again and then re infuse it. Obviously you need less resin and there will be some extra surface resin as well, but i"ve managed to save some parts I’ve made that had issues during the initial infusion.

#4

Thanks for the tips guys. I think I’ll try just infusing the dry area, after I demold and flip the part over. I’m thinking perf film, then infusion media, bag.

Do I need peel ply between the perf film and infusion media? I’ve never used a perf film for infusion before, but I do have some one hand, made for infusing.

#5

No need for peel ply. Though it is an option to infuse the whole thing, with a layer of peel ply over the whole lot. This would give you a uniform textured surface over the entire part, so you could just clear over the top with a high build clear with minimal prep work.

But bit unnecessary really. You’ll still need to do some prep work, and it’s all extra weight.

#6

Thank you again.

Another idea came up, on how to avoid this in the future. I’ve never tried it before, so I’m not sure if its a common thing, or if anyone has done it before.

What do you think about infusion media right on the mold surface, then peel ply, then the normal laminate stack, then peel ply, then infusion media. I’ve never done flow media on both surfaces, but that seems as it it would work well. I may also be able to remove all of the drilled holes through the core. Thoughts?

#7

It would work, but it shouldn’t be necessary at all. I’ve been involved in 36sqm infusions that were 7mm thick carbon skins on either side of a 25mm divinycell core. All infused in one shot, no dry spots. No special tricks involved there, just staged infusion with multiple feed points.

Something has gone wrong there. I normally drill on 2" centres, so 1.5" should be more than enough. Did you score the surface between the holes at all?

#8

No scoring the surface, just the holes. Green infusion media over peel ply on the top surface.

#9

That may be the issue then. I always connect the holes by lightly scoring the surface on the tool side. Doesn’t take much, just lightly drag a flathead screw driver or ruler across the surface. Enough to make a light groove, but you don’t need a trench. This is why I don’t use the off-the-shelf drilled and grooved divinycell, because their grooves are unnecessarily deep and just consume resin.

#10

What size holes do you drill? Does it depend on core thickness? I have a section of 3/8" core and a section with 3/4" bonded to the 3/8".

#11

I’ve never had an issue with core thickness, and I don’t see why it would effect anything. Holes would be roughly 3mm. To be honest, I don’t actually drill them, I just punch them out with a small screen driver.

#12

Thanks, I did closer to 2.3mm holes. What is a screen driver. I’d love to punch holes instead of drilling.

#13

Sorry, a screen driver is like a screw driver but typed on an annoying phone :smiley:

Just punch them out. I’ve done it with cores from 5mm to 25mm thick. Just punch it through from one side, and then push the screw driver through the hole from the other side just to clear up the hole. Much quicker and easier than drilling.

#14

Nice. Hah. Thanks.

Another thing I was thinking about. When I infused, I had the resin cup about 3 feet below the mold surface. Is this too low, creating too much of a difficulty climbing the resin tube to the mold?

#15

Issues that might have caused it are vacuum level. Go as low as you possibly can. This solves a lot of dry spots.

Also keep the vacuum on for a longer period before opening the resin valve: there is air in the foam, and this could also play its part.

Infusing with mesh on both sides is perfecly possible. The holes will keep the resin fronts somewhat equalised. The resin speed below the foam will probably be slightly faster than above the foam.

To create grooves in foam press in a piece of chicken wire. Simple but effective.

Just some loose thoughts…

#16

My pump will generate ~ 29 inHg. I have found that to be typically adequate, but what is your experience?

#17

Then keep the vacuum on longer before opening the valve.

#18

just as a side note…why so many plys of material when you have a core(you didnt mention it´s tickness)?? won´t that be waaaayyy overkill?
asking as i´m doing a similar project and i was thinking in two plys of carbon on top and one ply of glass+one kevlar on bottom.
I have done splitters with 5mm foam core with bonded sheets of carbon top and bottom (2 plys each) and the splitter is quite stiff. Not “racecar” stiff and thats the reason i´m going 10mm dininycell and infusion

#19

I have no idea what I was thinking on the number of plys. WAY too much. Significantly stiffer than required. I can literally jump on this thing w/o any measurable deflection by eye. I will likely re-do with maybe 2-3 layers per side or something like that.

#20

which core tickness did you use?
Any photos (or jumping on it videos, ahaha)?