Epoxy shrink/sink.

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#1

Hi…

I have a little problem.
When I make vacuum molding of carbon fiber and then when it hardened I get sink marks.
Have tried to cure in the oven, to ramp temperature, and let harden long at room temperature 4-6days.
have tried curing at different temperature as well.
Always the same problem, ugly sink marks.
Do all epoxy systems sink? I use Easy Composites epoxy.

Would have been nice to get a perfectly smooth and fine surface :smiley:

some ideas?

#2

Have you got some pictures?

#3

u using a core material

#4

Do you mean you can see the weave on the surface? If yes, lot of epoxy systems have this. I can reccomend the Rampf 2500, that’s the resin where I have seen this effekt only very little. I don’t know if there is a distributor in Sweden.

#5

I know you said you’ve tried letting it harden for 4-6 days, but just to be clear - is that prior to demoulding? So you’re letting it harden 4-6 days in the mould?

#6

By sink marks do you mean pinholes? You say you’re vacuum bagging, maybe you’re not pulling, or holding a strong enough vacuum.

#7

Sounds like fabric print-thru issues. Solutions include:

  1. Fully cure the part with a heat treatment before demolding the part from the mold.
  2. Cure the part more slowly to reduce the internal stress within the laminate.
  3. Change to a different resin.
#8

Have tried taking pictures but it will not be good.
The parts are wavy and not 100% smote in certain lights…
Do you feel with your fingers so you can barely feel the waves.
Much like the paint on some new cars (orange peel)

The parts are vacuum infused and may be in the mold at least 3 day usually 4-6, before oven curing.

Then oven cured to 80C - 0.1c/Min ramp. The parts are still in the mold with vacuum.
May perhaps replace/try different epoxy systems.

#9

I still want to see pictures.

I don’t think we can really understand what your problem is if we can’t see it!

#10

have the same problem with or without the core material.

If I don’t cure it in the oven and let it stand in the sun, the surface is 100% perfect. It’s a mirror.
The heat makes the epoxy “sink” a bit, and waves occur.

#11

I fond a picture on Google that shows how my parts lock like…

http://www.racechairs.com/v/vspfiles/photos/acc151-4T.jpg

#12

I don’t have any specific advice but as you know it seems obviously related to the heating. Maybe try less heat, a slower ramp, or no heat if this is suitable? or try another resin system?

Does your current resin system specifically require a heat cure?

#13

my resin curing at room rempratur to a low TG… 50-60’C.
Its a bit low to have in a car at summertime i think.
I think 80*C is better.

I will try a different resin soon.