issues with some parts....

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#1

Well i’m having some issues with pulling a perfect part from my mold and i’m hoping someone can help me out.

I guess the easiest way to determine the issue would be to outline my process…

I am making pipe guards for bikes using high-temp epoxy.
I have made a mold which is perfectly smooth and I have had no problems releasing my parts from now that it is properly waxed.
Basically, I start by mixing up a batch of epoxy…this stuff is really thick! I brush on a layer of epoxy when it is nice and thick, into the mold. Then I put down a layer of carbon in the mold, press it down, then heat up the epoxy in the cup with a heat gun so it is less viscous. then I brush on epoxy into multiple layers of carbon, fiberglass and kevlar. Then put in release cloth and finally absorber cloth. Then I bag the part, and am getting a very strong vaccuum.

After I release the part, it comes out nice and strong, pops out easily.

The issues is…When i release the part it has a number of small pinholes and also a few bubble-filled areas on the part.

I need to figure out how to eliminate these pinholes and bubbly areas from my parts…

I would really prefer not to have to spray a gell-coat on the mold as I beleive the epoxy is too thick and have no way to spray it.

Any suggestions would help!

Thanks

#2

You need an Epoxy face coat. Or thin your down?

NEVER SPRAY EPOXY as it is deadly fumes!

#3

ok…so if i heat the epoxy first before applying to mold would that help? I figured if I applied it while still thick it would make a thicker outer coat and prevent voids…

#4

Dude Id just use the gelcoat…and add epoxy to it.

Ive “fixed” other builders stuff like that and the first time I did it took 11 coats of clear coat as the carbon wicked up the clear like a sponge.

Youd be better served with an epoxy surface coat or gelcoat.

#5

ok…am I dreaming if I want to get a epoxy top coat that will handle 400F like my resin will?

#6

You could make your own surface coat using your 400F resin and mixing it with cabosil (or similar)and some pigment. I have done that before. What resin are you using?
In my experience, the sympoms you are giving seem like too much resin. The tiny pin holes will always be there (unless you have an autoclave), but the “bubbly ares” sound like too much resin to me. Is your breather (“absorber cloth”) saturated after the cure?
Another way of improving the surface is to cure only 2 layers, then add the rest after the first have cured. This reduces the chances of the fabric getting bunched up or bridging and helps trapped air to escape.

#7

you can purchase high temp clear gelcoat.

#8

Thanks for the help. I assumed that pinholes abd bubbly areas meant too little resin. I think that heating up the resin first should have an effect on the process. What does adding cabisol to the part do? also, where can I go about buying high temp gelcoat?

#9

Cabosil will thicken the resin up.

High temp gel coat try BJB Ent. in the products sticky section…

#10

If you are laying up more than 6 layers or using really thick resin you should do a debulk phase. That will blead out the excess resin, trapped air, and help the carbon lay down. After debulk you can lay-up the following layers.

After the first four layers a fifteen min. debulk, then continue as normal. I found that when using thick resins it is better to not apply resin to the mold first. Lay the cloth in the mold dry and then wet out. Yes it’s a pain but there are fewer pin holes and the part actually looks better.

HTH,
CCE

#11

Pinholes (worm holing) normally is a low vacuum issue. Which is why you wont come accross it (most of the time) with autoclaved parts.

#12

ok…Thanks for the advice, i’m pretty positive my vaccuum bag is pulling a strong enough vaccuum. I can easily infuse with thick cloth real quick i’ve found.

Will the epoxy dissolve spray adhesive if I use this to first stick down the initial resin dry?

#13

While resin shrinks on the y axis it wants to recess away from the mold surface. Areas that dont have cloth have nothing to prevent the resin from recessing. All those pin holes are located in the gaps between where the tows cross (i.e. very, very small areas of no cloth).

An autoclave can apply sufficient enough pressure to prevent the resin from recessing as described above. Most hobbiest pumps dont.

Not so sure that epoxy actually desolves spray adhesive. But the adhesive wont hurt the epoxy if you spray it sparingly.

#14

I like the technical description! You are very correct that the areas that are lacking resin are the spots between the weave…

#15

It makes sense right.

Your right though as you said earlier to little resin can cause the problem also.

Some radome covers I did a few months back had quite a few pinholes on the top hat part, but very few to none around the base. Im guessing the resin slowly drained towards the base and thats what caused it.

Theres was an article in compostits world mag recently that had a gortex bag (lets air out, and resin in), within the main bag to help prevent resin from running off of some of the sharper angled areas of the part. Not to sure I understand the science behind it but it worked. Just one more way of eliminating pinholes and dry spots i guess.