Pinholes

Hello, I’m Mario Modica, from Argentina.
I would need to do a question:
We work doing helmets and others products with carbon fiber finished. We were have always a big problem; we laminate a first lay of carbon fiber fabric (twill 2x2 around 198 gr) and continue the laminate with some glass fiber fabrics until to get the necessary thin.
When we desmold the piece there are a lot of pinholes on the surface of the piece, wich I must to refill with resin or poliuretanic clear PU(like used in refreshing cars), and then we must to sand a lot and repeat the step 2 or 3 times. The latest step is paint with clear poliuretanic varnish.
The pores appear usually in the intersection of each yarn. In the laminate I try to close the weave to avoid this problem, but isn’t enough.
How we could to get pieces without pores on the surface?
I have tried with a very light glass fiber fabric as first lay, wich it become almost transparent with the resin, but the problem persist and you can see that glass fabric.
If I put a first lay of transparent resin and let cure a bit, for continuing the laminate appear little bubbles instead of surface pores.
In all cases I do vacuum bag process, (I have tried with ¼ atmospheres, with ½ atmospheres and with ¾ atmospheres)
What do you recommend?
An autoclave would finish my problem???
Thank you very much, and greetings from Argentina!
Mario Modica

 

Your resin may be boiling as it is overheating due to the heat of curing. You may need to modify the resin system or cure schedule.

Jimbo

 

Pinholes can drive you crazy.

Some tips and trics:

-store your epoxy resin dry and closed. Water is your enemy. (do a test: mix epoxy resin, then mix in about 5% water and see what happens. Also record the time. Do not use this epoxy, just let it sit in the mixing cup) After this test, you will understand what I mean.

-keep your fabric dry, or even dry it prior to using it. With helmets this can be quite easy. Cut the neccesary fabrics, put them in a low basket, and put that in the oven at 60-70 degrees C. This will dry the fabrics.

-Apply a very wet layer of epoxy resin on the mould. You could thicken it a bit, if you do, also use a little bit of black pigment to remove the yellowish colour. Then laminate the first layer very wet. Subsequent layers can be laminated normally. Then apply vacuum. (not too much, 50% is usually enough, at least untill you control the pinholes)
This will force the thicker resin into the places where pinholes are, driving the air pocket into the glass layers, and ideally out of the laminate.

If all else fails, I have once removed pinholes by polishing the carbon with black shoe-shine...

 

Thank you very much Jimbo1490 and Herman!! I will try what are you saying, and then notice to you. The true is that I'm coming doing all kind of experiment trying of desmold a piece, apply lacquer and finish the part without refill hand and sand and I have always failed / unsuccesful.
Thank you!!!

 

I would be looking for a better resin with differant promoters and hardeners that dont react to form bubbles as much !!
Second vac can be a big part of the problem . TAlking in percentages i used as low as 1.5 percent of vac on really big panels and had 100% success 100% of the time with not a bubble to be seen anywhere !
Think , what are we actually using the vacumn to do ? and how much pressure is required to do what you are doing ? how low can you go !!

 

or a fast and easy solution is to lightly sand and with a featherlight autobody fill and try carbon powder or black pigment pigment catalize of coarse sand smooth after and dip the helmet in a system three clear, cut by 45%water hang and dry. A process I have used for clear carbon shafts for cosmetic perposes.

 

Hi this sound rather interesting got any pictures of what you have done and how it turned out :idea: ??

 

Just a thought

Sounds like you might be over catalysing the resin or putting it on too thick. If the resin is too thick it will not gas off correctly and the gas will be trapped against the mold. Try using less catalyst or a lower %. Also, you might try gel coating it with clear, letting it kick off and then doing your lay up.

 

Yes most of the responces are correct you may want to clear coat or look at the thicks of your expoxy. But if I remember correct your are bagging your helmets you may also want to go to a thinner bag or try a different product all together. Without having been apart of the process I can only speculate. But my solution to get the exsisting product out the door is a tried and true tested system to the paddle shaft process. For imperfections specially in blatter molded surfaces where expoxy flow and pressure go hand in hand. Due to legal retraints could not take pictures of the process.

 

vacuum bagging

If you're vacuum bagging I would definitely suggest spraying clear gel coat in first. Do a light "tack" coat and follow it up with a few more thin coats, making sure you let the passes gas off in between. If you're still getting porosity it's probably the catalyst, moisture or wax.

I would always gel a bunch of molds with "crystal clear" gel coat, let them completely kick off and then do my layup process.

 

Remember that vacuum lowers the boiling point of any liquid, including your resin system. So if the resin is getting hot while it cures, it may reach its boiling point sometime during cure, This is the reason there is a specific 'ramp up' rate for temperature when doing heat curing; you want to avoid boiling the resin. As the resin cures, its boiling point rises, so you can heat more, thus the ramp-up. But the temp. can pass through the boiling without any added heat if the resin system is very fast reacting. Boiling can produce persistent pinholes.

Jimbo

 

It still is not clear to me whether epoxy or polyester is used...

 

Gentlemen the responces here should be going to EXITcomposites email address he is the one looking for help. I am just trying to help him with suggestions. So please forward suggestions to the original reciepiant thanks.

 

Since he implied that the layup is carbon fiber, epoxy resin is a safe assumption. I'm not aware of any carbon fiber goods being finished for anything other than epoxy resin. If they are knowledgeable, they would know this.

Jimbo

 

@ carboncopy001: You probably get topic reply notifications. As standard, everyone gets them. You will get an email every time someone reacts on this or other topics that you replied in. You can turn them off in your profile. Also, in the Email you get there should be a link to turn them off for that topic only.

@ Jimbo1490: Yes, I do understand that epoxy is the most sensible option, but i have seen the strangest things. Just would like to hear it from that guy.
In case of epoxy, boiling off or overcatalising is less of an option. Moisture however is...