The aha cf pinhole-free thread

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#21

The cfm of a pump is not really that relevant.

For oil-lubricated vane pumps, it is important that they run within specs. Check these specs, as there are many around. I normally sell pumps which, by closing an oil drain tube, can run within 50% and 95% vacuum, or 90% and 98% vacuum. (I noted the vacuums in percentage, to avoid imperial vs metric issues)

When you start bagging, the pump runs at athmospheric. A pump does not like that. Running for too long at athmospheric will clog the exhaust filter, which then needs replacement. This already can happen within 10 minutes.

So for the cfm two things are important:

-enough to have the bag down within 10 minutes. (for large structures, before closing the bag completely, stick the vacuum cleaner hose in the bag, and extract as much air as possible from under the bag that way. You can just hold the bag around the hose with your hands, it is not critical. But at least a couple of square meters of air will get extracted. (1 m3 = ca. 33 ft3)

-enough to keep up with resin flow into the bag, when infusing. (at the pressure you are infusing at. See the pump capacity diagram for that, as cfm decreases with more vacuum)

#22

Im only using a refridgeration pump to do my Vaccum Bagging, im getting near perfect results, but its taken me a long time to get the process spot on,

I feel it has more to do with materials and prep rarther than the ammount of vacuum.

type of resins, thickness of resin, temp of resin, gel coats, wet lay technique, wax, quality of fabric, weave of fabric, surface of mould… alsorts…

Keep up with it and you will find what works best for you…

P.s. there has been some awsome tips and tricks in this thread that have also helped me get better results

#23

Great idea on using the shop vac to get most of the air out.

iMation, i’m glad the thread has helped :slight_smile:

I did try another lay up with vinyl ester resin, no gel coat for the part. Only problem was vacuum seal… darn bag tape wasn’t working. But the GOOD news is straight vinyl ester wet lay up solved the air bubbles in the surface… at least where the vacuum bag pushed the laminate down enough. I’m pleased in the progress. I’m not happy with my bagging tape issue lol. Yellow sealant tape here i come!

#24

That is the AT200Y from Airtech, which should do the job.

If you are not going over 140 degrees C, then you can opt for the Airseal 1 or 2 (1 = low tack, 2 = high tack, whatever you prefer).

It saves you a couple of dollars.

#25

I’m going to revive this thread,

I did a couple of tests recently, using different wax’s and resins.

At the mo the only resins I could use were, SP115 from Gurit (thin), and a Epoxy from Carbonmods.com (very thick)

The waxes I used were, Meg’s No8, TR102, and this Meguiars Deep Crystal Carnauba Wax Step 3,

All panels were wet lay with no gel time between laying fabrics and were squidgy on the last layer, then vacuum bagged till cured.

The Megs No8 wax goes on fine, comes off a bit stiff but a good clean lint free cloth works well, the TR102, again is ok! And the Car Wax is easy to put on and take off, a little bit powdery so I had to wipe everything after!

I found with the No8 and TR102 wax i got a small amount of pinholes where the weave interconnects, now this is probably due to the resin fisheye’ing on the wax before the first layer of fabric. But the car wax, it didn’t fisheye and there were a lot less pinholes after cure…

The resins i think play a massive part in quality, the Carbon mods resin is very thick, even when at 25 DegC, but the SP115 is a lot more runnier and i find easier to put on any surface…

Carbon mods resin had a few pinholes in and the SP115 had next to non, very good results.

One thing I am thinking, is my release film letting too much resin through into the breather/bleeder fabric?

I will get some pics up when I get home

Just my thought and practices for better results

Stu

#26

Thank you for your efforts. This probably shows that sorface tension of both mould and resin play a large role here. Do you happen to have access to Sicomin resins? If so, try their “Surf Clear” which supposedly should give good results.

#27

I’ll just highlight what I’ve read so far on the subject: This is mainly for clear cosmetic carbon fiber parts. Structural or parts that will get color painted just use surface primer on the part.

  1. mixed resin should be degassed in a vacuum pot chamber. 10hg/3.38 -mbar or maybe a little less should do the trick.

  2. use a very fine, lightweight layer of fiberglass cloth first into the mold

  3. surface coat the mold with resin prior to laying down any laminates.

  4. use a stippling roller on the first layer of carbon fiber in the mold to pop small air bubbles.

  5. a highly polished mold surface and a very good waxing job will reduce friction coefficient. The easier that resin can flow and move around, less air/gas bubbles will be trapped on the part surface.

  6. too heavy of a breather bleeder fabric can absorb too much resin. Try 4oz bleeder fabric.

  7. make sure your resin is up to at least 77f/25c degrees before working. The resin will flow better, and allow gas bubbles to escape more readily. Get mold temperature up to room temp prior to work.

  8. use 1K or 3K carbon fiber if possible as your first layer of cf. 6K and up will trap more air between the tows.

  9. if you don’t need a very compacted laminate use 15hg to cure.

Now i just have to do more practice runs with these methods to see exactly how i can achieve a pinhole free laminate.

#28

I have been producing clear carbon finish parts and always fighting pinholes and never being able to get rid of them. Until I tried infusion that is, by infusing I can now produce completely pinhole free finish.

#29

There is a place in Bristol that sells this, forget the companys name mind but should be on the tinternet, they advised me to use SR8100 Sicomin resin, which worked well, a lot thinner than the Carbonmods stuff (and cheaper!)

#30

From my (limited) experience degassing resin at only 10 inHg will do next to nothing. I degass at 29/30 inHg the resin really bubbles at this level of vacuum.

How many people here have tried this? Does this work? I see earlier in this thread that 1/2 oz glass was mentioned, I have only been able to find 25gm glass here which would be nearer 1oz, would this glass be fine enough?

#31

yes. it works. the cloth is like…linen. very very thin.

http://www.compositescentral.net/showthread.php?t=5107 heres a perfect example.

#32

I have some 2oz fg cloth i am going to try. If it doesn’t work i’ll switch to 3/4 oz.

I also tried some infusion resin for wet lay up… i got less pinholes. That resin was 500cps.

#33

This very fine layer of glass cloth, does this go BETWEEN the epoxy gel coat and the first layer of CF? i presume if it does then it goes completely invisible when wetted out?

Also whats the benefits of this?

I was pondering wether laying up just one layer of CF then vac bagging it would work any better, then pulling the peel ply off then adding the rest of the layers once the first layer had cured, that way there is a lot less layers for the air bubbles to have to struggle through?

Thoughts?

Thanks guys…Matt

#34

I gave this method a try only last week, I had been having some bridging problems on a motorcycle sprocket cover. It worked a treat. The only downside is the extra time and work it takes.

#35

I was thinking of this method but more to eliminate print through from the honeycomb. Did you pull less vacc. to keep a bit more resin in?

#36

if you have any pin holes when doing a 2 stage layup.you will get bleed through when you do the 2nd stage.so its best to do at least 2 plies and make sure you dont pull too much resin out on the 1st stage.this way you will insure you dont have a chance for bleed through.its happened to me a few times.i never do 2 stage layups anymore.

#37

What do you mean by bleed through?

#38

Yeah, I usually bag at 29/30 Inhg but I thought I would knock this back a couple of inches, so I did it at 25 Inhg.

#39

its when resin bleeds through your first stage when laying your second stage.it leaves your mold side with resin rich areas.it just happened to me this week.

what i mean by not pulling to much resin on the first stage is,you dont want your first stage to be light on resin ratio.i use fabric peel ply and perforated peel ply to control resin loss into the breather.you can pull full vacuum on it.just wait for the resin to thicken before throwing it in the oven.

#40

I tried some lightweight, 2oz, fg woven cloth yesterday. Not so great… too heavy i think. I would have had better results without it.

I used epoxy resin 400cps ( thin ). It does seem the thinner the resin = less trapped air in the surface of the laminate.

I asked a supplier today about air bubbles and he only uses general purpose polyester resin … I know this resin and it is very thin. Would be nice if i could get away with using polyester.

What I need is a very thin vinylester resin.

I took a look at 4 carbon fiber parts another company made. They were the raw finish out of the mold, many spread out tiny voids in between where the tows intersect. What they do is spray clear coat on the part, sand it, clear it again then wet sand 1500 grit, and buff/polish the clear.

It seems pinholes and small voids in surface resin are everyones ordeal with cf.