Vacuum bagging'

[TAftonomos]

Well, I've been trying to make a carbon/kevlar exhaust shield now for some time. The first few times, I think I was pulling to much vac (~22") and getting large voids in the resin surface of the part.

I tried turning the vac down, and finally got the exhaust guard to turn out without large voids in the resin, however I've got 3 spots now that have tiny tiny bubbles.

Not sure what I'm doing wrong, but any advice would be helpful. Here is my "process"

Wax the part with mold release wax - let dry/buff
wipe on PVA - let dry

cut out pieces of carbon to size
cut out breather and peel ply to size as well

mix up the epoxy. I stir for 4-5 mins, pour into another cup, stir, and then pour back in the first cup and stir some more.

I'll liberally brush on a coat of epoxy to the part first. Then I'll wet out the fabric on the table, and roll it to make sure it's throughly wet. Place the cloth in the mold/part, and brush it around. I will trace the outline of the part with my finger to make sure there are no bubbles/pockets in there.

I do this with the second and third layers as well.

Finally, in the bag it goes, squeezed to 12" last time.

Pulled them out this AM when they were still green to trim. Like I said, no voids, but tiny bubbles make the part ugly.

Sucks seeing seven of these nice looking things sitting here that I cant use, but I'm not going to let this crap beat me!

[neno]

I am just getting into this whole DIY composite stuff. As I understand vacuum bagging the more you pull the better. It sounds to me that 12" is not nearly enough, if you have bubbles. The 22" sounds closer to what you want. When you get done with vacuum bagging, the part will not a have a glossy nice surface it will have a very dull surface that looks like it has little or no epoxy in it. The the next step then is to finish the part with a clear coat or something of this nature.
If your max vacuum is 22" and you still get spots where there is glossy surface on your part (overly rich resin area) try using a epoxy with a longer pot life eg. 1-2hr.

Like I said I'm new at this also, but I hope this helps, let me know if you have any questions.

[TAftonomos]

Pulling 22" of vac caused resin to be squeezed out of tight areas, leaving the weave exposed. In addition, there were still micro-bubbles present.

[neno]

It will look like the weave is exposed. And with the weave exposed you shouldn't be able to see any bubbles, cause there shouldn't be visible resin to have bubbles in it. I will try to find some pictures and post them.

[TAftonomos]

All the wings/parts I've made before have had a smooth finish with miniman resin but without the weave exposed. Then it's just a slight scuff with scotchbrite and hit it with some 2k clear. Buff/done.

I'd have to put 10 gabillion coats of clear on the pieces with exposed weave.


Thought I just had.

I'm using the ASC vac bag tube. I'm wondering if possibly the bag isn't stretching down enough to press on the part, hence the bubbles. I've ordered some of the stretchelon stuff that is supposed to be 400% more "stretchy" than the tubes I've been using.

I have to wait a week before it shows up to see if it's going to help.

[neno]

I understand what your saying. You are correct. The surface should be as smooth as your mold. I agree it sounds like you are not pulling completely to the surface, just by intuition either your bag is not flexible enough or your epoxy is setting up to quickly. I'm not sure what pot life your resin is, but they say for the best results (fulling pulling, air bubbles, etc) with vacuum bagging the longer the better. Please let me know how your new bags turn out.

[TAftonomos]

using 60 minute pot life resin. I've going to try again (with just one part) in a few and try something different. Some suggest brushing a thin coat on and letting it "gel" before putting the cloth on.

I'm going to try that, and I'm also going to try taping the bag to the back side of the part to make sure there is enough bag to pull down on the inside.

That and crank the vac up as high as I can (30"?)

[neno]

Let me know how it turns out. Also pictures are worth a thousand words I would love to see the final product.

[vfrrider]

What it sounds like to me is the vacuum is degassing your epoxy.

To avoid this, place mixed epoxy (just use one container and mix thoroughly) in a vacuum chamber (an upside down glass cooking pot on a table top with a hole for the vacuum line) and pull a vacuum for a few minutes, say 5, to take out your air bubbles.

Now coat fiber on the mold and press resin into weave. Easy way to cover for vacuum is to use 2 part cover with a bead type seal. Smooth well, seal. Pull vacuum and let set. You SHOULD get little to no bubbles, no air left to outgas. Thats why prepreg works so well. Optimum concentration of resin and no air. Just remember, all vacuum baggin does is remove air for optimum resin penetration and supplies its own pressure for mold following.

Finish as before for shiny coat, or leave dull for racer look.

Larry
VFRrider

[mrgrn]

use a fast curing resin.

use another material like plastic layer with holes

you can use zip lock bags, or so i heard

let it cure for a bit b4 installing it in the bag

don't stir in too much air and let it sit b4 applying

i don't know much but hope this helps

[20_RC51_00]

Originally Posted by vfrrider

What it sounds like to me is the vacuum is degassing your epoxy.

To avoid this, place mixed epoxy (just use one container and mix thoroughly) in a vacuum chamber (an upside down glass cooking pot on a table top with a hole for the vacuum line) and pull a vacuum for a few minutes, say 5, to take out your air bubbles.

Now coat fiber on the mold and press resin into weave. Easy way to cover for vacuum is to use 2 part cover with a bead type seal. Smooth well, seal. Pull vacuum and let set. You SHOULD get little to no bubbles, no air left to outgas. Thats why prepreg works so well. Optimum concentration of resin and no air. Just remember, all vacuum baggin does is remove air for optimum resin penetration and supplies its own pressure for mold following.

Finish as before for shiny coat, or leave dull for racer look.

Larry
VFRrider

+1 for the degassing, what is happening is that there are microscopig bubbles present in the resin mix but they are next to invisible at ambient pressure but once you place it under the vacuum these bubbles enlarge obviously because of the decreased pressure. What seems to be happening is that you have not yet achieved suffecient vac to allow for a large enough motive force within the resin to pull the bubbles out and not just have then sitting there as the resin cures. There is never too much vacuum, even under full vacuum you will only achieve about 33% resin content (which is ideal) and that is if you are infusing... more pressure is possible in autoclaves and compression molding systems.

Also make sure that you have enough slack in the bag, don't jsut rely on the "stretchyness" of the bagging, it is not nearly enough....

Don't worry you guys sound like you are well on your way.


hey mrgrn..... tune in there is some decent info on here and it might remedy your issue of porosity aswell

[TAftonomos]

I did a small layup tonight (4 pieces) and it's in the bag now. I'll run down there and crank up the pressure, the resin has just started to kick off.

I did notice, as you have mentioned, there are tons of bubbles along the edges of the part under 15" of vac.

I think I can get 25-26" out of the thing, I'm going to go crank it up and see.

I'm a bit worried at the higher settings, as that seems to be where I had the large voids appear on the part.

I WILL FIGURE THIS OUT

[TAftonomos]

I dunno if it was the extra bag that I made sure the part had, or the extra care I used when putting the parts in the bag.

They turned out pretty darn good (no pinholes/no bubbles)

One question about trimming.

What do you use to trim the edges of a kevlar part? I remember doing it with model airplane hinges, and the edges would fray and you'ld need to re-epoxy them where you trimmed.

[marvin]

Are you using bleeder cloth?

[20_RC51_00]

Originally Posted by mrgrn

use a fast curing resin.

use another material like plastic layer with holes

you can use zip lock bags, or so i heard

let it cure for a bit b4 installing it in the bag

don't stir in too much air and let it sit b4 applying

i don't know much but hope this helps

Wrong, fast curing resins are a pita, you want all the control you can have to lay up your part and have it cure when you want. Ideally you want a resin that won't even start curing until you ramp up the heat. Curing too soon (rsult of short pot life) will ensure bubbles and porosity just like your rear sets you need to make sure that all the bubbles are gone and you have intimate contact so that there are no voids for large bubbles to form becuse they will collect there...

ya hahah zip lock... good idea genius....

Taking short cuts will see to haveing crap for parts and dissapointment every time you demold... don't skimp and use the propper materials, a well perforated release film will do you well

Here is a list of materials you will need starting form the mold and working upward.

mold>carbon/reinforecment>release/peel ply>perf. film>bleeder and breathers positioned depending on how much excess resin you are trying to get rid of

keep in mind that too much resin means that you will have to bleed out a lot....and chances are that it won't all bleed out and your parts will still be resin rich. When laying up make sure to only use as much resin as necessary to wet out, try and aviod the temptation to lather it on there excessively.

I'll post back whenever I can, I'm pretty busy right now.

[dalewrc30]

I wouldnt bother with vacuum bagging for wet lay up,too much mucking about.It should cure fine without the vacuum as long as you roll it out properly.

Dale

[TAftonomos]

Originally Posted by 20_RC51_00

Here is a list of materials you will need starting form the mold and working upward.

mold>carbon/reinforecment>release/peel ply>perf. film>bleeder and breathers positioned depending on how much excess resin you are trying to get rid of

I'm not sure what the perf film is in that list, I just use peel ply and then the breather layer (usually 2).

My epoxy is 60 min pot life

The last set I did last night I made sure there was enough excess bag, and whala, they all turned out great

Now I just need to figure out how to finish them. I guess scuff with 220 and then a good 2 k clear/buff ?

Once I get the stretchelon film in, I'll give some of the other parts a go. These were 999 heel guards, and monster headlight support brackets.

I've been using 100% carbon in my layups, no FG to speak of.

[TAftonomos]

Originally Posted by dalewrc30

I wouldnt bother with vacuum bagging for wet lay up,too much mucking about.It should cure fine without the vacuum as long as you roll it out properly.

Dale

Some of the parts I want to make are curved, and therefore the carbon isn't going to lay down in there by itself. S*R heel guards are one example.

[RCVTR]

Place a bleeder around the perimeter of the part. It looks like fiberfill insulation. This allows the vacuum to continue pulling resin and bubbles out of the part. Put a bunch of it around the vacuum inlet, too. the bleeder prevents the bag from sealing off on the mold backing plate.

Also, don't put too much resin in the part. Use a squeegee and put in just enough to completely wet the fibers. This will allow the layers of fiber to compress together, rather than squeezing excess resin. It also prevents filling your bleeder with resin.

[RCVTR]

Also...

You'll have better luck with an oven cure resin, if you can rig up a way to cure it. Reason is, the resin viscosity drops way off with temperature and it will flow out of the part better, along with the bubbles.