Vacuum Bagging Pinholes

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#1

I’ve several years using epoxy and hand layup, this is my first real delve into polyester and bagging.

I laid up 2 layers of 7.5oz plain weave, 0° off axis, with fiberglast 77 resin, mixed .0125% MEKP with a spray can primer on the mold surface. Vacuum bagged with release, .125" breather and stretchlon 800 bagging and 99.99% sealed, the only leak was the breach at the air connector an inch outside the part.

Before I bagged it, I made sure it was wetout a bit more than what I would if I was just doing a handlayup part. I figured the breather would absorb the extra, but… it took a little too much. or… I did something else wrong?

The part came out with pin holes in nearly the entire part. The fabric was wetted out, but the space between the fabric was dry, which good news, made for a nice flexible part, but absolutely unacceptable part and would be very difficult to fix the part. i.e. Trashbin.

What I know I didn’t do was lay the 2nd layer up at 45° axis and the spray can primer is obviously a single stage and is not optimal for “production” but for the first few parts may work. I’d like to think the primer isn’t the problem, but I don’t want to go out a buy a 75$ gallon of pain, 10$ gallon of thinner and acetone, and a new needle and tip for the gun, just to get the first few parts out while I learn. I don’t want to have to learn 5 things, when I could just learn 4… and especially when I don’t need more than about 6oz of primer at a time.

Suggestions to start tracing the problem first with the pin holes?

#2

Did you use a perf-ply between the peel-ply and the breather? If not, this could be your problem. The breather/bleeder can wick too much resin out of the laminate creating pinholes and voids. The appropriate perf-ply can prevent this.

#3

For the pin hole problem. I’d recommend using a perforated release film between the peel ply and the breather. This will regulate the amount of resin absorbed into the breather fabric.

As for the primer. I’d just purchase a pint of what ever you would like to use in your production parts, and brush it on for the first few test / promo pieces. That will allow you to figure out if thats what you really want to use.

Also, I wouldnt purchase materials from Fiberglast. They overprice everything they sell. For example. A can of super77 from Home Depot runs around $9. From Fiberglast last time I called. Almost $30. The price they charge for the carbon fiber and resins are equally ridiculous.

#4

Wet bagging does not take away the need for skill. You need to be a skilled laminator, and need skill applying the bag.

First of all, laminate your first layer resin rich. You do not want any air void in that layer. The rest of the layers go on “normal”. (in the old days, we even did not impregnate the last layer, when making thicker laminates.

If needed, use a peelply. The only reason for that is if you want a course surface, for secondary bonding. You could use strips on your glue joints.

Use a perforated film. Now the tricky thing is the amount of perforation. There are various styles. Check perforation styles of Airtech
The amount of “open area” is what makes the difference. It is dependent on resin viscosity, vacuum pressure applied, geltime and laminate thickness.

Viscosity down: open area down
more vacuum: open area down
geltime down: open area up
laminate thicker: open area up

For a P3 perforation I would not dare to go beyond -0,5 bar (-14Hg), unless you use thick laminates.

To get the most out of it, you would like a low pressure. This makes the air bubbles grow, then hopefully escape. After 5-10 minutes or so, throttle back the vacuum.

All in all I was happy to master infusion in a pretty early stage, which solved a lot of issues.

#5

I didn’t. I understand what you’re saying, and a follow up: Why use a peelply and a perferated release together. I’ve purchased some rollers too, and I do wet out the mold before laying the first layer. Like herman said, it does require skill, and mostly practice. the 2nd set came out much better, but still with (much less) pinholes. I figure the rollers will will help out with that. Next set should come out perfect. :smiley:

#6

i’ve priced out US composities for my bagging material based on chasing links for a few days and working on pricing for my “production.” Biggest cost is my labor of course, but if I can knock off another 10$ or so off front end materials cost I’d be pretty happy.

looking at HD website, the GP poly is about 35$/Gal. UScomp has it at 25$/Gal.

#7

You only need to use peel-ply if you need to do secondary bonding. If no secondary bonding is required then you can just use perf-ply. The role of perf-ply is to control how must resin gets absorbed by the breather/bleeder. If you don’t use perf-ply then the bleeder material will wick the resin right out the weave intersection.

Do a test. Do a hand layup without bagging and do the same layup with a bag. If the unbagged layup doesn’t contain pinholes but the bagged layup does, then know that the problem is with the bagging technique. Either you are wicking too much resin out of the laminate or there is trapped air within the yarns/tows of your fabric. If there is air trapped in the yarns the added pressure will squeeze the air out of the yarn and it will collect at the weave intersection (places of lower pressure).

You can also see variations depending on how much the resin has gelled before bagging. This can be due to layup time variations, hardener/resin choice, and environmental temps. As a tech learns to the do the layup faster they will often start to get pinholes because the resin has gelled less. Also temperature changes in the environment can cause problems. Often techs will have not problems in the summer and then start having problems with pinholes in cooler winter months. This again has to do will how gelled the resin has become. Changing the amount of perforations in the perf-ply will usually solve the problem.

#8

It’s certainly bagging technique. I dont’ believe I used enough resin the first time, I didn’t account for the wick. The 2nd set I used more than I thought and turned out better.

“Changing the amount of perfs will usually solve the problem.” Do you mean, use a different perf ply, or use more layers?

#9

I meant that you can use a different perf-ply that has less perforated area.

#10

Just a question more for my own education… if you’re vacuum bagging a part, you still need to go through the normal wet layup process of ensuring there’s no air bubbles/voids, correct?

I thought the purpose of vacuum bagging was just to compact the job and ensure that the materials conform to any tricky/sharp angles? You wouldn’t count on it removing air from laminate would you?

#11

In my opinion you are correct. In fact, you cannot count on the bag to press the fabric into corners and such. In most cases, if the fabric is bridging then it will just support the bag and the bag will bridge as well.

The only bubbles that will be removed are those that migrate with the excess resin.

#12

Agree with it fully. Bagging is just for compaction, and for better installation of core materials. If you want void free products, switch to infusion.

#13

I should have read this thread earlier tonight. I just did my first wet layup with Adtech 820, a very low viscosity epoxy resin. I only used peel ply, no perf film. I also used 2 layers of the breather and applied 25 inches vac. After reading this I’m afraid to see what the parts look like when they come out.

#14

I am curious as well. Did you use glass of carbon? The larger tows of carbon create more open areas, and these can wick empty.

I once attempted to repair my carbon mast, by vacuuming some carbon on it (small patch, some 25x50mm, 1"x2"). No perf film, full vacuum. The result was as dry as it could get.

#15

I used 5.9 oz 2x2 twill carbon. I’ll post an update when I pull the part from the mold late tonight.

#16

Kevin Doe,

What was your result? I am encountering a similar problem to the one in this thread and have yet to resolve it. I have tried many different techniques and still have dry areas or air between tows. I have even tried it with no perf film and no breather and still end up with small areas where there is no resin. I use Polymer Composites 1618 resin if anyone is interested. These are small motorcycle parts I am doing, but before I takle bigger parts I would like to get this one problem resolved. The last parts I did came out better that any others with much smaller voids. My vac pump wil only pull 24". My procedure was as follows:

Degass part A and B seperately at 24"
Degass mixed resin at 24"
Apply a coat of rresin to the mold
(Mold has already ben gel coated) This resolved surface pin holes
Brush resin on both side of first layer
Torch both side of first layer and coat of resin on the mold to pop any bubbles
Brush resin on both sides of 2nd and third layers and torch both sides before applying to mold
Apply peel ply
Apply release film
Bag
Pull light vacuum and ensure stack is in corners etc.
Pull vacuum to 20" (My hope was, that if I bag at a lower vacuum than when degassing, no bubbles would be able to form.)
Maintain under vacuum for 6 hours
Pull part after 24 hours.

The result is a resin rich part which is O.K. as these are mainly for aesthetics. The surface is very nice, due to the gel coat. The compaction is good in my opinion. The only thing wrong with the part is the fact there are silver dry or air spots between some tows that are visible at certain angles and would look terrible on a larger part.

Any advice to solve this would be great.

#17

To “banned” (nice name…)

What spec release film do you use? P3 perforation?

#18

I just used 15 mil poly with no perforations in the last attempt. Before that, I tried with perf that was 1" on center. I would post a pic of the parts but they just don’t photograph with my camera well enough to show the areas between the tows. The last part was very flexible (too high of a resin to fabric ratio). The parts are heel guards that are about 3" by 6" with a stack of three layers 5.7 oz 2x2 twill. I have gotten alot of information from this site that has alowed me to rectify other problems I was having such as surface pin holes, bridging etc. I have searched on this topic, but most of the threads get abandoned once some advice is given and as to whether or not the problem was resolved is only a guess. I am determined not to let this beat me. I want to master this before I go to infusion. These first parts are small and I don’t know if infusion would really work on them. Any help would be appreciated.

#19

Do you make these heels for a living? Or in other words, how many do you need to make?

Infusion is easier to master, and gives better results, but on a single heel it can be really fiddly. If you can make a mould with for instance 8 or 10 heels side by side…

By the way, feel free to post in the threads of your interest, inquiring for the outcome. It might revive the thread. Or create a new thread, post some pictures of your setup, and this should spark new replies.

The perforation style should be OK.

#20

These are just for my own bike and maybe a few for some friends. Any ideas on what I may be doing wrong that is causing my problem? I was going to try as a next possible solution, saturating one pice of fabric, no gel coat on the mold, and just bagging the one layer with peel ply only at a low vacuum, like 14". Once that is cured, laying up the two last layers on top of what would be the visible surface layer with peel ply and perf and breather and drawing 24" on the whole part. Do you think this will give a good surface while maintaining a low resin content?