Need a solution for vac bagging problem

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#1

.Hello,

First off, I know infusion is the answer but I am making one off parts and am bound and determined to master vacuum bagging. I have been able solve every problem I have encountered so far except for one. I have areas between the tows in 2x2 3K twill that are silver. I assume they are dry or air. I do not have bubbles or surface pinholes or pooled resin or bridging. All of these have been solved. My vac pump will pull a maximum of 25". I use Polymer Products 1618 Epoxy.

I have tried many things to solve this problem to no avail. I have tried using no breather and release film with no perforations. Release film with just a few perforations and one layer of breather. Etc. Etc. The last attampt was degassed at 25" vacuum. I made certain the CF was fully wetted. Applied resin to the tool, torched the wetted CF before placement to pop any bubbles and torched the resin on the tool for the same reason. Applied the CF to the tool. Put a layer of peel ply, release film with perforations at 1" on center and 1 layer of breather. I bagged it and pulled 20" of vac. (My thinking on this is that if I bag at a lower vac than when I degass, no new gas expansion would occur) Let it set overnight and pulled the next afternoon. Same problem. I did not have any leaks in the bag and it lost only 2" vac overnight. The part came out very flexible so I assume it is resin rich. Any suggestions would be greatly appreciated.

It doesn’t show too well in the pictures. It is mainly visible at a certain angle.

#2

Anyone? Herman?

#3

Hard to see but I would guess air entrapped,i have found it near on impossible to get predictable results using wet lay up reason being when you stipple resin into fabric you are also adding air,so even after degassing your introducing air,which is why infusion is better,ie when you have degassed you don’t disturb resin.Good luck.

#4

Put a light layer (2 ounce/yard) of glass on the backside of the carbon fiber. Make sure that this is fully wetted and that there are no voids or air on the backside of the carbon. This will give you visual. If there is a void on the frontside is will show up as a void between the carbon and glass on the backside. Any voids in the backside must be filled. You can fill them by dipping your brush in fresh resin and dabbing the tip of brush on the void (stippling). Once everything is void free, put perf-ply down on the layup, followed by some light glass or peel-ply. Don’t put bleeder over the layup. Put breather around the perimeter of the part to ensure equal vacuum. The glass or peel-ply behind the perf-ply should contact the perimeter breather. Use light vacuum for your first few. If they are coming out voidless then you can try increasing the vacuum.

BTW, the part is flexible because it is thin. It has nothing to do with being resin rich. A resin rich part will be less flexible than one that is pressrd thinner and contains less resin (higher fiber volume fraction).

#5

Thank you Shaneer22 and wyowindworks. I will give this a go this weekend. To make sure I have this right - I would do the following:

Gel coat tool and let tack
Brush on resin
Heat to pop any bubbles from brushing
Apply my lay up of wetted CF (3 layers)
Apply a layer of 2 oz glass and wet out ensure no voids
Applt a layer of perf ply
Apply a layer of peel ply
Put breather around perimeter of layup
Pull vac
Hope for the best

At what level of vac would you suggest I start with?

I will post the results once done.

#6

Missed this one. I never had luck with wet bagging. I have a couple of customers who do it, usually with relatively thin resins, and little vacuum.

#7

O.K. - here are the results of my latest attempt. Done the following way. I added on step to wyowindworks suggestion because I need to do secondary bonding to the back side.

Gel coat on tool and allowed to B stage.
3 layers of 2x2 CF twill fully wetted out
1 layer of peel ply wetted out
Perf ply with perf at 1" on center
1 layer of peel ply
Breather around perimeter with last layer of peel ply in contact
Bagged and vac at 25"

It appears that too much resin was drawn from the part. The result is better however as it looks like the dry areas are localized and are near the perforations in the perf ply. From the pics you can see the dry areas between the gel coat and the first layer of CF. From the back side, there are white, dry spots that correspond with the front side. For my next attempt I will use 18" of vac and see what that does. Hopefully, this will help someone else who may be experiencing the same problem. I am going to have to bite the bullet and switch to infusion I think.

#8

Update for those who may be interested in the future. Followed the procedure from wyowindworks as above. This time I pulled only 15" of vacuum. From two feet away the part looks fine. However, there are still spots between some tows that are dry. Much less than before, but still there to some degree. I think I will just enlarge the flanges on my molds and give infusion a go.

#9

You could ditch the vacuum bag all together. Just use some peel-ply on back to take up the excess resin.

#10

I could I guess but I plan on doing the bodywork for the bike also. This guy seems to have it figured out.
http://www.compositescentral.com/showthread.php?t=8156