"snow flakes" (dry spots) in Vacuum Infusion

General Composites Discussions Composites Talk
#1

…Have Vacuum infused “numerous” parts…with various mould surfaces…and applied a few post-bake methods. It seems that we cannot get away from having “dry spots” (I call them snow flake patterns) probably within the first 10-15 plies of fabric, near edge of parts.

…have tried mulitple feed lines, rearranging location of spiral tubing, heating up the mould surface lightly, slowing pull of resin

…we have pretty strict methods of resin infusing and have a variety of knowledge of infusion…and a long history of being in this business.

but I have always seen this issue and am trying to figure the causes behind this challenging problem.

the floor is open…

#2

how long do you leave debulking before infusing?Perhaps you have moisture in your laminate. Are using wooven or uni? Photos always help if you can show.

#3

pics or it didn’t happen.

Do you mean when you cut into the laminate, or visible on the surface…say, a whiter spot in the color of the panel when using glass?

#4

Pictures are definitely a “must do” to solve issues like this. There is a lot of info missing that could help pinpoint the problem.

It sounds like your dry spots are areas where the resin flow front goes around and does not close up before resin feed is stopped.
Is there core being used? Is peel ply or perf film used? What type of flow media? Is the flow media covering the entire surface? How much vacuum are you pulling?

So many factors…

#5

debulks vary…sometimes over a weekend, mainly overnite, we are pulling 28" or better on vacuum with a leak check of zero or .1 drop over 5 min.

7781 fiberglass fabric for most parts. Sometimes 1581.

they are dry spots…have UT many of these areas…to determine if any acoustic indifferences. our composites are very thick. Some areas are ok depending upon location, but it seems to always be on the mold side.

We maintain vacuum pressure of at least 17" upon completion of the infusion for at least 16 hours prior to post bake of part.

will get some pics tomorrow

we cut into it if a repair is needed, but it is visible from the mold side. But yes it is whiter than the “normal” dark green color.

#6

we have placed the feed line and the very bottom edge of part and have infusions that run over a 6’ span which allows for plenty of saturation time but we end up sometimes with dry spots (snow flakes). Flow media…black mesh not over whole area, porous peel ply, no core, no perf film.

#7

Is the vacuum level intentionally lowered after the resin feed is stopped, or just that 17" is the minimum if it drops?

So these dry spots are not visible through the bag? If they are dry areas on the mold side, it could be an issue of the resin not permeating properly for whatever reason.

Will wait for pics. It’s tough to analyze from written descriptions.

#8

intentionally lowered. mold side only visible once demolded. will get some pics. appreciate your input.

#9

Again, not sure on many things, but depending on how thick, 7781 ain’t the easiest to flow through, might be getting internal race tracking somehow, depending on where the DM is, and what side infuses first. Also, depending on the resin, and the thickness again, your resin might exotherm, and cause internal bubbling and VOC outgasing if that one spot gets too hot.

#10

Tough one. A photo or 2 will help. The black mesh, is that the Airtech one?