First resin fusion - fail: dry spot

This weekend, I finished putting together my vacuum bag system (vacuum press from joewoodworker.com / veneersupplies.com), and tested with a couple of small panels (6" x 6" x 4 layers), one wet layup and one resin infusion. Those went well ( also use butyl tape on those)

My first attempt at vacuum bagging several layers of fiberglass had a small dry spot. This job was resin infusion.

What did I do wrong? I couldn't see the dry spot until after all was finished, I took everything apart and flipped the panel upside down. It was not visible during layup.

Do I need to put some kind of flow medium between the layup table (UHMW board) and the layers of fiberglass?

Maybe I had too much vacuum and the dry area got pinched off by the pressure?

I ended up with a dry spot near the suction port. Here is a rough diagram of the issue (attached picture)

I slowly let the resin flow thorough to the vacuum bag connector and it was starting to suck up into the tube (and into the resin can)

Dimension of laid-up fiberglass panel is about 6" x 18" and the 12 layers ended up being about 3/8" thick.

I layered 1708, mat, 10 oz cloth, mat, 1708, mat, 10 oz cloth, etc... for about 12 or 15 layers

I also had a bunch of tiny air leaks. I expected the leaks because i didn't have any butyl tape and used clear packing tape. That was a mistake.

Even with the leaks, the vacuum pump kept up, vacuum ranged from 21" to 25" (that is the swing of my vacuum valve the cycles the pump.

When flowing resin into dry material, what vacuum value should be used? 10", 15", 25"?

Thanks for the tips.

 

Vacuum should be 30" for expoxy, you can't have leaks though that will mess you up in so many ways. Not only will you end up with dry spots but when you clamp the resin line, the resin inside the part will continue to be pulled out. It helps to shoot pics every few minutes of resin flow, it could be the resin found an alternate faster route (racehorse) to the suction in which case that part in the middle got cut off. Had you had perfect vacuum, the chances of the dry spot would have been reduced greatly. Also I am a fan of infusing inward in which case the resin line would have circled the part and your vacuum would have been in the center. Leave a flow media break before the outlet point to slow the resin down, 2 inches by 2 inches is enough.

 

Thank your for the help. I will try the running the inlet around the perimeter with suction in center.

 

You might also try coloring the resin, so that you can more easily watch it flow when you turn on the pump. And out of curiosity, what resin are you using? Also, is it the proper viscosity & chemistry to be used in this application?
Honestly, were it me, I'd just stick to wetting out by hand or via a resin impregnator (machine which uniformly wets out cloth) & vacuum bagging. As unless you're going to be doing a lot of panels, big ones especially, with lots of layers, it'll be faster to wet things out by hand & bag them, then it will to repeatedly be assembling & disassembling your infusion system, non?
Then again, I've very little hands on time with infusion, so...

 

Seeing the resin flow is easy, no need for color. Right now, I 'm just using polyester resin. I want to figure it out while practicing because I plan on using gelcoat on the parts I intend to make. There won't be a lot of the same parts, maybe a couple of one mold, a few off another mold. For example, I have a mold for a cable race the curves up the hull. I'll make two parts of that: one for cable, one for exhaust hose. They both run up the hull in plain view and I want a clean finish on those parts. There are a few shelves I will make and a couple of half bulkheads.

The other mold is for water tank hatches, need six of those. A big part is the fridge box. I tore out the old one and am designing a new one, which I want to make out of fiberglass and gelcoat so the interior is easy to clean.

I know there is a way to do this, I just have to figure out. I tried a wet layup and it was a pain because the wet resin gets in the way of laying down the bagging film and adjusting for/finding leaks. much easier to do that with dry layup, then infuse. I just need more practice.

I tried placing the feeder tube around the perimeter with suction point in center, but that failed also, same dry spot on underside. This was a 3" x 3" piece of plywood with 1 layer of 1708 top and bottom. Total width was about 6" x 6". I think resin is flowing too fast. I'll slow it down. This also failed because the intake hose fell out of the resin cup and I sucked air.

 

Post pics of your fail and setup some can better help. I have infused 4x8 panels both sides infusing inward no problem. You do need to put a hole through center so the bottom is getting vac too.

 

Yeah, a hole in the middle. I think that's it because it just seems like resin just can't get to it. I hope so, this doesn't seem that complicated. I just have to figure it out.

When I tested without core (before core testing), just 3 layers of 1708, there were no dry spots.
Here are the pictures of the three fails, one of which (lower left) is the one with perimeter inflow tube.

The top has a hole (nail hole, scrap wood) and resin did get to it.

These pieces are just tests with scrap 1/4" plywood. The shelves and bulkheads will have 3/8" to 1/2" balsa core. ONce I get those, I'll test to see if the balsa needs holes.


Here is a link to higher res pictures
Vacuum Bag - LA Gallery http://bodylens.com/Gallery/thumbnails.php?album=37

I'll drill a few holes and see how that goes.

 

If you want to infuse in a mold and have one finished side, get perfed or cut core so you can flow the resin across the top face and it will seep over to the mold side... Otherwise, in-or-out infusing is going to fail on the side against the mold. Leaks can not be tolerated and on bigger parts let the vac pump run a few hours to flash off any humidity in the glass.

 

FWIW most of the companies which make cores, have versions of them with holes in it every few inches. And I'm pretty sure that it's made that way specifically for vacuum bagging, & infusion. Though, obviously, many builders use the stuff with pre-cut kerfs as well. Or they'll even put kerfs into it themselves. Cutting them to a specific pattern, so that the core better conforms to the mold for the part they're making.

Somehow I get the impression that this project is as much or more about playing with new construction methods, than it is about getting the job done expediently, & with a minimum of effort.

 

Uncivilized,

You're partly correct. Initially, I wanted to test this method to compare the outcome with hand layup. Now that I have discoverd that the few panels I have made, even the failed ones, are much thinner, lighter and appear stronger. I notice that when I cut them (diamond blade on angle grinder), they are much harder to cut than the hand layed-up panels I have produced in the past.

If I can figure this out, I can produce parts that are lighter, stronger, and more uniform throughout the laminate. Next week, I'll get some core and test with that. All my tests so far have been with 1/4" plywood, which I have no intention of using.

 

Hey ya'll,

Thanks for the help so far.
I did three more experiments today, all failed.

1. Holes drilled
2. Holes drilled and grooves cut on underside
3. 5 layers of 1708, no core

Follow this link for additional pictures and hi res pics of these
Home - Vacuum Bag Gallery http://bodylens.com/vacuum
I'm going to make the following:

1. A cable race from a female mold I made
2. Water tank lids from a female mold I am making (from a male plug)
3. Some shelves for the dive tank locker (cored with 1/4" or 3/8" balsa)
4. Partial bulkheads under the V berth to divide that storage space.
5. Later on, a new refrigerator box (just the interior liner of the box) from a male mold

The part that concerns me about my failed tests is that I continue to get dry spots on the underside.

The parts I make from a mold will have no core and will have gelcoat. Is there any kind of flow medium that I can/should put between the just-sprayed-on gelcoat and the first layer of the fiberglass layers to ensure that resin gets to the underside?

For an example of one part, See attachment named Cable Race. This is a mold I made that will produce a tunnel to conceal cables that run up the ceiling of the quarterberth. I needs a nice finish, so I'll gelcoat it.

Maybe the orange peel texture of the new gelcoat will have enough air gaps to allow flow. I am working with smooth UHMW poly ethylene.Maybe that surface is too smooth?

Is there a max number of 1708 layers that cause dry spots? I just can't figure out why I get dry spots, even with just 1708 layers.

Perhaps I need additional layers of something to manage the flow.

So far, my layers are:
Fiberglass layer, core sample, fiberglass layer, peel ply, flow medium
Vacuum pressure is -25"
inlet hose, 1/4" ID
Outlet hose: 3/8" ID

I noticed on all of my tests, the resin will flow from inlet to outlet within about 30 seconds. After the first fail, I regulate the flow at the inlet by pinching the hose so it finishes in about 10 minutes.

I'm going to do some more tests next week
1. With the actual cored I plan to use
2. test piece with sprayed gelcoat to seehow it flows over the orange peel surface.

These will be more valid tests.

RE: pictures,

Vertical line on HolesAndGrooves.jpg is tape. The sample core (scrap wood) broke, so I taped it back together

Again, thanks for your help, ya'll have a good week.

 

if plywood is the core it needs to be sealed first before you infuse,perforated plywood wont work well the holes will absorb too much.flow media needs to be used and maybe your resin is kicking to fast.
A pic of the set up before you infuse will help.

 

Maybe the poly resin started gelling and stopped or hindered the infusion flow?

 

On small parts like these you need to slow down the flow, you don't want it to flow from the feed line to the vacuum line in 30 seconds, this shuts off the resin flow to the locations you see that are dry.

1. what resin are you using?
2. you can use products like Rovicore as part of the laminate to aid the flow.
3. don't use the current flow media on top of the stack, skip it on small parts.
4. the resin should flow across the mold evenly, and slow enough so that it doesn't just bridge across the top and shut down the flow.
5. on parts this size you should put the feed line on one side and the vacuum on the other side.

 

Found these pics you need a resin break,so your vac can be 5-6" farther away from the part.extend the peelply to the vac you can use spiral also on the vac, when the resin hits, it will slow down.Again i think your resin is gelling too fast.