Infusion issues - why is this bridging happening? (w/ pic)

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#1

Hi guys,

I’m getting this bridging like issue and I don’t know how to resolve it. I’ve attached a photo of my mold and the part that is being pulled from it. The infusion is done down the longest dimension, from ‘top to bottom’ in the mold picture, and this bridging issue is occurring at the rounded edge at the ‘bottom’, at the vacuum draw side (as opposed to the resin feed side).

I can’t figure out why this area isn’t being filled in with resin. W/ the way my infusion mesh is set up, any entrapped air (I’m pulling 29" vac) would have an opportunity to evacuate that corner before becoming sealed in.

I am pretty sure that the fabric is sitting very flush against the molder surface as I have a template to push it into place before I pull vacuum down. It also only happens on this side, and not the corner at the resin feed side, which would have an equally likely risk of not sitting flush since they’re identical curves. This has happened a couple of times so far.

This side is near the first ‘uphill’ portion of the mold; the resin feed side corner that comes out very well is a ‘downhill’ and then flat part and is about 5cm away from the resin feed inlet.

Is it a resin viscosity issue? The only thing I can think of is that the resin feed side floods quite easily since the it’s so close to the feed; the resin is moving quite quickly at this point. By the time it makes it all the way over to this side it’s moving at about .2 cm/second. Temp is about 70F, resin system is Adtech 820. Resin inlet valve is open for quite some time after this area is initially wet out though, it’s not like it’s shut off a couple of seconds afterwards. It’s usually open for at least another minute, although the draw is occurring much more slowly by this point.

I’m pretty stumped. This is the 5th part I’ve tried to pull and each one has some variation of the bridging void. I would’ve thought this entire void would be filled in with resin under this much vacuum.

Any input is appreciated, thanks.

#2

It’s obvious that you’re not pushing the fabric into the corners far enough, and/or your pleats aren’t large enough. Increase the size of your pleats by an inch and you’ll be fine.

As far as pushing the fabric down do your I fusion, once it’s done push the fabric in the corners. The resin saturated carbon will be slippery enough to move.

To repair those parts you have already, just brush in clear resin. It blend nicely. Sand, blend, clear.

#3

Have you made a drop test? May be a tiny pore in the mould so that air can get in after infusion. Can also be a mixture of bridging and not complete degassed resin. But the corners do not look that bad, so I do not think it is bridging. Do you have a pictuce from your bagged mould?

#4

I’m also finding it hard to believe that it’s bridging, but it’s definitely a possibility. I put a larger bag on today so we’ll see what happens when I demold tomorrow. The mold itself is 20x16 inches, the bag I put on today is 27x24 inches so it’s plenty big enough now. I was using 25x22 inch bags previously.

Resin is fully degassed and the mold is sealed very well (I have more than one and it’s happening on all of them…?). I do a drop test/dehumidification dwell and there is no vacuum loss so that probably doesn’t explain it. I don’t have a picture of the bagged part, I’ll try and grab one tomorrow.

Anyways, curiosity question about bridging. Why does it even happen in the first place? If the part is under near perfect vacuum, and the resin in fully degassed, shouldn’t the entire empty space between the mold surface and fiber reinforcement be filled in with a big glob of resin during infusion?

Edit: 2tall, another reason I don’t think it’s just bridging is that it’s only happening to that one far side. Never to the corner closest to the resin inlet. And it’s happened about 5 times now (every part I’ve pulled so far :(). If it was bridging because there wasn’t enough slack vacuum bag, then I would imagine it would be equally likely for this to be happening to the other side that always comes out perfectly.

#5

Well if it is bridging then the vacuum wouldn’t force the carbon in because carbon doesn’t stretch. But if it isnt, perhaps you have a tiny fracture in that area that would allow air to seep through and push resin away?

Do you gel coat?

#6

I liked his question about the resin pooling in the bridged space. Does anyone know why these spaces don’t just fill in with resin?

#7

I found the best way to avoid this is to pull very low vacuum at first which allows the material and the bag to be still moved and shifted, and push the material into where its expected to bridge and form voids ,

#8

In terms of why areas bridge and do not fill with resin, could be from the fact that as the resin flows through the DM and the fabric, it will take a long time to fill the void area. However, once the resin flows PAST this void area, the resin traps the void in the corner, and can not fill with resin. Remember, the vacuums we are using are only a step above a vacuum cleaner. You still have a butt-ton of air in the parts. Well, all relatively speaking for course. Compared to an ultimate vacuum, there is still a lot of matter in that void. This causes the bubble to form after the resin has trapped it in.

#9

Does the mold have a leak? Did you check the mold for vacuum integrity? A tiny leak can cause issues…

#10

Since these are smaller molds, I’m wondering if your manifolding placement will make any difference? Are you doing opposing sides flow and vacuum or are you doing a perimeter resin line and center vacuum or vice versa?

If you keep infusing the same way and getting the same results, changing up flow placement can change a lot of things, both good or bad. You won’t know until you try.

#11

I’ve had slight bridging on my last two parts due to complex shapes and my voids fill with resin. I’m using 4x layers of 6 oz fiberglass cloth, green flow media, USC 635 thin epoxy resin.

#12

So the part I de-molded today was so close to working out, but alas it still had a tiny chunk of resin missing.

Riffs’ explanation definitely makes sense and is what I assumed, but I also figured that whatever air entrapped in that void, if it’s at for example 29" of vacuum), would collapse to a nearly invisible size once the atmospheric resin front hits it. But it’s still the only explanation I can come up with as well, aside from maybe surface tension not allowing the resin to break away from the fibers and enter the void? IDK I’m not a physicist :stuck_out_tongue:

Anyways, the next step is decreasing the viscosity of my resin. I’m currently working in a 68F environment so I think the resin is quite thick by the time it reaches that part of the mold. I bagged a part today, I’ll demold tomorrow and see what it looks like.

Resin flow is occurring across the entire mold, there is no center placement of feed or draw. I’m going to try flipping my configuration 90 degrees if I continue to run into this issue, so that the first area to flood is both corners and then the resin flows vertically to the ‘top’ of the part which is eventually trimmed so IDC if there is bridging. Would like to solve the problem though just for good measure.

iWeasel: I’ve had instances where the fabric is bridged but the void still fills with resin, so I really don’t know what the deal is. It must have something to do with the resin being to thick and not having an opportunity to pool up before I clamp everything up.

Thanks for all the input so far, I’ll keep the thread up to date.

#13

Not sure if this will help, but one of my parts had a vertical wall with a fairly sharp corner about 6" long that was causing some air pockets or voids. What I did to fill those in was to infuse down (parallel) to the span rather than perpendicular. I found that when I infused perpendicular to the corner, the final part was prone to voids. I also did this test with and without flow media over the corner and it yielded the same results as parallel and perpendicular.

#14

+1 it might help to slow the infusion so that any potential bridged areas might fill instead of “running past” and trapping a bubble. But this is subject to working time of the resin. Best is to eliminate the bridging.

#15

even if you have less viscous resin, if the front flows around the corner then your going to have it happen again. I’d be interested in seeing your bag setup and I think some of the other folks here could probably help diagnose things a bit more.

the other option i would think would be to setup the infusion so it starts on that side, that way you can run the flow media over it and to the other side where the vacuum is connected.

#16

I’ll take a picture of a laminate stack in mold and post it by Monday. There is an identical corner feature on the other end so I can’t do that, I can only infuse top down which is looking like it’ll be the next step (the reason I’m trying to avoid this is because I eventually want to infuse a piece whose four corners are all similar to this, so I need to sort this out).

I’m still trying out various cuts of the infusion mesh to best fill in that area. I ran out and only received more yesterday so I haven’t been able to pull a part for the last couple of days :/.

Anyways, I’ll be sure to post results here when they come in - thanks for the help so far everyone

#17

Here are the photos:

The corner at the far end near the vacuum draw line is the one that’s giving me problems. I have a undersize plug that I use to push the fabric into position before applying vacuum so bridging shouldn’t even be a problem, or at least I’d imagine not.

In this set up, I’ve trimmed the perforated release film (airtech P16 WL3700) and even knocked out some of the peel ply to insure that there are no obstructions for the resin to get through from the infusion mesh to the laminate stack (2x19.7oz 12k 2x2)

Another question. In the picture labeled as spider air veins, those features occur nearly immediately after clamping off resin flow and then vacuum (in that order, takes roughly ten seconds to do both). The bag is very tight (drop test confirmed), so I’m no really sure where these air intrusions are coming form. They always start from the vacuum draw side. I’m pulling 29". For my brake zone I use breather/bleeder - could that have something to do with it? I’m going to switch to a peel ply brake some tomorrow and see how that works out. Please feel free to critique my brake zone as well!
Thanks

#18

if you get those “spide veins” as in your photos, this means your bag or tool is leaking. You are probably not doing a good enough vacuum check to confirm that your vacuum integrity is good enough for infusion. If you have a digital absolute pressure gauge, I would suggest a 0mbar drop in 10 minutes before infusing, and if you only have a cheap analog gauge then 0hg drop in 30 minutes.

#19

If he discovers his mold is leaking, can he just flip it over and throw 10 coats of PVA on it (on the outside exterior of the mold)? What is the best way to handle that?

#20

if you get the veins, it’s a leak! I knew it. ALways a bitch with infusion. If you clamp off vac and intake after your ‘done’ you can have this become very apparent. I usually leave vacuum on till the part cures. Not sure if that is the solution. Sadly the solution is finding the leak, which sadly for me, is usually on the back some where but could be anywhere. Since if there are any dry fibers, the vacuum can conduct along and be sucking in from who knows where. If you take it off vacuum and then come back later and the bag is loose, then you had a leak. Or use a vac gauge to check.

As to a solution… I haven’t tried this but I saw this junk: http://www.getflexseal.com/ on TV and thought, “hey, I gotta try that on a leaky tool!” supposed to stop water leaks and is supposed to be rubbery. I thought it couldn’t hurt to give it a try.

Another solution is to bag the infusion setup and then envelope bag the part. I’ve done this when I have a tool that I know has vacuum integrity issues.

Also, I have used the RT yellow sealant tape. I took some high temp sealant tape from work once to try it at home, and OMG. IT was great. Super tacky and soft and sticks like hell to my glass table. The crappy sealant tape has caused me issues in the past but, you get what you pay for I suppose.

And lastly, as to your break. It looks like the flow media goes to edge of part? and you removed the peel ply from the corner? The peel ply shouldn’t be hampering resin flow. I usually leave, depending on the part, an inch or so of break on the part, meaning an inch or so where there is no flow media and only peel ply. This gives the resin time to slow down and fully wet out. I guess on thin parts it’s not a major issue, but the extra time doesn’t hurt.

And finally… now that i’ve written this and been thinking about it. If you have that void in the corner, and a known vac leak, then it’s likely that it’s near/at/in the corner. since that is where you get the spider air lines and where you have the large air void in the final part. Maybe just leave the vacuum on? Maybe its’ just your clamp on the vac line? Or the way you’re sealing the vacuum line through the bag? I usually use a T fitting and razor it through the bag with sealant on the inside and outside of the protruding connector.

sorry to be so long winded and rambling…