Need to vent(no pun intended) heh...err..

General Composites Discussions Composites Talk
#1

So 3 different attempts now at creating a stable vacuum. Zero successes. I’ve tried a couple top layers with pleats. Putting my ear right down on it, I’ve gotten rid of any leaks I could hear. Finally, I said, this mold is small enough, Let’s envelope it. Invested in some tube bags. I sanded down all the reinforcement on the back and sides to make it smooth. Taped between the open ends. Taped outside the open ends on top of the previous tape. I get to -30, clamp off the ends, even put gum tape on the end of the resin side tube to make sure.

I’ve never felt like a bigger idiot or more frustrated in my life. I’ve gone through 4 rolls of tape with no success. People somehow do this on something the size of a boat, It can’t be this difficult. At this point, all I can think of is to double bag, but I’d have to wait for another connector for the pump to arrive. I’m ready to pay someone to come to my house to show me what an idiot I am.

#2

What type of pump system are you currently using? It could be a issue with your pump/resin trap setup, I would try to isolate the issue by not bagging the mold. If you run a test bag (empty) with your entire setup, you should be able to reach your desired vacuum.

What exactly is happening? Are you loosing vacuum after you achieve a good seal? Resin infusion or wet lay and then bagging?

#3

Thanks for the reply. I’m attempting infusion. The pump is a CPS 4 CFM model. The pump itself does not hold vacuum, although i’m not sure that’s important. Once -30 is reached, I close the valve on the hose going to the mold, and kink it and clamp it just in case. So, I’m guessing the pump/catchpot setup shouldn’t matter at that point? The resin hose is kinked and clamped, and has a piece of gum tape over the end of it. At that point if you wait a minute, you can start to hear the bagging inflating just slightly. After 20 minutes or so, there’s minimal vacuum left. It’s the same thing every time. Bag everything carefully to not make any holes. Get rid of any leaks you can hear. Re-squeeze the tape everywhere. Fail.

#4

What kind of tape and bagging film are you using?

#5

The tape is Airtech AT200Y. The bagging is 32" poly-tube 4 from fiberglass supply.

#6

What kind of mold release?

#7

Frekote 700-NC

#8

where are you measuring vacuum? Best to measure it at the resin inlet with a digital absolute pressure gauge. How are you isolating the bag from vacuum pump? just pinching the line? Are you sure its fully pinched?

#9

I’m measuring at the catch pot, which I know isn’t great(especially because the pump and catch pot itself can’t hold vacuum), but at this point I don’t need a meter to tell me anything. After a minute, I can hear it start to inflate. I’m isolating from the vacuum pump by closing the valve coming from the catch pot, kinking the line after that point, and clamping the kink.

I made another attempt just now. I let vacuum get up a little high before getting all the material adjusted perfectly. So I thought to myself, ok just wait for some air to leak, and then readjust everything. I waited a couple minutes and there was no movement. Ok, so I opened up the resin line to let some air in, and adjusted the materials. Applied vacuum one more time, and had a couple leaks right away… But not at the tape. One was right in the middle of the mold, and the other was completely off the mold but not at the tape either. Wtf? Do I need to put another layer between the mesh and bagging film because the mesh is puncturing the film?

#10

could be… sounds like something is puncturing the bag. I have not personally had issues with the flow media but, i know others have.

if you’e taking this much time to mess with it, you should just double bag it. I usually spend like 30 minutes or so, and if it’s easy to do, i’ll just double bag it. After the 2nd bag you, you should be golden. Maybe not the final solution as, if you do a larger part double bagging is more of a pain. But it would probably get the job done?

#11

The best investment I ever made was the purchase of a leak detector. You can make one yourself, but I actually found a STEAL of a deal on eBay. I bought a unit that runs a few hundred bucks for less than it costs to fill up my gas tank.

They will make your life so much easier… You can only hear the large leaks with your naked ear. The small leaks that are causing you fits are going to be nearly inaudible, so don’t even waste time trying to listen for them like that. I have found leaks using the detector, that I never would have found before. I’m talking leaks where the bagging tape looks perfect from above, but there is an almost microscopic leak on the bottom side.

#12

got a link to it ?

#13

It was a singular eBay auction, not a person who regularly sells them. I just got lucky and searched at the right time. Or did you mean a link to the one I built?

#14

For leak troubleshooting and checks, using a stethoscope is a great alternative.

#15

My leak detector will only find the bigger leaks so ones that are making the hissing sound.I’ve found the stethoscope to be useless,piece of hose put in your ear worked better.

On smaller set ups Ive resorted to filling the bag with compressed air from the inlet tube,only need a couple of pounds pressure.With the bag full i push down on it and with the leak detector you should here where its coming from.This may not always work pending on the set up but like the OP I’ve been frustrated to the point I’ll try any thing.

Normally the holes or leaks are in the bag/pleats and only show up when you adjust the pleats.

#16

I’m with you on the complete idiot thing. I find nothing more frustrating that trying to find vacuum leaks. As far as I’m concerned, anyone who can successfully bag and infuse something the size of a boat hull is some kind of other worldly wizard. I’ve never changed any of my processes over to infusion for that reason. I doubt I’ve ever had a “Perfect” seal on a bag ever, and I’ve been doing this for what is now a long time.

I have mostly converted to pressure molds instead of vacuum bagging. One reason was to drop the cost of consumables but more gratifying was not having to stand over a god forsaken bag with an undetectable leak somewhere.

I hope you get it sorted, maybe it will make your wizard transformation complete. Good luck.

#17

Personally I’m going to start using silicone bags for all of the new molds I create. You can build a countersunk “channel” on the mold flange, and then press the pre-molded silicone bag into that “channel” surrounding the entire flange. No more gum tape, no more bags, and what I hope to be a 100% perfect vacuum every time.