Hi, sorry that I did not answer that fast. At the moment I am traveling a lot but you can contact German Advanced Composites. He is in the states and can answer all your questions.
I’ve been using the MTI hose for about 3 years now and it’s the only hose I use. With that said I tried my first split mold with the mti hose and it was a huge fail. Mainly because of myself and not the hose but I want to know how do you route your vacuum lines for double bagging with the mti hose?
Do you just do one vacuum line from the hose to outside both bags, or do you do two lines and one going into the inner bag “mti hose” and one only going to the outter bag?
Or can someone break it down for me. I had a failed part which I double bagged “or I thought”. I only had one outlet going past both bags to the mti hose. I did a pressure drop test and nothing out of the ordinary. Keep in mind my outside bag was completely loose. As I infused everything went as normal but when I clamped the resin pot and the epoxy hit the hose I started to notice air bubbles forming. I’m guessing that was because the outside bag was loose. I then quickly while realizing there was air being sucked into the inner bag somehow connected another vacuum line and punctured a hole in the outside loose bag and pulled a vacuum.
Now where did I go wrong. Should I have connected a separate vacuum to the outside bag and turned that on as well after I made sure everything was fine with the inside bag?
I would think that if you pull a full vacuum from the outside bag, and you have a split mold with the mti hose, then you’d be degassing the resin inside of the bag itself since there’s a hole or something loose in your mold. Although the mti hose shuts off the inside bag vacuum, the outside bag vacuum is still pulling.
Any help or input would be appreciated.
Dump the double bag. I infuse some 3 to 5 piece molds with one bag pinhole free. Wax your fasteners first 
What do you use to seal molds? I thought about running bagging tape along the edges of the meeting molds but I’d need to do that to the bolts too.
Silicone. Best to put some dowdy washers on your bolts as well.
I most make a double bag. Seal the first bag at the flange and then envelope bag the whole mould.
Little more work but no problems. For sealing the moulds I most use Acryl, stays longer flexible.
What I already had was that it was sealed perfect and when it starts to become warm or you handle the moild it suddenly leaked.
I envelope bag the whole mold. Some of the bags are up to 3m x 3m .
Thanks for the reply everyone. I know what I did wrong and it was that I wasn’t pulling vacuum on my envelope bag… How dumb of myself. Lesson learned. At least I have a part now that’s not to bad and can be used. “non structural interior cover part”. Thank you for your help.
MTI hose sucks - i just lost a part when it quit flowing after resin got to it. From my understanding this was NOT supposed to happen
Yep, probably the fault of the hose and not your technique… :rolleyes:
MTI hose makes the process easier, and it reduces the chances of this happening, but it doesn’t make it impossible. You still need to think about your flow front. Once resin reaches the hose, it seals it and you lose your vacuum front, of course. The difference between MTI hose and regular infusion, is that a regular infusion would have started evacuating the resin once it reached the outlet, which can make things worse. It can also make things better, if you know what you’re doing and know how to fix these issues.
I think also your inlet shouldn’t be more than 2 feet from the Mti hose. I had a three foot run before but things took forever. What saved me was I use 1 hour epoxy. Which kicks early depending on how much I have in the pot, or rather get out of the pot and into the part.
Rank amateur that just used MTI hose for the first time. It was also the first time I’ve tried vacuum infusion. My part was a tube with a step and flange at one end. About 11" long and 7" in diameter with the good side out. I used a 2 piece mold that I drew up and 3D printed. It was a pain to bag with the first attempt refusing to seal. I inserted the inlet at the simple end and the MTI hose around the circumference just above the step & flange.
I checked for a perfect seal then went to town. Because of the rookie way I placed the inlet the resin immediately raced to the vacuum end. The MTI hose saved me. Without it the resin would have all gone right out the vacuum line. With it the vacuum continued to pull resin which then spread around the remainder of the part then pulled up to the hose. Not a drop passed through the hose (as it’s designed) and the part came out great.
I’ve been researching and watching the use of MTI hose for quite some time. Mine seems to be a perfect example of how and why it’s so important. As I say, I’m a rank amateur though it’s my opinion that there is nothing else that comes close to help get a properly infused part and helping save you from many rookie errors.
Thanks
Billy
I’ve been using the Mti hose since I started infusing parts. Truthfully it’s kind of sad because it’s the only way I know how to make parts but it’s worth it since I haven’t had a failed part for such a long time!
I did however have issues with my bags/tape/mold before. I spoke with DDcompound about the issues and he stated I check out the absolute pressure gauge they carry. I’ve been using that for a bit and didn’t know how I survived without it. I had some of the analog gauges before, and although they worked for drastic changes it wouldn’t account for a few mbars like the geisinger gauge.
i’ve searched a bit for but have not found an answer - has anyone had problems with the MTI not pulling down vacuum? i had a small part recently (12 in x 20 in pretty much flat) with inlet using spiral on one long edge and MTI on opposing long edge. while trying to get perfect vacuum the MTI seemed to flow slower and slower. it was very noticeable. finally got to point where it seemed to not flow much air at all. I was attaching to end of hose per instructions. and had end closed off per instructions. i had to scrap the setup and rebag using spiral and worked fine. I was using stretchlon 200 and was worried about the material surrounding the hose and blocking it. i tried to remedy that potential situation but no joy.
I had a similar problem when I used a tee into side of hose - quit flowing air after bening manipulated a little while working on good vacuum. I thought perhaps that part of the MTI was blocking the vacuum line. I had to scrap this bag setup as well.
Thanks
I use the hose the exact same way as described above on a flat panel about 30x18. The hose runs the long length on one side only and I have a resin inlet on the other side with about 6 inches of spiral tube going along that side.
Your problem is probably the stretchlon bag. I notice my vacuum is a lot slower when only one side of the hose is on the part vs 3x sides or around the full perimeter but you should still be pulling vacuum.
Basically i don’t know what to recommend other than maybe breather cloth wrapped on top of the hose or to get a new bagging material.
Are you absolutely sure that it wasn’t pulling vacuum? MTI hose is MUCH slower to pull vac, so much so that a bag that would get pulled down virtually instantly with my pump will take 10 minutes. It’s extremely slow, which is actually one of the reasons I’ve stopped using it so much.
I’ve never had it completely stop pulling air though.
I would recommend to preevacuate by the resin feedline and then switch to the MTI hose if you want to suck your bag down fast.
Also if you can’t keep vacuum with the MTI hose your bag is not tight! And stretchlon ist not suitable for infusion, it will always be leaking!
problem seems to be the slow pull-down rate which is concerning since i am worried part won’t get fully infused. i don’t need the part to pull down quickly - i just don’t want it to take a long time. i don’t want to have to switch back and forth between the inlet and exhaust lines when pulling bag back down while getting bag working (checking leaks) which is when i noticed problem. and forget about the bag having leaks - when i switched back to spiral tubing the bag sucked down immediately.Yep stretchlon is out - i was testing it out.
so, no, my problem wasn’t a loss of vacuum - it was just so slow to pull down (likely aided by complications from the 200) that i thought it had stopped. I now have a much larger piece that i have surrounded by the MTI hose and am hoping for the best (but making me nervous)
There’s no correlation between how fast the bag pulls down and how fast your part infuses. Different forces at work there, so don’t need to worry about that.
It does also work to do as DD suggested with pulling the bag down via the resin inlet, as once you’ve removed most of the air then you can switch to the MTI hose and let it do the job from there, no need to swap back. I just don’t like doing it because I prefer to leave the resin inlet alone until I’ve pulled the bag down and done leak checks. Once I know the bag is totally leak free, then I breach the bag for the resin inlet and recheck the seal. Just means I don’t have to be suspicious of the breach at the inlet on the initial leak check, and if there’s a leak after breaching then I can safely assume it’s at the inlet connection. Just easier for me.