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Old Feb 14, 2012, 05:19 PM
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Closed-Mold Vacuum Infusion with a Bladder

i am still up for suggestions for a shorter name for this process, but, here goes-

over the last few months i have been working on an idea to combine 2 composites production techniques: vacuum infusion, and bladder molding.

i have had limited success, stay tuned for pictures, those will tell the story much better than this explanation, but here goes. most of you probably get the idea just from the title, but hopefully this will help light the way and clarify things for those who are curious.

the process starts by creating the molds, which there are numerous threads about already. i have been using CNC'ed corian molds, and have had good luck with them thus far. the molds need to be sturdy enough to handle high clamping pressure and the inflation of the bladder on the inside to XXXpsi. i have gotten away with 80psi so far, but i think i could get more; i just dont know what i need yet. the molds need a few key features: vacuum retainer o-ring groove on one side, vacuum source port(s), and resin feed inlet with resin supply manifold, if necessary (which it was, for mine). they also need a hole through which the bladder pressure port will be inserted.

like i said, the pictures will light the way, shortly after this post.

the next thing that needs to happen is that a dependable bladder needs to be made in the approximate shape of the part to be molded. i have been using Wyowindworks' method of bladder construction, with a few modifications. i test the bladder before use by pressurizing it out of the mold, and applying windex or soapy water to the seam(s) and watching for bubbles, like checking a tire for a slow-leak. re-seal any holes if (when) found - typical bladder stuff i guess?

when all that is done, wax/release your molds, layup dry fabric using sprayglue as a temporary bond to hold the fabric in place. flow media needs to be placed within the fiberglass (or whatever fabric) laminate, and is left in the finished part. i have been using fishing line with decent success. allow fabric overlap for seems on bottom half of mold; i leave about 1/2". this overlap or seam idea is generally the same as what Wyowindworks does for his layups, except i leave overlap around one whole side of the mold, not half on the top side and the other on the bottom side, so to speak.

install bladder, in bottom mold, fold (more of a bend really) fabric overlap down over bladder so that the seems get pressed up against the sides of the top mold cavity as the bladder inflates. firmly attach the bladder inflation port mechanism to the mold. i modified a 1/4-20 bolt and turned a special aluminum washer with 2 o-ring grooves that stay inside the bag. this is a whole other topic, ill need to take pictures of that later to describe it. right now its closed up in a curing mold, so ill get pic tomorrow or the next day of that part of it.

install vacuum retainer o-rings around cavity of bottom mold. gently close the mold lowering the top half onto the bottom half, peak into the edges to make sure you arent pinching any fiberglass or bladder between the flanges.

bolt mold halves together firmly. install vacuum and resin supply lines into mold, sealing all ports with vacuum tape. install resin trap, hookup to vacuum source. clamp off resin feed line.

SLOWLY inflate bladder, i do this with the vacuum pump off so that i can hear leaks if there are any. the main indicator will be that the bladder pressurising port will not stop pulling air from the atmosphere. once vacuum is aqcuired, turn pump back on and pull as much as possible. in essence, the bladder at this point is acting like an inside-out vacuum bag; if appropriately sized and inflated, it should adapt to the contours of the cavity it is inside.

while thats going, mix resin.

place resin feed line into mixed resin cup, and once you think you are ready, let it fly. my infusions usually take WAY too long. i am working out this problem by tweaking resin pot life, mold temperatures at the time of infusion, and use of more, less, or different infusion media.

once the resin peaks out the other side, in the vacuum supply line(s), pressurize the bladder to just above ambient atmosphere; i use 20psi. then turn off (cut) the vacuum supply line and put the ends in your resin source cup. the reason for increasing the pressure in the bladder before shutting the vacuum off is to prevent any atmosphere (air) from entering the laminate once the vacuum is disconnected. that done, increase the bladder pressure to the appropriate XXXpsi. i have been using 80, but i havent had a whole lot of chances to mess with optimal pressure settings. i am sure this depends on resin systems, layup conficurations, flow media, etc etc etc.

as the bladder pressure increases and reaches its max point, you will see resin being pushed by the pressurized bladder back out of the mold through the feed line and the vacuum source lines. they are now all drain ports.

maintain XXXpsi until resin has cured through B stage or has gotten solid enough not to move around any longer. cure laminate inside mold according to resin specs.



so thats all ive got for now. i have failed numerous times EVERY STEP OF THE WAY. sometimes comical, other times things go flying across the garage lol... i am presenting this here so that maybe we can all bump heads and make this a viable process...

so far my answer to that question, "is this a viable process?" is NO. but i have only done a couple shots so far, and i am sure i will find ways to simplify and expediate the process.

right now the main enemy i have is the dry fabric layup itself. it takes hours. granted i am working with a DIFFICULT shape and my infusion media placement is cumbersome. i am open to suggestions.



thanks for reading, any and all comments and questions are welcome

pics coming in the next post

-david
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Old Feb 14, 2012, 05:32 PM
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the first shot came out pretty bad. it was about 2am when the resin went off, but hadnt peeked out the vac source yet. so i inflated the pressure in the bladder to 80psi while the vac was still on. it pushed the resin feed line out of the mold. i reacted quickly and stuck it back in, and allowed resin to flow out. however, once the resin was purged, air shot back into the mold through that line. i stared at it for what seemed like forever and wondered where all the dang bubbles were coming from, but i was thinking in reverse... it wasnt air being pushed out, it was air sucking into the laminate because the vacuum was still on. 2am brain fart. duhr...

i also determined later that the bladder did in fact have a leak. enter the soapy water/windex leak detection method. so far so good. i have layed up another part and expect to open it either tomorrow or the next day, and will relay the results then.

so for now, the process works, in theory... i believe with fine tuning i can get nice parts eventually. maybe even the part i have curing now will come out nice, i hope.

-david
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Old Feb 14, 2012, 08:05 PM
Just fly it!
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What keeps the mold from leaking around the flange during infusion?
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Old Feb 14, 2012, 08:43 PM
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You mean losing vacuum around the flange? the o-rings seal the vacuum.

Same for resin leaks too, if that's what you meant; the o-rings act as a seal from the outside world for the resin too

I think I answered your question? I hope I did lol, you've answered enough of mine

-david
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Old Feb 14, 2012, 08:45 PM
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Got it! I assumed there was kind of seal along the parting flange. I now see them in the photos...duh.

There are some other ways to combine infusion and bladder molding so no flow media is necessary. Unfortunately, they wouldn't be conducive to your part shape. Having a doughnut-hole in the middle of the parts definitely complicates the process.
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Old Feb 14, 2012, 08:46 PM
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Reading the question again, did you mean leak along the flange, and cheat the rest of the part out of infusing? Because that is/was a concern, and honestly I was just praying that in the end the molds would fit together tight enough to keep that to a minimum. So far so good anyways ::fingers crossed::
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Old Feb 14, 2012, 09:13 PM
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Quote:
Originally Posted by wyowindworks;
There are some other ways to combine infusion and bladder molding so no flow media is necessary. Unfortunately, they wouldn't be conducive to your part shape. Having a doughnut-hole in the middle of the parts definitely complicates the process.
like what??? Please share! Might shed some light on a different technique...
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Old Feb 15, 2012, 12:16 AM
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Quote:
Originally Posted by hawaiianspork226 View Post
like what??? Please share! Might shed some light on a different technique...
I've developed two proprietary methods for two manufacturers that I collect royalties per produced part. I can't share a lot but I will give you a hint:

To infuse without flow media you have to control the distance between the bladder and the mold wall. With typical vacuum infusion the vacuum bag is pressed down upon the fabric and mold wall via atmospheric pressure. The more atmospheric pressure pressing against bagging film the tighter the fibers are pressed together. The tighter the fibers a pressed together the harder the infusion becomes and the higher the vacuum level required to properly infuse. This is why flow media is required. The flow media creates space to allow the resin to flow. If you can control the space between the bagging film/bladder and the mold surface you can infuse with very low vacuum levels. One process that I devised uses infusion at 5" Hg. Then a pressure bladder is used to debulk the infusion.

I can't share more and I can't figure out how to practically do your part shape with any of my techniques.
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Old Feb 15, 2012, 05:39 AM
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So far I don't see the interest of combining both techniques.
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Old Feb 15, 2012, 05:46 AM
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Adam - gotcha, I think, very cool indeed. I'll ponder

Chetosmachine- the original goal was to create net shape parts without needing to do a wet layup, or touch wet resin aside from mixing it. That way, theoretically somebody could just load up a mold with fabric, close it up, infuse, pressurize, and wait. That way the skillset for a nicely done wet layup wouldn't need to be developed by every person who wanted or needed to make a part... That was the goal anyways. So far the end results' benefits do not outweigh the headaches, yet, for me anyways.

I'll keep tinkering

-david
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Old Feb 15, 2012, 04:04 PM
One Idiot is plenty...
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David,I looked up at Your all attachments .
You are hell of the craftsmen and very talented kid.
Impressed Yuri.
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Old Feb 15, 2012, 04:45 PM
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Very cool project! I'm no infusion expert, but is fishing line the best flow media? Have you tried low bladder pressure for the infuse portion and higher bladder pressure after?

I wonder if injecting instead if vaccuuming the resin is possible?
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Old Feb 15, 2012, 05:04 PM
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thanks Dbox

Ward - i dont know if fishing line is the best, but ive tried a few different materials to get the job done. commercially available media ive tried i have found to be too rigid to fit inside the tighter radius curves of this particular part. another possibility is drywall tape... i actually tried a little bit of it on the last shot so i will be able to see how it effected the infusion, and maybe determine if it is hurting, neutral, or adding to the overall part strength...

as for injecting the resin... no, unless i had a rigid bladder or mandrel of some sort. i tried injecting the resin in at 5 psi once on a test panel.. i figured it woulndt work too well if at all, but i had to see it. all that happens (with soft bagging film or any other non-rigid mold material) is the same thing that happens when you fill up a waterballon - the laminate doesn't infuse any faster, it just blows a resin bubble up right near the resin supply, expanding the bag as the resin gets pumped in. then the resin just sorta sits there until gravity or the vacuum pulls it to the dry parts of the laminate. inside a closed mold environment like with this particular experiment/method, i think the same thing would happen around the resin source. i would have no idea it was happening because i cant see anything, but thats my best guess. at some point i do want to try it with a rigid bladder/mandrel, however.

-david
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Old Feb 15, 2012, 05:11 PM
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Aahh, I can see the water balloon analogy in my mind now...maybe window screen or roofers tape?
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Old Feb 16, 2012, 06:51 PM
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The second shot turned out great!!! Still some mysteries, but great progress!!

Pics in a little bit

-david
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