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Old Feb 16, 2012, 07:18 PM
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pics

heres the pics from the second shot

the part actually busted my mold... ill repair and re-polish effected areas not too terrible though. the mold delaminated at one of the bond lines... must not have sanded it enough...

just measured the flashing from the flange - anywhere from .0005" to .003" not too bad for a homemade CNC and block sanding

-david
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Old Mar 25, 2012, 05:49 PM
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so ive been pecking away at this since the last post, and things are going fairly well, learning a lot. had another mold delam, fixed that, back in business. the first few carbon ones look pretty decent, but ill refrain from posting pictures of them until i get a really pretty one that im not afraid to show you all...

but i am having one persistent problem-my bladders are failing under pressure. typically, they survive a dry test run to full 29"hg of vacuum, then pressurizing to 80psi before introduction of resin. the pressure holds, the vacuum does not turn on; good to go. so i depressurize and then proceed with the infusion using 29"of vacuum. infusion finishes, and i slowly increase the pressure to 80psi to consolidate the laminate and evacuate extra resin. the problem happens then. after about 20psi the telltale hiss of a leak starts and makes its way out into the laminate and then back into the vacuum. vacuum turns on but its an uphill battle fighting 80psi... no chance.

so i guess what im asking is what bladder material are you guys using that is compatible with MGS resin with the slow hardener? i have a hunch that the vacuum bagging material i am using is not completely compatible... it bonds pretty well to cured MGS resin...

thanks for any help, its been frustrating. but i am very close to being successful!

-david
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Old Mar 25, 2012, 07:05 PM
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Are you using the green Stretchlon 200 bagging film? If so, MGS will melt a hole right through it.

I use 1 to 2 mil poly drop cloth plastic from Ace hardware.
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Old Mar 26, 2012, 01:15 AM
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Quote:
Originally Posted by wyowindworks View Post
...the green Stretchlon 200 bagging film? If so, MGS will melt a hole right through it..
I've heard this mentioned before. Care to venture a reason why MGS does this over other epoxies?
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Old Mar 26, 2012, 01:16 AM
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david-
One question that your post did not address:
Assuming you get a good bladder, you are infusing with the bladder at 80 psi and lower the pressure if you think there is a leak( pls confirm I have that correct).
Here is the question:
after the resin reaches the other side of the part, do you have a way to shut off the resin supply or to add resin pressure?
Why am i asking?:
In RTM processing, the tool is held closed and the resin is pressurized to fight resin shrinkage during gel. to do this we wait until we get resin out the vacuum port and then shut it off. From there we add more resin pressure to fight gel shrinkage and to suppress air bubble formation in the part. We increase the resin pressure as needed( but not enough to lift the press that is holding the tool closed) until the resin gels- typically at elevated temperature.

you might benefit from a variation on that theme where once the vacuum port sees resin flow out, cap it and inject a bit more resin pressure while increasing the bladder pressure.
This will make the hydrostatic resin pressure increase in the tool.

clear?
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Old Mar 26, 2012, 01:50 AM
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Quote:
Originally Posted by ptxman View Post
I've heard this mentioned before. Care to venture a reason why MGS does this over other epoxies?
Not a clue as to why. It just does. I was trying to use Stretchlon 200 for bladders. I would fill up a bladder, brush on some MGS with hardener on the bladder, and 5 minutes later the bladder would be deflated with a gooey hole where the MGS was. Also, almost every resin that I used with Stretchlon 200 sticks to it like mad.
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Old Mar 26, 2012, 11:20 AM
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Curing agents are often corrosive. We get samples in glass jars.
Drop cloths can handle some chmicals. Other blown films are quite thin and a corrosive can attack them. Some oriented films are highly amorphous structures to allow deformation which impacts their ability to resist chemicals.
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Old Mar 26, 2012, 01:04 PM
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erm , can we ask what the part is ?
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Old Mar 26, 2012, 01:10 PM
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Quote:
Originally Posted by wyowindworks View Post
Also, almost every resin that I used with Stretchlon 200 sticks to it like mad.
OK thx. I got the impression it worked fine on every other epoxy resin, but not on MGS which had me wondering. Kind of sound slike its just not as well suited in general. I haven't used it myself. Always been tempted so saved me the heartache. Maybe its one of those 'works great with polyster' systems that gets listed by suppliers alongside epoxy systems so we just assume...
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Old Mar 26, 2012, 09:58 PM
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well this is actually really great news! yes, its the green stretchlon 200 film im using. i have not observed the complete meltdown scenario that you described, but i can confirm that it bonds really dang well to MGS resin. and if under higher psi im sure any flaws in the bladder become victim to the MGS solvency...

awesome guys, thanks for the help! im going to pick up some poly drop material tomorrow at ace, thanks for the tip Adam!

sarmoby-

the infusion is done with the bladder inflated via vacuum, so theoretically about 14psi. im sure i would get very little if any infusion at 80psi. the 80 psi is applied once full infusion is achieved to consolidate the laminate and evacuate excess resin.

i understand how the RTM process works with continually injecting resin into the laminate during gel. however im not sure how well this would work if the tooling is not rigid... whenever i tried to inject resin into a bagged infusion environment, the bag just inflated with resin in a local spot and it just sat there in a blob until it infused out into the laminate by itself... i just picture the same thing happening inside the mold with this thing... but maybe youre right, if the bladder is at higher psi than the resin being injected... i may need to experiment with that soon... thankyou!

thanks again guys for your advice!!!

-david
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Old Mar 27, 2012, 02:28 AM
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try it and report back.
I considered using a new grease gun to generate the resin pressure in a close mold.
If you exceed the bladder pressure you will fill it up with resin.
Scott
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Old Mar 28, 2012, 02:34 PM
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Just an FYI gents.. I did a quick test on Stretchlon 800 (the pink / orange stuff) with MGS and after 24 hours was able to peel the mostly cured blob off of the sheet with no sweat, and no sign of permeating..

Ray
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Old Mar 28, 2012, 07:03 PM
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Did you seal the tool prior to mold release? and it still delaminated?
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Old Apr 01, 2012, 11:47 AM
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no, i didnt seal the tool before waxing. seemed to me that the corian was dense and homogeneous enough to where sealing was unneccessary. in retrospect however that may have helped in the areas where the epoxy holding the corian laminations together was exposed. i need to make a new set of molds soon anyway so i will look into doing this.

i got .7, 1, and 2 mil poly drop material from home depot. Ace was closed by the time i had a chance to go out and get the stuff. layed a part up, made a bladder, and proceeded as usual but i FORGOT TO CHECK THE BLADDER WITH WINDEX... i was tired. but i did remember to check the bladder at 80psi while holding vacuum. it passed, no problems there...

so anyway, the part infused just fine. then i pressurized to 80psi and the resin purged; i am quite surprised actually how much resin was forced out, very impressive. however there must have been a tiny leak in the bladder because the resin feed line started to bubble almost immediately after the main resin blob got pushed out. not a strong hissing leak like the stretchlon bladder produced, but a small gentle leak that didnt get any larger throughout the cure. the stretchlon leaks tend to get louder and stronger as they continue to break down, i guess.

also, i found an infusion media that is waaaaaay less time consuming to use, for me at least- its HEAVY fiberglass tooling cloth that has a sort of 3 dimensional weave, so that under vacuum, the rovings do not compress to nothing so easily as with regular cloth, allowing the flow of air and resin to occur. i found a source for it at fibreglast.com, where it is known as 20oz tooling fabric, with a "thick, Mock Leno Weave". i think there is also another source for the stuff from thayercraft, though they list it as 38oz/yd, and as style 1597. everything else seems to match though... from the pictures, it looks like it might be the same. keep in mind however that i am not using this as a topical infusion media; i am leaving this infusion media in the laminate after the cure. the part geometry does not lend itself to removal of the bladder much less an infusion media. it also strengthens the laminate considerably in the areas it is used just due to the thickness it generates.

so i took the part out this morning and it looks OK. not great, some surface blemishes, but not the mess i was envisioning. i think it is useable though.

the part is a piece of a Stand Up Paddle project my dad and i are working on. we have patented it, and are trying to make it produceable. i am finding all the wrong ways, it seems. we are looking into injection molding as well. also a headache. anyway this is one of 2 identical parts that will be on the paddle. heres a link to the website, so you can visualize the product. its called the "power glider". i dont like the name but thats my dads deal. i think it makes it sound like some sort of early to mid 90's workout equipment from nordik track.

http://racehawaiistandup.com/content...i-power-glider

anyway, check out the link, and thanks for the help guys!

im gonna try and lay up another either today or tomorrow

-david

PS - i CANNOT WAIT to start making airplanes again...
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Old Apr 01, 2012, 12:42 PM
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Cody, WY
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David, maybe you should try using less pressure. The higher pressures start to show diminishing returns. 20 to 40 psi is noticable. 40 to 60 is a less less noticable. 60 to 80 barely noticable difference.

Also, try inflating the bladder very slowly and see if that helps. I usually let the bladder sit a 4-5 psi for a few minutes, then up it to 10 for a few minutes. Once I get to 20 then I just slow turn it up to 40 or 60. The highest that I usually go is around 60 psi (DLG, UAV). I do most of my sloper stuff at 35-40 psi.

Adam
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