Molded fuse Bladder

[Juko]

I need some help here, I have a couple fuse molds and would like to lay up some fuses.
What I want to do is, use a pressurize a bladder inside the mold, but I have no idea on how to make a bladder or what type of bladder material to use for this process, can someone step foward and offer up some information on how to do this?
Thanks!

[hayman]

Why?

Bill

[capncrunch]

I think the standard way to do that is to make the fuse in two pieces on male molds and vacuum bag the composite layup.

-barrett

[Juko]

capncrunch- I don't want to vacuum bag any molds, I want to use a pressurized bladder inside the mold?

[steve lewin]

I'll move this to the Composites forum for you.

Steve

[davidfee]

Juko,
For testing of the process, I have used just a long polyethylene tube... the plastic tube my porous release film came in. I made a thread on the subject here: http://www.rcgroups.com/forums/showthread.php?t=235039

-David

[Juko]

Where can I buy this tubing? Is there anyother type of material out there that works?

[davidfee]

There must be a cheap and easy supply of it but I have not looked so far. Too busy with other projects at the moment.

-David

[davidfee]

Here is another thread on the subject:
http://www.rcgroups.com/forums/showthread.php?t=235585

[DLD]

Why bother, just use a paper towel to get rid of excess resin, and join the two halves wet. I made several thousand fuselages this way from 1991-1997. If you are concerned about the glass staying in contact with the mold, lay up a thin layer first and let it get semi-hard before you proceed. Once you've done a few, you won't need to do this. I wouldn't waste my time fussing with a bladder. I produced Saturn Sailplanes, my business was David Layne Designs.

David Layne

[davidfee]

If you need to ask why... :rolleyes:

[A6INTRUDER]

I have been using the same method that DLD suggests, in fact he has given me some
helpful suggestions on how to do it, but I must confess that I have thought about the
bladder method too. After making about 6 fuses from the mold I made and showed in this forum, I still have trouble making the wet layup seams come out to my satisfaction. I get a wrinkle hear or a bubble there.........
I had thought about some type of bladder, not so much to pressure the layup but to make the seams come out really nice.
Since I am not concerned with hight pressure I had thought about some type of balloon, but I have not tried it yet.

TIM

[davidfee]

In my experience, a bladder does not guarantee that your seams will come out perfect. What it does do is apply pressure to the laminate from the inside... much like vacuum bagging. So, your messed up seam just gets squished against the mold, wrinkles and all.

Done correctly, a bladder can greatly reduce the bulk of a laminate. This means you can use much less epoxy. Less epoxy means less weight. Another way to look at it is, it's often possible to get twice the material in a layup for about the same finished weight. That means double the strength and stiffness, with little or no weight gain.

But it's a complicated technique to master. (I'm nowhere near mastering it). I currently do basically all my fuselages the way David (DLD) mentioned.

-David

[J Solinger]

I was looking at the bladder method for making boat hulls. The type of moulding I'm looking at is for an outrigger and it will look simular to a plane fuse. The concept was to place a braided carbon sock over the blader and insert it into a female aluminum mold and inflate it. What kind of weird things can I expect?

[Zoomzoom]

I've been playing around with a setup just like your talking about for a customer. It's not RC related, but I'm using a aluminum two piece mold and carbon fiber sleeving with a latex tube blatter.

It's trail and error, all error so far. I've made two using 60 psig pressure on the blatter. Anymore pressure and the fittings blow off. Both pieces came out with voids on the exterior because it's not tightly conforming to the mold. I "think" it's because the air isn't allowed to escape. When the pressure is applied it seals up both ends of the mold. Not using any bleeder cloth or anything like that, just two layers of carbon fiber sleeving and the latex tubing.

I'm wondering if I need to drill some small bleeder holes in the mold, but that could lead to other problems.

[J Solinger]

I can visualize just how that is happening, the ends sealing off first and stuff. Would a bleeder cloth breath well enough to let out all the air?

[Zoomzoom]

Bleeder cloth won't work in this application. No room between the latex tubing and the carbon fiber on the inside and can't put it on the finish side. The O.D. is approx 3/4" with two 120 degree gradual bends on each end and it's about 26" long. There has to be a simple way to do it.

[J Solinger]

I think that vent holes through the mold would work if the eccess resin was removed from the composit before pressing it. We would need to ensure that no, or very little, resin will be squeezed into the vents. Make the vent holes tapered towards the cavity side in such a way that what ever resin does get into them and hardens will stay attached to and come out with the moulded part. These would look like little spikes that could be removed from the fuse later.

[Sled Driver]

Silicone pressurized bladders are widely used in the aerospace industry. Caution: you need a mold made to take the internal pressure of an inflated bladder, e.g., 40 to 100 plus psi, and you need a bladder made from silicone rubber. Checkout: http://www.torrtech.com/

This technology is nothing new and it doesn't cost that much more. But, you have plan to do it and it does take more time to build the bladder. You endup making a small "plug" that you can form the silicone sheeting onto, kind of like a shoe maker, and glue the silicone together with RTV. Don't get the uncured silicone sheet; it is a mess to work with.

Vacuum bagging the laminate into the mold is easy, see the photos attached. A really nice thing to do is to make joggle gaskets so that you can have a nice lap seem, e.g., Mark Drela's SuperGee fuse.

[wireit]

I've been working on internal bladders for awhile... it's not easy. I use latex (5~6 layers, waxed after low heat cure) for the bladder, cured on a flat plug slightly smaller than the part.....no vent holes or you pop the bladder!!! In fact it needs to be sealed in, my pipe exits at the end of the fuse and that needs to be sealed and clamped in place. I use 50psi and that forces the excess thru the mold seam. In all honesty its tough and it limits the material used in the part...If you need to cut openings afterwards and use CF or Kevlar you in for it...
On my project I've switched back to wet layup.
There is a place for this method and it works but you have to cover all the bases ahead of time, right part, material, bladder size, openings, etc.

My rate was 1 in 6 such fun,

Joe

[Sled Driver]

I've been working on internal bladders for awhile... it's not easy. I use latex (5~6 layers, waxed after low heat cure) for the bladder, cured on a flat plug slightly smaller than the part.....no vent holes or you pop the bladder!!! In fact it needs to be sealed in, my pipe exits at the end of the fuse and that needs to be sealed and clamped in place. I use 50psi and that forces the excess thru the mold seam. In all honesty its tough and it limits the material used in the part...If you need to cut openings afterwards and use CF or Kevlar you in for it...

You must be very good if you are able to produce latex bladders that hold 50 psi. It is much less of a problem with silicone bladders, but eventually they pop also...

[wireit]

The mold completely suports the bladderso it can take allot. If remember right, latex can be run over 100 psi if done correctly, but I agree they all pop.

joe