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Old Feb 28, 2013, 07:39 PM
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Foaming agent, epoxy

I've heard some talk about "foaming agent", not sure about it's application in regards to making machined foam core parts like DLG tails and wings.

Does this help the resin create a better bond to the foam? What application are you guys using it for? I'm about to start making some tails with rohacell cores using MGS.

Thanks
Ali
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Old Feb 28, 2013, 07:48 PM
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tom43004 made a video of molding his DLG tails. I think he uses foaming agent to lighten the epoxy mixture for the skin join at the leading edge. He also uses it for the mounting hard points in his wings.
http://www.rcgroups.com/forums/showt...ght=foam+agent
http://www.ustream.tv/recorded/19977162
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Old Feb 28, 2013, 08:01 PM
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Foaming agent is commonly used when you want/need the epoxy to "fill in" an area after you've closed a mold or in some other way encapsulated the foam/fabric/reinforcements you're working with. For example, you may want to have a high-density foam spar in a hollow-molded or solid-core molded wing, but you don't want to mill that spar oversized as it may not compress well. However, you need to ensure that the spar is well bonded to the skins. You can mill the spar a little undersized, put some epoxy with foaming agent on it before closing the mold, and be confident that your mold will close properly, your spar will be intact, and that you will still have a good bond between the skin and the mold. Another common application is at the leading edge of a molded wing as Wazmo notes. The foaming epoxy can help to fill in any small gaps at the leading edge so that in the final product you have a leading edge that exactly matches your molds. The only place I know of to get it is from R&G in Germany:

https://shop1.r-g.de/4DCGI/ezshop?ac...COUNT=45112026

Looking forward to seeing your tails! Will you be bagging or molding?

-John
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Old Feb 28, 2013, 08:53 PM
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Quote:
Originally Posted by jbarnhardt View Post
Foaming agent is commonly used when you want/need the epoxy to "fill in" an area after you've closed a mold or in some other way encapsulated the foam/fabric/reinforcements you're working with. For example, you may want to have a high-density foam spar in a hollow-molded or solid-core molded wing, but you don't want to mill that spar oversized as it may not compress well. However, you need to ensure that the spar is well bonded to the skins. You can mill the spar a little undersized, put some epoxy with foaming agent on it before closing the mold, and be confident that your mold will close properly, your spar will be intact, and that you will still have a good bond between the skin and the mold. Another common application is at the leading edge of a molded wing as Wazmo notes. The foaming epoxy can help to fill in any small gaps at the leading edge so that in the final product you have a leading edge that exactly matches your molds. The only place I know of to get it is from R&G in Germany:

https://shop1.r-g.de/4DCGI/ezshop?ac...COUNT=45112026

Looking forward to seeing your tails! Will you be bagging or molding?

-John
Cool thanks for the info guys, i was guessing that was what it was for, but wanted to be sure it was not for wetting out glass or other material.

These are Foam cored tails, made in Corian molds but non DLG related.
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Old Feb 28, 2013, 08:59 PM
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Any issues with shipping that stuff from germany to the states?
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Old Feb 28, 2013, 10:10 PM
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They fedex it and you will have to fill out a customs form and provide the product safety sheet (available on R+g website) once it is in the US. It was pretty painless and I just faxed the info to fedex. It may not even be required on every order.
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Old Mar 09, 2013, 06:55 PM
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I have some of it here if you'd like to sample it. I bought 2x200ml bottles about three years ago and I use about 1/3 of a drop in 30g of epoxy... so I'm only part way through the first bottle.

Last few times I ordered from Germany (few weeks ago) I added some to the order for other folks and Fedex passed it straight through with no questions asked. That order had 400ml included.

Foaming agent will cause most epoxy systems to foam up. It's not a 10x or 30x expansion like a urethane two part foam, but rather a slow expansion to 1.3-2x the original volume depending on mixing ratio and method. It used to be primarily used to increase the surface area of the bond for honeycomb materials used with epoxy, but has found alot of uses as a filler. I use it in the trailing edges of wings and tails where the rohacell stops to fill all of the volume left between the skins. It will also make its way out into the resin channel greatly reducing the finished weight of the product.

FWIW, I've stopped using it in the LE of my wings, because if you need to slightly wetsand the LE to remove mold flash, the foaming agent leaves tiny voids that sanding "opens" causing roughness. Now I just use microballoons and cabosil for leading edge fillers. In hardpoints, I use it very sparingly also now. Most of the hardpoints are made with milled glass, cabosil, and few microballoons. If you pinch a wing bolt down hard, it has a tendency to crush the tiny "bubbles" in the cured epoxy.
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Old Mar 11, 2013, 09:06 PM
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Quote:
Originally Posted by tom43004 View Post
I have some of it here if you'd like to sample it. I bought 2x200ml bottles about three years ago and I use about 1/3 of a drop in 30g of epoxy... so I'm only part way through the first bottle.

Last few times I ordered from Germany (few weeks ago) I added some to the order for other folks and Fedex passed it straight through with no questions asked. That order had 400ml included.

Foaming agent will cause most epoxy systems to foam up. It's not a 10x or 30x expansion like a urethane two part foam, but rather a slow expansion to 1.3-2x the original volume depending on mixing ratio and method. It used to be primarily used to increase the surface area of the bond for honeycomb materials used with epoxy, but has found alot of uses as a filler. I use it in the trailing edges of wings and tails where the rohacell stops to fill all of the volume left between the skins. It will also make its way out into the resin channel greatly reducing the finished weight of the product.

FWIW, I've stopped using it in the LE of my wings, because if you need to slightly wetsand the LE to remove mold flash, the foaming agent leaves tiny voids that sanding "opens" causing roughness. Now I just use microballoons and cabosil for leading edge fillers. In hardpoints, I use it very sparingly also now. Most of the hardpoints are made with milled glass, cabosil, and few microballoons. If you pinch a wing bolt down hard, it has a tendency to crush the tiny "bubbles" in the cured epoxy.
Thanks for the offer Tom! I just ordered some along with some spread tow from RandG.
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Old Mar 14, 2013, 08:39 AM
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I don't use any in the wing LE's and after a hard point failure don't use it there either. My hard points have a fair amount of microballons in them so I won't put the failure entirely on the foaming agent.
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Old Mar 14, 2013, 09:23 AM
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Foaming agent and cotton flox with a pinch of milled glass makes an interesting combination for light duty hardpoints. Mix some up and put them in a scrap piece of foam, drill, tap, and test.
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Old Mar 23, 2013, 03:02 AM
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Well, got my box of goodies from RandG last week, some spread tow, and the foaming agent. Time to lay up some parts.
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Old Mar 25, 2013, 10:47 AM
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Have you looked for core splice adhesive?
This is typically used to fair in core slope and honeycomb-to-honeycomb bonds.
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Old Mar 25, 2013, 04:52 PM
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Here is my first attempt to make some Rohacell cored parts, came out pretty good for a first try! Used the foaming agent, did not "foam" nearly as much as I thought with just one drop in 10g of MGS.

These tails are a bit bigger than a DLG

The still need to be trimmed
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Old Mar 25, 2013, 04:57 PM
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Nice. IME it only expands about 2x the original volume, and only if you mix it really well. I use a small whisk I made from music wire and stir it for a full 3-4 minutes.
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Old Mar 25, 2013, 05:55 PM
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Quote:
Originally Posted by tom43004 View Post
Nice. IME it only expands about 2x the original volume, and only if you mix it really well. I use a small whisk I made from music wire and stir it for a full 3-4 minutes.

Wow, ok I'll make up a little whisk. I did notice that my resin did not look as opaque and milky as the resin I saw in one of your vids with the foaming agent.

Another question. Do you guys thin your resin at all? I am thinking about cutting the resin about 5% with some denatured alcohol on my next attmept with the hopes of being able to wet out the material better/faster/lighter. I need to try and shave another 2g off my layup, and I had a hard time soaking up excess resin because it started to gel up a bit pretty fast even with the slow hardner.
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