Expanding Foam Tutorial

[Green Jello]

I've been trying to learn about expanding foam. I've looked through countless threads here and I just can't seem to find some good info that shows the whole process from start to finish. Does anyone know of a good webpage/thread that explains everything about it. What to buy, where to buy it, how to use it, etc.

I like the idea of using it to fill in motor mounts like Sharon did with this Jart:

https://www.rocketryforum.com/showthread.php?44203-Sharon-s-Jart-Build

 

[Tronman]

Check out the Wild Child / DarkStar Mini instructions: https://www.wildmanrocketry.com/productimages/Instructions/Wildman/Instructions/mini_ds_wm.pdf

 

[JordanT]

I got my foam as a two part kit from US Composites. You have to order it by density; measure, mix, watch it foam. It starts foaming pretty quickly I suppose that by knowing the final density and choosing your mass properly you could get a very accurate fill volume (less waste). Here's the stuff: https://www.youtube.com/watch?v=g8u_ax1vnZE (though I got 1lb/cf). Not very scientific, but you can see how fast it sets up.

 

[Green Jello]

Wow, that stuff is expensive.

https://www.uscomposites.com/foam.html

 

[Hardline]

Wow, that stuff is expensive.

https://www.uscomposites.com/foam.html

I used Public Missiles two part expanding foam which I bought from Jack at What's Up Hobbies at the GHS launch but it is available here:

https://publicmissiles.com/secure/components.asp?groupid=19

halfway down the page there is a link to a .pdf which discusses using the material.

 

[Green Jello]

And I think I've heard that Great Stuff is a bad idea?

 

[Green Jello]

Thanks Hardline. That Public Missiles stuff looks like what I need / want.

 

[CCotner]

It isn't sticky-a good chunk of the benefit of foam filling an airframe is that it sticks to the fins and the tubes really, really well. The instructions for the small wildman kits now say to fill the fincan with foam instead of trying to do interior fillets, because the hobby-standard foams (US Composites, GLR's Megafoam, and the PML foam) are strongly adhesive.

I use Megafoam currently but I'm not terribly happy with it-it has zero documentation (MSDS sheets, for instance, which is a big problem for me since I work in a college lab) and it's expansion ratios are a little random-seeming and are certainly inconsistent. That said, it is superb structurally as long as you get enough in.

 

[Green Jello]

What does Wildman carry? There is no info here:

https://www.wildmanrocketry.com/ProductDetail.aspx?product=2873

 

[dixontj93060]

Wow, that stuff is expensive.

https://www.uscomposites.com/foam.html

You need to get the calculator out... US Composites sells you 1.7q or 54.4 oz for $22.50 while other vendors sell you 16 oz for ~$15 so the US Composites foam is less than half the cost.

 

[Green Jello]

Well, that is true. I guess I more meant that since I've never used it before and I'm building my first ever fiberglass rocket, I wasn't sure if I wanted to large quantity of it right now.

 

[stealth6]

A couple of expanding foam tips:

* Yes, the PML stuff is excellent. The instructions that come with it are very good - if you follow that and Wildman's tutorial you will do just fine. It cures quickly, is very adjustable, reacts consistently, has an excellent strength to weight ratio, etc. I've used it on many projects and have been quite happy with it. Just bought a new batch in fact.

* Yes, the Great Stuff is NOT excellent. The main problem is that it cures more like glue than epoxy. By that I mean that it really needs air to cure well, whereas epoxy cures via chemical reaction. With Great Stuff, if you fill a large volume, there is a good chance that the "stuff" in the middle won't cure well. This is not good. It's also much more difficult to control volume-wise.

* Be prepared to move fast. Do a minimum of two "dry runs" to work out your steps before actually mixing the parts and doing your fill. Once it sets off, it does so very quickly and if you aren't ready for it you will end up with a nasty mess. In fact, it's not a bad idea to just do a test run on some scrap to get used to exactly how much time you have from initial mixing to that start of the expansion. The first time you do it, it will seem instant, but if you practice a couple of times, you will find that you can move fast enough to do it well.
I found that the hardest part is getting it into the syringe (if you are injecting) after it was fully mixed, but before it starts to expand. It's very easy to find yourself with foam expanding all over the place at the very same time you are trying to get it into a small compact space. But again, with practice, you will get the timing right.

* Wear nitrile gloves. And work on a surface other than your nice kitchen table. Expect a bit of a mess.

 

[JordanT]

Oh, the extra is useful for all kinds of stuff: making mushrooms in cups, modeling the shape of animal cells, making vacuoles to glue onto plant cell models. Okay, so I have a 5th grader. It's amazing how frequently we break out the rocketry gear to make non-rocketry stuff for science class.

 

[Tronman]

The stuff Wildman sells comes in 2 plastic bottles that look to be about 10 or 12 ounces each.

Another tip: It takes longer to expand in cool temperatures.

 

[Tarasdad]

I'm not sure if it's still the case but that stuff used to have an odor that was nearly intolerable.

 

[Green Jello]

I just heard back from Tim at Wildman. The foam he carries is the PML brand.

 

[JordanT]

I'm not sure if it's still the case but that stuff used to have an odor that was nearly intolerable.

Hmmm, we mixed the last batch up in the kitchen for a science project and I don't remember any odor at all. Certainly less than mixing a small batch of epoxy. At least, that's for the US Composites version.

 

[Hardline]

I'm not sure if it's still the case but that stuff used to have an odor that was nearly intolerable.

The PML foam I used did not have any odor that I recall. The first time I used it was outside at GHS but the whole Jart project was in our rocket room and there was no discernible smell (and theoretically women use a larger chunk of our brains when processing smells - for whatever good that does......)

 

[FredA]

I like PolyTek-15 foam.
Billed as 2-part, but you can buy a Part-F "foamer" ingredient....lets you vary the density from "plastic wood" to light foam.

We always foam our fincans.
Pouring in foam from the aft end before installing the aft CR.
We put some blue tape on the inside and outside of the BT and outside of the MMT where the CR needs to bond so the cleanup is easier.
Jam paper towels into the MMT to keep it from filling if you overflow.

Then we put the rocket in a near-empty trash can to hold it upright and contain spills.
Let the foam mushroom over the top and harden -- keep a paper towel handy soaked in Isopropyl to clean up the outside if you really overflow.
Chop the dried top off with a saw....dremel out the foam where the CR goes and pull out the blue tape.

 

[UncleVanya]

Maybe a better question is WHY do you want to use foam?

A lot of people foam the fincans - personally while I have done this I have learned that when you crash the rocket it makes repair harder. I'm not sure it adds anything other than weight in the rear of the rocket for most of us which isn't a good idea. Some people have designs where the foam is an integral part of the structure and it works for them - but there are other techniques that might be better in many of those cases. I use the foam sparingly for many other tasks but I try to keep the junk out of the trunk these days.

 

[CarVac]

When does a rocket crash and damage the fincan and not the rest of the rocket?

 

[dixontj93060]

When does a rocket crash and damage the fincan and not the rest of the rocket?

Flat spin and hits right on the tip chord of a fin.

 

[Fdog]

I've had very good luck using the US Composites 4 lb. density urethane foam.

I've found the 4 lb density to have a 11:1 expansion in cold temperatures; 13:1 in warm, like summer.

The most common use for me has been nosecones. I'll calculate the interior space to be filled (good help for that is HERE <linky>, don't forget to add the volume of the shoulder), then, divide by the expansion ratio.

So, for a nose cone with an interior volume of, say, 380cc, I'll mix up 35 cc of foam liquid in the winter.

I've actually had good luck with just leaving a 1/4" hole in the bulkhead. Tape everything off around the hole, and use a 10cc syringe to inject the foam liquid after mixing. You need to move smartly but it works well for complicated structures.

Here's a nose cone where if you look closely between the screw holes you'll see the injection hole.

I've found this size hole is more than adequate to inject epoxy resin, then, pour lead shot into. The lead shot sinks to the bottom of the epoxy easily as long as it's a typical thin resin. Finish it off with foam, and nothing will move.


All the best, James

 

[FredA]

Not foam related...but looking at James' photos made me think of this....
Everytime I've epoxy'ed in Kevlar like shown, it snaps reight at the glue line.
I now classify this as a very bad practice.....
What are other's experiences?

 

[CarVac]

I have foamed Kevlar in. It is softer and less brittle than epoxy, so the joint is no more likely to snap.

Perhaps five minute epoxy, which is more flexible, is also preferable. But usually I rig up something which doesn't need gluing at all.

 

[Fdog]

Normally I'd agree...solidifying the material in place will cause the union to be the weak point; plus, the more off-axis the load, the more the material's strength is eroded.

In this case, it's a 230 gram nose cone with 1/4" Kevlar. Even if the epoxy robbed the Kevlar of 50% of its strength, it would take ~2400 G's to break the Kevlar, at which point there might be a few other more pressing issues.

I absolutely agree it's something to consider, but wouldn't classify it as a very bad practice. For example, in this case, the final product (kevlar loop + epoxy) only weighs ~4 grams, far less than a (weaker) forged eyebolt, and there wasn't room to place an eyebolt, anyway.


All the best, James


[/hijack]

 

[Pantherjon]

And I think I've heard that Great Stuff is a bad idea?

Yep..It is 'open cell' as opposed to 'closed cell'. Meaning it is prone to expand further in high humidity and heat conditions..The PML brand and USComposites is closed cell.