Has anyone used the Home Depot Great Stuff foam in a rocket? I have the 2 part foam, but want something lighter. Mine is 4lb stuff. Since the Great stuff is air dry, will it dry in an enclosed space? Thanks.
xpando foam
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Nope, the spray foam will not cure in a closed space.
I've heard that adding a tiny bit of water to 2-part urethane foam will increase its expansion and reduce its final density. Once uppon a time I added a few drops to a mix and it appeared to expand more than usual. But, no science here.
I've heard that adding a tiny bit of water to 2-part urethane foam will increase its expansion and reduce its final density. Once uppon a time I added a few drops to a mix and it appeared to expand more than usual. But, no science here.
Bummer.
The rap on it has been that it's expansion and hardening are not predictable, I've heard stories, admittedly anecdotal evidence, about airframes being damaged well after the foam was thought to be cured. The stuff that you mix yourself is easily observed giving one more confidence in the process.
Jim
Yup, just ordered some 2lb stuff. be here on Saturday. Want it to stiffen up a 3D print that will fly.
rharshberger
Well-Known Member
Or buy the Sika Post Fix 2-part foam its what I use it is approx 3lb density, and I have not tested it with the addition of water to see if it reacts same as the PML foam. Its also much cheaper than the PML foam.
https://www.rocketryforum.com/threads/sika-post-mix-expanding-foam.150303/
https://www.rocketryforum.com/threads/sika-post-mix-expanding-foam.150303/
Since Great Stuff cures via moisture from the air, it *can* be used fairly well if applied in multiple, THIN layers. I wouldn't recommend it. Did it with a nose cone and ended up with a slight bump and depression.
An alternative discussed elsewhere is the expanding foam sold in bigbox stores. I just tried some of the stuff below and it works nicely, giving roughly 15x expansion. A 1:1 mix by volume seems to work well enough though there's more of the isocyanate than the other part. I'm going to find a better estimate of the ratio sometime soon.
You have to separate the two parts. GLOVES! GOGGLES! OUTSIDE!
On this brand:
Do not remove the clip. Get heavy PETE or metal containers, with mouths wide enough to easily pour in. There's about a pint of each component. I'd avoid glass as the lid of the isocyanate often glues itself in place, and a wrench is needed to get it off.
The bags tell you which component is the isocyanate. That's the one to be most careful to avoid skin contact.
I held the bag with one corner up, snip off a small opening, then bend that corner to the mouth of its container and slowly raise the bag so the contents flow into the container. Watch out for drips (newspapers if you're working on a table). Repeat with the other bag.
Label both containers and use within a few months.
Wash your hands. Especially wash your hands before going to the bathroom.
Best -- Terry
An alternative discussed elsewhere is the expanding foam sold in bigbox stores. I just tried some of the stuff below and it works nicely, giving roughly 15x expansion. A 1:1 mix by volume seems to work well enough though there's more of the isocyanate than the other part. I'm going to find a better estimate of the ratio sometime soon.
You have to separate the two parts. GLOVES! GOGGLES! OUTSIDE!
On this brand:
Do not remove the clip. Get heavy PETE or metal containers, with mouths wide enough to easily pour in. There's about a pint of each component. I'd avoid glass as the lid of the isocyanate often glues itself in place, and a wrench is needed to get it off.
The bags tell you which component is the isocyanate. That's the one to be most careful to avoid skin contact.
I held the bag with one corner up, snip off a small opening, then bend that corner to the mouth of its container and slowly raise the bag so the contents flow into the container. Watch out for drips (newspapers if you're working on a table). Repeat with the other bag.
Label both containers and use within a few months.
Wash your hands. Especially wash your hands before going to the bathroom.
Best -- Terry
Follow-up: the ratio of isocyanate (dark brown liquid) to polyol (almost black liquid with some solids) for the Fast2K post anchor is just about 1.34 grams of isocyanate to 1 gram of polyol, according to the masses of the two components. I'll try mixing some at that ratio to see what happens.
Terry
Terry
Follow-follow up: The ratio of 1:34 g isocyanate to 1 gram polyol, and the volume ratio of 1:1, appear to give very similar results. In both cases the final product is nicely non-tacky, and expansion is roughly the same; at a guess, 10:1 expansion. Use whatever is easier for you, weight 1:34:1 or volume 1:1.
I'll be filling a nose cone tomorrow to see how it works.
Terry
I'll be filling a nose cone tomorrow to see how it works.
Terry
SEWAR
The Rocket Lodge
I’ve had great luck with the loctite spray foam. I’ve had some rockets fall from apogee and have zero damage. I use it especially on high G force motors. (H550…etc)
A common issue with spray foams is their inability to cure completely when applied in a too-thick layer, as they rely on moisture in the air to cure. Another is that some foams will expand or contract significantly with temperature, causing a bump or hollow in a nose cone. Had it happen to one of my rockets and to a friend's. It may be related to the irregular sizes of the voids in the cured foam, I don't know.
And of course, most of the canned spray foams must be used up shortly after their first use. Two-part foams are good for some months as long as they're tightly sealed.
And of course, most of the canned spray foams must be used up shortly after their first use. Two-part foams are good for some months as long as they're tightly sealed.
SEWAR
The Rocket Lodge
One can per rocket unless I line them up and prepare all of the rockets for foam. It works for me every time. I’ve put G-80’s in rockets that normally launch motors like F26… the G force alone tells me the foam works. Obviously, i do not know how much force is at the tip of the rail/rod but all I have to do is repack and put another motor in.
Attachments
Well I did get some 2lb stuff. Worked well and cured hard. Was sticky, like I wanted, to fill the NC of the Mercury LES rocket.
It's not a matter of strength. Yes, can in a foam and two-part foam are strong enough to prevent most damage to a thin-walled cone.
In my Big Daddy nose cone the foam in a can ended up expanding a bit more on one part of the nose, leaving a perceptible bump. And on my mentor's 7.5" Phoenix the space between TTW fin tabs was filled with foam in a can. Apparently there was one or more oversize bubbles during expansion. Whatever the cause, if he left the rocket in the sun too long or just outside on a hot day, a bulge formed in the body tube between two fins.
Once there is a bulge or depression, about the only thing that can be done is to live with it. Which I did for the Big Daddy until the last landing, when it ended up only partly assembled.
There are other similar accounts I've read about on the forum. It's common enough that I'd prefer to go with two part foam, either the stuff I'm using now, or a commercial variety; the commercial stuff that comes in two cans/bottles is roughly 4-8 times as expensive as the Fast 2K.
rharshberger
Well-Known Member
I pour my 2 part foam in "lifts" about 2-3" cured depth per pour, by doing it in stages I dont normally get swelling/distortion issues. My 2 part foam of choice is Sika Post Fix also a fence post setting foam.It's not a matter of strength. Yes, can in a foam and two-part foam are strong enough to prevent most damage to a thin-walled cone.
In my Big Daddy nose cone the foam in a can ended up expanding a bit more on one part of the nose, leaving a perceptible bump. And on my mentor's 7.5" Phoenix the space between TTW fin tabs was filled with foam in a can. Apparently there was one or more oversize bubbles during expansion. Whatever the cause, if he left the rocket in the sun too long or just outside on a hot day, a bulge formed in the body tube between two fins.
Once there is a bulge or depression, about the only thing that can be done is to live with it. Which I did for the Big Daddy until the last landing, when it ended up only partly assembled.
There are other similar accounts I've read about on the forum. It's common enough that I'd prefer to go with two part foam, either the stuff I'm using now, or a commercial variety; the commercial stuff that comes in two cans/bottles is roughly 4-8 times as expensive as the Fast 2K.
I also did it in stages. Worked well so far.
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The Rocket Lodge
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I wonder if building it up in layers with some cure time in between would work for you project.
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The Rocket Lodge
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rharshberger
Well-Known Member
So why use foam for a cardboard and wood, mid-power rocket or even for a L1 type rocket? Personally I try and avoid the use of foam but it does have certain uses.
On mine, I 3D printed a hollow shell and wanted to make it landing proof. New term I just thought up. Only added a couple of ounces and , at least I think it is stffer.
rharshberger
Well-Known Member
Thats what I did for my 8" PNC-80BB upscale nosecone that was two pieces, glued them together and used a piece of 6" sonotube as a structural element and recovery anchor point, then filled the void space with Sika Post Fix 2 part expanding foam.
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The Rocket Lodge
Just a choice.
rharshberger
Well-Known Member
I respect that.
This was almost a glue thread
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a sticky conversation for sure
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The Rocket Lodge
Hahaha
