expanding foam help

[AcadiaRockets]

OK, I don't know what else to do. Three failed tests. This stuff goes off fast!. Like on the count of one pour one chilled half, count of two, pour second chilled half, a ONE, TWO, THREE count, three stirs and boom, can't get it out of the cup in under 5 seconds. This after chilling the product, the cup, the stir, the rocket fin can. What gives? Am I missing something? Is there a retarding agent to use other than chilling? I can't even pour it out of the cup - a syringe and injecting is never going to happen. Feeling frustrated. Is it a rocketry joke / right of passage? Am I being hazed? Any thoughts or commiseration appreciated.

 

[Steve Shannon]

That’s not how it has worked for me. I can usually add A and B together, stir a few times until it just starts looking creamy, and then pour.
You don’t say what brand foam you’re using. I don’t know if there’s different reaction times or speeds of expansion. I’ve only used PML brand.
Never use a full amount. Add it in lifts, just a little at a time and let it fully expand before adding the next lift.
Personally I think there’s usually very little value in a fin can for foam, but a nosecone can sure be strengthened by it.

 

[Sandy H.]

I haven't used any 'rocket branded' urethane foams, but I have used the 2 part foams from US Composites in various applications. I have never heard of injecting it, it has been more of a pour. I would say it does nothing, nothing, nothing and then 'ooooooh mamma!' pretty fast, but I'd guess closer to 10-15 seconds at room temperature in the summer, not just a couple of seconds. Largest volume I've done was probably 2 quarts and it was exciting and made one heck of a mess. I've done smaller pours with much less excitement and even at times, mild precision. When experimenting, it is always outside on the grass, as it will eventually get mowed up if I screw up. Not easy cleanup in general.

Part of me thinks that water was an accelerator, but I could be mistaken. Maybe the chilling is getting a bunch of moisture involved? Just a possible theory, not a solution.

Sandy.

 

[jFlds]

Mix and pour in small amounts. You don't have time to inject it. Plan on quick stirring a couple seconds then pouring immediately. I've been using the stuff for decades. It's always treated me good. You have to be fast. Cover up what you don't want it on. Work small batches. If you need to get it in small spaces drill a 3/8 hole in the tube and pour it in. Cute off the spoils and add filler or epoxy to seal said hole.

 

[AcadiaRockets]

Thanks everyone. I wanted to try the foam as I am doing a fin can on a boat tail Eagle Claw Sport. The internals are inaccessible due to the integrated boat tail. Its PML foam and I was mixing 10ml of each. I don't see how injecting is possible it goes off so fast. I did have some success in pouring each individual part into the fin can on the side that was still assessible and then using a kebab stick to jab and sort of mix it IN the can. This had satisfying (ish) enough results.

 

[Zyzzyva1000]

As some others on here have mentioned I have used the fence post 2 part foam you can get at home stores and you definitely have more than just a few second. I mix until it looks creamy and then pour. I tend to do small pours sequentially rather than trying to do large areas all at once. I haven't used the PML foam in about 20 years, but I do remember it being fast. Honestly the stuff you can get at home depo is far cheaper and very easy to work with.

 

[rharshberger]

As some others on here have mentioned I have used the fence post 2 part foam you can get at home stores and you definitely have more than just a few second. I mix until it looks creamy and then pour. I tend to do small pours sequentially rather than trying to do large areas all at once. I haven't used the PML foam in about 20 years, but I do remember it being fast. Honestly the stuff you can get at home depo is far cheaper and very easy to work with.

Yep here is the write up and testing I did using the Sika Post-Fix 2 part foam found at my local Lowes and Home Depot.

https://www.rocketryforum.com/threads/sika-post-mix-expanding-foam.150303/

 

[G_T]

Measure out part A in one cup. Measure out part B in a second cup. Put a third cup between the two. Pour in simultaneously. Mix rapidly but not whipping in air, for about 20 seconds. Pour where you want it, and watch!

I use little mixing cups; rather small quantity at a time. 2lb density expands a lot. High density doesn't expand all that much. So it depends on what you got. But in any event it is better to end up a little short and mix up a little more, than to have it go everywhere. At least for most applications!

 

[Lord Rory Gin]

Measure out part A in one cup. Measure out part B in a second cup. Put a third cup between the two. Pour in simultaneously. Mix rapidly but not whipping in air, for about 20 seconds. Pour where you want it, and watch!

I use little mixing cups; rather small quantity at a time. 2lb density expands a lot. High density doesn't expand all that much. So it depends on what you got. But in any event it is better to end up a little short and mix up a little more, than to have it go everywhere. At least for most applications!

With the PML foam, you can add a couple of drops of water to either Part A or B for more expansive properties. I was mildly surprised at how stiff the foam is after it cures but it cuts easily with a knife or can even be filed. PML withstands heat better than other expanding foams but if you are putting foam into a non-heat sensitive location, like nosecones, then practically any expanding spray foam would be more convenient than a 2-part mix.

 

[Steve Shannon]

With the PML foam, you can add a couple of drops of water to either Part A or B for more expansive properties. I was mildly surprised at how stiff the foam is after it cures but it cuts easily with a knife or can even be filed. PML withstands heat better than other expanding foams but if you are putting foam into a non-heat sensitive location, like nosecones, then practically any expanding spray foam would be more convenient than a 2-part mix.

Unlike 2 part foam spray can foam requires exposure to atmospheric moisture. Spraying a large quantity into a confined volume like a nosecone runs a risk of failing to cure completely.

 

[ThirstyBarbarian]

 

[Lord Rory Gin]

Unlike 2 part foam spray can foam requires exposure to atmospheric moisture. Spraying a large quantity into a confined volume like a nosecone runs a risk of failing to cure completely.

So in either case, you are going to apply/fill in layers rather than a large quantity.

 

[G_T]

With experience you can do larger quantities with a bit of accuracy. Without experience, don't even try!

 

[prfesser]

View attachment 533418

FWIW...30% hydrogen peroxide in one beaker, sodium or potassium iodide solution plus dishwashing liquid in the other. This demo is sometimes called "Elephant's...................................................................................................................................................................................................................uh.............................................................................................................................................................Toothpaste." Yeah; "toothpaste."

 

[prfesser]

With the PML foam, you can add a couple of drops of water to either Part A or B for more expansive properties. I was mildly surprised at how stiff the foam is after it cures but it cuts easily with a knife or can even be filed. PML withstands heat better than other expanding foams but if you are putting foam into a non-heat sensitive location, like nosecones, then practically any expanding spray foam would be more convenient than a 2-part mix.

This can be done with any expanding foam; water reacts with the isocyanate part to form CO2. Additional water = more CO2 = lower density foam. It's probably better to add the water to the polyol part, not the isocyanate (isocyanate is usually the darker-colored liquid). Adding water to the isocyanate part means the reaction will begin immediately, cutting down the time you have to mix and pour.

 

[G_T]

It likely also results in weaker foam. Generally if one wants different density foam, one uses different density foam. It is available over a wide range of density.