Expanding foam question? 2 - part

Any of you guys use expanding foam on card board fin cans? I was told that if you used it on card board it would distort the body tube? How true id this? I know that some of the thick walled tubes are pretty strong

AfterBurners said:

Any of you guys use expanding foam on card board fin cans? I was told that if you used it on card board it would distort the body tube? How true id this? I know that some of the thick walled tubes are pretty strong

Click to expand...

I learned the hard way...even heavywall .021" craft body tubes not only deform the will split if you use expanding foam. Not only that but most of the brands I've seen Once you start the can it continues to flow until the can is empty....What a HUGE mess I made all over the kitchen, back porch and back yard trying to get the darn thing out of the house while it was still pouring out foam. Never Never again! LOL! The better 2/3rds and I laugh about that episode often. The stuff is a mess.

While I've never used spray foam from a can, I have used various brands of two part foam, and, have never had an issue. I like to mix small batches, rather than try to fill a fin can all at once. I have heard of the spray can foam, continuing to expand over time with thermal, and humidity changes.

Yeah I meant to put 2 part

Isn't this in a sticky somewhere by now?
Everyone STOP even trying to use canned expanding foam in your rockets! The canned stuff requires exposure to air to cure. When in a confined space (fin can?), it will not fully cure, and may continue to expand as it tries to do so.

The 2-part epoxy foam is very different. It is a chemical reaction cure, and when it's cured, it stops expanding. Density can be adjusted by adding (very) small amounts of water to the mix. Always best to leave a path for excess foam to "boil over", as it often happens, especially when you're learning how to use it. The blowing out of thin-walled tubing is easy to do in a fincan where all the hoop strength of the tubing is gone from slotting for fins. Just make sure you leave off the aft centering ring, so the pressure has somewhere to go.

NO CANNED FOAM. EVER! just stop it.

-Ken

FYI, for two-part foam, I can't find any numbers on this, but it since to me, from my experience, that the expansion ration is about 2:1; i.e., if you are filling a 30 cubic cm space, use 15 cubic cm of mix.

Back to the OP, I have never tried to fill a cardboard tube, but it is not an idea I would entertain. The solidified foam is hard and very solid. It's light because it is extremely porous; but it is not soft or pliable in any way.

I did foam my MAC Performance canvas phenolic booster to great success.