Expanding foam?

I was working on my PML kit and decided to foam the fin can and it cracked the QT? Has anyone experienced this with QTs? I know you don't foam cardboard tubing, but I never would have expected this to happen.

Using the small mixing cups I used equal amounts of each parts A and B and added 5 drops of water to part A. Mixed the two parts together and poured. It foamed up nicely. I waited until it set up and then made the second mix, which is all it needed.

wowzer!! i foam every fin can-QT and cardboard- and never had a problem. however, i dont add the drops of water

The water shouldn't have been the problem. The water just lessens the density. I've done Phenolic tubing, but not LOC tubing. Should've worked as long as the foam wasn't trapped.

I’ve not seen that, but I don’t foam that end. It looks like there was maybe a stress riser where the expansion of the foam resulted in crack propagation. I have seen cracks run in QT before.
When I first looked at the picture it looked like it was just a stringer of polyurethane laying on the QT.

jd2cylman said:

The water shouldn't have been the problem. The water just lessens the density. I've done Phenolic tubing, but not LOC tubing. Should've worked as long as the foam wasn't trapped.

Click to expand...

I think water would absolutely make a difference. If someone wants to do a basic experiment it should be fairly easy to rig a pressure sensor to a container with differing amounts of water added.

I would expect more water == higher pressure for constant volume up to the limit of the water-added reaction.

dhbarr said:

I think water would absolutely make a difference. If someone wants to do a basic experiment it should be fairly easy to rig a pressure sensor to a container with differing amounts of water added.

I would expect more water == higher pressure for constant volume up to the limit of the water-added reaction.

Click to expand...

But, the end was open, which should have let the pressure of the foam expand out the end. Now, if for some reason the end cured before the middle, the expansion has to go somewhere...

I sanded the crack flush, but it still remains and of course the rocket will and continue to fly, but over time and not so many soft landings on the desert floor I'm sure that it will get worse. Thanks for the feed back guys. I contacted PML to see if they would send a new parts or if they have some type of suggestion(s) We'll see I guess?

i dont know it it would work on QT but on some plastics its possible to stop a crack from going further by drilling a hole at the end of the crack.

tomsteve said:

i dont know it it would work on QT but on some plastics its possible to stop a crack from going further by drilling a hole at the end of the crack.

Click to expand...

That will work.

I've foamed two PML QT booster sections in the last few months and have not experienced any problems. One with zero water and the other with three drops and both opened ended when pouring. I like to do three or four smaller pours rather than one or two larger. One thing I like to do is swill the foam rapidly after pouring until it starts expanding.

The foam doesn't have a heavy "push out" when not constricted but does exhibit a mild "heat" as it cures. Perhaps a heavy pour, small space and the cure heat exposed a weak point in the QT tube.

Techniques and timing do vary and so does ... millage

I don't have a clue, of course, but my guess is that your tube had a weak spot or a defect. Be interesting to see what PML comes back with.

I like the idea of drilling a hole and then filling it. I was able to level it out pretty well, but its still there. I hate to invest in a paint job and find out later my rocket will look like a cracked egg. Anyway lets see what PML suggests. Maybe they have experienced this with other customers and maybe it is a common issue? I'm sure they will be supportive with a resolution of some type, most vendors are.

Anyway PML got back to me and basically said it was a slip of a knife that caused it while removing epoxy drips and if it was a crack it was going the wrong direction. I do have the email, but will wait before posting. I want to see what their response is after they see the following pictures. I sanded the area with 150 and then 220 and the line is still visible. If it was a scratch caused by a knife wouldn't it have sanded out? When they suggested this I denied that and explained that I didn't cut it with a slip of a knife because I'm very careful and my blade was nowhere near the area in question. An Xacto knife you would hardly see the cut mark and for it to still visible would take a lot of force to leave deep cut if that's what they are suggesting?

It is a scratch in the surface. Nothing more, nothing less.

One can tell that it is merely a scratch because your first photos show a "tail" at the end of the scratch, above the surface of the Quantum tube. I have seen this before many times when scuffing Quantum prior to bonding. The photos in the most recent post show the tail is gone, after you sanded the area with 150 and 220 grit paper.

Prime it. Fill the scratch if necessary. Paint it. Move on.

okay lets end this thread no need to post anything more. My rockets only last half dozen launches before I take a core sample then I throw them in the trash where they belong. I salvage what I can and move on..later