Getting foam into deep tight places

[amiliv]

The problem: getting foam mix to the bottom of a deep and very narrow fincan. 38mm airframe and 29mm MMT. The depth to be filled with foam is 7" down to the forward centering ring, out of that fin tabs extend from about aft end down 4". So there is very narrow space between airframe and MMT.

If using 30x foam, I'd need only about 2ml of it. If I were to just squirt it in from the top, I suspect it will not flow all the way down to the bottom of fincan. That small amount, it'll just stop wherever it first makes contact with either MMT or airframe. I expect it to just push itself out the top as it starts expanding, instead of filling entire volume evenly (especially if it start expanding from the spot that is between fin tabs).

I kind of have two ideas, but not sure if either would work:

Idea 1: Buy 14 gauge 10" long dispensing needle (something like this https://smile.amazon.com/Rachels-Closeouts-Dispensing-Needle-Syringe/dp/B07MKQFVLQ). That's about fattest and longest needle I saw on Amazon. However, I'm not sure if foam mix is viscous enough to flow through it. If it is, problem solved... I can apply foam directly to the bottom of the fincan.

Idea 2: Drill a hole towards the bottom of fincan, inject foam mix through it, and attempt to quickly plug it. E.g. thick CA glue + accelerator. Or tightly wrapping it with masking tape.

Anybody else done it? The foam I'd be most likely using is TAP X-30.

 

[rharshberger]

60ml Syringe with a piece of tubing that fits tightly over the tip, mix foam, suck up in syringe ( or if daring remove plunger an load by pouring in top), slide tubing on and put tube down in hole, empty syringe (or however much you need), once syringe is empty toss it in trash or attempt to clean (I usually toss em).
Sika post mix available at some Lowes stores (and other home improvement stores) is a good 2 part foam and its cheap at about $11 for enough to do several rockets (I store the two parts in quart Ziploc containers with screw on lids).
My experiment thread on the Sika product is linked below.
https://www.rocketryforum.com/index.php?threads/150303/

 

[les]

My concern would be the amount of time you have between mixing and when it starts expanding. Is there enough time to suck it into a syringe/tube and then inject before it starts "growing"?
I've only used PML 2 part expanding foam, and after it is mixed you don't have a lot of time (like 20 seconds).

 

[amiliv]

Status update. Initial experiments attempting to use syringe don't look promising. Mixed the A+B, and attempted to dispense it into an empty cup and let it expand. From top left to bottom right:

1) Mixed in a cup, pulled into syringe and dispensed through 10" long plastic tube. Uneven foam, small cavity formed at the bottom.

2) Mixed inside large syringe, and dispensed through 10"long plastic tube. No cavity, but foam is still uneven and far from good.

3) Mixed inside large syringe, and dispensed through 10" long dispensing needle. I had higher hopes for this one, but it turned out with huge cavity and very uneven foam mix.

4) Control sample, just mixed it in a cup and let it expand; this is how it should ideally look like. Even mix bottom to top, no cavities.

More work needed....

 

[Steve Shannon]

The other test you should do is mix in a cup and pour from that cup into another cup right away.

 

[prfesser]

My concern would be the amount of time you have between mixing and when it starts expanding. Is there enough time to suck it into a syringe/tube and then inject before it starts "growing"?
I've only used PML 2 part expanding foam, and after it is mixed you don't have a lot of time (like 20 seconds).

Possibly chilling the ingredients? I'll give that a try later. Taking the ingredients from room temp to near freezing should provide about four times the work time. Will let you know how it turns out.

 

[dhbarr]

Maybe an empty 2-part syringe and a mixing tip?

 

[amiliv]

The other test you should do is mix in a cup and pour from that cup into another cup right away.

That'll work. The trouble is, I can't pour it that way into the real thing. Too narrow between airframe and MMT.

Maybe an empty 2-part syringe and a mixing tip?

Too deep, and again too narrow. The mixing tip would need to be 10" long, and very narrow. 1/8" ID plastic tube barely fits. 14 gauge needle is better. But any mixing tip would be way too fat to slip it into the space between airframe and MMT.

 

[amiliv]

I'll give this thing few more attempts... If all else fails, I'll just pour some epoxy over fin tabs to form internal fillets. I've a feeling foam is really meant for much larger fincans than what I'm building

 

[rharshberger]

Given the small annular space, put the rear CR on, drill a small hole on each side of the fin root and inject epoxy into the internal root area. It's a Crazy Jim technique that works great. I do each adjacent pair of fin roots at once, let cure, roll airframe and do next pair, repeat as needed.

 

[tOD]

Given the small annular space, put the rear CR on, drill a small hole on each side of the fin root and inject epoxy into the internal root area. It's a Crazy Jim technique that works great. I do each adjacent pair of fin roots at once, let cure, roll airframe and do next pair, repeat as needed.

That's the technique I used to build my Mach 1 Black Hole. Same dimensions, 38mm airframe, 29mm motor mount. I used West Systems and a pinch of chopped carbon fiber.

 

[Tyler P]

Just out of curiosity, could you use a polyurethane glue like Gorilla or Elmers Ultimate to achieve a similar effect to foaming? Poly glues foam as they set creating a similar, if not quite as dense, foam. I'd be temped to try it, especially if the gap is smaller like what the OP described.

 

[c0c0m0ke]

I have used Great Stuff to fill between motor tube and paper transition that I was quite happy about. The foam comes out and expands. It comes with a narrow application tube that you can squeeze into narrow places. The foam is sticky and messy. Have Acetone handy to clean up afterwards. My rockets were small, so all I had to do was to shake them to get the foam where I wanted it. But like i said,it expands and keeps expanding. The danger is putting in too much and the foam excretes out of weak joints or bursts the container (in this case a paper transition, or crushes the motor tube). Do it slowly and keep an eye on what you are doing.

The other problem with Great Stuff is the inability to use it again if you stop and you still have a lot left over. The nozzle will clog and the acetone doesn't seem to get in there and dissolve the clog. I think I remember taking the nozzle off and trying to clear it by soaking in acetone, to no avail.

The problem: getting foam mix to the bottom of a deep and very narrow fincan. 38mm airframe and 29mm MMT. The depth to be filled with foam is 7" down to the forward centering ring, out of that fin tabs extend from about aft end down 4". So there is very narrow space between airframe and MMT.

If using 30x foam, I'd need only about 2ml of it. If I were to just squirt it in from the top, I suspect it will not flow all the way down to the bottom of fincan. That small amount, it'll just stop wherever it first makes contact with either MMT or airframe. I expect it to just push itself out the top as it starts expanding, instead of filling entire volume evenly (especially if it start expanding from the spot that is between fin tabs).

I kind of have two ideas, but not sure if either would work:

Idea 1: Buy 14 gauge 10" long dispensing needle (something like this https://smile.amazon.com/Rachels-Closeouts-Dispensing-Needle-Syringe/dp/B07MKQFVLQ). That's about fattest and longest needle I saw on Amazon. However, I'm not sure if foam mix is viscous enough to flow through it. If it is, problem solved... I can apply foam directly to the bottom of the fincan.

Idea 2: Drill a hole towards the bottom of fincan, inject foam mix through it, and attempt to quickly plug it. E.g. thick CA glue + accelerator. Or tightly wrapping it with masking tape.

Anybody else done it? The foam I'd be most likely using is TAP X-30.

 

[c0c0m0ke]

I think your second solution would be easier and more efficient. You will get the foam where you want and need it. The long needle is too "iffy" if the stuff you are using is anything like Great Stuff. I seem to recall the applicator popping off in the middle of the fill. Have acetone handy, if it is like GS.

The problem: getting foam mix to the bottom of a deep and very narrow fincan. 38mm airframe and 29mm MMT. The depth to be filled with foam is 7" down to the forward centering ring, out of that fin tabs extend from about aft end down 4". So there is very narrow space between airframe and MMT.

If using 30x foam, I'd need only about 2ml of it. If I were to just squirt it in from the top, I suspect it will not flow all the way down to the bottom of fincan. That small amount, it'll just stop wherever it first makes contact with either MMT or airframe. I expect it to just push itself out the top as it starts expanding, instead of filling entire volume evenly (especially if it start expanding from the spot that is between fin tabs).

I kind of have two ideas, but not sure if either would work:

Idea 1: Buy 14 gauge 10" long dispensing needle (something like this https://smile.amazon.com/Rachels-Closeouts-Dispensing-Needle-Syringe/dp/B07MKQFVLQ). That's about fattest and longest needle I saw on Amazon. However, I'm not sure if foam mix is viscous enough to flow through it. If it is, problem solved... I can apply foam directly to the bottom of the fincan.

Idea 2: Drill a hole towards the bottom of fincan, inject foam mix through it, and attempt to quickly plug it. E.g. thick CA glue + accelerator. Or tightly wrapping it with masking tape.

Anybody else done it? The foam I'd be most likely using is TAP X-30.

 

[rharshberger]

I have used Great Stuff to fill between motor tube and paper transition that I was quite happy about. The foam comes out and expands. It comes with a narrow application tube that you can squeeze into narrow places. The foam is sticky and messy. Have Acetone handy to clean up afterwards. My rockets were small, so all I had to do was to shake them to get the foam where I wanted it. But like i said,it expands and keeps expanding. The danger is putting in too much and the foam excretes out of weak joints or bursts the container (in this case a paper transition, or crushes the motor tube). Do it slowly and keep an eye on what you are doing.

The other problem with Great Stuff is the inability to use it again if you stop and you still have a lot left over. The nozzle will clog and the acetone doesn't seem to get in there and dissolve the clog. I think I remember taking the nozzle off and trying to clear it by soaking in acetone, to no avail.

The problem with Great Stuff is that it will not fully cure in a sealed environment like a fin can.

 

[prfesser]

The other problem with Great Stuff is the inability to use it again if you stop and you still have a lot left over. The nozzle will clog and the acetone doesn't seem to get in there and dissolve the clog. I think I remember taking the nozzle off and trying to clear it by soaking in acetone, to no avail.

Once cured, polyurethane is largely impervious to solvents, at least short-term.

To clean out the Great Stuff nozzle, pull the two parts of the nozzle apart and let them cure. A stiff wire -- I think I've used #14 bare copper -- will push the material out of the tube. If there's any uncured residue on the inside, let it cure and repeat. Small needle-nose pliers will pull the cured stuff out of the other part. Don't forget to remove the cured bit that's in the nozzle of the can.