Why no nozzle bonding?

[Walldiver7]

I'm building an AT M1500 for the next launch coming up and this has always made me curious: Why doesn't AT want you to bond the nozzle to the liner? The included yellow sheet addendum states that after bonding the grains in, you are to insure that there is no glue where the nozzle will seat. So what's the reasoning behind the decision to not bond the nozzle to the liner?

 

[tim cubbedge]

I believe the whole reason behind bonding grains to liner is to prevent the grain paper casting tube from plugging the nozzle.

 

[3stoogesrocketry]

I'm building an AT M1500 for the next launch coming up and this has always made me curious: Why doesn't AT want you to bond the nozzle to the liner? The included yellow sheet addendum states that after bonding the grains in, you are to insure that there is no glue where the nozzle will seat. So what's the reasoning behind the decision to not bond the nozzle to the liner?

A liner should never be used as a pressure vessel . If you glue your nozzle into your liner , there is no room for thermal expansion and if your liner is slightly loose , you run the risk of splitting your liner .

 

[Walldiver7]

A liner should never be used as a pressure vessel . If you glue your nozzle into your liner , there is no room for thermal expansion and if your liner is slightly loose , you run the risk of splitting your liner .

As you pointed out, too much expansion would cause a problem, and that is why we pay dearly for these cases with close tolerances. None the less, some degree of expansion does take place. At operational temperatures and pressures, I would guess that everything inside that case swells/molds itself to the volume of the case,.... It my opinion (and that's all it is), everything inside a motor case operates as a system to contain the pressure and direct it through the nozzle. I started bonding the top closure of my CTI 54 motors some time ago.... why? I noticed that my 54 cases were being "cut" by the escaping gases at the joint between the delay module (forward closure) and the liner. It worked.

 

[jimzcatz]

I believe the whole reason behind bonding grains to liner is to prevent the grain paper casting tube from plugging the nozzle.

That's correct.

 

[Walldiver7]

That's correct.

Yes, but what about the nozzle? Why doesn't AT recommend bonding the nozzle too?

 

[DavidMcCann]

Yes, but what about the nozzle? Why doesn't AT recommend bonding the nozzle too?

Because the nozzle isn't going to tear free and block itself? Bonding the grains is done to stop the nozzle from getting clogged. Claiming that's a reason to bond the nozzle is confusing.

 

[tfish]

Another thing that grain bonding does is, it keeps the grains from compressing down on each other. On high G flights this could actually affect the core size or crush the bottom grain(s).

Tony

 

[Walldiver7]

Another thing that grain bonding does is, it keeps the grains from compressing down on each other. On high G flights this could actually affect the core size or crush the bottom grain(s).

Tony

That makes sense.

 

[Walldiver7]

Because the nozzle isn't going to tear free and block itself? Bonding the grains is done to stop the nozzle from getting clogged. Claiming that's a reason to bond the nozzle is confusing.

Confusing? Aerotech goes to the trouble to tell you to be careful to clean out any excess glue after the process of gluing in the grains, but I cannot come to any conclusion as to why they do not want you bonding in the nozzle during this phase of the motor build. Using your reasoning, then why would it hurt to bond the nozzle in anyway? The last CTI 75 reload I flew,... I think, .. did have the nozzle glued in (or maybe it was pressed in so tightly I couldn't tell the diff).

 

[sghioto]

The liner is designed to slide over the shoulder of the nozzle a short distance. You don't want any glue is this area or the liner will be hard to fit, that's all it is.

 

[Walldiver7]

The liner is designed to slide over the shoulder of the nozzle a short distance. You don't want any glue is this area or the liner will be hard to fit, that's all it is.

It's just that simple.... Polyurethane glues tend to expand and that would cause a problem when it came time to slide the reload into the case. I will now focus on other global problems. lol Thanks sghioto.

 

[DavidMcCann]

It's just that simple.... Polyurethane glues tend to expand and that would cause a problem when it came time to slide the reload into the case. I will not focus on other global problems. lol Thanks sghioto.

so, glueing the nozzle will expand the liner too much and be bad.... but gluing the huge length of grains is totally cool? got it.

><

 

[dhbarr]

so, glueing the nozzle will expand the liner too much and be bad.... but gluing the huge length of grains is totally cool? got it.

><

I'm merely observing here, but grains & nozzles don't tend to have identical levels of flexibility

 

[Walldiver7]

so, glueing the nozzle will expand the liner too much and be bad.... but gluing the huge length of grains is totally cool? got it.

><

Yes sir, ... you have identified the area of argument regarding sghioto 's hypothesis. I'm now guessing that Aerotech is directing the flyer to assure this area (where the nozzle seats) is void of glue because they are concern that, during the curing process, the foam (polyurethane glue) will expand and push the nozzle farther aft. I think it's pretty tricky business using any glue that will expand (although, Elmer's Glue-All Max has low foaming properties) for grain bonding.

 

[cavecentral]

Not sure what the 98mm look like. The 54mm had a thin O-ring go on the nozzle shoulder, then the liner. Glue might screw up that fit if it is supposed to seal anything. The O-ring might just have been there as a padding so the liner didn't crack too.

 

[Walldiver7]

Not sure what the 98mm look like. The 54mm had a thin O-ring go on the nozzle shoulder, then the liner. Glue might screw up that fit if it is supposed to seal anything. The O-ring might just have been there as a padding so the liner didn't crack too.

The AT M1500 Mojave Green is a 75mm motor, and the nozzle o-ring is placed between the nozzle and the aft case closure.

 

[cavecentral]

The AT M1500 Mojave Green is a 75mm motor, and the nozzle o-ring is placed between the nozzle and the aft case closure.

Oops 75mm then. The 54mm had a thin one that I thought was for a seal disk, but it wasn't. It was for on the nozzle shoulder. The 2 standard O-rings for the closures were there too. Just a thought.

 

[cherokeej]

I'll try my hand at this...

There are multiple reasons one might want to liner-bond propellant grains in a motor. I'm not going to go into that here, so for purposes of discussion, let's agree we have a motor that requires liner-bonding.

A lot of folks will want to pre-assemble a motor like that to make sure their glue has cured. They glue the grains in per the instructions one morning, with plans to fly the next day. They get up the following morning, only to find the glue ran inside the liner, and now there's a big glop on the shoulder, and the nozzle won't seat.

I don't think the good folks at AeroTech care if you glue in the nozzle, but they do want to make sure you can get the darn thing in there...

 

[DavidMcCann]

Yes sir, ... you have identified the area of argument regarding sghioto 's hypothesis. I'm now guessing that Aerotech is directing the flyer to assure this area (where the nozzle seats) is void of glue because they are concern that, during the curing process, the foam (polyurethane glue) will expand and push the nozzle farther aft. I think it's pretty tricky business using any glue that will expand (although, Elmer's Glue-All Max has low foaming properties) for grain bonding.

I can see how expanding glue would have unique issues. I've only ever bonded in loki grains using epoxy, which for obvious reasons you wouldn't want any on the nozzles.

 

[blackjack2564]

I've glued in grains & nozzle [graphite] in liner of 7600 case AMW. Usually burns/cooks epoxy old way.....Gorilla glue...new way, to the point of falling off.

If it does not, just toss it in a fire & burn off the residue, certainly comes nowhere near the heat of propellant going through it.....LOL.

After spitting a few research casting tubes, I began gluing them. Always stand the stack on the nozzle to cure, it gets glued in. Bottom grain is longer and core larger than others....erosive burn.

I have a M1450 loaded in the case now...all glued up & nowhere to go.

 

[aeg]

I'm building an AT M1500 for the next launch coming up and this has always made me curious: Why doesn't AT want you to bond the nozzle to the liner? The included yellow sheet addendum states that after bonding the grains in, you are to insure that there is no glue where the nozzle will seat. So what's the reasoning behind the decision to not bond the nozzle to the liner?

A simple call to Aerotech should get you the right answer with no guesswork involved. aeg.