Nozzle blowout due to waxed tubes?

[mabuse00]

After a long time of abstinence I'd like to work on my endburners again...
How you people feel about endburners and waxed tubes? I've got a stash of waxed tubes ready for use, but when I waxed the tubes I had cored whistle motors in mind, so I did it all the way.

 

My worry is that such a setup is prone to nozzle blowouts. Is it even worth a try?

[MadMat]

A properly pressed nozzle actually expands the tube slightly and ISN'T flush with the end of the tube. The 1/8" of so of tube that sticks out past the nozzle is what does the majority of the work of holding the nozzle in place as it isn't expanded. I don't normally use waxed tubes as I make Rcandy rockets that are hot filled and hand pressed, but I can't see a problem. Go ahead and give it a try

[justvisiting]

I agree with MadMat. I don't have blowouts on my waxed tube end burners. I would strongly suggest using 2% water in the propellant to get maximum compaction.

[Bourbon]

I agree with MadMat. I don't have blowouts on my waxed tube end burners. I would strongly suggest using 2% water in the propellant to get maximum compaction.

Have you had any trouble with the moisture affecting the clay nozzle. It seems odd that some folks say they press a motor, then travel to another state and minute moisture in the air expands the nozzle and shrinks the hole. Yet others effectively press dampened fuel over a nozzle and have no issues. I must be missing something.

[justvisiting]

Bourbon, I have not had that trouble. I have read about that issue, but never seen it in real life. In David Sleeter's second book, he suggests dropping a few wax shavings onto the nozzle area before pressing the first propellant increment to reduce migration of moisture. Sleeter's motors are mostly core burners though. I have good reason to believe Estes end burner motors are pressed damp. Their motors are stored under varying climatic conditions all over the continent, and seem to have no nozzle shrinkage issues.

[Bourbon]

Thanks for the input.

[davidh]

Estes engines are pressed dry and VERY hard. I understand they are pressed from corned powder.

 

http://www.vernestes.com/images/Sport%20Rocketry%20Articles/EstesArticle-Part2-Reduced.pdf

 

FYI, Orv Carlisle originally wanted to sell model rocketeers the equivalent of pyro rocket tools to make their own motors.

https://en.wikipedia.org/wiki/Orville_Carlisle

https://www.polytechforum.com/rockets/early-model-rocket-timeline-73260-.htm

 

(Also, Orv's glitter formula is pretty good)

Edited July 20, 2020 by davidh

[justvisiting]

My information came from the previous general manager of Estes. His guidance allowed me to duplicate their density in my own rockets. The water was the key to achieving the density, just as it is with commercial black powder. If you press black powder damp and dry, the differences between the two will be obvious, and the better method will be easy to choose, based on experience.

 

EDIT: P.S. Davidh, the first link wouldn't open for me.

Edited July 21, 2020 by justvisiting

[justvisiting]

To clarify: I was not specifically told that Estes uses water for their end burners. I was specifically told to use it, and it made my propellant grains much more dense. It all came about when I was told that I could check the volume of a propellant grain by displacing alcohol with it in a graduated cylinder. My end burner propellant grains sucked up the 99% isopropyl alcohol. The Estes D-12 grains did not. Either Did their C6 grains that I checked. There was no amount of dry pressing that gave me a density anywhere near 1.7g/cc., the generally accepted density of black powder grains. Estes propellant grains are at least that dense. IIRC, the density of the grains I checked was +1.8g/cc. As soon as I used water as a compaction aid, my black powder pucks and increments became impervious to the alcohol- just like Estes grains.

 

In any case, the value of small amounts of water as a compaction aid for black-powder is well-known. Rockets up to 6lb have been made, tested, and documented. My own testing has only been up to 3lb rockets. Ned Gorski dampens his rocket powder now, and so does TR (the master).

 

My opinion is that the value of damp pressing is much more pronounced with end burners than with core burners, which is why I mentioned it

[davidh]

If that first link doesn't work, you might try downloading the link, since it's a PDF file.

[justvisiting]

"Couldn't download, network issue." is the message I get.

[Mumbles]

That's strange. Seemed to work okay for me. Would you like me to download and attach it here or pm/e-mail it to you?

[justvisiting]

Thanks, Mumbles! I can only get email on my phone right now, so PM would be great.

[mabuse00]

 

A properly pressed nozzle actually expands the tube slightly and ISN'T flush with the end of the tube. The 1/8" of so of tube that sticks out past the nozzle is what does the majority of the work of holding the nozzle in place as it isn't expanded

I'm aware of that.

Only I can't really press with the often quoted 9000psi, since I'll be working with an arbor press.

 

I'll give it a try.

 

 

Considering this wet pressing technique:

My standard nozzle mix contains a little wax, so swelling should not be a problem.

 

But how do you process your BP?

I usually prefer dried ganules without binder. Some time ago I used the ethanol/redgum process (what also produces very delicate granules that are easily crushed).

Do you use powder or granules?

[justvisiting]

mabuse00, the often quoted 9000psi is as much the cause of problems as it is the solution. Pressing damp propellant allows for MUCH better compaction at greatly reduced pressing forces. Some of us have been experimenting with lower pressing forces lately. Commercial black powder is pressed at about 3500psi. It has been proven that pressing damp 75-15-10 into a rocket motor tube (3lb) makes a monolithic grain of similar density.

 

In an end burner, it's particularly important to get maximum consolidation of a very energetic propellant. My untested hypothesis is that you can press 1lb end burners on a 1 ton arbor press with damp propellant, due to the addition of the water. Getting damp mill dust to go down the funnel can be annoying, as it likes to stick to the funnel, etc.. The shape of the funnel is important too. Since we want the best consolidation possible with what we have, it's also handy to have the propellant in a free-flowing, 'pre-densified' form. To achieve this, I make soft pucks with the damp propellant, and force them through a tough screen. I use this mixed-mesh powder to press the rockets. I store the damp propellant in a sealed container. It stores well. I have shared this method with other better pyros than myself and they see the same value in it that I do. I've written about it fairly extensively, so I'm not going to bore everybody by writing it again. Any specific questions will be answered to the best of my ability.

[mabuse00]

@justvisiting:

thanks for sharing this knowledge.

 

What I meant to convey in my last post was the idea that my pressing force might not be sufficient to compress the tube enough, so that the resulting bulge might not be deep enough to prevent it from beeing pushed downwards.

 

I'll find out.

 

 

Considering your wet pressing precess, I heard of this the first time, now you aroused my curiosity.

That wetness and pressing force are somewhat interchangeable is nothing new for any cometpressing experienced pyro enthusiast, but with rockets one would expect new troubles, like tensions in the grain when drying.

 

Do you use a special process or do you just leave the motors lying around?

And considering an endburner in a waxed tube - drying times must be rather long?

 

 

I store the damp propellant in a sealed container. It stores well.

Any fungal troubles?

 

 

I make soft pucks with the damp propellant

Can you elaborate this?

What equipment is used here? As if you would normally press pucks, only with lower pressure?

 

 

My feeling is that the riced BP granules dry rather quickly, leading to constantly changing properties / prompting one to work in a rush. Is that justified or am I counting beans here?

 

 

 

 

PS:

since you seem to be an endburner ethusiast - would you share your prefered nozzle diameter?

 

When I did the last experiments a few years ago, my feeling was that the typically prefered nozzles are far to wide. I have very nice alder charcoal made by a fellow pyro and dare to suggest that my BP quality is quite good. But even with 1/5 of the tube ID nozzle diameter, no motor ever popped on me, not even with wistlemix.

Since efficiency (and viciousness of sound ) can only improve with smaller nozzles I'd like have a setup as aggressive as possible. The commercial tooling set's 1/4 of tube ID seem rediculous to me...

(Be aware that all my experience is limited to 15mm/~8oz motors)

 

How do you feel about this?

[MadMat]

there is something that many people seem to forget/ignore/just not know, that 9000 psi is read out in pounds per square inch. If you are pressing 1/2 diameter rockets, that comes out to 4500 psi on a 1/2 piston or ramming tool. Don't forget the pressure listed on a press or bottle jack is relative to the diameter of the ram. I have made a number of successful nozzles by hand with a hardened ramming tool and a hammer. I do just the nozzles, because I normally make Rcandy, that is hot poured and hand pressed.

I know people who have done it, but personally I wouldn't hammer the grain for a BP rocket.

Edited July 23, 2020 by MadMat

[Mumbles]

Also, to be most accurate, you also have to take into consideration the cross sectional area of the rocket rammer. A lot of rockets have cores, and that further reduces the area that the force is being directed.

[justvisiting]

mabuse00, people hand ram nozzles in place, and hand-ramming is said to generate only 500-1000psi. Of course, it's impact force rather than pressing force. I don't hand ram rockets myself. When pressing rockets, I notice that nozzles and bulkheads bulge my (supported) tubes noticeably, when the same size increment of (any) propellant does not. That makes me have less worry about nozzles blowing out. Pressing a nozzle in 2 increments is an option. Steve Laduke uses broken flowerpot clay as grit in his nozzle mix to give better grab on the tube. But then again, he's the guy that popularized pressing dry to 9000psi I like a lot of his techniques, but not all.

 

Tensions in the grain when drying are not a concern for me. It's been my experience that the slightly damp BP propellants stay slightly damp, even in nozzleless coreburners with a long exposed core. It could be that some of the moisture in the black powder is absorbed by the tube. My tests have shown the dampened grains to be very stable to weight loss. I'm not concerned about how difficult it might be for moisture to leave an end burner, since it doesn't seem to want to leave anyway.

 

I press my rockets in a cool environment, so I'm not too concerned about evaporation. An amount of propellant for one rocket can be taken out of the larger container of prepared propellant to minimize evaporation of moisture. I've stored dampened propellant for over a month with no fungal issues.

 

As far as nozzle aperture, I just use off the shelf tooling. I've experimented with end burners, because I was using them to try to evaluate my black powders. As it turned out, that method of testing black powder was not well-received, and I moved on. I mostly use nozzleless coreburners for pyro rockets, and standard nozzled coreburners for more dim effects.

 

Now I'm curious again. It's been said that a 1 ton arbor press is not strong enough to press 1lb rockets. But, with damp propellant, if 3500psi is sufficient pressing force, a 1 ton press would do the job. A solid 3/4" rammer face has an area of .441". To get 3500psi, I need 1543 pounds of force. That's within specs for the arbor press. I checked my torque wrench on the arbor press at its maximum setting of 250 foot pounds, and it clicked at 3500psi on my PtoF gauge. BUT, I had to hang off that thing like a monkey! If I needed to press a 1lb rocket on a 1lb arbor press at 3500psi to save my life, I could do it. Hand ramming would be way easier, but I'm not doing that either. 5/8" (8 ounce) rockets would be a piece of cake on the 1T arbor press with damp propellant.

[Bourbon]

It would seem to me anything that can be hand rammed "successfully" could be done with a 1 ton press even if you had to use a cheater bar on an arbor.

 

As I said though. "Seem to me". Purely speculation from a newbie who knows nothing.

[justvisiting]

Bourbon, it's not an unreasonable way to think about it, but I don't think it's as simple as that. I think of driving a nail. With a hammer, the nail is driven by small impacts. To simply push the nail would take a lot more force. Maybe I'm looking at it all wrong too Nobody's perfect. I made a GLARING error in the post above. I'll give folks a chance to 'nail' me before I remove it and give better information.

[BetICouldMake1]

I use a 1 ton arbor press for my 1lb BP rockets. Works great. I also use a torque wrench and find it easier to press by leaning into the wrench rather than pulling down. More of a down and out push so I can use my bodyweight leaning forward more than pulling down with my arms.

[Bourbon]

Justvisiting, ahh ok. I think I see your logic here. I didn't look at it that way. I always did wonder why someone could hand ram a motor but when pressing all the sudden have to use tons of force where a couple of taps with a hammer did the job. Pushing a nail was a good analogy.

[mabuse00]

I'll will test this myself when I have the chance, but in your experience: how much burnrate do we sacrifice on 2% water content?

 

@Bourbon:

Think of the hammer as a moving mass. It needs force for a certain time to change it's direction.

If it happens in an infinitely short time, the force has to be indefinitly large.

And when the hammer hits the target, it is stopped not indefinitely fast, but very fast, so for a short time, the force must be very great.

 

@justvisiting:

Can you provide some more information about your granulation process?

Especially the

 

soft pucks

?

(I wonder how crucial that is?)

I figure that is not the typical ricing process?

 

 

[dagabu]

mabuse, long time my friend! Welcome back!

 

We have been making a lot (thousands) of Cohete style rockets the last few years on small arbor presses and with NO nozzles for a very short lift. From that, I changed my endburners as well so they also could be pressed with an arbor press, anywhere in the world!

 

These folks have the right idea, a little water, a little help with evaporation, small increments and the right size nozzle for your powder.

 

Here is what we do with great success: #1 endburners, compress the nozzle in two increments, don't use an extension bar or anything mad to get all the pressure you can, just press and hold for a good 30 seconds, add the other half and compress again. Add more clay if need be to get the throat depth to at least 1/2 the nozzle diameter.

 

Erosion will reduce thrust, to long a throat will foul and RUD.

 

For the black powder, spread out your BP on a sheet of waxed paper or an analog, use 70% Isopropyl Alcohol and using a scale, zero the spray bottle and use no more than 50g on 1000g batch. Quickly mix it by hand, cover in a small tight container and dispense from the container.

 

Use small increments, perhaps 5mm per increment but not more (pressed size, about a 1/2 teaspoon of powder) and use dwell time to compact the powder.

 

**CAUTION**

 

Here is where 90% of the people making BP rockets experience in one way or another.

 

Relaxation.

 

This is severely compounded when certain charcoals are used and is also why you will NEVER find some charcoals used in commercial BP. Try this with your BP, dampened or dry: Split a short section of PVC pipe, use hose clamps to keep it closed and press 1 full increment with your press. Open the hose clamps and eject your increment. Make another but this time, press the increment then press another on top of the first one, eject and after allowing it to dry, pick them up and try to crush/break them.

 

If they both remain in a solid state (some chipping is fine) then your charcoal is good-to-go. If the increments delaminate, if the increments swell, come apart, dont fully compact, you need to change the charcoal.

 

Back to the OP, will a waxed tube cause the nozzle to blow out? Yes, unless you create a physical indentation in the tube trapping the plug, it will eject. If you crush the pulp and create fractures, the tube will fail. Just scratch the paper a little to remove a little of the wax and load one up!

 

Good luck!