Nozzle reinforcement/pre-formed nozzles?

[Varmint]

I did a quick search, probably not in depth enough, but I wanted to ask:

 

Has anybody tried adding sodium silicate ("water glass") in a resonable percentage to a damp bentonite nozzle mix before pressing.

 

Once pressed it would then oven cured it to drive out moisture and cause the water glass to do its transition?

 

Seems to me the resulting nozzle should be much stronger and errosion resistant.

 

The other thought I had would be pre-formed nozzles made from standard firing clay. Make up a batch, fire them, maybe even glaze the cone surfaces, and use features cast into the outside of the nozzle to aid retention in the motor tube.

 

These "features" could be as easy as a series of ramps (like a barbed hose nipple but more tightly packed with shallower peaks/valleys). Juice it up with some good wood glue or similar, press the nozzle into place, glue sets and it HAS to be more rigid than a formed in place compressed nozzle.

 

Obviously fired goods change dimensions, that's where the research lies, design a nozzle that post firing meets the required final dimensions.

 

Feedback appreciated.

 

DAS

[Aquarius]

Tried it once, the nozzle gets hard as rock. I experienced a problem with something that looked like mould that grew on the clay. But it worked all right.

[leedrill]

can i ask are you having trouble with erosion on your nozzles cause i really dont see it to be necessary at all to make a grog if you have high quality bentonite i have never used kitty litter or made grogs and i basically get no erosion at all id rather use the na sali as fuel than as heat prevention

[Varmint]

leedrill:

I've had several blowouts, and several instances of either extreme erosion or partial blowouts.

 

My presumption is a packed clay bulkhead for cato management (emergency safey valve!) plus an absolutely solid nozzle eliminates at least one variable.

 

Imagine the "comfort" knowing that either method (reinforced bentonite or fired clay nozzles) means your bottom end could be essentially eliminated as a point of failure. I especially like the fired nozzle idea, seat it, forget it, the material will easily endure the typical burn time. In fact if you accomplish a recovery by some chance, you might be able to cut it free from the motor casing, wire brush the adhesive residue off, slop on some fresh adhesive and reseat it in another casing.

 

Another advantage of the fired nozzle would be the opportunity for impressive levels of thrust multiplication, meaning at a minimum, less fuel to lift a given load to a given height, or the same fuel and load to a greater height.

[Col]

The adhesive holding the nozzle in place is likely to be the weak point. Pressed cat-litter or grog based nozzles that bite into the tube wall wont let go without a fight

[Seymour]

What kind of rockets are you thinking of making Varmint? Perhaps with some very high temperature fuels on quite serious motors special nozzles could be beneficial.

 

Nozzle erosion might also be more of an issue with some fuel grain configurations. Typically for us firework rocket folks this would mean end burners, but it would be true of other geometries with a relatively flat thrust curve, like bates grains. However for typical firework core burning rockets, a moderate degree of erosion can be beneficial, if you can get it to complement the increase in surface area burning as the core expands.

 

I think you would need an exceptionally hot fuel and/or a very long burn time for this to be necessary. I believe oxides with high melting temperatures can aid in slowing erosion, such as Al2O3.

 

With good cardboard tubes up to and above 1" dia, and a suitable, but ordinary clay based nozzle mix pressed or rammed in to place, you can quite easily make very high performance rockets with a wide variety of fuels. This takes only a few seconds once you are set up, and I am not convinced doing any more is necessary, at least for the kinds of rockets I make. If I was flying model rockets I could see a point in having a weak end to prevent destruction of the whole rocket, though I'd personally rather have the nozzle blow out to avoid roasting the insides of the rocket.

 

When I have had bulkheads or nozzles blowing out I've typically taken it to mean that the point of failure was too weak. Either the clay was not gripping or digging in to the tube because it was a poor quality mix or it was poorly compacted. With good tubes I typically have the whole tube, or with long end burners, half the tube blown to bits when they cato, and I like it that way. It means that everything is good about the motor casing, I just need to tone down the fuel or geometry.

[leedrill]

ill agree with that when starting out {before having a press i had problems with nozzle blow outs } but now my tube will blow way before my nozzle ejects which i also find a good thing just lets me know my nozzle is not going anywhere if i decide to put a salute or shell on an end burner i would much rather the whole thing blow up rather than lose a nozzle and thrust and yet still have a motor burning not knowing where it will land

[gregkdc1]

Fired clay “ceramic” works great for nozzles in sugar motors and I am assuming they would probably be the same for black powder motors.

The ceramic has no erosion and holds up well when making smaller motors with a burn time of 1-2 seconds. They eventually fail by cracking, mostly on the convergent side, but can actually be re-used anywhere form 3-5 times before I don't feel comfortable with them. I did a test once with a little PVC motor to see how many times I could use a nozzle. The motor held 60 grams of rocket candy and I had launched a mid sized rocket with it many times. Anyway I used it over 20 times and probably could have even more; all the while the nozzle maintained the same throat diameter even though it was full of cracks. Last the clay I used had a low firing temp so I was able to make a mini kiln out of refractory bricks and a propane torch.

One thing that I need to test is what the addition of graphite does to the nozzle?

I have made a 50/50 graphite/clay nozzle and fired it in a reducing environment so the graphite didn't oxidize and it worked, basically the same thing as a pencil lead. Anyway my I hope is that the graphite will help conduct heat into the nozzle and reduce the amount of thermal stress and hopefully limit or stop the cracking.

It is interesting to note that even though the nozzle is fired at temperatures too low to make graphite there will still be some bonding between carbon atoms so all of the strength of the nozzle won’t just come from the clay.

Last I want to test what will happen to a ceramic nozzle when using it with APCP. I know it will probably erode but I what I don't know is to what extent and if it is acceptable or not? I have seen rocket candy erode phenolic nozzles quite a bit and this is acceptable in the rocketry community, while rocket candy can't erode fired clay?

 

I think if you pressed the clay dry and then fired it you should be fine. It is true that the clay shrinks a little when you fire it but it isn’t that much when making small pieces. For example I would make a green nozzle and after it dried drill it out with a ¼” drill bit. After firing it the drill bit still slid through the throat with no problems and it seemed to be the exact same diameter as before. The clay shrinks way more when it dries so you have to take this into account if you are going to process it wet. If you are going to use paper tubes for your motors you could probably just epoxy them into place, but wouldn’t it be easier to use pressed bentonite?

[Varmint]

Col,

 

But the built in "barbs" would probably be good even without glue, I'm shooting for the ultimate "don't even think about it" bottom end.

 

The idea is, let's say the tube inner dia is exactly 0.750. The nozzle would be 0.765-0.775 (armchair estimates) so it actually displaces material and bites in.

 

I guess I'm trying to work in the middle, pyros want payloads up in the air via rocket or motar, and advanced rockettiers use mathematically perfect nozzle designs out of sometimes exotic materials that offer signifiant force multiplication. I figure if there was a way to get cost effective precision nozzles in "lower class" rockets then everyone wins.

 

One thing I need to do is improve my press. I currently use my 20 ton press (car bearings and such) but it has too much flex. If you want 6000 lbs, moving the handle also flexes the double I-Beam, so when things do move, there is a spring-type action that seems to overdrive the packing. On the other hand, my reloading press has essentially zero stretch, smooth as glass to achieve high pressures, while the shop press seems to "bump" into position on everything thanks to the spring effect I attempted to describe.

[Col]

The barbs may expand the tube as you push/press the nozzle in from the bottom. The expansion may compromise the tube integrity as its unlikely to return to the original size due to the barbs, It would probably hold if the tube closed back in behind the barbs but do you want to use a tube that springy for a high performance motor Pressed nozzles create the bulge in situ so the tube integrity below the nozzle isnt affected that much.

6000lbs is plenty for a 3/4" motor, its 13,500psi on the comp.

[Varmint]

OK, did a lot more forum scouring, and the word from the top (a moderator or two) in other threads made note of the dangers presented with nozzles being too durable.

 

That is to say, it is recognized as poor form to have nozzles that could endure a cato.

 

It makes perfect sense, out of all the combined dangers with what we do, why step up and add another to the mix by having a nozzle that could be forecfully ejected, representing somthing on terms with a bullet.

 

In that light, I'll stick with the proven clay nozzles, and won't even attempt the water glass variation either.

 

Thanks for the feedback, regardless.

 

DAS

[dagabu]

yup, that's about the long and short of it, durable but not unbreakable. No junk that cant be reabsorbed into the fields by getting wet or decay. You certainly can make nozzles that don't erode from clay and a bit of wax that will bite in hard enough to withstand a tube split.

 

Plus... Clay is cheaper and faster to boot.

 

One word about convergence and divergence, you can turn tooling to make any bell shape you want, find an efficient nozzle shape and have tooling turned to meet the shapes.

[Maserface]

Ive read that diatomaceous earth moistened with sodium silicate makes a nice rock hard nozzle, no personal experience though

[Zerohour]

You guys should try using some latex fortified tile grout. The stuff is amazing! It's full of adhesive and is super durable. Even though you need to wet it slightly, it does not contract AT ALL upon drying. Also, you can abuse the nozzle all you want and it doesn't ever crack or chip thanks to the latex. Put a little bit of oil or grease on the base of your spindle to keep the grout from trying to stick to your metal. If you decide to try it make sure you get the sanded variety (most common and cheaper). Let dry for at least 72 hours.