Ceramic/Porcelain Nozzles

[edwardw]

Okay, I have no experience with either of these materials, ceramic or Porcelain, but I do know that they are very heat resistant. My main question is this:

Can I pour/pack the material into a mold and harden it. Then put it on a lathe like a graphite nozzle and machine it. Then I would glaze and fire it again.

Is this feasible?

Edward

 

[Ryan S.]

sounds like an interesting idea, If your going to go through all the trouble I would use graphite.

ceramic is really really fragile and I would think the glaze might begin to burn off of the clay pretty fast

 

[edwardw]

Graphite is also really fragile - it has a very low shear strength and erodes quite nicely. The glaze they put on ceramic is actually a layer of glass. I have never seen it burn off - even with an oxygen/acetelyne torch. The reason I want to do this is that cermaic is way cheaper than graphite. I have a shop here who sells the powder for $20 a 50lb bag. That would be a lot of nozzles.

My main concern is machining it - I can probably find a way to pack/pour it but I want to know if I could machine it or if I would have to create a mold. I have seen them slip cast parts in plaster of paris. I could use a graphite nozzle as a model and then cast plaster around that and then the ceramic/porcelain, but I would rather just have a blank and machine it.

Edward

 

[Ryan S.]

I know, you paint the glaze on and in the Kiln the glass melts to form a shiny layer. You might be able to cast a grain, then sand out the clay (I have done this before on projects that were imperfect) then glaze and fire the nozzle.

If I remember things correctly, you cannot fire anything more than like an inch and a half thick, any more and your work will probably explode due to built up pressure. I have actually seen (well saw what went in and what came out) what happens when you put something in too thick, it explodes, and if you have any other nozzles being fired at the same time, they will probably get destroyed too. So I guess it would work as long as you ddont get too big

 

[MarkABrown]

I remember while growing up that my mother used to make stuff out of ceramics. If I remember correctly, you usually fire ceramics in 2 steps. The first step gets it to what they call the "green" state. At this point you can still work with the material. Its hard and brittle but you can scrape off the flashing and shape it with a sharp knife. You may be able to machine it while its still green. Afterwards, you paint on the glaze and fire it again to get the piece to its final hardness. I doubt you could machine it after it has been glazed.

Take what I said with a grain of salt. Its been over 25 years since my mother made anything with ceramics and my memory's warranty ran out after 15!

 

[Micromeister]

Both material are clays, fineness of the grain determines the density and hardness. True Porcelain is actually Glass frit ground very fine, suspended in water for application to "enameling Iron" a very low carbon steel than fired at 1800 to 2000 degrees. It also could be poured into a mold before firing to obtain the Nozzle shape.
Most of the Hi Temp Ceramics and Porcelains don't do well in after fire machining. They are also very prone to damage for impact.
Hope this helps some

 

[DavRedf]

I think you would be better moulding the nozzles as in the green state it is very fragile and I dont know how you would fix it in the machine to turn it to shape without damaging it.

I f I remember my pottery lessons correctly, it has been more years than I care to remember, there are tools that will machine ceramic/porcelain in it first fired state. I think they are tungstan carbide or diamond.

Hope this is of help.

David

 

[edwardw]

Today I am going to made a mold of a graphite nozzle I have. The mold will be plaster of paris. I'm going to make it a two piece mold. Either way I mold it I'm running into some problems. If I lay it flat on it's side and just pour halfway, then some plaster of paris is trapped in the convergent and divergent sections and I won't get the nozzle out. On the other hand if I sit it rightside up and pour, the convergent/divergent cones are okay but now the o-ring grooves are trapped. I'm thinking covering the o-ring grooves and getting the convergent/divergent since this is more material and if I had to alter it in the green state the o-ring grooves are less material to take out. Anyone good at molds? I have done some before but not complex shapes.


Edward

 

[nOrM]

go to https://www.mcmaster.com and search for ceramic. Many are listed that are machinable via standard or diamond tools. The prices on some of them however, may make you wan to use graphite.

 

[Micromeister]

I think the materal could be poured and removed from the molds as greenware, with the nozzle bell molded in, While ceramics shrink slightly during firing, if the nozzles were fired to bisque then the throat might be drilled with tungsten-carbide dremel type mill end cutters. breakage during milling would be pretty high but is doable. The Family had a ceramics shop for awhile, Toyed with the stuff a good while until the business was sold. Some of the higher temp ceramics fire at 2500 to 5000 degrees, some of the porcelains even hotter... very difficult in most Hobbist type kilns.

 

[Loki]

Originally posted by edwardw
Graphite is also really fragile - it has a very low shear strength and erodes quite nicely. The glaze they put on ceramic is actually a layer of glass. I have never seen it burn off - even with an oxygen/acetelyne torch. The reason I want to do this is that cermaic is way cheaper than graphite. I have a shop here who sells the powder for $20 a 50lb bag. That would be a lot of nozzles.

My main concern is machining it - I can probably find a way to pack/pour it but I want to know if I could machine it or if I would have to create a mold. I have seen them slip cast parts in plaster of paris. I could use a graphite nozzle as a model and then cast plaster around that and then the ceramic/porcelain, but I would rather just have a blank and machine it.

Edward

Ed -

I've been down this road for the same reasons you are considering it. Let me save you some trouble, don't bother. Here's a few of the reasons that it doesn't work.

Ceramics, even with a good glaze erode badly.

Ceramics are nearly impossible to machine after they've been fired and they dust from machined ceramic will reduce your lathe to junk in a short time.

You can't machine it before you fire it, as it will crumble and chip badly.

Ceramics shrink when fired making it difficult to hold tight tolorences.

Ceramic nozzles work ok, if you use a graphite insert for the throat, but then you are back to using graphite.

I don't know where you got the idea that graphite erodes badly. It doesn't. I have graphite nozzles around the shop that have dozens of firings on them with no measurable erosion. There is some erosion with high chamber pressures and high metal propellants, but even then they are fine for several firings, much more than I was ever able to achieve with ceramics.

Graphite is great stuff for nozzles, and if you shop around it's probably not as expensive as you think. The biggest evil (and it's a big one) is that graphite is horribly messy to work with.

 

[rocwizard]

How about aluminum nozzles? Sort of like the ones used by (dare i say it?!) U.S. Rockets. I know they have graphite inserts. Are there any advantages/diadvantages with these? Erosion a problem?


Jeff, you might be able to help me with this question. I was thinking about using titanium for special purpose motors. The only thing i am unsure about is whether or not titanium would fragment (Shrapnel anyone?) like steel if overpressurized, or would it just banana peel like aluminum? If fragmenting isn't a problem, It would be very cool to be able to run motors beyond the limits that aluminum puts on most EX ventures. Obviously a severe price premium exists, but if one wants to run chamber pressures say 1000+ psi, or mix up an O20,000 per se, well you know...:kill:

Ramble mode off now

 

[edwardw]

In TRA Rules you can't made the nozzles out of metal...only the parts that hold it in can be metal. If I could do metal nozzles I would make them of steel and put a nice divergent cone on there - ala Richard Nakka.

The MX Peackeeper I believe runs at a PSI of 750, not a whole lot.

But I wil be using graphite - and going home all grey.


If you had your own land and wanted to pull a waiver you ***could*** made a casing out of steel. Just stay away in a bunker. You do pay a penatly of weight. But it would hold your pressure. This is an idea - don't go CATOing a steel casing unless you want your new nickname to be Peg Head.


Edward

 

[bobkrech]

Hey Guys. Don't reinvent the nozzle. There's a lot of information on nozzle design and construction online. Do a google search to find it. Also Sutton's book has a wealth of info on nozzle materials.

Here's a short summary.

1.) Estes nozzles are made of a clay something like Durhams Rock Hard Water Putty, an extremely inexpensive and heat resistant cold curing rocket nozzle material. Just add water then cast into your desired shape. Can be machined after cure. It's ok for BP and sugar, but APCP will erode it.

1 pound can - $6.00
4 pound can - $14.00

https://www.aeroconsystems.com/misc/motor_making.htm#Durhams

2.) Aerotech uses an injection molded thermoplastic glass-phenolic resin. It erodes, but you can characterize the erosion, and make the grain burn progressively to account for it.

Injection molding is too expensive for amateurs, but the commercial ones are available cheap. You can get them and all Aerotech hardware from https://www.rocketmotorparts.com/ for a few bucks apiece.

3.) Animal Motor Works, Kosden, Loki Research and others use graphite. Graphite is tough stuff, and is probably the cheapest, best and simplest stuff to make HP nozzles from. You can get 10's of flights from a graphite nozzle if you don't drop it the wrong way. As Jeff said, the only downside it that it makes a mess when you turn it on a lathe. If you set up a shop vac with a good filter and suck off the dust as you make it, you don't have much to clean up.

ATJ grade is the best, but the EDM grade is ok. Look for small grain sizes for the best results.

check out https://www.mcmaster.com/ page 3355 for info on graphite

https://www.aeroconsystems.com/graphite/index.htm

4.) If you really want a stable castable ceramics check out pg 3352 from mcmaster. This stuff is expensive but it is simple to use. You simply machine an UHMW polyethylene mold in the final shape you need, spray the mold with mold release or PAM, mix the ceramic powder with the liquid, pour the pase into the mold, wait 24 hours, and voila you have a ceramic nozzle. You want to fire it to get maximum strength and toughness, however it won't be as good as graphite.

https://www.cotronics.com/ supplies the stuff to mcmaster.

5.) Forget the machinable ceramics. If you can't machine graphite, you won't be able to machine ceramics.

6.) Aluminum looses all strength at 300C. It will fail in a nozzle in a second or less. Most readily machinable metals such as brass (will melt) or steel (will erode) won't last long. Even if you could machine titanium (which you probably can't), it will burn up. The only viable metals for nozzles are tungsten and a few other refractory metals which are unaffordable and unmachinable to amateurs.

7) Finally, if you're going to make you own motors, the cheapest way to go about it is to buy standard hardware and supplies from places like Loki Research (Jeff's company), Aerocon, Animal Motor Works, etc. You're fooling yourself if you think you can make this stuff for less in quantities of 1 or 2.

https://lokiresearch.com/products.asp

https://www.aeroconsystems.com/motors/diy.htm

https://www.animalmotorworks.com/hardware01.htm

Bob Krech

 

[Tools R Us]

Other than being compressed filth, graphite is the best. Another good source is the Graphite Store;

https://www.graphitestore.com/index.asp

 

[edwardw]

I have used Durhams - at higher pressures >500psi it erodes a lot in my experience.
I know that intially it isn't cheaper to make your own casings, but I have a lathe and the aluminum cost me $30 and the graphite I have is $20. For $50 I can make two 2" x 24" long casings. I roll my own liners (Apogee has a tutorial on it) and I'm happy. I would rather turn my own to as I like to make stuff. For me, it is cheaper to buy the raw materials and make them than buy them commercially. My fiance also likes that I'm saving some money making them.

 

[LBarron]

I know this thread is several months old but I just want to thank you guys, especially bobkrech, for posting and providing such helpful information. I've been struggling with an am/ex liquid fuel motor project for quite some time, primarily preventing the darn thing from melting after about 5 seconds, and the info I found here has led to success.

I used the zirconium oxide compound from McMaster-Carr to line the inside of a copper combustion chamber, as well as to make the exit nozzle and convergence section of the c.c. It is easy to use, cures in a day and has worked perfectly. It gets charred up a bit but so far has not chipped or broken apart at all.

I tried to attach a short mgeg of our test fire today but it's too large a file. If anyone cares to see it or knows how to include it, let me know.

Cheers, and thanks everyone for chipping in.

Leland