NOZZLE CLAYS AND COMPOSITIONS
I am going to attempt to break down what I know about nozzle clay. I am learning and documenting what I learn here as I go.
The first attempts at rockets I built, inspired by David Sleeter's five cent sugar rocket, I used Durham's rock hard water putty. While this works fine for small bore rockets, it is no surprise even a 5/8 in diameter rocket will blow the ends out if used in this way. I had heard of people ramming or pressing kitty litter and other forms of clay but I didn't see how a pressed powder could be as strong as a plaster. Well it is , and much stronger in fact. For one simple reason, the density it is rammed and the fact it swells up, deforming itself into the walls of the paper tube. I had some roman candles that where burnt up in my garage. I decided to experiment with clay so I crushed the clay in them and extracted it into a pile. It was a deep red and oily in appearance. I poured it into a tube and rammed it with a mallet. Much to my surprise it turned into a nice hard plug, not what I would have expected. This was the moment I realized that ALL black powder rockets should have a rammed or pressed clay plug.
Next I put some generic clay kitty litter into a food processor (warning it will ruin a food processor) and baked the resulting powder in my over at 350 for half an hour mixing in some melted paraffin wax. This was the defining moment in my rocketry hobby. Had I not used this mixture my rockets never would have worked. Up until then only about 2 in 30 rockets I made flew, even using a weak black powder. After I switched to ramming my nozzles with clay and paraffin about 8 in 10 flew, even using full strength black powder. This began my ongoing study on perfecting nozzle clay.
Any comments/suggestions/corrections ,email: perihelionvfx@gmail.com
Links to pages with more info
RAW MATERIALS
List of materials I have used for nozzle Clay. I am still experimenting.
Durhham's Rock Hard Water Putty - water based plaster. good for small rockets up to 1/2 inch
Graphite - haven't tested yet, according to Wolter, this additive helps the spindle come out better after pressing, a real problem in rocketry
Carbospheres - (from FireFox ) Helps lighten the weight of the nozzle, adds heat resistance, and helps with spindle removal
Bentonite - plastic clay, shrinks heavily , use as a binder
Kyantie - ( link ) strong refractory, high temperature resistance. I have not tested this yet.
FireClay - generic clay , use as a filler
Ceramic Clay - ??? Is this the same as fireclay? I need more info .
Grog - Grog is clay that has been fired and crushed, resulting in a it more heat proof nozzle.
Skylighter grog - the grog from skylighter is very gritty, I screened mine
Georgies Grog - If you live in Eugene Oregon there is a great ceramics store called Georgies that carries tons of clays and even some usefull chemicals.
I found some fine mesh grog there. It is so fine I add some sharp sand to my mixture to rough it up a little.
Sharp Sand - used in sand blasting, seems to add heat resistance, cuts into the tube while pressing and forms an angular matrix in the medium
Kitty Litter - get the cheapest most generic, it should only have one ingredient -clay
Cement - there seems to be many types of cement. I have a can of "crack sealing water cement" I have not tested this yet.
Plaster of Paris - Untested
SOLVENTS/LUBRICANTS
Acetone/Water - My standard solvent is 90% acetone and 10% water. I use this for both fuel (with red gum binder) and nozzles
Acetone - I had the idea to use a chemical solvent instead of heating the wax to melt it, I have not tried this but it should work, perhaps better
Floor Wax - untested
Parafin - normal old wax buy it at a grocery store or some ceramics places
BINDERS
Dextrin - seems to add strength to water based mixtures
Red Gum - untested for nozzles, seems to work to make propellant into a grain. Dry for 24 hours.
Gum Arabic - untested
RECIPES
Standard Nozzle Mix
(From the Teleflit rocket book . I dont have the book in front of me, I will add the amounts later. Go buy the book if you at all interested in home made rocket engines.)
?-FireClay (georgie's CH450 )
?-Grog (Georgie's finest mesh available)
?-Parafin
I make it with fine mesh fireclay and grog from Georgies ceramic shop in town here.
Mix the powders thouroughly (wear a dust mask!) put them in a baking pan and bake in the oven at 350 for a half hour, stiring every ten minutes. Melt the parafin in a pan and pour it in
stiring with a fork. Do it outside, it will be messy. This clay will be an off yellow, tan color. It is very fine mesh so it should only be used for rockets up to 5/8 in diameter. To use it for bigger rockets
add some coarse material to rough it up. Sharp sand seems to work well for this purpose.
I use this mix dry , but moistening it a LITTLE may increase the strength.
Variation with Carbospheres
95% - standard nozzle mix
5%-carbospheres ( I add carbospheres to make it more heat resistant)
Nozzle Clay Test #3 (for high temp, large bore Rockets)
200 g - Standard Nozzzle Mix
80 g - Sharp Sand
5 g - Dextrin
10g CarboSpheres * if not in the standard mix already
Mixes with Dextrin are to be moistend with a LITTLE water. The powders can be used dry but I think a LITTLE water will stengthen the resulting nozzle. Dry for 24 hours.