Casting cement nozzles - the best quick set.

[Redrocketman]

Hi all, I'll try to keep it brief, as according to my wife, I'm getting " obsessed "!!

 

I make large, cored nozzle-less r candy motors, but wish to gain substantial performance increases due to casting my own nozzles. I'm making my convergent & divergent tooling, but need advice on a good, quick setting cement. I have cast some test nozzles using air set refractory cement, but 4 days later & there not near setting. I live in Australia, if anyone knows of a reliable type or mix available here, would be much appreciated

[OldMarine]

Is there a reason pressed clay nozzles wouldn't work? Durham's Water Putty sets fast and is castable.

[Redrocketman]

That's it!! Durhams or similar! The reason is I have had extensive trials using clay nozzles in "E" class motors, using a rather fast burning and aggressive recipe with about 40% C.A.T.O. Ratio all resulting in end plug or nozzle blowouts. ( in the test chamber of course! ) I even took nozzle out to 38% of grain dia, Though I'm yet to try a more moderate fuel, been a bit busy.

 

The reason I want to concrete/ putty is to get optimal convergent and divergent angles, hopefully resulting in supersonic exhaust. My dies are hand cast out of lead, and pouring cement solution and gaining optimal grip to the nozzle chamber this just seems logical.

 

Divergent throat will be cast 1st, when set to touch, a centred washer of the desired throat diameter will be inserted to help prevent throat erosion. Then convergent cone will be cast in. Lastly throat will be centeraly drilled out. Make sense??

 

I want to keep with my own hot fuel for these late "J" and " I" class motors, and with my thrust meter nearing completion, can't wait to get some results to share. . p.s, thanks for the advice u know who!!

[Mixer]

CaSO₄

[kramrocket]

Hi all, I'll try to keep it brief, as according to my wife, I'm getting " obsessed "!!

 

I make large, cored nozzle-less r candy motors, but wish to gain substantial performance increases due to casting my own nozzles. I'm making my convergent & divergent tooling, but need advice on a good, quick setting cement. I have cast some test nozzles using air set refractory cement, but 4 days later & there not near setting. I live in Australia, if anyone knows of a reliable type or mix available here, would be much appreciated

 

I reckon pressing a much drier form of what you are using would be better... less shrinkage and drying time... but you will need the press and tooling.

 

Slowly dry it in your oven while continually mashing it around every so often in a mortar and pestle until it's nearly dry, then press the hell out of it and you will find it takes much less time to harden.

[dagabu]

Red Rocket,

 

Perhaps form the throat when forming the convergent/divergent? I have attached an endburner tooling, nozzle former for you to look at. This is perhaps the single most used design for casting preformed nozzles I have seen. The design is simplicity at its finest and you only need a drill press to make the former but I do suggest you use delrin or nylon instead of wood.

 

As you can see, the throat length is completely adjustable and is as smooth as you make it. The washer as well can be placed on the tooling after the divergent is somewhat compacted. Better yet, why not use two?

 

[Redrocketman]

That's better than mine, having threaded rod with both cones tapped out, giving the added step of having to clean out the leftover thread in the throat. Though still adjustable, I like that idea of simple slide fit. Thanks!!

[dagabu]

Also, keep in mind that Durhams Water Putty will not bite into the motor tube walls, there are about 100 different ways of anchoring it in the tube. They are easy to blow out!

[Redrocketman]

Please don't worry about my anchoring technique. I dill out 6 equally spaced holes in the coupling ( to allow cement to anchor into), plus dimple the inside of the nozzle casing with a fine tip soldering iron. Tho I am now going to use couplings with one side threaded so the diversion cone has even more to anchor to. There is a collar inside, which acts to seat the erosion washer, & anchor the convergent cone. This has resolved my issue with high pressure "E" class motors , which I was having nearly constant plug blowouts, using pressed bentonite.

Thanks again, and I will let you know how things go

 

P.S. I'm off to the machine shop to have my new tooling turned up. I'm just being lazy, but what are the ideal convergent & divergent angles? I think I'm way off but I thought convergent angle : 16deg, divergent angle aroun 65deg?? I'll check that again!!

[Redrocketman]

I have since researched, and found 60deg to be a more appropriate divergent angle.