Recommendations for Rocket Nozzles

[jmshiloh]

I'm part of a group of hobbiests who make ther own model rocket engines. We have been using graphite for nozzles. It is quite expensive and needs to be machined.

I found a material from Contronics in NJ called Rescor 770. It is a 2 part (powder and activator/resin) castable silicon carbide ceramic. It is lower in cost than graphite and moldable at room temperature as well. However, it is still too expensive at about $10 per pound.

Does anyone have a recommendation for a suitable castable ceramic of either tungston or silicone carbide. The material will have to be castable at room temperature, However, post curing at elevated temperatures is OK (hopefully not at kiln levels).

We have tried pourstone concrete anchoring material and it works fairly well. However, it erodes and degrades motor performance. The actual working pressure in an engine can exceed 1000-2000psi.

Tha actual nozzle is 2" in diamter X 2" long and is held in the motor casing by a snap ring around the front face of the nozzle. Combustion gas temeratures can exceed 3500C for periods of 10 seconds or less.

 

[Chatterjee]

Dear JmSiloh,
The combustion gas temperature and the pressure as stated by you may not sustain Silicon carbide type materials.Have you tried glass ceramics.There are machinable glass ceramics where the extent of crystallization can be controlled to give required strength and refractoriness against heat. Other wise the best is boron nitride.It is a new age ceramic having high temperature resistence and strength .However I do not have an idea whether you can cast it.
Hope this is useful to you.

 

[Ceramicguy]

Tungsten and silicon carbide are fairly expensive materials when measured against hobbyist applications. Additionally, tungsten carbide is heavy which can be a major penalty especially if you're trying to see who can go higher. Two other possibilities I suggest you try are alumina fiber castables or fused silica castables. I'm not sure they will survive your extreme environment so you'll need to test making sure you're in a safe area when you run the testing. The fused silica is light, and thermal shock resistant. It will probably have a tendency to erode but the low thermal conductivity and expansion may aid you here since the burn time is 10 seconds or less. Internal pressures may also be a problem causing the silica to crack. (As a side note I generally don't recommend internally pressurized ceramics above 1 atmosphere over ambient pressure due to the risk of catastrophic failure. The alumina is not especially thermal shock resistant although the fiber type castable will significantly improve the characteristic. It is heavier, more refractory, stronger, more erosion resistant than the fused silica. Again, test it with care. Multiple tests are advisable.
A possible source for the fused silica is Ceradyne Thermo Materials in Scottdale, Georgia. They have a Netshape 900 material that may meet your needs. A source for the alumina fiber castable is Zircar Products in Florida, New York. You read that right, Florida is the town, New York is the state. Good luck with the search and be careful out there.

 

[JimMetalsCeramics]

Try Cotronics or Aremco.