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Aluminum Rocket Engine - 3D printed - It's possible?


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#1 PHI

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Posted 18 November 2020 - 10:09 AM

Hi,

I was using pvc rocket engines with a a concrete noozle, as explains Richard nakka.

But now, I have a 3d printer, and I want to print a rocket engine(de laval nozzle included), and later use this PLA engine to make a mold and melt aluminum (I will melt aluminum from cans).

I need to know a two thigs:
1. It's this possible to melt aluminum and use a 3d pieze (immersed in cast) as mold. When hot aluminum touch PLA, the plastic burns and the aluminum occupy the space, creating the engine and the noozle.

2. I need to calculate firs the max pressure that muy engine can support, because I can calculate the max pressure than the engine will produce (using burnsim or open rocket) but I need to know how must be the wall thinness of the engine in order to support this pressure. How I can calculate this?

#2 Arthur

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Posted 18 November 2020 - 01:26 PM

First cans are a source of a reasonably pure aluminium, a rocket body may well need to be a good alloy.

 

Second why not model a motor and make a two part mould with cope and core in the usual way and have the pattern removed and hence reusable and no PLA fumes.

 

Beware that cast aluminium is often porous and may vent gas sideways

 

Note that aluminium is a poor material for a nozzle -it simply erodes until it melts away. 



#3 Jeffdyjeff

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Posted 06 December 2020 - 09:11 PM

I think a casting might be kind of scary. The metal grain structure is like salt clumped together. Also, plastic might be too dense to be boiled off and replaced by aluminum, especially in tight spaces. Foam would be good, but if youre investment casting anyway just do as they do with aircraft parts: melt the plastic out of the mold before pouring aluminum.
Also, not sure where you live or what laws are like but I searched "solvent traps" on aliexpress and found what are basically unfinished silencers, but work great as motor cases!

#4 SeaMonkey

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Posted 07 December 2020 - 07:54 PM

There are a number of YouTube videos which demonstrate how to make a

Mold for Aluminum Casting and how the casting is done.

 

Search "Mold for aluminum casting."

 

Learning Aluminum Casting would be a valuable skill.

 

I use the DuckDuckGo Search Engine.  Here is their result.



#5 Crazy Swede

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Posted 08 December 2020 - 04:37 AM

Nozzles made by aluminium erode very quickly!



#6 MadMat

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Posted 08 December 2020 - 12:16 PM

Among the problems already listed, you also have a problem with the gases that will be evolved when the molten aluminum hits the PLA, not to mention how do you plan on getting the molten PLA out of the mold? What you are describing is a sort of "lost wax" casting process. This is used very often in the jewelry making industry. the thing is, the wax model or "pattern" is melted out of the mold before the molten metal is poured. Your idea is going to create a very porous casting from the escaping gas and molten plastic. I don't want to discourage you but I truly feel this won't work. Seriously, if you want to try casting a rocket casing, you would be better off carving a pattern out of wax, attaching a sprue (a rod of wax that gives you access to the pattern in the wax) to your pattern, submersing your pattern in plaster of paris. Once the plaster is hardened, put your mold, upside down in a HOT oven and allow the molten wax to pour out of the sprue hole. Then you can pour your molten aluminum immediately into the hot mold and recover your casting by simply immersing the plaster in water and scrubbing it clean. You  have to be aware that this is only a one shot deal. You must also be aware that molten metal has a very high surface tension and will not readily flow into fine detail in a mold without either centrifugal force or a vacuum forcing the metal into the mold (my sister is a jeweler, which is why I know about this stuff). the fact that you thought of this in the first place means you ARE thinking.... Keep it up


Edited by MadMat, 08 December 2020 - 12:32 PM.


#7 SeaMonkey

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Posted 08 December 2020 - 11:38 PM

Machined Aluminum Rocket Motor Casings (re-useable) are available in the U.S.A. in a variety of sizes.

 

It should be possible to make suitably sized "Fuel Grains" to fit the casings.

 

Has anyone had experience with such devices or perhaps know how to use them?

 

There are quite a number of videos available for view on making and launching Rockets.

 

 

This video is all about Reloadable Rocket Motors.


Edited by SeaMonkey, 09 December 2020 - 12:02 AM.


#8 MadMat

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Posted 09 December 2020 - 01:22 PM

Machined Aluminum Rocket Motor Casings (re-useable) are available in the U.S.A. in a variety of sizes.

 

It should be possible to make suitably sized "Fuel Grains" to fit the casings.

 

Has anyone had experience with such devices or perhaps know how to use them?

 

There are quite a number of videos available for view on making and launching Rockets.

 

 

This video is all about Reloadable Rocket Motors.

I believe Stix would be the guy to talk to about that. He does reloadable aluminum rockets



#9 jamesj01

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Posted 11 January 2021 - 07:21 AM

Nozzles made by aluminium erode very quickly!

very true!



#10 RayRocha

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Posted 12 January 2021 - 08:23 PM

I have casted quite a few things with patterns made using a 3d printer. the easiest way is to use green sand casting and make a split pattern that puzzles together with the 3d printer. budget casting supply has a lot of inexpensive tooling to accomplish this including petrobond as the green sand. to get started you can melt the cans in a coffee can in a hole in the ground with charcoal and a hairdryer. I must warn you that once you get started you wont stop and soon you will have an electric temperature controlled furnace before you know it. 

 

you can cast a bulkhead that you can line with graphite/clay to form the nozzle if you are worried about the aluminum eroding. 



#11 Arthur

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Posted 13 January 2021 - 01:42 PM

One of the machinable, heat resistant, erosion resistant materials is graphite. Take a block of graphite machine the correct (for your design) nozzle form and fix it in a tube using heat resistant epoxy.   Formerly a Bakelite mix was used but the heat resistance was given by the asbestos wool included. Now it's naughty to machine asbestos loaded plastics to make asbestos loaded dust.






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