I’m actually working with Dave Hakkens, we would like to make our own aluminum models using a DIY rocket stove. So we could use these models to work with the injection machine.
Melting models by yourself is interesting for two main reasons : First because of the price. It is really expensive to get some CAD machines, or order these pieces from somewhere else whereas aluminum melting is a really cheap way to work, and it seems really easy.
In a second hand, we also would like to have a break with smooth industrial aspects. Making our own models with a rocket stove would allow us to create some textures, patterns, we couldn’t have with CAD process.
So this first post is about the rocket stove building :
I found many different ways to build a rocket stove, to melt aluminum it needs to go at least until 650°C.
These videos are good examples :
https://www.youtube.com/watch?v=VCZSR3CFn8U ( Models 2 & 3 )
https://www.youtube.com/watch?v=hHD10DjxM1g ( an easier and good model )
It is important to have a good isolation, to keep the heat inside, you can use :
refractory concrete and bricks
a mix between 35% plaster, 35 % sand and 30% water
sand ( we tried, it was all right )
As container you can take a bucket, a gas bottle just be sure that it is in steel and thick enough.
We also put a tube at the bottom of the stove to feed the fire with an hairdryer, it’s really POWERFUL !
It took us around 15 minutes to melt 25 cL of aluminum.
There was a kind of waste on the aluminium, that is why some tutorials advice to melt the aluminium in two times. The first one to make pure aluminium ingots (small ingots will melt faster) and the second one, when you use your ingots for your real castings !
That would be an other topic, coming soon !Toggle replies
2nd TEST, Casting aluminum to get the texture of another material
Before trying to cast some molds in aluminum, we try to cast samples in different materials to see how does the liquid aluminum react on it:
Steel seems to be the better one, it is the only material that didn’t make bubbles or exploded ! However, steel is even harder to work than aluminum so that doesn’t make sense… BUT we learned that the bubbles could also due because of the oxygene present in the air, maybe we could try with a mold closed, and only one hole to poor the aluminum.
So we decided to keep making some test with plaster, maybe some other metals softer than the steel but still with a high melting temperature. ALSO we decided to make some test with SAND often used in foundry, we are curious to see as much detail we could get with it …Toggle replies
3rd TEST sand and plaster molds for aluminum casting :
We made several tests to find the good sand making
100% dry silica sand ( sand from sea )
5-10% dry clay (bentonite clay is advised )
you can add 2% of wallpaper glue is your sand is not sticky enough.
Ensure your sand is well mixed !
We took an old phone to make our casting test. To make the sand mold, we made two wood frames with the same size. We put the phone in the first one, filled the frame layer by layer, compressing the sand between each layer. Between the two parts of the model we put some talcum powder, you can also put some in your model before, it will be easier to take it out.Toggle replies
The aluminum casting in the sand model was great, quite clean, but still not enough to make a clean mold
The plaster model still makes bubbles, and the shapes are note very… smooth..! Even if we dried it in an oven during several hours.
We learned that, during the casting, aluminum is making a lot of gas, the sand mold is able to absorb it whereas the plaster doesn’t … However plaster molds are often used in foundry, there must be a solution ! We will do another test, with two holes in the plaster mold, one for poor the metal, the other one for the gas…Toggle replies
Hello ! Here we are for some news about aluminium melting !
We kept making some tests with sand molds, we didn’t find some solutions for the plaster ( to many bubbles in the aluminum and impossible to get some smooth textures)
We bought some special foundry sand to compare with our DIY sand. The foundry sand is thinner than ours and it is also easier to keep it sticky ! We managed to get more details, even if you wait a day before casting into your mold, the sand is strong enough, it doesn’t get to dry. SO we decided to keep it to make our first aluminum mold for the injection machine !Toggle replies
Our Aluminum mold made from our rocket stove :
first I made a kind of bowl in clay, with smooth surface inside, edges and textures outside
Next I made a plaster mold of this. This plaster mold is in two parts. For each part of the plaster mold I took a print with the foundry sand. So I made a sand mold for each part of the plaster mold : two sand molds for one plaster mold so.
I have always wanted to have my own mini furnace to melt soda cans at home, but I don’t currently have enough room to safely build one.
Something I heard about bubbles in plaster molds, is that the only way to have a smooth mold is using a vibrator. That’s actually how dentists make your clay/plaster teeth molds, by pouring clay into a silicone/alginate mould and then placing it over a vibrator for a few minutes to remove bubbles, and the end result is perfectly smooth.
you guys rock! 🙂 We too had this planned.
here are a couple of interesting resources
I’m sure you are aware of Studio Swine’s Can City project
and some images of the products
Although it’s not related to aluminium casting, check out also the sea chair project 😉
This other project is awesome too: “Lost PLA Casting from 3D Prints”
which uses PLA 3D printed positive parts that are then employed like waxes in the thousands of years old “lost wax” technique (the heat of the metal sublimates the wax/PLA object
@lyricalpolymath @davehakkens @tafnstuff I have nothing important to add here but id really like to take a moment and appreciate the fact as to where we all are going with this forum/website. It no longer is limited to those 4 machines and is also highlighting different methods, different projects, different ideas and different causes. All of which may help someone or other in making this place better than we found it. Every now and then someone like @lyricalpolymath posts a link which teaches me something totally new and truly appreciate that.
Thanks Precious Plastic,
Howdy Ho !
Sorry of being so late ( i spent these last months without any single computer ).
This is the conclusion about the experimentation we did in October :
We finally managed to get our first aluminum handmade mold ! it looks exactly like the plaster one, from which we took the print. To easily connect it with the injection machine, we directly put a thread pitch into the sand so it got “stuck” in the aluminum. ( but after a few uses it came out … )
The special foundry sand allow us to keep almost all the details.
We also experienced that:
– you can use some polyester mastic ( Sinto ) to work on the aluminum, even at 200 °C, and after 10 casting, the mastic was Ok !
– you can put a bit of talcum powder inside your mold, it will be easier to take of your casting !
the last picture show you all the tries we did with different kind of plastic !Toggle replies
To reply to your questions #andyn , there is no discoloration with the polypropylene, in fact we put some yellow, orange and pink plastic in the same time expecting for funcky pattern..!
On the fird picture i put two température degre for each plastic, the first is the setting on the top of the injection tube, the second at the bottom, it has to be hoter.Toggle replies
Never tried, especially because it’s TOXIC !
I think that lead is too soft to do a mold with it, it might twists too easily ( when you try to take out your casting from the mold for instance :S ) i guess it depends the shape you want to make.
There are also silicones strong enough to cast aluminum and bronze into, didn’t try yet !Toggle replies
@traplocz That’s awesome
Did you have to add borax into the aluminum to remove the waste material? I’m looking forward to make one soon but haven’t decided if I should make it with sand and plaster or silica bricks.
Did you get a Graphite crucicle for yours as well?
@xxxolivierxxx No i did not use borax for my project and yes i used a graphite crucible. The waste material aka slag floats on top of the molten aluminum inside the crucible. I would pick up the slag and separate it from the crucible. Once the slag is out of the crucible, only molten aluminum should be left inside, and ready to pour.Toggle replies
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