Aluminium Foundry

This is my second Ible of my homemade foundry. My first one was my :
Mini Charcoal Furnace.

In  this instructable I will explain how I made my second bigger foundry yet again mostly constructed from scrap I collected and recycled it into something more usefull.
The biggest advantage of this design is that it has a very strong body made from an empty gas cylinder and the best part is that it will last for a long time, the only thing that might have to be changed or repaired is the inside refractory.
 As I wrote on my last ible my aim is to create some aluminium sand casting of differrent objects.
At this stage I piled my aluminum ingots and did a few experiments with my foundry, some successful others went wrong which I have learned from. It is really exciting to create some new aluminium object knowing what it was in its former "life" cycle.
I will also try and explain a little bit about sand casting to my knowledge.
I am no expert it is all based on my hobby experience so I  hope you enjoy it.

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A few Saftey words: Coming  into contact with fire and boiling melted metal can be very dangerous so always work safe using proper full body protection including respirator mask against toxic fumes and dust from mixing refractory materials. Never melt in a wet area or near water, if water comes into contact with the boiling aluminium it might "blow" in your direction.
The info in this instructable is based on my experience. 
I disclaim any responsibility for any resulting damage, injury, or expense.
All use by you of this website is at your own risk, work safe.
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First I made sure the cylinder is empty then I drilled 2 holes. One hole to fill the cylinder with water the other as an air hole which also makes it easier to empty the water and to fill it again. After all the gas is gone I marked where I want to cut and used my small grinder for that job. When I cut the cylinder I had it full of water, just to be on the safe side. It took me less then 10min to cut the cylinder handle, top nozzle and cylinder top including grinding the rough bits of metal. It is a good idea to mark lines over cutting so later on when welding the lid will fit well.
When using a grinder it is recommended you wear eye and ears protection.


If you dont know what you are doing take it to a professional. Mis-use of pressured gas cylinders can cause injury and even fatalities.
This not an instruction or a guide how to do it, I am sharing with you how I used a gas cylinder based on my own experience and knowledge.
Anyone who attempts this he/she will do it on their own risk 
I will not be liable for any injuries in anyway.

I cut the inlet air hole and welded 2.5" pipe in an angle so the air will swivel and create more heat in the center. I kept the pipe 2" inside that will be the thickness of the refractory in the furnace. I found my welding magnets very usefull for holding the pipe in place. After getting all my welding gear ready the pipe was perfectly welded into place. Small tip: when placing the cylinder on the side place 2 wood battens under it to prevent it from rolling aside when using the grinder on it.

Next thing I made was the hinge system for the furnace lid. I used 20x20mm box iron from scrap metal I kept for a "rainy day". I used my drill press for accurate 10mm holes. The 2 box iron that I welded to the lid I made longer to act as stopper preventing the lid from falling back. Before welding I set the lid in the correct position using the blue mark as guide. After the lid was in place I secured it with large welding magnets and welded the hinge into place. I am very happy with the result and the hinge is very strong and sturdy. After finishing with the hinge I cut the outlet hole on the top of the furnace.

Sometimes the refractory shrinks or moves so in order to keep it in place I used metal screws all around the furnace body and lid part.

At this stage the foundry is almost ready for the refractory stage. I used a plastic can of paint with a bit of extra cardboard on top to form the inner furnace core leaving 2" space around for the refractory. For the lid I used some cardboard pipe from an empty gravy box to form the oulet lid hole. The refractory I used is ready made fire cement it comes in a big 25kg bag, all that is needed is to add a bit of water. I started mixing it using a very small amount of water until I got sticky paste. Too much water is bad for any refractory. On the internet many home made refractorys are combined of Perlite (cruashed)+cement+silica sand and fireclay. Good refractory means good insulation, good insulation keeps the needed high temperature in the furnace. I started filling the furnace from the base ramming the refractory all the time with a timber block to get all the air bubbles out, then I placed the plastic core into position and filled it all the way up with refractory keeping 2" width and after that filled the lid.

Every type of refractory has its own curing time and manufacture guidelines. If refractory is not cured properly it might crack under high temperature. The type of refractory I used had to be cured by lighting the foundry for a few hours keeping the tempature at 100°C, this type of refractory is good for up to 1200°C (cured). After refractory was cured I lit the foundry first time with charcoal and after one hour when the tempature was over 1000°C. I placed my hand on the outerside of the furnace and it just felt warm, that was a good sign that the refractory is doing its insulating part by keeping the heat inside the furnace.
After the furance body was cured I welded handles for the furnace lid and welded 4 support washers to hold the refractory in the lid.

The foundry was ready for action at this stage but I found moving it quite a task with all that heavy refractory. So I welded handles from 5mm rebars I took from my first furnace broken lid. After that I made a small trolley for the furnace made out of scrap metal from a hand trolley with 2 good wheels that I found in a rubbish skip. To close the outlet hole I welded the metal I cut from the cylinder top to a hinge and part of a bathroom hook as a handle.

When we look around we can see aluminum all over the place molded into different objects that we use daily. I took a few photo's of the aluminum parts I used in my foundry and turned them into aluminum ingots that will be used again when I will start my sand casting. I also separate the aluminum alloys and mark on the ingots what object it was before. In my images I melted a nut cracker, lock parts, cooker parts, door handles, tap handles, tripod legs, scooter parts (choped to fit the crucible), aluminun brackets, toy car, glasses stand, toilet hinges, wine bottle cork and ladder parts.

Now its time for some melting, My furnace is HUNGRYso it's time to feed it with some aluminum. I collected some aluminum from my house, some unused items.
I made some tools for my old furnace and they are still good for this one. To get rid of the dross I used a big spoon with holes as a dross skimmer. I'm starting my first melt with charcoals and in the near future I hope to make a waste oil burner.
After the charcoals where red I checked the temp with my multimiter and it showed over 1000�igh temperature.
 My first successful melt were parts of an aluminum ladder, I used my muffin tray to cast the aluminum ingot.
The second time I used the pot it broke under the heat and all the molten aluminumn spilled out. Not too bad news It could have  been much worse if it happend when I lifted the crucible.

Now I just have to chop the chunks of aluminum and throw them back into a new and much thicker cruicible made from metal pipe and steel plate.
This is a short clip of my furnace in full action...

After making a good foundry (still working with charcoals) and after making a strong crucible that is not failing after a couple of uses it is time for my first aluminum sand casting.
I started experimenting with sea sand casting which wasn't very successfull so I decided I wanted a good quality mold so I purchsed a 25KG bag of PETROBOND and I have to say it is super for aluminum casting.  It was a bit expensive but I will reuse it many times.
I made a simple Flask for the sand mold made from timber.
I was delighted with my first ever aluminum Star Trek Federation Insignia that I duplicated from a custom plastic resin kit I bought a few years ago.

For more info and links to Metal / Sand casting I made a new blog and everyone is welcome to have a look:
 http://flamingfurnace.blogspot.com/