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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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Step 1: Cutting the gas Cylinder

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
.

Step 2: Inlet air hole

Picture of Inlet air hole
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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.

Step 3: Lid Hinges

Picture of Lid Hinges
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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.

Step 4: Refractory Support

Picture of Refractory Support
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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.

Step 5: Refractory

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.

Step 6: First time lighting the foundry

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.

Step 7: Foundry Trolley

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.

Step 8: Aluminum is everywhere

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.

Step 9: Foundry tools, Ingots and clip.

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...

Step 10: My First Aluminum Sand Casting

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/
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stansell1 month ago

Hello! Brilliant instructable, but i'm having some trouble understanding the final section about sand casting.

How did you get from the 5th to 6th photo? they seem to be very different. Also the 7th to 8th photo seems very different - how do you get from one to the other?

Kevanf14 years ago
Excellent ible. Trouble is, now I don't know whether I want to make a stove for my workshop or a furnace suing the old gas bottle I have :)

I have a question if I may? Do you have any problems with the surface of your castings? I need to make some aluminium moulds (for pouring molten lead into for fishing weights) but they really have to be nice and smooth. Any ideas how I can achieve this?

Take care.

Kevan
NutandBolt (author)  Kevanf14 years ago
Thank you I am happy you liked my ible. The best way to decide is which one will be more useful in the long run. Most of my  castings are very good. I had of course some casting gone wrong but usually the reason is running out of aluminum, bad mould construction, porosity (small gas deefects, air holes) or just doing some experiments. I am using petrobond sand for my moulds and it's great sand to work with and to get very high quality finish.
You are welcomed to visit my blog I have a few projects using sand casting. I believe you can get very good results using this type of sand and you can make a mould for many fishing weights in one pour.
Just one thing and this is up to you to decide, I wouldn't melt any lead at all,  Lead is a poisonous metal and can cause serious health problems especially among children. Link:
Lead health effects
 If you have any questions I will be happy to answer thanks again.
You would have to heat lead up to an insanely high temperature (3180F!) to have any dangerous effects from casting it. Just don't eat it and wash your hands.
I have to tend to agree with 'klincecum' here, sorry 'NutandBolt'. Most people who cast lead fishing weights do tend to do it outdoors or at least with very good ventilation anyway. So there's no real health concerns with it. I suppose there may be secondary risks from using scrap lead though. Unless you know for certain that the lead has not been used with nasty chemicals next to it. I'm thinking lead pipe work that is used for chemical transference. That could cause problems....
Hiya mate. Just noticed something, I am not 'suing' any old gas bottles :) I will be using them of course...

Anyway, Petrobond sand. Any idea what makes it special as opposed to ordinary sand. It sounds like a trade name and it's not one that I know of here in the UK. I was thinking of using what we call silver sand. This is a very fine and very clean sand that is used for children's sand (play) pits. It has to be fine, soft and ultra clean because of this. I'll add fuller's earth clay to this to create my moulding sand but don't yet know in what quantities.

Lead. Yep, nasty stuff but then so is aluminium fumes. Lead casting is quite common still over here in the UK and I will only be doing it outside. There are still an awful lot of houses that have lead water pipes ours included. Having once been a plumbing and heating engineer I can tell everybody that the danger from lead is real but very much overstated. It's bad if you ingest it in anyway and that does indeed include fumes, hence my proposing to cast the weights out of doors, it's safest that way.

Thank you for the health warning though it is appreciated :)

Take care.

Kevan
NutandBolt (author)  Kevanf14 years ago
Petrobond vs green sand. petrobond is oil-bonded casting sand, theoretically you can leave the sand in a closed container and it will be good for use years later. Also the final casting will be very high quality. The downside: it is expensive in comparison to green sand. Play sand is also good but you have to make sure you make a good mix ratio of the play sand+Bentonite(clay)+water (not too much water). Petrobond is available in the UK and is mostly sold in foundrys and less in hardware shops such as B&Q. I know that because the petrobond I have is made in the U.k. I am not promoting products but this is the link of the commpany   in case you want to have a look.
:-)
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Fantastic :) I'll e-mail the company and ask if they can give me a list of stockists (local hopefully as we do have the odd foundry still dotted about).

Thank you and take care.

Kevan
RingoWild1 year ago
I know how thrilling it is when you try something and it works so well! What a great feeling. Congrats! But what is petrobond?
Could you tell me exactly what refractory you used? I am having an extremely hard time finding a good tutorial on refractory, and would be extremely grateful.
Try
http://makezine.com/2012/04/05/how-tohomemade-castable-refractories/
Great job...! Thanks for the Instructable... I will try out the aluminium forging some day. Make spare parts, machine them, and plate them with copper,nickel, or chrome :)

Kjetil
SLaorr2 years ago
Big fan of the project! I'm thinking about doing it myself. Now, I know you mentioned what size bag of cement you got, but how much did you use? I'm trying to be economical and I want to get the smallest size I can for this design.
hriosm2 years ago
Be careful. I heard sometime you shouldn´t use old tanks because of something could explode besides the gas.
Schmidty162 years ago
very cool u will have to sell ur alimuium and can u melt steel with it or what about gold or silver
n1cod3mus2 years ago
learned something a few days back, dont use charcoal briquettes they produce too much ash which clogs up the air flow, use lumpwood charcoal burns nice and hot with much less ash.
zomfibame2 years ago
I'm digging your hinge design. and the whole thing is very nicely done.
i found the hindge method good as well but i didnt want to reach over the furnace even with gloves. so i made a pedal lift lid

http://www.instructables.com/id/Aluminium-Foundry-From-a-Gas-Bottle/
I have heard that a lot of blues and yellows in paints have cadmium in them, thus their names...
www.backyardmetalcasting.com and the sister site www.alloyavenue.com will provide as much information as you can use and can answer almost any question you may have on the subject !!
bherrboldt3 years ago
Again you rock. I have done 2 melts and poured 24 aluminum ingots. Im going to pour more tomorrow and then I think i will be ready to sand cast. Thanks again.
I've actually done the same thing (with a propane tank that is) Very nice job! I ended up scrapping most of it, because I couldn't get a decent enough mold to make it work. But I've never heard of petrobond. Then again, I built the whole thing for <$50 because I was on such a tight budget...

One thing I would recommend though is that you modify it a bit and put a propane burner in instead. Much easier than charcoal, and you have a more controllable heat. From the looks of yours, all you would have to do is insert a propane line into the blower pipe, and you're pretty much there. You would just need to add a flame holder, but that's fairly simple.

Very well done!
For decent molds, I would highly suggest trying out lost-foam casting. You can do it with junk Styrofoam and an X-Acto knife or something similarly sharp, and sand from your backyard. It's just about the cheapest and easiest method to produce fairly high-quality objects.
rhulett13 years ago


How long is the inlet pipe ?

Is the length critical ?

Is the flange important ?

Great job.....Roger
EmmettO4 years ago
As for crucibles, I struggled with making a crucible for melting copper. It would melt through every steel crucible I made. I eventually found a site that sells cheap fire clay crucibles and thats what I use now. http://www.lmine.com/mm5/merchant.mvc?Screen=PROD&Store_Code=LMS&Product_Code=17703&Category_Code=economy_repacks
i got mine for around $60 at foundry101.com and it comes with a lifting shank..
Omnombulist3 years ago
Wonderful ible! I just finished making a similar furnace and will be adding a hinge after seeing how nicely yours worked. I used regular portland cement and cured it for 18 days before firing. It is pretty thoroughly covered in hairline cracks after 4 firings and the outside gets terribly hot. I am guessing I will have to recast the cement before too long and am interested in fire cement.
How well Is your refractory holding up? How many times have you fired it?
bherrboldt3 years ago
All I have to say it thank you so much. I just built my refractory/foundry almost exactly like yours. All I have left is to get ahold of some refractory cement and Im in business. This is awsome. You rock!
imbignate4 years ago
Firstly, what sort of sensor are you using for a temperature gauge, and where is it mounted?

Second, what are you using as a mold for the ingots? They're all a nice standard size and very professional.

Third, this is awesome.
NutandBolt (author)  imbignate4 years ago
The sensor I used is a simple and trusted multimeter that I got on Ebay. All that is needed is to set the multimeter setting to tempature and place the tempature wire in the furnace.
As for the ingots, I am using metal muffin tray (not teflon). All you have to do is pour the molten metal into it and you get a nice aluminum muffin. You can also make a container for the ingots DIY style like the one I welded from metal angles. I am using it to make slim ingots for my pipe cruicble.
Thank you.
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Nice technique with filling the gas cylinder with water! An elegant solution to the problem of flammables. 

A professional iron worker once told me that cast iron cookware works well for a crucible. There are a variety of pans, pots, "dutch ovens" and other styles to choose from. Maybe there are cast iron muffin pans waiting to be found at a junk sale.

DIY-Guy
NutandBolt (author)  DIY-Guy4 years ago
Thank you, That is correct I heard the same thing regarding cast iron cookware used as crucible the only thing is finding the right size that will fit into my furnace ;-)
Check out the book by David Gingry. Then you can make your own cast iron cricible
just so you know it's Gingery, not Gingry. :-)
Details, details. And I suppose you want a crucible instead of a cricible?
I have been warned about using cast iron cookware if it has not been cleaned of all rust. If I understood correctly, what I was told is the combination of rust and molten aluminum can form something akin to thermite (possibly thermite itself?). If this is the case it could be very dangerous.
Ferrous oxide (rust) and aluminium do make thermite. Although the exact ratio's are industry secrets for each company they boil down a lot of rust powder and a lot of aluminium powder mainly for surface area considerations (occasionally it is doped with magnesium to help things along). At any level of rust build up on a pot that doesn't affect it structurally I don't think you have much to worry about. I've never had a problem. but if your worried put the offending rusty item in the smelter with it going full bore for a few minutes (be careful cause this smelter can easily melt cast iron if you are using charcoal ... I speak from experience of loosing an entire melt to this whoops(!?!)) by the time the pot has a barely visible glow in normal light there will be no more rust on it.
cendit3 years ago
I can´t see if the refractory partially blocks the air inlet. I'm asking in case that is some kind nozzle, because the area reduction. Thanks
Doddity4 years ago
My dad recently got several dead lawnmowers from junk heaps.
I repaired the oldest one and we are restoring it but he tore the rest apart for the pistons and such that he uses to make statues.
The rest of the mowers were set to be thrown out but I grabbed a large amount of aluminium pieces. Just testing my furnace i threw a chunk in and it melted beautifully and was quite strong when I later pulled it out.
I recommend saving them and smashing the cast base into smaller pieces as well as the tougher engine pieces.
gunspyop24 years ago
cool
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