Melting and casting metals...

Cadillac

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I use propane with a home built burner fairly easy to build. Then I use a separate air line and inject about 10psi of air. my forge is a 40pound propane tank Lined with 2” of kaowool insulation. Takes about 15 min to get up to temp for aluminum. I usually do multiple pours since I have everything going. A 20pound propane tank last a long time for me. Could probably do a dozen or so melts on one tank. I was surprised at how Long tanks lasted.
I’ve seen where with a cement perilite mix they cure the kiln by running it on a medium heat for a extended period of time. Idk I also thought they skimmed the surface with a different mix maybe some ceramic based stuff to reflect the heat?
 

MrCrankyface

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not trying to discourage your furnace build. I have several large crucible furnaces. It's just that I would never use them for jewelry..
I get your point and appreciate your point of view.
If jewelry etc was a more common occurence, and smaller bits, I would definitely go down that route.
Currently the silver-bit is a one-off project whilst 99% of the useage will most likely be melting aluminium, brass and possibly trying copper.
Furthermore the thing I want to cast is nearly 300 grams of silver, if I remember correctly.
Just by instinct it feels like a lot to melt with a small-ish torch, granted I have no experience in that department.

I have been looking around though, because a good torch has a lot of use for what I do, but the cheapest budget-level "kit" is >$200 here, and replacement bottles are then another $35 or so, quickly making it real expensive.
In the sense of long-term cost I think an acetylene/oxygen setup would be the cheapest, at least I already have most of the kit for that, but still quite expensive compared to just running the electric furnace(especially with solar power in the near future).


I’ve seen where with a cement perilite mix they cure the kiln by running it on a medium heat for a extended period of time. Idk I also thought they skimmed the surface with a different mix maybe some ceramic based stuff to reflect the heat?
There's definitely a bit of a procedure on initial startup.
My current plan is as following:
-Cure/harden for a week whilst controlling the moisture(so it doesn't dry out too fast)
-After a week let it sit at 150c or so for at least an hour and monitor what happens, if anything happens.
-Progressively start increasing by 100c or so and let it sit at those temps for a while.

Should help get the last moisture out, as carefully as possible, whilst also giving me plenty of time to see if any problems show up.
The big danger is going too hot too fast, with moisture still trapped inside, basically making myself a little steam-powered bomb. :ghost:
I'm relatively sure the worst that could happen is that it cracks excessively, but patience is key, both for a better final result and for me to get comfortable with it as these are temperatures I've never been close to playing with.
I googled around a bit regarding ceramic refractory, and that could be something to try to be honest, reflecting more heat back towards the crucible might be good from an efficiency point of view.
 

rwm

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I am sure it will work fine for your first furnace. Even commercial refractory develops cracks so don't let that worry you. The long term issue with using cement is durability. The cement/water reaction is reversible at high temps and the cement will fail. Commercial refractory cement is different and will last a lot longer. You will do fine for aluminum but getting to brass will damage the lining.
Yes 300g of silver is a big chunk and that would be crucible furnace size. I am not sure how cement will do at silver temps. BTW, one good thing about using electric is avoidance of gas porosity. Please keep us posted on your work.
 

rwm

Robert
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Here is an old pic of my first furnace using dense firebrick and insulating wool. propane fired.
furnaceicon-edited.jpg

It is not really necessary to fill in the gaps in the brick with mortar as you did, but it won't hurt anything. That will almost certainly crack though.

Also, I assume you are here?
 
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kcoffield

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If you haven't already, consider joining www.TheHomeFoundry.org. I'm a forum Admin and there are all kinds of casting disciplines practiced there along with many examples of practical home/hobby solutions for foundry equipment.

I have several furnaces but the most often used is a low mass, 10" bore, 8kw, resistive electric. It can accommodate an A20 crucible and will melt 10lbs of Al in an A10 from a cold start in under 30 min. I think electric is a superior heat source for hobby aluminum casting because the furnace atmosphere is never worse than air and in practice quickly becomes oxygen depleted air, which is a great furnace atmosphere for aluminum. Not having to store fuel and being able to flip a switch is great not to mention very low melt costs......pennies.

With careful (lean) tune, you can certainly get good aluminum quality melts with propane, but one thing you can never evade is the massive volume of atmospheric air that is forced through the furnace and the melt is exposed to any/all humidity along for the ride which can be detrimental to (aluminum) melt quality.

Downside of electric is the limited operating temp. At the outside, you may be able to do some bronzes, else you're limited to low melt point metals. Fuel fired furnaces are most sensible for bronze/iron duty hobby furnaces. Induction furnaces are better for everything but unless you only want to do relatively small melts, cost, power, and operating complexity can make them impractical for most hobbyists.

Best,
Kelly
 

MrCrankyface

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Alright so as I suspected, I ended up making a new lid, which also gave me an opportunity to document the process I used for the bucket as well.

Several strips are cut, cleaned and welded together to make one long band, at least slightly longer than the circumference of the lid.
A thick aluminium bar with a convenient ledge on it is underneath, helps align the pieces.
Weights on the sheet just keeps it down to free up my hands.
IMG_4487.JPG

Absolut chaos in the background, sorry about that, quite behind on cleaning up.
Either way the strip gets sent around a couple of times in my real ****ty roller.
The radius is quite forgiving, as long as you get it vaguely close to what you want to end up with, you're good to go.
Also the welds need to be blended decently to roll nicely.
IMG_4488.JPG

A brim was cut from the cutout from making the buckets bottom brim, roughly tacked on.
Unfortunately I was tired and started making mistakes here by taking shortcuts.

I had already tacked it halfway around when I noticed the brims outer diameter was larger than the rolled ring, definitely not close enough for me to "hide" it.
Stupid call of the moment was to cut the ring and keep tacking, makes problems further down the road.
IMG_4490.JPG

Here's todays little experiment.
I tried rolling this in an english wheel to get some shape to it.
Overall finish is pretty garbage, but for my second try ever I'm pretty satisfied.
This is however when the ring/brim mismatch showed up.
The lid was matched to the ring and is now too small because I increased the size of the ring to fit the brim...
Instead of taking a step back I just kept tacking, trying to force things into place.
Considering how thin the steel is on the top it's amazingly strong now when it has some shape to it, easily pulled everything else out of shape. :grin:
Live and learn I guess.
IMG_4493.JPG

So now I have a furnace that looks like some droid from star-wars.:grin:
I put the foil back on after taking the photo ofc.
Also it was horrible trying to lift the now HEAVY furnace off the workbench, but once down I'm real happy with the wheels on it.
The entire lid will be filled with perlite-cement, maybe also some kind of reinforcement to help it stay in place besides the brim piece.
I made the diameter as such that the steel brim is several centimeters away from the firebricks(super warm), so it should be perlite-cement on perlite-cement(less warm).
IMG_4495.JPG
 

MrCrankyface

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Robert
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I will be curious to see how long it takes to melt aluminum in that design. Electric is typically slower than fuel fired and that has pretty high thermal mass. When you try it, I suggest you weigh out the quantity of material and time it to complete melt. Keep in mind that a second or third melt will go faster since the furnace is already up to temp.
 

Larry$

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I've been casting aluminum alloys using propane in a home-built furnace someone else made. Steel angle iron frame Large hard "brick shell, soft insulating firebrick lining. Lid is a steel frame with the firebricks suspended by putting grooves in them to keep the steel away from direct heat. It works but has the usual disadvantages of fuel fire for aluminum and trying to control the amount of hydrogen bubbles. I've bought commercially available compounds that are supposed to help with the hydrogen. I'm now convinced to build an electric furnace.

The furnace lacks sufficient insulation to get to melting copper. In the past I helped my sister build a ceramic kiln. 55 gallon drum lined with 2" of Kaowool, fired on propane. We could hit cone 9, 2300°F.
 

Firstram

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I've been casting aluminum alloys using propane in a home-built furnace someone else made. Steel angle iron frame Large hard "brick shell, soft insulating firebrick lining. Lid is a steel frame with the firebricks suspended by putting grooves in them to keep the steel away from direct heat. It works but has the usual disadvantages of fuel fire for aluminum and trying to control the amount of hydrogen bubbles. I've bought commercially available compounds that are supposed to help with the hydrogen. I'm now convinced to build an electric furnace.

The furnace lacks sufficient insulation to get to melting copper. In the past I helped my sister build a ceramic kiln. 55 gallon drum lined with 2" of Kaowool, fired on propane. We could hit cone 9, 2300°F.
What's cone 9?
 
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