Melting and casting metals...

[MrCrankyface]

Bit more progress. Mitered and mortared.
Potentially had problems with the mortar, time will tell.
I dipped the stones in water but the mortar still really struggled to stay on and wanted to dry up and flake off.
Added some extra around the edges and joints just to give it a fighting chance of holding together long enough for me to get it down into the furnace.


Printed a quick little ring to help me align everything as I put it together.
This also let me put some bungee cords on the outside to keep it squezed together while hardening.

 

[rwm]

Very nice. That’s gonna have low thermal mass and work well. Don’t worry when the mortar cracks/fails. You don’t need it. At high temps most of the heat is lost by radiation, not convection.

 

[MrCrankyface]

Thanks! I hope so.
A bit of a belt and suspender situation but rather safe than sorry. Decided to keep it together with some metal bands before I lift it down into the base.


This time I have just poured down loose perlite instead of mixing it all with cement.


Then for the top interface I mixed it with cement and put the lid down onto it to get matching shapes
The white edge is a 3D print that will be heated out later.

 

[rwm]

Looking good. Waiting to see how you bring your wires out of the body and all that. I originally thought I would need a controller of some kind on mine but I quickly realized I would just let it run on full power until I had melt temp and then unplug it!

 

[MrCrankyface]

Thanks! That's something that troubled me with both the first revision and this.
First revision I put several layers of heatshrink on the kanthal, a few centimeters in from the steel casing and the casing itself is grounded so it will trip the RCD if the casing were to get energized.
I also had some problem with a residual current growing and eventually tripping the RCD, I suspect this could be both due to the hotface maybe being ever so slightly conductive and moisture content in the insulation itself as it seemed to get better over time.
With dry packed perlite this should be less of an issue.

This time I found some silicone/fiber sleeves that I will use to protect against shortcircuits/unintended connections. Might heatshrink as well just to add an extra layer of safety.
I will also try to plug the holes from the inside once the kanthal is in place, found some kind of "fire sealant" I should be able to pump in a tiny bit of to stop air movements.

For single melts the controller is definitely overkill but it was pretty nice when I was doing several consecutive melts, this let me take the crucible out and let the furnace keep charging up the temperature without overshooting if I took too long. Probably doesn't save me many minutes but it's one less thing to think off and that can go wrong.

 

[rwm]

If you ever see an old electric oven they usually have some heat resistant fiber insulation on some wires. It is useful in this application.

 

[MrCrankyface]

That was initially what I was trying to find but turned out impossible to find a supplier.
Finally got the spools in the furnace, 2x 3kW, entry at top and bottom, common exit at center.
Sealed it with the previously mentioned "fire sealant", says it can handle 1250*C once hardened so should be plenty for this.


Since heatshrink worked in the last "version" I decided to keep that as an innermost layer, 3 layers of it for some thickness and the silicone/fiber thing ontop of that.
The outermost sleeve handles 300*C so should hopefully not have a problem here, finally filled in the void around it with the fire sealant.
Furthermore all the kanthal "exits" are tripled or quadrupled for a lower resistance and heat output.


Also added a sealing rope around the top, should help it seal better and make a better cushion for the relatively delicate lid to sit on.


Description of the fire sealant says it can also be used to repair smaller cracks in bricks/mortar so decided to test it out on the inside of the lid.
It had a lot of cracks and a little piece missing so worth a shot.

 

[MrCrankyface]

It's been a long project for something I thought would be simple, but it's finally nearing "permanently useable"..!
The coils burnt off their common groundpoint because I isolated them too much and they got too hot.
Managed to splice it which has worked for many hours but at 2/3 of the power, still plenty to melt copious amounts.
I've ordered spare coils and ceramic couplers so I can replace the coils if they give up completely.

Whilst I was making my rough ingots I also sandcast two nicer ones as giveaways.
Far from good gating but I was very limited by space.
Afterwards sanded and polished the surfaces, came out pretty good I think!


And the pile of ingots for later projects is growing steadily, now around 150kg / 330 lbs.
Another thing is that it's been a lot of good practice, really let me get used to the whole process and get more comfortable with handling a bucket full of molten metal.
Should make future projects much easier and safer!

 

[rwm]

That is quite a pile of aluminum bricks! Especially for an electric furnace! It must be working well.
You might consider not casting ingots unless your material is a shape that is hard to work with. Every time you melt the material you introduce gas leading to porosity. It is better to melt the raw material only once if you can.

I should add: Gas (hydrogen in solution) is less of a problem with electric furnaces. That is the one big advantage. If you ever need a pristine casting you could start with commercial ingot and inert your furnace with argon and it should be ideal.