Author Topic: Building electric furnace to melt aluminium  (Read 10196 times)

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Offline 691175002

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Re: Building electric furnace to melt aluminium
« Reply #25 on: April 11, 2017, 09:30:38 pm »
Kilns are actually quite easy to build.

The most common brick is K23 which can be cemented or just stacked.  The heating elements are normally mounted in milled grooves, but you can also "staple" them to the brick with loops of wire.

Drill a hole for the thermocouple and element leads, and buy a $20 PID + SSR off ebay.
 

Offline CaptainNomihodai

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Re: Building electric furnace to melt aluminium
« Reply #26 on: April 12, 2017, 03:24:02 pm »
I'm gonna design universal wire holders inside the furnace, so that the wire could be easily replaced (preparing for the future ;) ). Was thinking a lot about it, the use of ceramics and other heat-resistant elements or just "standard" grooves in the bricks. The easiest way I've though of was prepared pieces of steel, kind of "steel holders", put between the bricks that are glued together with mortar.
Could thermal expansion of that small steel element create problems?

Absolutely do not use steel to hold your elements. At those temperatures steel will form a cool-looking black oxide layer. As it heats and cools the oxide will flake off, and these flakes can short out and destroy your element (I know this from experience using a steel crucible). They will also eventually oxidize away to nothing. You may also get the element and the steel "welding" themselves together (not an actual weld, just the oxide layers growing together). Finally, it just seems, intuitively, like having the element touching another metal that isn't Kanthal can't be good for it. Also, if you're using soft firebrick as your hotface, I would not recommend gluing them together with mortar. Those bricks are very fragile and you want to be able to easily replace one if it breaks.

Quote
I did not know about proper wire surface load values then. I did read Kanthal datasheet though. They are being weird about this. The SL seems to depend on the application.
Basically the more "stretched" your element is (i.e. larger diameter and pitch, for a coil), the more surface load it can take.
 
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Online T3sl4co1l

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Re: Building electric furnace to melt aluminium
« Reply #27 on: April 12, 2017, 04:42:58 pm »
Also, iron oxide is a flux, so it will melt into the firebrick, staining it at least, but probably causing melting, especially around the element.

Tim
Seven Transistor Labs, LLC
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Bringing a project to life?  Send me a message!
 

Offline ^_^

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Re: Building electric furnace to melt aluminium
« Reply #28 on: April 15, 2017, 05:41:46 pm »
@691175002:
I have used a similar brick to K23: IFB23. They have good parameters as well.
PID and SSR coming in the near optimistic future.

@CaptainNomihodai:
That's interesting as I've seen guys build whole crucibles out of welded steel :D
But I did listen to your advise and went with the in-brick grooves.

As for the mortar - I've already bought it, and the bricks do not seem *that* fragile, so I've went with it.

### UPDATE ###

Inventor screenshot vs. Inventor 48h render:


Right now the mortar is setting, 4 (+1 divided into pieces) more bricks will be added on top.

The wire i have now:
Code: [Select]
### Main ###
Power = 2000 W
grid voltage = 230 V
 ### Wire ###
wire Ohm/m = 1.85 Ohm/m
wire dia = 1.00 mm
wire current = 8.70 A
wire resistance (24*C) = 26.45 Ohm
wire length = 14.30 m
wire Surface Load = 4.45 W/cm^2
 ### Coil ###
coil diameter = 15.00 mm
min. coil length = 0.91 m
max. recommended coil length = 1.82 m

With a coil length of 1m (dimensions of the base of the inside of the furnace are roughly 25 x 25 cm).
Having three levels of grooves I can add the same coil two times (and get overall 3-phase 6 kW furnace...  >:D).
However, realistically I can add it only once because of my house power limit.

If I had more money for this project and higher current limit per phase in my household I'd go for 2mm Kanthal, one-phase 4.3kW furnace:
Code: [Select]
### Main ###
Power = 4300 W
grid voltage = 230 V
 ### Wire ###
wire Ohm/m = 0.46 Ohm/m
wire dia = 2.00 mm
wire current = 18.70 A
wire resistance (24*C) = 12.30 Ohm
wire length = 26.63 m
wire Surface Load = 2.57 W/cm^2
 ### Coil ###
coil diameter = 15.00 mm
min. coil length = 3.39 m
max. recommended coil length = 6.78 m

And obtain a nice SL of 2.57 W/cm^2.
It would need 2 more levels of grooves in the top bricks to fit 5m coil.

... but 2mm Kanthal is expensive and I have 16A current limit, so no  ::)

Will get back to you guys soon.
 

Offline CaptainNomihodai

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Re: Building electric furnace to melt aluminium
« Reply #29 on: April 17, 2017, 02:08:29 pm »
@CaptainNomihodai:
That's interesting as I've seen guys build whole crucibles out of welded steel :D
But I did listen to your advise and went with the in-brick grooves.

Using a steel crucible is fine, in fact I usually use schedule 40 pipe welded to some plate, as long as you're not too worried about the precise chemistry of your melt (i.e. you're okay with a little bit of iron in it). My point was that you can't have steel touching the heating elements or the brick, because that's when this (see image) happens.
 
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Offline ^_^

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Re: Building electric furnace to melt aluminium
« Reply #30 on: June 25, 2017, 01:14:20 pm »
Hello again after a long break :)

I've ordered stuff for PID from ebay (PID controller, K-type thermocouple rated to 1300 *C and 2x 40A SSRs).
They took almost whole May to get shipped from China.
Lately I've had some time to put it together and it's done!

The furnace still needs little work: putting the electronics/cables in boxes as well as the proper lid.
The lid will be made from 2 firebricks cemented together, firewool in the opening of the foundry and some welded steel elements for the holder and keeping it together.
With the proper lid I can make a comparison between calculated and real time to melt alu.

Thank you all again for contributing in this topic, your posts were of great insight  ;D

Here's a photo:
 

Offline SeanB

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Re: Building electric furnace to melt aluminium
« Reply #31 on: June 25, 2017, 04:38:24 pm »
Would not cement the 2 bricks together for the lid, but make a steel frame for them that holds them, and a steel handle to lift it with a lifter. Cement will fail in this use, it is too brittle with heat and stress.
 

Online T3sl4co1l

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Re: Building electric furnace to melt aluminium
« Reply #32 on: June 25, 2017, 06:53:47 pm »
Presumably it's furnace cement, which is strong and refractory.

The bricks themselves don't look all that abrasion-resistant though, and for that reason, a frame would be a good idea.  They could also maybe be faced with cement too, if it doesn't cause expansion cracking problems.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 
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Offline ^_^

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Re: Building electric furnace to melt aluminium
« Reply #33 on: June 29, 2017, 09:23:10 am »
Presumably it's furnace cement, which is strong and refractory.

The bricks themselves don't look all that abrasion-resistant though, and for that reason, a frame would be a good idea.  They could also maybe be faced with cement too, if it doesn't cause expansion cracking problems.

Tim

You're double-right  ;)
The cement is actually most heat-resistant element used in the furnace as it's rated to 1700*C (the firebricks are 1260 *C).

And yes, the firebricks are very, very NOT-abrasion-resistant. Putting them somewhere leaves tiny firebrick-dust. They need to be handled very carefully.

That is why the lid as a moving part needs special care. Hence the firewool as it will take care of the brick-to-brick friction problem.
I was thinking about steel frame as well to make it even more robust as the steel would hold everything and take on all the force.
The firewool in between would provide the thermal isolation.

Cheers!
 

Offline ^_^

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Re: Building electric furnace to melt aluminium
« Reply #34 on: September 09, 2017, 02:17:27 am »
Just before moving away from Europe, I managed to do first electric furnace cast.
Well, technically, electric furnace was used to heat the cast in a proper temperature profile.

I've used "Kerr Cast 2000" in 5 hour profile, which was in the end around 6h profile.
Cast temperature was around 400*C when I put the form out of the furnace.

The form cracked halfway through the temperature profile, but it did not affect the process. Maybe a form this big would need the longest, 12h profile.
I've also experienced problems to remove the wax, as I needed to physically remove the form, pour the melted wax out, and put the form back again in the furnace.

Though, it DID work, and I'm happy with this first time result.
Aluminium was melted in the old, coal powered foundry.

Pictures below.

Wax fist used to make a form (back in 12.2016 ::) ):
https://github.com/stawiski/electric-furnace/blob/master/photos/P_20161209_155233.jpg
https://github.com/stawiski/electric-furnace/blob/master/photos/P_20161209_155252.jpg
https://github.com/stawiski/electric-furnace/blob/master/photos/P_20161209_155338.jpg

Casting result:
https://github.com/stawiski/electric-furnace/blob/master/photos/IMG_2642.JPG
https://github.com/stawiski/electric-furnace/blob/master/photos/IMG_2647.JPG
https://github.com/stawiski/electric-furnace/blob/master/photos/IMG_2656.JPG
 

Offline negativ3

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Re: Building electric furnace to melt aluminium
« Reply #35 on: September 16, 2017, 09:33:32 am »
 


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