homemade electric furnace build

Discussion in 'Furnaces and their construction' started by JamesLeon, May 12, 2020.

  1. JamesLeon

    JamesLeon Copper

    Hi all, I've been interested in metal casting for a few years and have made my fare share of plaster ones that lasted a day or 2, so I opted to make a more robust one. I also wanted it to be quiet and cheap, so I went for a an electric one. The 2kw element can run completely free off my 3KW solar power for around 5 hours during the day, which is plenty of time to melt even large volumes of metal.

    I didn't really take many photos of the build process, but I think most of you will get the gist

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    I purchased 15 insulation bricks, which were a mixture of 2300F and 2600F grade. And I arranged them in this box-like fashion with 1 cut up brick making the floor and 2 whole bricks making the lid. no mortar was used for anything, but it could've easily been applied (again sorry for the lack of detailed photos).

    I welded up 2 angle iron frames to hold everything together and clamped it with threaded bar, as many people have done on youtube, but I ended up ditching the threaded rod as you’ll see later. everything sits on a thin piece of sheet metal

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    For the heating elements, I made 2 of these dirt cheap kanthal ones, using a jig shown in a video by the Vegoilguy (). These are 20 gauge and I got 2 spools from aliexpress for about $4 all together. Here’s the link to them; (https://www.aliexpress.com/item/32948165785.html?spm=a2g0s.9042311.0.0.15614c4dRCaMyN).

    I used a multimeter to get the required resistance that would give me 9 amps at 240 volts

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    To fit the elements in place, I ground circular grooves using a round file. Half the groove is in the lower brick and the other half is in the upper brick and a small gap is ground to let the heat out, but not the element. As you can see, the elements are trapped between the upper and lower shelves of bricks, making it impossible for it to fall out through creep. This eliminates the need for staples to hold the element in place, but it also means you can’t use mortar to glue the upper and lower bricks together, as you wont be able to remove the element when it breaks. This would probably make it unsuitable for applications that require everything to be completely mortared(I think), like a heat treatment oven, but its perfect for metal casting were you need gases to escape.

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    To contain everything nicely, I decided to ditch the idea of clamping the 2 angle iron frames with threaded bar, and instead use stainless steel sheet metal bolted to the top and bottom angle iron frames. I found this 1.2mm thick stainless in a dumpster and cut it to size. Normal steel that’s painted with high heat paint would work fine too.

    The 2 elements exit the inside of the foundry through a small groove and they are attached to steel bolts, and the bolts are attached to high heat electrical cables. Search ebay for “mica” wire. Again, this whole method of holding the elements came from a video by vegoilguy (). I made the electronics box housing the elements through cutting a hole in the sheet metal wall and bolting on another piece of sheet that I bent. Eventually I'm going to replace the mild steel bolts with stainless steel ones, as they wont corrode. holes were drilled in the top of the box to allow adequate ventilation. Overall this seemed to be very safe
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    I also welded 2 more angle iron frames for the lid and attached it with 2 hinges.

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    Here’s a completely overkill PID electronics box made of 5mm thick steel and angle iron. It was way too heavy, but hey, it’s what I had on hand. The steel ended up being too thick to fit in the switches and fuses, so I replaced the front and back with thinner aluminium.

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    I later attached a double illuminated rocker switch. The top switch turned on the pid and relay and the botton switch powered the elements. This bottom switch is handy as it lets you key in the desired temperature before the elements are turned on and also allows you to turn them off when taking the crucible out, to avoid shorting out the coils and/or getting electrocuted

    I mainly followed the wiring diagram from vegoilguy (http://www.vegoilguy.co.uk/_maingifs/pid1.png), but adding the illuminated switches required a few additions. I used a 10 amp fuse for the 9 amp element and an additional 5 amp fuse to protect the PID. I’m also planning to fix up the messy wiring at some stage and adding strain reliefs.

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    I later decided I wanted everything insulated in ceramic fiber blanket, so I welded some 10mm thick flat bar to the sides of the angle iron frames, which would allow the 13mm thick wool to compress very lightly between the bricks and the stainless steel sheet panels. These particular blankets are bio-soluble (often called "superwool"), making them less hazardous to the lungs and I didn’t find them to be itchy, but it’s still recommended to wear a mask and gloves. All 4 sides of the foundry had blanket, including where the electronics came out (I cut holes in the blanket to allow the terminals to come through). I also put some blanket at the top of the lid beneath some more stainless sheet. I might add blanket on the floor of the foundry at some stage too.

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    After this, I finished up the stainless steel walls, covering the corners with some stainless bent at 90 degrees, and sprayed all the mild steel with 1000 degree C paint. I ended up keeping on of the threaded rods behind the lid, as it holds the lid when opened. and I’m finally done after many months. Unfortunately 3 of the k23 bricks have already cracked in half so far, I think this might’ve been a result of trying to melt copper (which had it only 60C within its temperature limit), but everything still holds in place fine and I have mortar if things get worse. The K26 bricks are completely fine though, so if I were to do it again, I’d go fully with the higher grade. There’s a tonne of stuff I didn’t mention, so ask me something if you’re interested and feel free to suggest some improvements. Big shout out to the Vegoilguy. His tutorials were incredibly detailed and he gave me a tonne of advice via messaging on his patreon, which ill link here if you're interested in donating (https://www.patreon.com/vegoilguy/posts)

    I'm also going to use this for burning out investment molds and might have a crack at heat treating steel. Let me know if you think heat treatment will be possible with the amount of insulation I'm using. Eventually I may also add in a ramp, soak and step PID controller for the burnout purposes.

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    Jimmymmm likes this.
  2. DavidF

    DavidF Administrator Staff Member Banner Member

    Nice build, and first post. Cant wait to see what you cast up :cool:
    Sounds like you fell victim to the king of random furnace build with the plaster??
     
    JamesLeon likes this.
  3. JamesLeon

    JamesLeon Copper

    Yep haha. But like many people he did get me interested in the hobby.
     
  4. DavidF

    DavidF Administrator Staff Member Banner Member

    He did do some pretty fun stuff and I enjoyed his videos. Its sad how things ended for him..
     
    JamesLeon and Jimmymmm like this.
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Welcome aboard. What a great first post. You did a great job on the furnace build. It should almost be moved to the furnaces and construction subforum. We can do that for you if you like.

    You can heat treat with your furnace but there are some tricks and tips for preventing hot spots due to radiation from the coils. If you try to do a T6 aluminum heat treat without some shielding you’ll likely experience localized melting and damage the casting being heat treated. T5 is usually no problem. You furnace looks to be about 6” x 6” square opening.

    My primary furnace is an 8kw resistive electric, 10” bore, lift-off I built about three years ago. It can accommodate and A20 crucible and 20lbs of aluminum per melt. It was originally based upon Insulating Fire Brick. There is a crazily detailed build thread at Alloy Avenue forum at the link in my signature below. The AA website is down right now. Here are a few related links that may be of interest. You can take them in your leisure. The links take you to a particular post in the thread but you can start at the beginning if you like.

    The current incarnation of my furnace is described here.

    Low Mass Electric Furnace

    One of the previous versions here:

    Dense Castable Refractory Electric Furnace

    Here is the controller build:

    Electric Furnace Controller build

    Here is my larger furnace. It has a 14” bore and was intended to be fuel fired but it also has a removeable 8kw resistive electric insert.

    Larger 14" Bore Furnace with Electric Insert

    Best,
    Kelly
     
  6. JamesLeon

    JamesLeon Copper

    Thanks mate. I thought it was already in the right subforum? If I'm mistaken then feel free to move it there then. Thanks for the info on heat treatment and I absolutely love your builds, makes mine look like a toy :D. keep it up!
     
  7. DavidF

    DavidF Administrator Staff Member Banner Member

    Dont worry, your in the right spot :)
     
  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    My bad, you posted in the correct forum. I confused your post with another member's introduction post.

    Best,
    Kelly
     
  9. Jason

    Jason Gold Banner Member

    That's a very pro looking build. Where did you stick the relay? Those suckers can get screaming HOT. I hookie joed my control setup and opted to leave it shock ready for the curious finger!
    My little fan flips on and off and things stay nice and cool. The sound of the fan lets me know from across the garage it's cycling as it should.

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  10. JamesLeon

    JamesLeon Copper

    The relay is just mounted on the heat sink provided with the PID kit. I thought about adding a small fan with a mini 12V power supply, but I think it might be overkill?? I just finished up adding power plugs, which connect the PID box to the furnace, as I want to detach it from the furnace when its not in use coz its operated outdoors. Here's what it looks like inside, also yeah i need to paint over that rust;

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  11. Jason

    Jason Gold Banner Member

    No need here for an extra power supply. I tapped into the power for the PID. Probably depends what version ya bought. Good thing with these relays, they are dirt cheap. With that said, dont trust them one bit. When they fail, things can get hairy fast and ya dont want to be down the street at home depot.

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    JamesLeon likes this.
  12. JamesLeon

    JamesLeon Copper

    Thanks mate. I also noticed you're using an Auber ramp and soak PID, which I might grab at some stage. How's that been working for you? I looked up a few tutorials on how to use it. It's the only cheap one that has a manual and tutorial not written in horrible English. Having a look at those tutorials, it seems pretty easy to program a ramp and soak, but can it also "step", i.e. increase/decrease the set value instantaneously so it goes up or down in temp as quickly as possible? cheers
     
  13. Jason

    Jason Gold Banner Member

    It's easy to use. Some of the guys here helped me understand the programming. Of course the furnace can only go up as fast as it can, but no it doesnt have a typical 9999 function like most pottery kilns. So it does take a little fiddling to make it work quick. For dropping rapidly, I open the door and set 5mins. I make sure I'm there for rapid drops. Sometimes, I switch the kiln off on it directly too until I get the pid advanced to the next step.
     
    JamesLeon likes this.
  14. JamesLeon

    JamesLeon Copper

    corrections;
    • The brick cracking I'm getting is normal, even new kilns experience it and it shouldn't be an issue as the brick assembly is still held in place strongly.
    • the 5 amp fuse for the pid is probably not optimal, as the power consumption of the pid is only around 0.02 amps. So a 0.1 amp or less fuse is probably the way to go but I've read that the pid may not even need a fuse.
     
  15. garyhlucas

    garyhlucas Silver

    Those FUTEK SSRs have a bad tendency to fail ON not off!
     
    Jason likes this.
  16. Jason

    Jason Gold Banner Member

    Exactly. Mine hasn't screwed me yet, but I read a lot of guys have gone Chernobyl with them.:eek:
     
  17. Peedee

    Peedee Silver

    If the triacs on the output fail it doesn't matter what the fusing is at on the input.

    Edit: SGBTs and I mean tightening the input to below 5A wouldn't wouldn't matter a bit if the output fried. Most SSRs are opto isolated so if the front end cooks, well you can't really fuse down to that level, but the emitter circuit can/will die, so no signal, but if the load end collapses, spikes or whatever it could just go short.
     
    Last edited: May 23, 2020
  18. JamesLeon

    JamesLeon Copper

    yeah gonna forget about the 5 amp fuse
     
  19. JamesLeon

    JamesLeon Copper

    Mine is inkbird SSR. any idea about their reputation?
     
  20. Jason

    Jason Gold Banner Member

    Cant help with that, but I do know the fuktek is knocked off something awful. My PID thread had photos and info of the real vs fake ones. Leave to the scumbags to knock off a 9dollar part.:rolleyes: If I'm going to knock something off, I want 3 figures at a minimum.:D
     

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