[paprjam]

A few weeks ago I built a small electric furnace for melting less than 10 pounds of Aluminum. I got the elements from e-bay and bought the firebrick used. This is actually the second one I built, the first one's brick had been damp and crumbled when I heated it up. I cut the bricks for the shell and the grooves for the elements with a table saw. It's wired for 240 volt and draws about 14 amps at 3200 watts. I was able to melt 3 kilos of Aluminum in 40 minutes and about the same amount of Brass in an Hour. I'm working on some type of temp control, right now it's off or on.





I used it to make a tool holder for my little CNC machine, it worked very well. I cut it from pink foam and poured it using the lost foam method.

[doorknob]

Very interesting, great photos.

Do you melt the aluminum inside a crucible or some other container? Do you have any photos showing that, as well as photos showing the pour?

Did you salvage the aluminum stock from previously-cast parts, or did you use virgin material? What alloy?

[brian257]

Cool, I didn't think you could melt that much aluminum with a home made electric heater. What are the specs on the heating wire you used?

Thanks for sharing this.

[paprjam]

This is the Brass melt. The pour is taken one handed while trying to avoid the zinc fumes. The crucible is from Legend Mining supplies.
Legend Inc. Sparks, Nevada USA: Size "K" Fused Silica Crucible - Each



This is a link to the Kiln elements I used.
Kiln Heating Element,115Volt-1600 Watt,14GA (5683) | eBay

[B-RAD]

I have a good start to a temp controller just laying around, its has 2 - 75amp ssr's and a burst fire controller, all mounted in a box mounted to a liquid cooled aluminum block. Let me know if your interested and I'll get some pics and more info.

[paprjam]

I have a place I can get large Reostats.I plan on using a bank of 3 or 4 of them with a rotary switch to step up the resistance. I tried it with one huge one that had slides on it, it got very hot and burst into flames.

[B-RAD]

Yep, heat, and your wasting energy, my way is very effecient for resistive loads. Google "burst fire control" or something like that, you could also do phase angle (like a light dimmer) but with that much wattage you may get a call from ur power company...

[Al_The_Man]

I have a place I can get large Reostats.I plan on using a bank of 3 or 4 of them with a rotary switch to step up the resistance.

A Triac control would be way cheaper, more efficient and consist of less than half doz. cheap components, 15amps is very low for current Triac devices.
You would probably find many circuits on the web.
http://www.learnabout-electronics.org/diodes_07.php
http://www.digikey.ca/product-detail...025L6-ND/15237
I recently took apart one of our light dimmers that quit, 3 components total.
Al.

[B-RAD]

Triac sure if your power company doesn't charge you for reactive power and/or you aren't running any electronics while your furnace is running....

[Al_The_Man]

No reactance with heating elements, P.F. not a problem, all the stoves in current use generally use this method for temp control.
All you need is a RC snubber across the input if worried about RFI.
Al.

[brian257]

How many of the heating wires did you use?

[B-RAD]

No reactance with heating elements, P.F. not a problem, all the stoves in current use generally use this method for temp control.
All you need is a RC snubber across the input if worried about RFI.
Al.

I thought phase angle control would cause it with resistive loads because of when/where it chops the wave. Its been a few years, I may have got things mixed up. They make ssr's now that only act at zero volt crossing due to this issue... I thought...

[Al_The_Man]

There should be no concern about P.F. with resistive circuit, All SCR's and Triac's are inherently zero crossover switches, but if switching a resistive load, there is no collapse of inductive energy anyway, which is what can cause very high inductive generated spikes.
Many Triac controlled heaters do offer burst firing, which is what I believe you alluded to?
This can be simulated by keeping the Triac or SCR on all the time but vary the time interval between off and on, this can reduce the switching noise when phase angle switching occurs.
IOW, when switching ON and OFF both occur at zero voltage.
It is easy to set up this using the simple Triac circuit if a variable interval timer is used to keep it either full on or off.
Also Solid-state relays : ELECTROMECHANICAL RELAYS
Al.

[paprjam]

There are 2 120 volt elements wired in series for 240 volt.
I had an old Powerstat on it but I took it off because it's only rated for 7 amps, I had a larger one somewhere, I just can't find it.
You can see the small one here. It's from an old leadcasting machine used for printing.

[Al_The_Man]

You could always pick up a light dimmer and open it up and replace the Triac from the DigiKey link.
Put the Triac on a good heatsink, only take a couple of $$ to try it, if you don't feel like building from scratch.
With the higher triac, it should still be ok on 240, there is a Pot,Triac,resistor and capacitor, thats it.
Al.

[B-RAD]

Al, your title fits you well. Thanks.

[diyengineer]

A few weeks ago I built a small electric furnace for melting less than 10 pounds of Aluminum. I got the elements from e-bay and bought the firebrick used. This is actually the second one I built, the first one's brick had been damp and crumbled when I heated it up. I cut the bricks for the shell and the grooves for the elements with a table saw. It's wired for 240 volt and draws about 14 amps at 3200 watts. I was able to melt 3 kilos of Aluminum in 40 minutes and about the same amount of Brass in an Hour. I'm working on some type of temp control, right now it's off or on.





I used it to make a tool holder for my little CNC machine, it worked very well. I cut it from pink foam and poured it using the lost foam method.

Wow, that looks awesome.

[paprjam]

I'm going to be working on Al's temp control for this furnace. I overheated it a couple times and the elements got brittle. Right now we are moving so I'll work on it when we get to Tennessee.

[BAMCNC.COM]

I used B-Rad's method with an old electric smoker that I use for a Powder Coating oven. I have the plug going through a Kill-a-watt monitoring plug. I've matched the wattage used with temps, so its simple to dial in and the temp stays solid and doesn't fluctuate that I can see with the thermometer. I'll get a picture tonight. And yes the Triac method (AL's) is not the best for this application, especially if you have any sensitive equipment in your house being used at the same time....

[Al_The_Man]

And yes the Triac method (AL's) is not the best for this application, especially if you have any sensitive equipment in your house being used at the same time....

A resistive load - zero switched Triac is far less prone to electrical noise than say a Universal motor, of which there are usually quite a few in the average residence.
The only draw back is the lack of temperature feedback.
Al.