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Homebuilt Electric Melting FurnaceFiled under: Aluminum Foundry,Store — dynamodan @ 7:22 pm March 8, 2008

Detailed plans now available

Build your own melting furnace! Melt and pour aluminum! Due to an overwhelming

response to my improved foundry furnace, I have made available DETAILED PLANS

that you can purchase and instantly download for a small fee

USD 3.95 / Download

You get 52 pages of instructions, CAD drawings, photos, time-saving parts

checklist, suppliers list, step-by-step construction notes, and all the

FAQ’s, in printer-friendly pdf format!

USD 3.95 / Download

…or, you all are welcome to browse the (as always: free) photo gallery of this project

below. Enjoy!

This is a homebuilt electric melting furnace. For my 25th birthday, my

wife got me Dave Gingery’s book “Lil Bertha, a Compact Electric

Resistance Shop Furnace.” So I started right off building by Dave’s

plans…

The main problem, in my opinion, that one encounters

in making a resistance furnace is the structure that holds the elements

in place. Dave’s book describes one solution to the problem, and that

is to form grooves in castable refractory.

My attempt at

forming the grooves by Dave’s designs failed miserably. The refractory

Dan's Workshop Blog » Homebuilt Electric Melting Furnace http://www.dansworkshop.com/2008/03/homebuilt-electric-melting-fur...

1 of 10 1/9/2013 2:47 AM

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that was suggested in the book was AP Green’s Kastolite castable

refractory, and after ordering and having shipped about a hundred

pounds I got right to work. (Can you say ‘UPS charges’ 10 times really

fast? Thank you. Now you feel my pain.)

Well, when I tried to

pull the rubber hose out of the newly formed groove, the Kastolite

chipped and broke out horribly. The element barely stayed in place in

this malformed groove, but hey, I was following the instructions.

To make a long story short, I used the remaining Kastolite to make some

‘donuts’ with a little trough around the inside diameter, at the top.

The inside of these donuts was the inside diameter of the furnace, and

when stacked one ontop of another, nice, well-formed element grooves

resulted. However, the making of these ‘donuts’ required some styrofoam

cutting to make forms, and that’s another story…

This method of forming the element grooves worked well indeed, and the

Lil’ Bertha was up and running at last. After a few melts, I discovered

the great benefits of using electricity for melting. (I had indeed

tried gas burners, but they were noisy, required close supervision,

drank fuel like Coca-Cola on a hot day in the desert, and held the

temperature about as steady as a roller coaster.)

The Lil’

Bertha was a great success. I made a good many melts with ‘er. However,

the Kastolite began crumbling from the many heats. (An AP Green

technical support rep told me that Kastolite was intended as a backup

lining, and that I should have used Mizzou!) Well, the original Lil

Bertha finally went south, so the rest of this page is devoted to the

process of producing the New and Improved Lil’ Bertha!

The original Lil’ Bertha

Another improvement that I made to the melting furnace is the

controller. Instead of using a range control mounted right on the

furnace body, I designed a beefed up version of a lamp dimmer and

mounted it up away from the heat of the furnace. As you can see in this

photo, the furnace and its controller are located in a corner of my

shop next to the electrical panel.There are a quite a number

of improvements to be made to the original Lil’ Bertha design. If you

are considering building this furnace for your shop, you may be able to

benefit from one or more of these improvements that I found useful.

There are two that I consider the most significant: 1. Using hard

firebrick for the furnace interior and 2. Making your own castable

refractory with high temp mortar and perlite.

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…

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2 of 10 1/9/2013 2:47 AM

The melting corner

Making grooves in firebrick is not as much a problem as first expected.

I took three abrasive fiber masonry cutting saw blades and mounted them

like a stack on my table saw arbor. I tilted the arbor to 30° and

raised the stack of blades so they made about a 5/8″ deep cut.

Detail of grooves in firebrick

Since the furnace was to use 6 firebricks in a hexagon, five

straight-grooved bricks were made and one with angled grooves. When

cutting the grooves, I cut each groove on all the bricks before making

adjustments to the fence, and spaced the grooves on exactly one inch

centers. The angled-groove brick serves as the terminal brick.The firebrick dimensions

are 4 1/8″ x 8 1/4″.

A straight-grooved

and an angled-grooved

firebrick for the

terminals

In making the bevels on the edges of each brick, it took some extra

attention to the angle needed to correctly align the ends of the angled

grooves with the straight-grooved bricks.Note how the path

formed by the grooves in the bricks resemble the ramps in a big-city

parking deck! This allows a single element to be used, spiralling from


3 of 10 1/9/2013 2:47 AM

top to bottom.

How the grooves in

terminal brick align

I used long hose clamps to solidly clamp the six firebrick together.

These clamps were left in place around the bricks and the refractory

rammed in around them.

Firebrick clamped

together in a hexagon

For the furnace body I used readily available galvanized 26 guage

heating/cooling air duct pipe. The furnace is 12 inches in diameter,

and so it used two 6″ pipe sections snapped together parallel to each

other to make one 12″ round shell. I put srews and nuts through right

at the seams to keep them from popping apart.The wooden formers were handy to


4 of 10 1/9/2013 2:47 AM

keep the furnace body nice and round while ramming in the refractory.

Wooden formers in place,

ready for refractory

I wish I had discovered this very simple and durable formula sooner! I

got the perlite at a local Wal-Mart, and the Worcester Brush High Temp

Furnace Cement at a hardware store.The recipe is very simple,

it’s just a 4 to 1 mixture, using 4 quarts of perlite to 1 quart of

cement. I used two types of cement, the black 3000°F and grey 2700°F.

There was quite a difference, and I recommend using the black stuff, it

thins a lot better and is smoother.Complete details of this do-it-yourself formula are

available at John Wasser’s Coffee Can Foundry site.

All you need to make

your own lightweight

castable refractory

The refractory compresses a fair bit as its rammed in, so I had to be cautious not to ram

it too hard.


5 of 10 1/9/2013 2:47 AM

Rammed full of home

made refractory

The handles are garage door lift handles, and I attached them with the

long carriage bolts that came with them. Also, I put two extra carriage

bolts in, so there’s extra reinforcing support for the refractory

Furnace lid before

filling with refractory

The legs are 1/2″ galvanized water pipe.

Three-legged furnace base

before filling.

Similar to the lid, the mounting hardware is left long, extending into the space that will

get rammed full of refractory. This is especially important here because the weight of a


6 of 10 1/9/2013 2:47 AM

full crucible rests in the center of the base.

Leg mounting hardware

is also refractory support

After having the bottom of the furnace base fall out several times

before it was fully cured, I decided it was time to devise a way to

support the very bottom of the base.So a series of 1/16″ holes

were drilled all the way around the bottom edge of the base, and a

pattern of wires woven so that there were no more than an inch square

of unsupported refractory in any area. This solved the problem and also

provides extra insurance against failure of the base under the weight

of a full crucible.

Making the refractory

support wires tight

This gives a better view of the base section with its supporting wires.


7 of 10 1/9/2013 2:47 AM

Completed furnace base

The home-brew refractory steams a LOT while it’s being cured, and this

can cause it to soften and stick the sections together. So a liberal

amount of baby powder (talc) was applied to the base first. It’s

probably still there.

Preparing to fire the

base and lid

The vent hole was formed when the lid was rammed up. I used a 6 oz.

dixie cup, rammed full of refractory (simply for support) to form this

hole. (Note the tapered sides of the vent hole.) The dixie cup was

removed after a few days of air drying.

Vent hole in lid

Furnace measures a mere 18″ tall and will handle a two quart crucible.The handles are

ordinary inexpensive garage door lift handles.


8 of 10 1/9/2013 2:47 AM

Furnace height is 18″

In this picture, I’m using the base and lid from the original Lil’

Bertha while air drying the new base and lid. Also, the new furnace has

a slightly deeper and bigger diameter chamber, so a larger crucible can

be used.Now you can purchase and download plans to build your own melting furnace!

USD 3.95 / Download

Melting a charge of aluminum

Comments


9 of 10 1/9/2013 2:47 AM

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Tariq Khan · Non

I want make furnace for m.s casting.

Reply · Like · November 25, 2012 at 11:46pm

Timothy Raynor

Do you sell these completely finished?

Reply · Like · October 7, 2012 at 5:24pm

Dynamo Dan

No, I do not sell them finished. But, they are easy to build, and that's why I

did not buy a completely finished one, lol.

Reply · Like · October 8, 2012 at 11:23am

B Scott Williams · Brigham Young University

I think this would be great to make so one can cast things. It is one of those projects

that I will be doing.

Reply · Like · July 17, 2012 at 11:53pm

Larry Gray · Russellville, Arkansas

What's the hottest this gets up too? and do you foundry guys think of using KAO Wool. or

also called KWool. Its a modern replacement for asbestos and isn't all that expensive.


Dynamo Dan

Yeah K-wool and Cerablanket etcetera are great, I have not personally used

them, but I've seen youtube vids of propane fired bronze melters using them

where the outside was still cool. I want to try it out sometime.


Dynamo Dan

This furnace gets up to bronze melting temps but its a whole different thing,

need flux and special crucible and tongs, I just like to stick with aluminum

because it's so easy to do, and just use a steel pipe crucible.


Alper Özdemir · Istanbul Technical University

Can you give brief explanation about the electric consumption? How much energy does it

take to smelting 1 kg aluminum scrap?

Reply · Like · September 7, 2012 at 11:13am

Dynamo Dan

I think it was something like 1 kwh for a pound of aluminum. Very

economical IMO. Much cheaper than propane, although it's slower.

Reply · Like · October 8, 2012 at 11:25am


10 of 10 1/9/2013 2:47 AM

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