7 years ago
Long time lurker, very infrequent poster.
Let me introduce myself. I'm John DeArmond, Chief Engineer for
, a company that manufactures low cost induction
heaters. My personal interests are non-ferrous metal casting and
My business and personal interests came together after we received
several requests for a small induction heater metal melting furnace. I
decided to design a small table-top-usable furnace and see how it
worked. Here is the result.
And here are the ingredients
For obvious reasons, I call it my Kentucky Fried Furnace :-)
The crucible is a squat disposable propane tank with the top cut off.
On top of that is a blanket of Frax to electrically insulate the
crucible from the winding that follows. On top of the Frax is a
winding of fiberglass tape to hold everything in position. In use the
tape melts away but that doesn't matter because the refractory holds
everything in place.
The refractory is Kast-O-Lite. This was some 3000 deg rated stuff
that I had laying around the lab. It isn't the right refractory for
the job (relatively high thermal conductivity and high thermal
expansion coefficient) but it works adequately.
For the first melt I decided to set it up in my kitchen (yes, I'm
From left to right, a power meter to measure the power consumption, a
yogurt cup containing stuff to melt, a little white cube that is an
Onset Hobo 4 channel thermocouple data logger, our Roy induction
heater, an induction range with a batch of iced tea brewing and
finally the furnace.
The crucible holds about 6 lbs of aluminum and with the 1500 watt Roy,
takes about 18 minutes to melt, using between 1 and 2kWh (about a
$0.25 worth of electricity at our local rate). Using our soon to be
introduced Roy 2500 (pictured), the melt time is reduced to around 9
minutes and using the same amount of power.
Some aluminum parts during the melt.
Here is a photo of the melt ready to be fluxed, skimmed and poured.
As you can see, the Kast-O-Lite cracked despite my following their
casting and curing instructions to a Tee. It's also too thermally
conductive, allowing the surface temperature to rise to around 500 deg
F by the end of the melt. Nonetheless, the furnace is lightweight and
the whole thing is picked up wearing heavy welding gloves to make the
pour. My aim with the proper refractory is to keep the surface
temperature below 200 deg F.
I put a large worm gear pipe clamp around the top of the unit to
prevent the crack from expanding. After several melts, it has
remained about the same.
On Monday I'm going to talk to our guy at Larkin Refractories
about an appropriate
refractory for this application.
This has worked well enough that I've ordered materials for a 20lb
furnace to be built into a 5 gallon steel pail. I'm using this ladle
as the crucible. This unit will use a 3500-4000 watt heater to keep
the melt times in the same ballpark.
So now my businessman instinct kicks in and I wonder if there is any
market interest in small furnaces that can be used indoors and without
any special ventilation. Let the discussion begin.
Tellico Plains, Occupied TN
See website for email address