My  Cheap Electric Pot Furnace
I was very impressed with Brice and Thumb's electric furnaces
that were a variation on standard ceramic kilns. I thought that there might be a way
to improve on element life by completley sealing off the melting chamber. I'm also interested
in preserving the heat that is lost through the large door openings of the ceramic kilns. The third place I wanted to
modify was the element replacement procedure. I hope that this furnace will make melting with
Kanthal A-1 elements an inexpensive and easy option.

I was able to get this furnace up and melting for under $1400.00
It will probably cost me another $150.00 to finish the pneumatics for the door.

$185 controller ( Eurotherm ramping with guaranteed soak-Surplus)
$150 thermocouple
 $50 SSR (surplus)
 $25 Mercury Relay (ebay)
$270 crucible (Engineered Ceramics)
$180  9 A-1 elements (jen-Ken)
 $50 85# frax (surplus 25 cents a pound + shipping)
$125 steel
$100  casters
$115 IFB
 $60 Castable
$40 (Assorted surplus and new electrical parts)
        Nema 4 enclosure, muffin fan, cord, lugs, conduit etc.

Total $1350.00

I have had this furnace running since 8-17-01.
I used the same elements in Brice's custom Jen Ken kiln.
6-12.7 ohm 15 guage 63" long elements run 2 each in series for
3 sets of 25.4 ohms. this gives 1743 watts per leg with my 208volt 3 phase power.
I've melted batch successfully but with only 5.2 KW it seemed a little slow in its
max recovery rate while batching. It was only going up about a degree a minute at 100% power.
I ran another line into the extra unused set of elements that I had installed for spares, ala Thumb.
I'm controlling them with a second SSR. I now have a better recovery time and almost 7 kilowatts of power.
I'm working with Mark at Duralite to come up with a hotter set of elements in
a heavier guage to use the next time around.

I'm using about 70-85 KW's a day which I feel is decent and it's making great glass.
I have my controller set to 80% maximum possible output to the elements.
It idles at 1850 when I'm not blowing at about 35% power. I've been blowing at 2150, Charging at 2250, and cooking at 2325.
The "s" type thermocouple reads between the elements and the pot about
5" down from the top of the chamber.
 
  All photo's are linked to quick loading high res images.

2" x 2" x 1/8th" box steel frame. 34" x 34" x 1/4" steel plate with 2 3" x 3/16" angle braces on bottom.

1 course of mortared 2800 degree IFB for the floor sitting on 4"
of fraxboard scraps.

low iron 2600 degree IFB brick with 3 gooves per brick.
I read that iron content in the brick is the thing that eats the
protective oxidation that the elements produce so I spent a few cents extra
and bought special low iron bricks.
I mortared the bricks together and used band clamps to hold them
while they dried.

I rigged a chainfall system for easy crucible removal/ replacement.

at this point I've added 1/8th " plate sides with a back section of
concrete tile board to insulate where the elements poke through.
(this tile board was a great tip I found on the Hot Glass Board!)
I packed it with scrap frax
and put the E C crucible in on a 8" x 8" x 2" piece of kilnshelf.

This is the hinged frame that will hold the crown and lid/ door assembly.
This should be the key to quick and easy element replacement.
I will be able to empty and cool the furnace one day, then return the next
and just open this door, hoist up the pot, and change out the elements without
any repacking of frax, etc.

I put down a piece of plywood to leave the desired thickness of a gasket space
between the crucible and crown and made foam negatives for the crown and gathering port and then cast in 5"
of 2900 degree lightweight insulating castable. ( sorry I forgot to take a shot before I packed it in. )
I used my roll the casting around on a rough floor trick to vibrate the castable well.

a shot of the back.

    This is after the castable cured for 2 days and I removed the molds.
I took less than 100 #'s to cast this piece.

This crown with it's frax gasket creates a "covered pot" that will isolate my Kanthal A-1 elements from any corrosive
fumes that the melting batch creates. Also eliminates cullet popping onto the elements and unfortunately keeps direct
radiant heat from the elements away from the batch.
 

The bottom side of the casting showing the hole for the thermocouple.

A view through the gathering port into the crown. I wanted to keep the "crown
area as small as possible as it has no direct heat from the elements. It's just a 2" bump over the crucible.
The gathering opening is 8" x 11".

This is the frax gasket going in  that seals the lid and base and will hopefully make it quick
and easy to pop the lid, pull the pot, and pop in new elements when I need them. I estimate it being a 1 hour job the way
I have the furnace configured. ( I feel at this point now that the thing is running that I should have used 6" more insulation all around.
There's about 6" of frax between the IFB and the steel walls and they are hotter than hell when it's up to temp.)

I've added a replaceable 1" kilnshelf sill, some IFB and a 5" fraxboard door seal.
I then filled in the rest with 5" of scrap frax and put on the steel plate lid.

Another view of the female portion of the door. ( I was inspired by Thumb's door and I'm
happy with how it's working! )

This is the mold for the cast door. the erector set angle holds 4 bolts in place that the castable surrounds.

The cast door after curing. I've got a temporary hinge system in place now that I will
automate with a pneumatic footpedal.

The back view of my furnace. Note the innovative use of the 4 jaw chuck
from my lathe as a counterweight.

here's the description of what's going on in here, and how I wired in my spare
elements as a single phase booster circuit. It comes in in a separate cable from it's own breaker.

One nice thing about this door system is that it is cool to gather from.
I was afraid that the door might radiate alot of heat on your hand but it's
not that hot, very comfortable.

I just need to paint it now and find some needle vales for my pneumatic cylinder
so I can automate the door. 2 weeks and it's still making glass!
I've posted my parabolic gloryhole page here:
http://www.kurtwalrath.com/para/parahole.htm
I've posted my revised studio page here:
http://www.kurtwalrath.com/largeglassstudio/studio.htm