Subject: Re: Oven/Furnace, advice?

From: [email-masked] (Phil Duclos)
Date: 11 Aug 1994 17:04:42 -0600

Not sure where oven/furnace/kiln boundary is either but I have built a 
few kilns so maybe I can help.

	Insulating (not structural) firebrick is used inside. This is lightweight
clay based brick with some silica/other added for fire resistance. It is
rated by the max temp it will survive. I forget who makes it but the ratings
go something like K-12 (1200F) thru K-32 (3600F). Higher temps cost more money
and translate into a "sandier" brick. K-12 are quite soft and lightweight. Easy
to cut with a hacksaw or file. Note that you are cutting an abrasive so expect
some serious wear on the tool.

	The outer shell better be metal as some heat gets through. I used light
gauge galvanized sheet. A shear and brake work best, but snips and a 2x4 can
work also. I used #6 sheet metal screws. One of the biggest decisions is
whether to have a "north-south" door or an "east-west" door. The problem with
a "north-south" door is that the inside of the door, which is hot, is directly
below your hand when inserting/removing items from the kiln. The "east-west"
door requires side clearance. Take your pick. I used a piano hinge for the door.

	You'll need some resistance wire for the heating element. We call it
"nichrome" (nickel-chromium) wire here and almost nobody in today's typical 
hardware store has heard of it. I found some in one of the few remaining
traditional hardware stores, you know, the ones where not everything is wrapped
in plastic? Electronic scrap yards are another good source. In a pinch a wire
specialty dealer or industrial supply should have some. I used 18ga wire which
had a resistance of 25 ohms per foot. I decided that I wanted a 10amp max
draw at 120 volts which resulted in 48ft of wire. I wound it on a mandrel
resulting in a 1/2" OD coil about 3ft long. It is very stiff and winding it
up definitely hardens it. Be careful!

	The large kiln I made is approx 9d X 12w X 9h. I used two heating elements
in series and ran it off 240V. The bricks I used were 9 X 4 1/2 X 2 1/4. I 
chose dimensions which required as few cuts as possible. Pick your own size.

	I laid out the bricks which constituted the interior walls and cut slots
about 3/4" deep for the heating coils to go into. The heating coils will anneal
and stretch when heated so its important to have a way to hold them up and
firmly in place. You really don't want contact between the work and the coils.
The ends of the heating coils were unwound a bit and stuck out the back where
they attached to copper wire with screws and nuts.

	A door handle and magnetic door latch finished it off.

	I have seen kilns where the bricks were pinned together to lock them in
place. I haven't tried this but it should work OK provided the wire is quite
stiff and fairly small gauge.

	I used "kiln cement" on one kiln to lock the bricks in place. Bad mistake.
The cement dried and shrunk, which pulled the edge of the brick off. It 
continues to flake off to this day, much to my exasperation.

	The kilns I have made easily attain 1400F. The large one is a little 
overpowered by the twin heating elements. Its temp swing is larger than I would
like once it gets up close to 1400F. I should change the programming of the
controller, but I'm lazy. Oh yeah, I used a "K" thermocouple and small panel
mount temp controller. Total cost ~$200, purchased from Thermx Southwest.
The controller is mounted separately from the kiln although beneath would have
worked OK, I guess.

	If you want a really big "oven" you might look for a "Blue M" brand oven.
They are used for burnin, etc and might go up to 700F, I don't know.

	Anybody need a heat treat furnace with inside dimensions of 9 X 2 X 5 and
built like the proverbial brick outhouse? I've got one and want to unload it.
email for details. cheap, works good! pick it up!

regards,

phil
[email-masked]
[email-masked]

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From: [email-masked] (Brian Springstead)
Date: 11 Aug 1994 22:45:08 -0400

Phil Duclos ([email-masked]) wrote:
: 	Not sure where oven/furnace/kiln boundary is either but I have built a 
: few kilns so maybe I can help.

[explanation deleted (save some bandwidth)]

: 	You'll need some resistance wire for the heating element. We call it
: "nichrome" (nickel-chromium) wire here and almost nobody in today's typical 
: hardware store has heard of it. I found some in one of the few remaining
: traditional hardware stores, you know, the ones where not everything is wrapped
: in plastic? Electronic scrap yards are another good source. In a pinch a wire
: specialty dealer or industrial supply should have some. I used 18ga wire which
: had a resistance of 25 ohms per foot. I decided that I wanted a 10amp max
: draw at 120 volts which resulted in 48ft of wire. I wound it on a mandrel
: resulting in a 1/2" OD coil about 3ft long. It is very stiff and winding it
: up definitely hardens it. Be careful!

I know of a good mail order source for "nichrome" wire.

Kelvin Electronics
10 Hub Dr
Melville, NY  11747

(516) 756-1750 or 800-535-8469
FAX:(516) 756-1763

Besides wire they sell all types of electonic goodies. Volmeters, Soldering,
breadboards, electronic parts, etc..
Hope this helps.

-- 
Brian Springstead | Remember no man is a failure who has friends.
                  | Thanks for the wings!
 [email-masked]  |                          Clarence

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From: [email-masked] (Carl F. Ijames)
Date: Fri, 12 Aug 1994 19:30:58 GMT

In article <[email-masked]>, [email-masked] (Phil Duclos)

> gauge galvanized sheet. A shear and brake work best, but snips and a 2x4 can

If the outside gets hot then I think aluminum would be a better choice than
galvanized.  Why breathe even a little zinc when you don't have to?

Carl Ijames     [email-masked]