Max. Kiln Size??

This is the main board for discussing general techniques, tools, and processes for fusing, slumping, and related kiln-forming activities.

Moderators: Brad Walker, Tony Smith

Post Reply
Gil Reynolds
Posts: 9
Joined: Thu Mar 13, 2003 4:06 pm

Max. Kiln Size??

Post by Gil Reynolds »

Kiln Size??

Anyone have a formula to calculate the biggest size kiln interior I can have using 120 volts and 12.5 amp? My two KW per cubic foot is falling short. I’m using 2â€
Carol Craiglow
Posts: 37
Joined: Mon Mar 10, 2003 10:48 pm
Location: Santa Fe NM USA
Contact:

Post by Carol Craiglow »

Well, here are my calcs, having just recently designed a kiln! I think they're correct.

Okay: amps = watts/volts so,

12.5 amps = X watts/120 volts.

Multiplying both sides by 120 to solve for X gives 1500 watts.

According to the euclids.com website, a kiln for glass slumping/annealing should be designed at 2 - 2.5 watts/square inch. Using the high end of the range to include fusing, let's use 2.5 watts/1 square inch.

We've got 1500 watts available, and the question is how many square inches will 1500 watts heat?

1500/X = 2.5/1

so to solve for X square inches, divide 1500 by 2.5 which gives 600 total square inches for the kiln. There are 6 surfaces in the kiln, so dividing by 6 gives 100 square inches for each side. So the easiest solution is for each side to be 10 inches by 10 inches. I'm not sure how much insulation the 2.5 watts/sq inch is based on...but this should be close.

Carol
Bob L Workshop - Take Two
June 10-11-12
Santa Fe NM
http://www.warmglass.com/phpBB/viewtopic.php?t=10420
David Williams

Re: Max. Kiln Size??

Post by David Williams »

[quote="Gil Reynolds"]Kiln Size??

Anyone have a formula to calculate the biggest size kiln interior I can have using 120 volts and 12.5 amp? My two KW per cubic foot is falling short. I’m using 2â€
Brian and Jenny Blanthorn
Posts: 353
Joined: Mon Mar 10, 2003 5:25 pm
Location: UK
Contact:

Re: Max. Kiln Size??

Post by Brian and Jenny Blanthorn »

[quote="Gil Reynolds"]Kiln Size??

Anyone have a formula to calculate the biggest size kiln interior I can have using 120 volts and 12.5 amp? My two KW per cubic foot is falling short. I’m using 2â€
Image
Bert Weiss
Posts: 2339
Joined: Tue Mar 11, 2003 12:06 am
Location: Chatham NH
Contact:

Re: Max. Kiln Size??

Post by Bert Weiss »

[quote="Gil Reynolds"]Kiln Size??

Anyone have a formula to calculate the biggest size kiln interior I can have using 120 volts and 12.5 amp? My two KW per cubic foot is falling short. I’m using 2â€
Bert

Bert Weiss Art Glass*
http://www.customartglass.com
Furniture Lighting Sculpture Tableware
Architectural Commissions
PaulS
Posts: 155
Joined: Mon Mar 10, 2003 6:45 pm
Location: Belize
Contact:

Post by PaulS »

Not exactly what you had in mind Gil, but you can see what I've done with help from Dudley Gibberson at Joppa Glass works on the following page;

http://www.artemisglass.co.uk/studio5/s ... ninfo.html

Image

The shelf size is 400mm square, fuses and slumps fine. A 300mm square plate fuse firing uses 8 units of electricity.

Hope this helps,

Paul
It ain't where you're from, it's where you're at!
Kevin Midgley
Posts: 773
Joined: Mon Mar 10, 2003 11:36 am
Location: Tofino, British Columbia, Canada

Post by Kevin Midgley »

Your heat loss is through air flow through the fibre. Beat that and a 6 cubic foot kiln will run on 23 amps (30 amp) 220v breaker. Kevin
Tony Smith
Posts: 1037
Joined: Sun Mar 09, 2003 5:59 pm
Location: Massachusetts, USA
Contact:

Post by Tony Smith »

Your heat loss is through air flow through the fibre. Beat that and a 6 cubic foot kiln will run on 23 amps (30 amp) 220v breaker. Kevin
Kevin:

Is this a custom made kiln that you are talking about? Any limitations on high end temperature? What about ramp rate? How did you beat the airflow problem? Was it just from building a tight fiberboard box?

Could you post a photo?

Tony
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun
Gil Reynolds
Posts: 9
Joined: Thu Mar 13, 2003 4:06 pm

Post by Gil Reynolds »

Thank you all for your input. There is a lot of good stuff here. What I am finding out is that it is not a cut and dry affair. Quite a few variables need to be considered and addresses.

Carol – You numbers make the most sense of all the info I have read. Many Thanks, that’s good stuff.

David -Yes, you. I’m thinking just smaller than a bread box, and no you are not clueless, your wealth of knowledge doesn’t support that claim.

Brian and Jenny – Thanks, I’ll check it out.

Bert – You make a good point. Watts per Sq. Ft. is not necessarily a fixed ratio. Shallow does reduce cubic size, but increase the risk of thermal shock. There is a fine line between trade offs. I am hoping for a hot rod performance for say, quick firing painted piece in 15 – 20 minutes as well as slow fusing cycles. I’ll let the controller do the slow firings. I‘ll try adding more insulation to the roof. Thanks

Paul – Great looking kiln. You did a really good job. Is it 220 volts? I am not sure what 8 units of electricity would equal in terms of kilowatt hours, is it a strait conversion? Thanks

Kevin and Tony - Fiber heat loss – isn’t it density related? How do soft bricks compare?

Gil
Don Burt
Posts: 574
Joined: Sun Mar 09, 2003 8:45 pm
Location: Bloomington, Indiana
Contact:

Post by Don Burt »

Gil Reynolds wrote: snip
I am hoping for a hot rod performance for say, quick firing painted piece in 15 – 20 minutes
snip
Yes, Gil, please solve this. The Hoaf is too pricey. I'll buy your prototype electric painters kiln.

not sure why you're putting the 120v constraint on yourself though.
Brian and Jenny Blanthorn
Posts: 353
Joined: Mon Mar 10, 2003 5:25 pm
Location: UK
Contact:

Post by Brian and Jenny Blanthorn »

Gil Reynolds wrote:Thank you all for your input. There is a lot of good stuff here. What I am finding out is that it is not a cut and dry affair. Quite a few variables need to be considered and addresses.

Carol – You numbers make the most sense of all the info I have read. Many Thanks, that’s good stuff.

David -Yes, you. I’m thinking just smaller than a bread box, and no you are not clueless, your wealth of knowledge doesn’t support that claim.

Brian and Jenny – Thanks, I’ll check it out.

Bert – You make a good point. Watts per Sq. Ft. is not necessarily a fixed ratio. Shallow does reduce cubic size, but increase the risk of thermal shock. There is a fine line between trade offs. I am hoping for a hot rod performance for say, quick firing painted piece in 15 – 20 minutes as well as slow fusing cycles. I’ll let the controller do the slow firings. I‘ll try adding more insulation to the roof. Thanks

Paul – Great looking kiln. You did a really good job. Is it 220 volts? I am not sure what 8 units of electricity would equal in terms of kilowatt hours, is it a strait conversion? Thanks

Kevin and Tony - Fiber heat loss – isn’t it density related? How do soft bricks compare?

Gil
I am no expert in this but

Consider more insulation

From some chat over craftweb

At low temps fibre should B loose at high temps like in hot glass it should B packed tight
Image
PaulS
Posts: 155
Joined: Mon Mar 10, 2003 6:45 pm
Location: Belize
Contact:

Post by PaulS »

Gil Reynolds wrote: Paul – Great looking kiln. You did a really good job. Is it 220 volts? I am not sure what 8 units of electricity would equal in terms of kilowatt hours, is it a strait conversion? Thanks
Gil
Thanks. Yes, 220.

@ 8 pence per unit it is cheap to run. Maybe 2US$ for a full fuse.

The hearth is brick for strength & rigidity, the lid is 3 x 25mm thicknesses of fibreboard on the top and sides.

The fibreboard roof allows heat to escape at such a rate to not allow devit. I thought if brick was used for the lid it would stay at fuse temp too long. Also in time the brick would deteriorate and drop bits onth the glass.

So cooling from full fuse (800degC) to the upper annealing point (570degC) takes about an hour.

The controller then kicks in and controls the rate of cooling down to the strain point (370 degC).

Paul
It ain't where you're from, it's where you're at!
Lynne Chappell
Posts: 186
Joined: Fri Mar 14, 2003 2:05 am
Location: Surrey B.C. Canada
Contact:

Post by Lynne Chappell »

One hour from full fuse to annealing point sounds like it's holding a lot of heat. I've got brick kilns that cool way faster than that.
PaulS
Posts: 155
Joined: Mon Mar 10, 2003 6:45 pm
Location: Belize
Contact:

Post by PaulS »

Lynne Chappell wrote:One hour from full fuse to annealing point sounds like it's holding a lot of heat. I've got brick kilns that cool way faster than that.
Perhaps I over-insulated then; too much and it won't cool, too little and it would take a lot of current, even on the annealing ramp.

Must be within that fine balance of insufficient insulation to hold heat too long to cause devit, and enough insulation to stay warm enough for the elements to not cut in, if you see what I mean.

I heard a Doctor on the radio say that if he studied anyone long enough, he could find something wrong with them!

Meantime, it works pretty good and it's satisfying to get predictable results. :D

Paul
It ain't where you're from, it's where you're at!
Post Reply