bottom heat kiln. - WarmGlass.com

bottom heat kiln.

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Michael Stevens
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bottom heat kiln.

Postby Michael Stevens » Mon Mar 16, 2020 6:02 am

I ordred a kiln that has a heating element on the sides and the bottom. I assume I need a thick shelve on kiln posts above it so shelf won't crack and airflow

anyone have experience with bottom heat

Brad Walker
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Re: bottom heat kiln.

Postby Brad Walker » Mon Mar 16, 2020 8:13 am

What does the manufacturer recommend?

Sharol
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Location: Tennessee

Re: bottom heat kiln.

Postby Sharol » Wed Jul 22, 2020 11:33 am

Hi.

I’m considering a new kiln with top and floor elements and saw this post. I’m curious if anyone here sees a disadvantage to this arrangement. I’ve seen where some European manufacturers offer this as an option in their glass kilns. The kiln I’m considering has a 27” x27” x 17” (depth) chamber. Clamshell design. All rigid fIber sides and top and a brick floor.

Your input would be very much appreciated!

Thanks!
Sharol

DonMcClennen
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Re: bottom heat kiln.

Postby DonMcClennen » Thu Jul 23, 2020 8:59 am

I've been firing glass (large and small) going on 30yrs. Always with top elements and a few side ones.. I can think of numerous reasons to not want bottom elements. I suggest you reconsider!
"The Glassman"

Brad Walker
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Re: bottom heat kiln.

Postby Brad Walker » Thu Jul 23, 2020 9:13 am

Bottom elements have been used in pottery kilns because a clay piece (especially a flat piece) on a shelf at the bottom of the kiln may not get enough heat to fully fire. (Top of kiln hotter than bottom of kiln) The bottom element helps even out the heat. This is especially useful in pottery firings where multiple shelves are used. Multiple shelves, which are common in pottery, can also contribute to lower temperatures at the bottom of the kiln.

In a glass environment we don't have the same kinds of worries as the potters do. Elements in the bottom of the kiln would be useful for casting large pieces, but I'm not sure they're useful for firing glass on a single shelf.

Does the kiln you're looking at allow you to turn off the bottom elements if not needed? Many of these kinds of kilns do. The big risk with bottom elements is crap (technical term) falling onto the floor elements and potentially damaging them.

Michael Stevens
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Re: bottom heat kiln.

Postby Michael Stevens » Thu Jul 23, 2020 9:42 am

well overall this little pottery kiln has done quite well. when slumping it really helps. overall I've had very few bubble problems that I got with top heat.

if I fuse 2 or 3 shelf layers the bottom is hotter so I put things that need hotter temp at bottom.

I do put 3 inch stands to raise bottom shelf.
I do sometime need to crack the lid to keep temp raise slower before 500c if close lid even with a slow ramp. can crack large sheets.

a glass kiln would be ideal but at 4 times the cost I'm. pleased with what I have

Sharol
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Location: Tennessee

Re: bottom heat kiln.

Postby Sharol » Thu Jul 23, 2020 10:19 am

Thank you all for your replies.

Brad, the “crap” issue has been one of my primary concerns with this configuration. No, the proposed bottom elements can not be controlled separately from the top elements.

I will not be doing any deep casting and never fire multiple shelves, so I’m going to pass on the bottom element configuration.

I posted a few months ago about my search for a replacement kiln and received great Input from Board members. I don't have the wherewithal to build a kiln myself and so I am discussing a quasi-custom build with a manufacturer I have had good luck with in the past. It was his initial recommendation to install the floor elements.

As things stand now, it is:

1. Clamshell, single opening design
2. Sides and top hard fiber board
3. Floor brick
4. Interior chamber 27 x 27” x 18” height (To accommodate 24” square shelf)
5. Quartz encased top elements
6. 45 amp, single phase wiring (NEMA 6-50 receptacle & plug). I have 200 amp service to my shop and so could handle more juice, but was avoid to avoid hardwiring or going to 3 phase.
7. Solid state relays

I’d appreciate your opinions andwisdom on this.

Thank you!
Sharol

jim simmons
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Re: bottom heat kiln.

Postby jim simmons » Thu Jul 23, 2020 11:39 am

As long as you are having it built, why don't you have a switch installed so you can turn the bottom elements off?
The other Jim

DonMcClennen
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Location: Ontario

Re: bottom heat kiln.

Postby DonMcClennen » Fri Jul 24, 2020 10:25 am

someone once made a wise statement: Glass needs to "see" the heat.. while pottery only needs to "feel" it! That is why elements in glass kiln roof and no multiple shelf layers when firing :) . Don
"The Glassman"

Buttercup
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Location: S.E. Queensland Australia

Re: bottom heat kiln.

Postby Buttercup » Sun Jul 26, 2020 10:32 pm

Hi Sharol,

I'm curious about the 'Hard Fibre Board' you mention, having a bad experience with a fibre kiln: see my post in your earlier thread: viewtopic.php?f=2&t=43134&p=362735#p362735
Do you have a link to the material, please. It would certainly cut down on weight and space compared to a brick kiln.

Sharol
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Location: Tennessee

Re: bottom heat kiln.

Postby Sharol » Sun Jul 26, 2020 10:50 pm

Hi Jen. I’m sorry, but I don’t have a specific spec sheet or manufacturer link for the hard fiber board. I believe it is the same material as is fairly common in kiln lids and also in Jen-Kens all fiber kilns.

Buttercup
Posts: 555
Joined: Mon Jan 28, 2008 5:22 pm
Location: S.E. Queensland Australia

Re: bottom heat kiln.

Postby Buttercup » Sun Jul 26, 2020 11:18 pm

Thanks, Sharol.

I've heard of, but don't know anything about Jen-Ken kilns but I can check their website.

I'm sure the technology has improved since the disaster I described before. Good luck with the new kiln.


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