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Michael D

Corelite shelves...need Advice

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Hello Ceramics Friends!

I'm starting a small business that involves making smaller handmade tiles. I bought a really nice ConeArt 27" square kiln and had hoped to stuff it full with shelves on 1 inch posts, maxmizing the number of shelves per fire. I'm only a half year into this and it is clear to me that investing in alumina shelves (3/4"") was not wise as it seems like half my electricity is spent in heating them up (and a half day longer waiting for them to cool down).

I would love to buy a kiln full of advancer shelves-- the weight, the thinness-- but I just can't afford that right now. 

So I am looking seriously at the Corelites. I plan to have two rectangles instead of a full square, wet-sawed down to about 11"x 22".  I have two questions:

  1. Is it ok to get the 5/8 thickness? I need as many shelves as possible, and will only be holding small tiles on them (covering over 90%). Do any of you forsee any problems with going this thin? (I almost always fire to Cone 6).
  2. I've read warnings about having a ramp more than 200f increase per hour.  My favorite schedule calls for double this. Can any of you share your experience and knowledge? Will it matter to fire a ramp at, say. 300f/hour? 

I really think these are going to work better for me. I hope I'm right.

Thanks in advance for your advice!

Michael 

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1 hour ago, Michael D said:

Hello Ceramics Friends!

I'm starting a small business that involves making smaller handmade tiles. I bought a really nice ConeArt 27" square kiln and had hoped to stuff it full with shelves on 1 inch posts, maxmizing the number of shelves per fire. I'm only a half year into this and it is clear to me that investing in alumina shelves (3/4"") was not wise as it seems like half my electricity is spent in heating them up (and a half day longer waiting for them to cool down).

I would love to buy a kiln full of advancer shelves-- the weight, the thinness-- but I just can't afford that right now. 

So I am looking seriously at the Corelites. I plan to have two rectangles instead of a full square, wet-sawed down to about 11"x 22".  I have two questions:

  1. Is it ok to get the 5/8 thickness? I need as many shelves as possible, and will only be holding small tiles on them (covering over 90%). Do any of you forsee any problems with going this thin? (I almost always fire to Cone 6).
  2. I've read warnings about having a ramp more than 200f increase per hour.  My favorite schedule calls for double this. Can any of you share your experience and knowledge? Will it matter to fire a ramp at, say. 300f/hour? 

I really think these are going to work better for me. I hope I'm right.

Thanks in advance for your advice!

Michael 

Core lites have been in use for quite some time and I believe there are qualifiers to that Sensitivity to rate, as in the very large shelves maybe prone to uneven heating especially face to face or a gradient across a large shelf. For normal use for which most automatic firing schedules go (up to 570 degrees per hour for fast glaze, 400 degrees per hour for normal glaze)  they I believe have performed well. @neilestrick has a bunch at his studio he has used for years without trouble I believe. If he doesn’t weigh in, maybe PM him.

An interesting add here is that if you intend on loading the kiln full of shelves with lots of small flat work you likely at some point will run out of power, especially to fire evenly as most kilns are nominally powered. So it’s almost  essential  That you use some form of light shelves. The heavier the shelf, the more energy you will need and firing shelves to perfection every time doesn’t seem to improve their appearance. They just look like shelves in the end. 

I should also add that from say 1500 degrees to end of firing radiant heat does all the work which is why offset stacking can keep things even in temperature. If the wares can’t see a glowing element or your shelf lags too much as a glowing radiator the kiln tends to fire unevenly. Especially with fast climbing schedules.

So in your case, core lites might be a great compromise between less mass and overall thickness limiting how much you put in the kiln to some practical level.

Edited by Bill Kielb

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I used a mix of high alumina and Corelites when I had a front loading electric. Corelites were 20 X 20 X 1" thick, they all warped after a few years of heavy use, firing to cone 6. I know other people haven't had warping issue with 1/2 round Corelites so maybe warping was due to the size of my shelves. I didn't have any cracked shelves and heated using typical ramps. 

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Bailey carries that size 11x22 in 1 inch corallites -$42 no cutting needed

seems cheap-the 5/8 at cone 6 with tile loads will warp over time I'm sure but the 5/8th thickness will warp earlier (less fires) I/m also sure.

I see with all tile loads the issue is the shelve thickness. Their is some other alternatives -the Chinese thin shelves -the are about 3/8 thick and will warp over time  as well these are from Laguna clay co.-also Kiln shelve .com has some cheaper shelves as well.The nitrate boned ones will not cut well as they are to hard.

If you cut the corallites (they cut easy on wet diamond saw)pay attention to the hollow spaces and try to cut so the edges have support (honeycomb inside)if possible . The stilts need to land in internal scripture otherwise they can slowly collapse . I have seen this happen at cone 10 in a friends kiln

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If you need to cut a Corelite, you can do it with a $4 masonry disc on a circular saw. You don't need a wet saw, although that would create less dust.

I've used 14x28x1 Corelite shelves in my big kiln for many years, and have never had problems with them. After several hundred firings they are still as flat as when I got them, and I've never flipped them. I've also got a bunch of 15" full round shelves for my small kiln that are 5/8" thick, and they have not warped, either. Every firing I do has a ramp faster than 200F/hr, sometimes as high as 500F/hr. As to which thickness to get for your tile work, I don't know. 11x22 is not very big, so they'll probably be  just fine at 5/8". I'd start with those and just budget for possibly needing to replace them after a few hundred firings.

According to the ConeArt web site, that kiln should use 10x20 shelves. Don't crowd the walls. You want at least 1" clearance between the shelves and the elements. 1 1/2" will give you more space for fingers when loading.

Firing tiles makes for a lot of mass in the kiln. You may find that you have to adjust your firing schedule to accommodate that. The kiln may or may not be able to keep up with fast ramps near the high end of the firing. Like Bill said, staggering the shelves may help distribute the heat better. Have you looked into tile setters? Depending on what size tiles you're making, they may be a better use of space in the kiln. Or even cut down Corlite shelves to make your own setters.

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Thanks for all of your advice!

It sounds like 1" Corelites would be fine; And maybe even the 5/8" .  If they warp after 50 firings, for example, maybe I could flip them or just replace them. And maybe I could strategically move the posts in a little-- say two inches toward center -- and give the shelf more support that way. 

Right now, if I place the shelves I have (which are modified 11x22"-- there is a good inch in there for clearance and fingers. 

I was originally going to use setters but because I am experimenting with different and small tile shapes it didn't add up. I figure that with thin and light shelves I could fit maybe 11 levels or more into the kiln for Cone 6. But having only filled it about 1/2 way each firing, I am seeing that the energy to heat up the tiles and especially the shelves is going to be enormous. (Not to mention how long I have to wait for it to cool down....)

 

unnamed.jpg

Edited by Michael D

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No matter how you fire them- sitters or shelves- you're going to have a lot of mass to heat up besides the tiles. That's just how it is with tiles. When pricing the tiles for sale, don't forget that your costs for firing also include wear and tear on the elements and shelves, although it will be difficult to know just how long the shelves will last. It may only be pennies (or less) per tile, but it adds up with volume.

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I am going to be doing some repeated firings of flat & low profile "smalls", such as herb markers (plant stakes) , business card holders, small catchalls etc. I have to decide (quickly!) between Corelite and Thermal-Lite. I am thinking the Thermal-Lite for long term-money is not the primary issue-I need light weight due to physical issues that are not going to go away and may get worse & I hate kiln wash. Is there any downside to firing loads like these with the Thermals that would make the Corelite preferable? I fire to 5-6/electric  L&L EZ. Thanks in advance-I'm ordering from Bailey.

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The only downside is they cannot be rapid cooled-but most electrics do not rapid cool anyways .

I would go with them as they are so much lighter-you will be amazed. They are brittle and the so take care of them outside the kiln.

Make sure of the sizing before ordering-that you have space for your fingers to load them.

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Thanks so much-I didn't think about finger hold! I really must gauge that---the kiln is 28" & the shelves are 26", but with the coils about 1/2" out from the sides, so I may have to go with the 21". I have fat fingers LOL. I do slow fire and also slow cool a fair amount & never fast cool. I have good dry storage, off the floor, for the shelves. 

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2 hours ago, LeeU said:

Thanks so much-I didn't think about finger hold! I really must gauge that---the kiln is 28" & the shelves are 26", but with the coils about 1/2" out from the sides, so I may have to go with the 21". I have fat fingers LOL. I do slow fire and also slow cool a fair amount & never fast cool. I have good dry storage, off the floor, for the shelves. 

I have customers that use the 26" Corelite in their e28 kilns and they work fine. The typical shelves are 25 1/2", so you're only losing 1/4" on each side. Plus with half shelves you can overlap them slightly if you're staggering the shelves. 

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OK, the deed is done! Six 26" half rounds on order-should be here by the approach of  fall. The Thermal-Lites will probably outlive me, but I had to get lighter shelves in order to keep on truckin'  

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