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Silicon Carbide Shelves

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Does anyone here actually use the cheap silicon carbide shelves in a gas kiln?  They come in 2 flavors, one with a slit on the side and one that is solid.  I'm wondering if anyone here has actually had one fail in a fire?  I have 3 of the solid kind that have cracks.  None of the slotted kind have ever shown a crack.  I need to cut one for a damper.  I also have a solid that has a significant warp.    That would be my first choice to cut up. 

If we ever get back to business as usual, I'll be able to get a second set of Advancers and the cheapies will go to the back of the bus.

The shelves appear pretty solid.  I can't see any flex across the crack when I put the shelf on the edge of a bench and try to flex it.  I'd like to hear if anyone has had a catastrophic failure.

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I bought a few of the slotted ones in 2006 or so, and they all warped in my gas kiln at cone 10, and continued to warp at cone 6 in my electric kiln. Now I just use them as a cover shelf at the top of the kiln load. None of them will be all that easy to cut. If you don't have a diamond wet saw it will be a real bear, and even then it'll put a lot of wear on the blade. You may want to consider just buying a cheap cordierite shelf that's close to the right size from your local clay supplier and cutting it to fit. Those can be cut with an abrasive disc on a circular saw, only takes a minute, and they work fine as a damper shelf. That's what I've always used in the kilns I've built.

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(Does anyone here actually use the cheap silicon carbide shelves)

These are actually the recrystalized silicone carbide-not true silicon carbide as they all once where.

All made in China but still rock hard

They still are much harder then a old school silicon carbide shelve The process is much different and thats why they are so hard. The only way you can cut them is a wet diamond saw and they still are one tough nut to cut.

Does not matter if they have the slit or not they are recystalized which means they where made in a nitrogen rich enviroment (no oxegen at all)fired in electric arc furnce about cone 25-30 if I recall. They are hard and brittle at the same time. They lay waste to diamond saws

I have 4 of them-I do not use them in loads anymore-Except the top the load in my salt kiln to protect from fallouts-they all warp at cone 10 temps

Yes I know of some crack failures  taking doewn the load-stilt the crack as it can open anytime. Let us know how the cutting goes????

I have a wet diamond saw (MK Brand) and I like my blade so I only cut soft stuff like high fire bricks a high fire tile

 

 

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3 hours ago, CactusPots said:

Does anyone here actually use the cheap silicon carbide shelves in a gas kiln?  They come in 2 flavors, one with a slit on the side and one that is solid.  I'm wondering if anyone here has actually had one fail in a fire?  I have 3 of the solid kind that have cracks.  None of the slotted kind have ever shown a crack.  I need to cut one for a damper.  I also have a solid that has a significant warp.    That would be my first choice to cut up. 

If we ever get back to business as usual, I'll be able to get a second set of Advancers and the cheapies will go to the back of the bus.

The shelves appear pretty solid.  I can't see any flex across the crack when I put the shelf on the edge of a bench and try to flex it.  I'd like to hear if anyone has had a catastrophic failure.

I have a bunch of the so called bonded nitride From Axner. Look alike with no slots. They probably have fifty firings or more on them, some are slightly warped. Some arrived slightly warped. No sign of failure yet  Glaze does not appear to stick to them. Have gingerly cut with a diamond wet saw but they are very hard. Maybe harder than the 1” silicon carbide. Never expected them to last forever, just was a cheap way to fill a budget for a new kiln install and try them out. Overall I say they have worked out acceptably. No cracks yet.

Edited by Bill Kielb

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I need a 3/8" thick damper, so I'll do what I can to cut one of these shelves.  1/2" might have worked, the used shelf I picked up for this last firing had enough warp to keep it from closing easily at top temperature.  Most of the shelves I have don't have a significant warp.   They sit flat when 4 posted.

I only have a Skilsaw, not a wet saw, so if the diamond blade makes the one cut, that will be it for the blade.

No hurry, since I don't expect to have another load any time soon.  I'll try my supplier again and see if he has anything better.

No one has ever had a failure with these shelves.  More than the alumina shelves in electric kilns can say.

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1 hour ago, CactusPots said:

I need a 3/8" thick damper, so I'll do what I can to cut one of these shelves.  1/2" might have worked, the used shelf I picked up for this last firing had enough warp to keep it from closing easily at top temperature.  Most of the shelves I have don't have a significant warp.   They sit flat when 4 posted.

I only have a Skilsaw, not a wet saw, so if the diamond blade makes the one cut, that will be it for the blade.

No hurry, since I don't expect to have another load any time soon.  I'll try my supplier again and see if he has anything better.

No one has ever had a failure with these shelves.  More than the alumina shelves in electric kilns can say.

Maybe rent a wet saw from the big box. Skill saw and no water might be really really tough. Ruin their blade.

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1 hour ago, CactusPots said:

No one has ever had a failure with these shelves.  More than the alumina shelves in electric kilns can say.

I would hardly say that the experiences of 3 people on this forum means that they never fail. Plus way, way, way more people use the cordierite shelves in electric kilns, so you're way more likely to hear about failures. Plus shelves are more likely to crack in electric kilns because of the way they heat, regardless of what type of shelf they are. But yes, 3 people here have had good experiences with the cheap thin shelves in gas kilns in terms of them not completely cracking in a firing. But half of the ones I had warped so badly that I had to throw them out after just a few years of use, so I wouldn't call them a success. And one did crack at the slot, but did not totally fail during a firing. I threw it out before that could happen. I'd say my Corelite shelves have out performed them big time. But none of that matters when it comes to damper shelves. They just don't get very hot in that location.

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17 minutes ago, Bill Kielb said:

Maybe rent a wet saw from the big box. Skill saw and no water might be really really tough. Ruin their blade.

I'll check out renting a wet saw.  It's an 18" cut though,  there are some big floor tiles out there, so there must be a saw.  I really don't care about the blade.  One cut is all I want.

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7 minutes ago, neilestrick said:

I would hardly say that the experiences of 3 people on this forum means that they never fail. Plus way, way, way more people use the cordierite shelves in electric kilns, so you're way more likely to hear about failures. Plus shelves are more likely to crack in electric kilns because of the way they heat, regardless of what type of shelf they are. But yes, 3 people here have had good experiences with the cheap thin shelves in gas kilns in terms of them not completely cracking in a firing. But half of the ones I had warped so badly that I had to throw them out after just a few years of use, so I wouldn't call them a success. And one did crack at the slot, but did not totally fail during a firing. I threw it out before that could happen. I'd say my Corelite shelves have out performed them big time. But none of that matters when it comes to damper shelves. They just don't get very hot in that location.

Corelite are the hollow shelves?  Aren't those like 3/4"?  The Advancers are big bucks, but definitely the best, don't you think?

The used shelf I got for a damper for this last firing was 12 x 20 x 1/2 ".  It had a full 1/4" warp.  It slid into my damper opening when the kiln was cold, but when I went to close it up at the end, I had to force it in.  I'm guessing it expanded with the heat.

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4 minutes ago, CactusPots said:

Corelite are the hollow shelves?  Aren't those like 3/4"?  The Advancers are big bucks, but definitely the best, don't you think?

The used shelf I got for a damper for this last firing was 12 x 20 x 1/2 ".  It had a full 1/4" warp.  It slid into my damper opening when the kiln was cold, but when I went to close it up at the end, I had to force it in.  I'm guessing it expanded with the heat.

Sure, Advancers are the best, if you have the money. There have been a lot of discussions about the cost/benefit  of using Advancers here on the forum, and the general consensus is that they're more worth the cost in a large gas kiln than in a short electric kiln. Some Corelites are slightly thicker than standard cordierite shelves, but they are much lighter and less prone to warping. I've got a set of 14x28 that have gone through hundreds of firings without the slightest warp. For me they're the best combination of cost and durability.

As for your damper, I never make damper shelves fit that tight because they're bound to warp a little bit just from being hotter on one side, even if it's not a permanent warp.

Just as a side story in regards to heat expansion warping- on electric kilns the lid always warps like a contact lens during firings due to the hot face expanding more than the cold face. On my L&L DaVinci top loading electric kiln, which has an interior of 31x44 inches, the center of the original 3" thick lid would be a full inch lower than edge at the peak of the firing. It looked like it was about to fall in. Totally normal, and they never had a failure, but man was it freaky to see. I've since rebuilt the lid at 4.5" thickness, and it doesn't move like that any more due to the thickness and different construction. But over the length of a kiln shelf damper I wouldn't be surprised to see 1/4 expansion.

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On the 18 inch cut . The saw say cuts ( 9inchs) then turn it around for another 9 inch cut=18 inch cut.

many full size saws do14-18 inches-12 for sure-flip the piece and cut the other side-harbor freight sells a cheap one as well

MK is a spendy brand

wet diamond saw is your only option-you might make it with  alow flow hose on the skill saw and maybe 2-6 blades

The mullite 1/2 shelve will be a better damper as they can take the thermo shock about 100 times better than recrystalized silcon carbide shelve which do not like uneven heading which a damper is.

I had one of those Chinese shelves crack on my floor on car kiln -I tossed it into the scrap pile. 

Edited by Mark C.

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I'm wishing I didn't get these SC shelves.

Should have got the Corelite. Ah well.

I got mine cut, and I reckon the cutting warped em more. 

I certainly wouldn't spend the time and energy cutting em if there is a possibility it won't work, and that possibility seems large.

You're almost better off vicing it up and karate chopping it.

Sorce

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When I built the kiln, the flue box is a set of cast inter locking pieces that have a 1/2" slot for a damper.  I should have allowed for the slot to be larger, it would have been easier to fit a damper.  I had been using a broken SC shelf for a long time.  Basically worked fine, probably was cracked.  I knocked it over onto the wood floor and it broke.  I've got some time to look into this, maybe cutting a shelf isn't the best way to go.  If I rent a wet saw, I'll have to buy a blade for that I'm sure.

If anyone was interested in building a fiber downdraft, I'd suggest checking out my flue design.  It's original and works really well.

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Seems like all good points but picking a material for a particular use is key. Also seems like for damper use, cordierite or high Alumina  Have proven themselves so maybe pick the best material and provide reasonable clearance for the damper. As far as resistance to glaze, non issue in this case.

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1 hour ago, CactusPots said:

Is there any other shelf besides the SC in less than 1/2"?    A 3/8" shelf is the best fit, but I don't think cordierite or high alumina comes in those sizes, right?

Maybe worth just cutting out the top of the slot 1/4 -1/2”. You can always easily mitigate any excess dilution air sucked in above the slot. I doubt you would need to, many of these have significant excess clearance and seem to work fine.

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Its pretty common to have the damper slot not be right. Its one area thats often ignored until its to late. Or not thought out for long term. Most are made what left over after kiln is just about done and not thought about until it fails

I have been around many a kiln already built where the damper is just a mess. Many times there is 10 feet of hard brick on the chimney so the fix is not easy

I know of no shelve other than a sic thats less than 1/2 inch

The standard damper slot is made with splits thats a brick cut in half the longways-they are 1.5 thick 4.5 x 9 inch wide-they work best with a 1 inch thick shelve-so mullite or high alumina shelves work great in that slot.They even sell them on Amazon.

dampers take a lot of abuse-hot at one end cold at the other. Sic shelves do not like that at all.

If possible (often not) you would be better off thinking about a way to enlarge your slot to take a better shelve.Thats the best long term solution

You could with a portable grinder and a grinding CUP grind down a mullite shelve to less than 1/2 inch pretty easy-mullite shelves are soft and gring easy-it will not look pretty but can be made to be less than 1/2 inch pretty fast with a grinding cup on a large hand grinder (I show one of these setups  in a post on shelve washing if you look it up)

Thats my best suggestion -maybe a 20-30 minute job on a new 1/2 inch mullite shelve-leave one side smooth grind it all on the other side-wear a good respirator .

Edited by Mark C.

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41 minutes ago, Bill Kielb said:

Maybe worth just cutting out the top of the slot 1/4 -1/2”. You can always easily mitigate any excess dilution air sucked in above the slot. I doubt you would need to, many of these have significant excess clearance and seem to work fine.

I was thinking along the lines of modifying the slot myself.  Lifting the chimney off looks like a engineering job I'd rather avoid.  Awkward and heavy.  I castigated myself already for making the slot too narrow. 

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I've always made damper slots a half brick in height (1.5"), then blocked the opening gap with a piece of angle iron or flat steel. If the shelf warps, it's only the entry point that's narrow so it can still go in and out. And if it does happen to bind, you can just grind the welds and move the steel. I've also used kilns that have a big gap at the damper shelf entry point, and you just sit a piece of brick on top of the shelf to block the gap. It doesn't have to be perfectly sealed, just not a big hole that would act as a passive damper and spoil draft.

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ok, guys, i know nothing about building a kiln, less about gas firing.  BUT if the heat is no more than a typical cone 6 firing, maybe a pizza stone could be cut to fit.  some are not able to go that high but i use 3 different ones at cone 6.

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3 hours ago, CactusPots said:

I was thinking along the lines of modifying the slot myself.  Lifting the chimney off looks like a engineering job I'd rather avoid.  Awkward and heavy.  I castigated myself already for making the slot too narrow. 

Not sure how it was built but have you ever watched a mason cut a hole in an existing load bearing  wall?  I would think a single jack would be fine to work the wide side. Maybe there is a relatively easy way?

 

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2 hours ago, oldlady said:

ok, guys, i know nothing about building a kiln, less about gas firing.  BUT if the heat is no more than a typical cone 6 firing, maybe a pizza stone could be cut to fit.  some are not able to go that high but i use 3 different ones at cone 6.

That's a great idea! Many pizza stones are thinner than kiln shelves. The hard part will be finding one big enough. @CactusPots what size shelf do you need?

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1 minute ago, neilestrick said:

That's a great idea! Many pizza stones are thinner than kiln shelves. The hard part will be finding one big enough. @CactusPots what size shelf do you need?

Pizza stone? Maybe, figured they would only be good for 500-800 degrees. Will they go to 2000?

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Just now, Bill Kielb said:

Pizza stone? Maybe, figured they would only be good for 500-800 degrees. Will they go to 2000?

Most are the same thing as kiln shelves. Some are listed as not useable under a broiler or direct flame, though, but most can go right onto a grill. If he can find one at a decent price it would be worth a try.

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