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Silicon Carbide Shelves


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5 hours ago, neilestrick said:

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.

I built the kiln with basically the only knowledge from books and having fired 2 different up draft kilns at the UCSD Craft Center.  The usual books, Olsen, Gregory and others.  I saw a Geil once.

There are definitely things I would do different.  The flue and damper are right on though, damper opening being the exception.  If you've never built a kiln from scratch, I recommend it.

Learning assignment:  Your kiln design must include at least one original feature. 

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@CactusPots I was considering These boards for my flue wall before opting for a Corelite shelf.

The stamped 3k is the melting point.

10 hours ago, Jodie said:

electric

Just making sure you are aware of the electricity warnings accompanying them.

https://kilnshelf.com/kiln-shelves/advancer-electrical-conductivity-info/

 

Sorce

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36 minutes ago, Sorcery said:

@CactusPots I was considering These boards for my flue wall before opting for a Corelite shelf.

The stamped 3k is the melting point.

Fiber boards, while called 'rigid', are only rigid compared to fiber blanket. They are light and stiff, but not at all hard or durable. It's just a stiff form of fiber blanket, made of spun silica fiber. Moving the shelf in and out of the damp slot would quickly degrade it, as well as release silica fibers into the air.

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6 hours ago, neilestrick said:

Fiber boards, while called 'rigid', are only rigid compared to fiber blanket. They are light and stiff, but not at all hard or durable. It's just a stiff form of fiber blanket, made of spun silica fiber. Moving the shelf in and out of the damp slot would quickly degrade it, as well as release silica fibers into the air.

I have to agree, you can even go graphite to over 3000 degrees. KISS rule here seems like it would be the wise choice. Incidentally there are rigid boards that are flexible and can be formed but once fired they become rigid.  Cool stuff for special uses, but dampers? I think whatever one could find simple is probably best.

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I once converted an old square top-loading Amaco electric kiln to a  downdraft gas for a friend of mine- welded on a chimney, had two small power burners, one on each side of the chimney, and lined the walls with 1" of the rigid board for extra insulation. Sweet little kiln, and the appropriate use of those boards- insulation that would not be touched.

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I am currently using fiber boards as dampers on my wood kiln.  I got them along with some kind of liquid (I think a silica) that I painted on the boards heavily.  After drying they are pretty strong.  I have used the first set about 4 times and they do warp a little but have remained intact after 12-hour cone 11-12 firings.  I would prefer to use kiln shelves but not sure any can handle the temperature differential across the shelf.  I have used 1/2" thick steel plates, but these warp and degrade quickly. 

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I got quite a few firings from the used busted up kiln shelf that I just broke.  In excess of 30 for sure.  It had a hard life before I got my hands on it and probably would have gone on for a while if I hadn't knocked it over.   I'll probably have to cut  one of my 18 x 18  3/8" silicon carbide shelf to fit this time.  I'm a little concerned about leaving a 8" piece of the shelf outside the damper.  Which is what I'd be doing using a standard 12 x 24" shelf without cutting it.  That would give a heat differential from one end to the other.  16" is all I need to close completely and leave enough to pull the shelf out the next morning.  I think the next cheap silicon carbide shelf will work fine as a damper.  Thanks for all the other suggestions.

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Mullite shelves can handle the heat differential from the flue. Every gas kiln I've ever fired used a mullite/cordierite shelf for the damper, and it always hung out so it was cool enough to touch at that end. Even in a wood kiln, they can handle the heat. In a typical damper location, about halfway up the height of the kiln, the temperature drops quite a bit from the inside of the kiln.

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  • 10 months later...
On 5/26/2020 at 2:26 PM, Jodie said:

I just moved to Australia, are there any suppliers for advancer shelves here? im firing midfire electric front loading kiln.. any suggestions for a good alternative?
 

 

 

What size shelves are u after and where is Aust are u based?

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Follow up on the original post.  Rented a very large wet tile saw.  Thing had a 20 inch throw. It was loaded on my truck with a fork lift and I ran it in the bed of the truck.  Went through the SC shelves like butter (almost).     New damper works fine on 2 firings so far.  Problem solved and 1 warped shelf eliminated from the rotation.

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On 5/27/2020 at 6:17 PM, fergusonjeff said:

I am currently using fiber boards as dampers on my wood kiln.  I got them along with some kind of liquid (I think a silica) that I painted on the boards heavily.  After drying they are pretty strong.  I have used the first set about 4 times and they do warp a little but have remained intact after 12-hour cone 11-12 firings.  I would prefer to use kiln shelves but not sure any can handle the temperature differential across the shelf.  I have used 1/2" thick steel plates, but these warp and degrade quickly. 

Use mulite shelves for wood and salt no issues-they are the go to damper shelve for all applications .I use the 1 inch thick ones for suoer long lasting proformace. All other materials will warp more. Silicon carbide is way worse with uneven heating. Mullite is low cost easy to cut and will take red heat on one end and the other cool to touch.I have used them for 48 years and more firings that you can imagine. 

In my cermic life making kilns (over 12) the damper is a key element . Back in the 70s we used silcon carbide as that is what we had for shelves . I soon learned that warped dampers did not work well-be using 1 inch mullite ever since with zero issues -

I have written up shelve threads before explaining all the options plus or minus but for dampers it a bit different as the damper is not in a cone 10-11 sitution no matter how much flame you think it gets. Mullite warps in gas kilns at cone 10 no doubt about it but the damper never gets that hot hence the long lasting ability-also mulllite with its increable  long strong matrix makes the uneven heating a non issue.

The other good material is the enghlish dry pressed  high alumina shelves also in 1 inch if you have them. They are overkil as a damper but work great I used them for decades replacing my warped silicone carbite shelves at cone 11. They weigh 33# per 12x 24. I now use them in my salt kiln where that are super.I have a huge pile of them as I do with older warbed silcone carbite shelves-no I use advancers . The car kiln averages 35 shelves per fire so I have had lots of types of shelves for over 4 decades and really get to know how that work at cone 11 every other week . They all have some good qualities and some bad qualities-Advancers do not like thermo shock  for example  and for that matter any silica carbide product is the same-not good at thermo shocking. mulite is great at thermo shocking with those long crystals I mentioned. 

That liquid silica you coated the fiber boards will make them stiffer and more abrasion resistant but they will fail over time (been there already myself) You can add  milled zircon to that coating when wet and apply for better results but they will also fail over time (the  milled zircon adds more heat resistance) I love that stuff with colidical silica (liquid) really reflects heat.Great for burner ports and bag wall coatings.

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Mark,

  I tried to find mullite shelves for dampers but was not able to .  Not sure they are made any more.  Do you know anywhere I could get them?  The fiber boards mostly hold up, but warp a lot.  I am on my 6th firing with the first set.  They hold up better than my previous attempt which was 1/2 thick steel plates.

 

 

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28 minutes ago, fergusonjeff said:

Mark,

  I tried to find mullite shelves for dampers but was not able to .  Not sure they are made any more.  Do you know anywhere I could get them?  The fiber boards mostly hold up, but warp a lot.  I am on my 6th firing with the first set.  They hold up better than my previous attempt which was 1/2 thick steel plates.

 

 

Pretty common as shelves still I believe, try searching for “High Alumina Cordierite,  mullite “ shelves I believe you will get lots of hits.

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1 hour ago, fergusonjeff said:

was told "new" shelves don't work like the old ones and will crack as dampers.  That is why I was trying all kinds of other options.  Would something like this work?

I know these to be the same, cordierite/ mullite  / high alumina. see below comment from dogwood (shelf maker) perhaps the “new shelves” reference was core -lite  (hollow core)  or bonded nitride.

 

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Edited by Bill Kielb
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Bill,

That is helpful.  I'll be doing my last wood firing of the spring in a couple weeks and will limp by with my fiberboards, but that gives me all summer to find some shelves before the fall firings.

I am pretty sure they were not referring to core-lite or the nitrile bonded stuff, just newer (according to them, non-mullite) shelves.  The thought was no one made "mullite" shelves any more and the newer shelves cannot handle the temperature differential of a damper in a wood kiln. 

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Yes those in your ling are the ones to use. Cheap and tough for dampers

those highn alumina will handle the heat well

another cheaper option but also a little less quality is these

https://www.axner.com/cordierite-shelf-12x24x1rect.aspx

since dampers take a lot of abuse I would spend the extra 10$ for high alumina ones

Edited by Mark C.
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