Core-lite shelf cracked in half

[GEP]

I unloaded a kiln this morning and found that one of my Core-lite shelves had cracked in half. It is broken mostly along one of its tunnels. The shelf is 6 years old and has been through 100s of firings without any signs of trouble. There was nothing unusual about the kiln load. It was tightly packed, and the broken shelf was in the middle zone where the pack was the most dense.

The platter that was on this shelf is still flat. And the pots that were underneath are mostly fine. One of them has some grit from the broken shelf stuck in its glaze now. So I think it broke during the cool down. 

Anyone ever seen a Core-lite do this before? Any thoughts on why it happened?

 

[neilestrick]

I have heard of those cracking, but no more than other shelves, and I've never seen it myself. All shelves crack eventually. I imagine having a large platter on it contributed to it heating unevenly top to bottom, and it just gave out. There was probably a hairline crack there already. Those big shelves also heat unevenly from the edge to the center, so lots of stresses at play there. You can clean up that edge with a masonry disc on a circular saw and use them as two half shelves, or just rub off the sharp edges with a silicon carbide stone or angle grinder.

[MFP]

I had wondered Neil about these new "honey comb" shelf designs. Do they break more frequently than the solid ones?

[liambesaw]

12 minutes ago, MFP said:

I had wondered Neil about these new "honey comb" shelf designs. Do they break more frequently than the solid ones?

They're supposed to break less often because they cool more evenly.  At least that's what the store told me when I found out they're almost twice the price of alumina shelves 

[MFP]

Of course.....if it is "new", it must be better....and therefore you should pay more for it.  I noted the darkening in the center of the shelf....almost as if it had sucked in some carbon....it looks like a highly reduced stoneware body. 

[fergusonjeff]

MFP - I think what you are seeing as "darkening" is just the shadow of the hollow sections of the shelf.

 I have been using a few of these corelite shelves and they have held up well.  Seem to warp less than the solid shelves at cone six. 

I just got a couple 1/2 round 26" advancer shelves and they are even better than I expected.  Plan to order more once they get back in stock.

 

[neilestrick]

9 hours ago, MFP said:

I had wondered Neil about these new "honey comb" shelf designs. Do they break more frequently than the solid ones?

I've been using 17 of the 14x28 inch rectangular Corelite shelves for several years now, and haven't had any crack or warp. I've used them for at least 400 firings and still haven't flipped them. I've also got half a dozen of the 15" rounds that have at least that many firings on them without any problems. They are much lighter than regular shelves, and stay flat. 

Just checking Sheffield Pottery's web site, a 20" half round Corelite is $33.39, a 20" half round high alumina is $25.99. Not that big a difference. The Corelite will stay flatter and your back will appreciate the lighter weight.

[liambesaw]

43 vs 70 at my local place for a full shelf

[MFP]

Well despite being 30 years old....my shelves have never been fired. I did notice when setting up the bottom shelf yesterday that they are not even. I used the level and everything was level....the shelf just was an eighth inch higher than the other one. They still had the packing strap around them on the  pallet. Setting up that bottom shelf was very tedious....I had to measure all around the shelves to make sure they were the same distance from the walls and the burners are not on the shelf points.....it's going to make for some interesting flame patterns. I used the 1.5 inch wide posts because of all the weight they are going to have on them. Three inches high. I did figure out an appropriate direction to set up the gas line.  There are going to be places that the pots are going to be in the flame--but that was also the case in my former kiln. 

[glassBob]

Hi ceramists,

I just bought a CoreLite shelf for a large, oval glass fusing kiln. Check out the instructions available for the large CoreLite shelves. They are very susceptible to thermal shock on the heat up! I was surprised that they recommend such a slow ramp. 

[Bill Kielb]

4 hours ago, glassBob said:

Hi ceramists,

I just bought a CoreLite shelf for a large, oval glass fusing kiln. Check out the instructions available for the large CoreLite shelves. They are very susceptible to thermal shock on the heat up! I was surprised that they recommend such a slow ramp. 

I have not seen that reference anywhere except for the very first firing to make sure they are completely dry. What speed are they saying, and are you sure it’s not just for the first firing? Or maybe for very large shelf shapes?

[neilestrick]

I think those recommendations only apply to the large oval shelves for glass firing. Glass kilns typically only heat from the top, which puts different stresses on the shelf than in a pottery kiln, where the heat is from all sides. It sounds like it has trouble when there are large areas that aren't covered by glass, and small areas that are. The uncovered areas heat up a lot, the covered areas don't, and that uneven expansion across the top of a large slab with much less expansion on the bottom causes problems. I've used 14x28 Corelite shelves for years in my pottery kiln with no problems, and have never paid attention to how my firing schedule may affect them. I even start the kiln with slight damp kiln wash on them and have never had a crack. I use a small Corelite on my gas grill for making pizza. Just like with clay and glass, large slabs have more problems than small ones.

 

corelite-manufacturer-guidelines.pdf

[Bill Kielb]

3 hours ago, neilestrick said:

I think those recommendations only apply to the large oval shelves for glass firing. Glass kilns typically only heat from the top, which puts different stresses on the shelf than in a pottery kiln, where the heat is from all sides. It sounds like it has trouble when there are large areas that aren't covered by glass, and small areas that are. The uncovered areas heat up a lot, the covered areas don't, and that uneven expansion across the top of a large slab with much less expansion on the bottom causes problems. I've used 14x28 Corelite shelves for years in my pottery kiln with no problems, and have never paid attention to how my firing schedule may affect them. I even start the kiln with slight damp kiln wash on them and have never had a crack. I use a small Corelite on my gas grill for making pizza. Just like with clay and glass, large slabs have more problems than small ones.

 

corelite-manufacturer-guidelines.pdf 11.29 kB · 2 downloads

Thanks, makes total sense as I think these have been around so long and  have proven reasonably shock resistant.

[Sorcery]

On 7/11/2019 at 8:54 AM, neilestrick said:

been using 17 of the 14x28 inch rectangular Corelite shelves for several years now

Are you using them in gas?

I'm going to be using one for a flue wall in my kiln and am concerned, looking for input, going to cone 10.

I'm liking what I'm hearing already.

Thanks!

Sorce

 

[neilestrick]

1 hour ago, Sorcery said:

Are you using them in gas?

I'm going to be using one for a flue wall in my kiln and am concerned, looking for input, going to cone 10.

I'm liking what I'm hearing already.

Thanks!

Sorce

 

I'm not using them in gas, but lots of people do