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Fractured Kiln Shelves...


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for anyone else using 26" full shelves and fast firing what I was told by manufacturer was:

 

...."I think the fast fire may just be too fast for a shelf of that size.  If the 18†full rounds work on that schedule and both and new and used 26†full round did not work on that schedule, I’d tend to think the larger shelf just can’t handle the fast cycle.

 

It’s interesting to me that only the bottom the shelf broke however.  Perhaps the combination of the load and the cycle is too much.  I’d suggest trying 2 half rounds on the bottom layer and continue using full rounds above that too see if that scenario is successful."......

 

this is from Cole Sadler at Resco

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I think it is the fast firing too. But Also stick with 3 post patterns. Not all posts are the same height even straight from the factory.

Simple geometric rule #1:  3 points define a plane.   With 8 posts you are pushing it.

 

Keep us "posted" on your future firings. Let us know if you resolve the problem. Next time you vacuum. line up all the posts and check their height. Just curious.

 

Marcia

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  • 2 weeks later...

@Mike, if you are still checking this thread, possibility of getting those shelves replaced from manufacturer. I sent you a pm with some details of what they told me about that. 

 

Min... 

 

I have my distributor working on replacements... As an update, we have now lost an additional five 26" Corelite shelves.That's a total of seven fractured shelves in the last ten days. The situation is a bit out of control. I've contacted our distributor and they are contacting Standard who wholesales them for Resco. I've also sent an email to tech support at Resco. 

 

Here are my new observations:

  • Shelves are now splitting in glaze (^6) and bisque (^05) fires in addition to the fast ^10 fire mentioned at the top of the thread,
  • I pulled all the shelves, vacuumed the kilns, leveled each spacer, put in a flat shelf on the bottom, and checked for level, and then we lost the additional 5 shelves.
  • I believe 4 out of 5 of these shelves were about 90 days old and had less than 20 to 25 firings on them.
  • The new floor shelf is supported by three spacer posts (1.5" x .5") in a triangular pattern. 
  • All kiln stacks were built over top of the spacer posts.
  • Shelves are fracturing in multiple kilns,
  • I tested all elements and ran diagnostics on the kilns, they are working fine,
  • Cooler fires tend to produces fractures along multiple axises, hotter fires along one axises nearly dividing the shelf in two pieces.
  • On the last glaze, the load shifted and one cup slid into the kiln wall. It WAS NOT fused to the fire brick. (Shelves splitting on the cool down?)
  • I checked dates and all of this started 3 days after we increased our firing frequency to near daily to clear a few large orders we are processing. We started firing the kilns 5 or 6 times a week.
  • Each shelf was loaded with approximately 30 to 33 cocktail cups, each cup weights about .75 - .85 lbs.

 

Question:

Could the rigors of firing near daily have an affect on the shelves?

Alternative shelves to consider for production environment?

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Have you thought of switching to advancers ?Big upfront cost but huge space saving, They do not like thermo shock. Maybe you got a bad batch of the cordilite ones. Do you use 1/2 shelves at all? and if so are they cracking as well?

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I use 1/2 shelves in my large 1227 but I only bisque in them.

I know a tile company in New Mexico (silver city) that fires every day to glaze temps in Skutt 1227. This should not affect the shelves.

They fire one day unload the next and reload and fire that day and so on.

The 3 point stand is standard

Not sure how a load can shift?can you explain this?

any other new things? like new stilts?When you get a new shelve run it thru a bisque cycle 1st before the high fire.

Make sure 100% posts all line up  from floor to top shelve.-sound like you have done this.

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Guest JBaymore

Given the scenario you are giving...................

 

I'd be looking at how the shelves in question were stored BEFORE you received them.  Were they all in one shipment?  Were they all tat the distributor before you go them or shipped direct from the manufacturer?

 

To me this sounds like either an original manufacturing defect, or a defect caused by the way the shelves were handled in storage or shipping. 

 

How do you STORE the shelves in your studio?

 

Failures happening in too large a range of conditions.

 

best,

 

................john

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Crazy! There's definitely something goofy going on. Odd that they would crack after 25 firings, though, if there was a handling issue. I would expect hairline cracks from mis-handling to open up a lot sooner than that. I'm thinking it's just an issue with it being such a large shelf. I used to have a student who did glass slumping in her 28 inch wide pottery kiln, and when she did big 22" platters we realized there's a huge difference in the melt/softening of the glass from the edge to the center. To get an even slump, the firing had to be slowed down quite a bit, and to a lower peak temperature. So your full shelves are under a lot of stress, especially when firing fast. Imagine trying to fire a large platter multiple times.

 

Definitely keep us posted as to what's going on, though.

 

I've got a set of 14x28 rectangle Corelite shelves I've been using for several years now with no problems. Still as flat as the day I bought them, firing to cone 6 every week.

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I use 1/2 shelves in my large 1227 but I only bisque in them.

I know a tile company in New Mexico (silver city) that fires every day to glaze temps in Skutt 1227. This should not affect the shelves.

They fire one day unload the next and reload and fire that day and so on.

The 3 point stand is standard

Not sure how a load can shift?can you explain this?

any other new things? like new stilts?When you get a new shelve run it thru a bisque cycle 1st before the high fire.

Make sure 100% posts all line up  from floor to top shelve.-sound like you have done this.

 

We only use 1/2 shelves when we are firing off size wares like large vases or flower pots. That's only about 5% of our time...

 

When the shelf split, the fracture ran between two of the three post stacks. As it turns out it also ran between cups. The cups along the fracture weighed it down and caused it to fall toward the center of the kiln along the fracture. This resulted in one of the posts sliding into the fracture, which in turn caused the entire stack to list to the back of the kiln. The cups at the top of the kiln slid down the shelf along the plane of the now tilted stack. The ones closest to the edge slipped to the edge, which was in contact with the kiln wall, and came to rest against the kiln wall. So the load shifted based on a chain reaction.

 

Yes, Advancers are absolutely under consideration. Even if I have to buy a two or three a month...

 

Yes, we temper all of our kiln furniture at bisque.

 

Yes, we did just buy a new set of posts / stilts for the shelves. These were in use in all incidents where the shelves fractured. In all but one firing, they were above the point of fracture.

 

We use to use 1/2 shelves, but stopped using them to reduce the number of posts and increase the number of pots per shelf.

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Given the scenario you are giving...................

 

I'd be looking at how the shelves in question were stored BEFORE you received them.  Were they all in one shipment?  Were they all tat the distributor before you go them or shipped direct from the manufacturer?

 

To me this sounds like either an original manufacturing defect, or a defect caused by the way the shelves were handled in storage or shipping. 

 

How do you STORE the shelves in your studio?

 

Failures happening in too large a range of conditions.

 

best,

 

................john

I have no idea how they were stored before they got to me. From what I can tell, the distributors don't stock Corelites, they order them and have them delivered to them or drop shipped to us. I can't speak to how they may have been stored before I received them. We store them on their edge up against the wall in the kiln room. That was up and until recently, I added a set of padded hooks on the walls in the kiln room, now they are stored on the hooks / on their edge up against the wall to keep them off the floor.

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Guest JBaymore

 

...........to keep them off the floor.

 

 

Concrete floor?  Damp?   Do you wet mop it frequently?  Has it been rainier than usual?

 

best,

 

...............john

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John I asked these same storage questions early on as well.Damp floor or bare concrete (I always suggest wood over concrete)

I have seen new mullite shelves crack as they all where from a bad batch from Thorley (Laguna bought them out years ago)This actually is pretty common I'm told not-the coralites are not made by Thorley.

 

Mike with the advancers you still will need to pay attention to thermo shock.They cannot be Quick cooled.

Can you say how long the entire glaze fire is in hours (say like 9 hours) and how are you cooling the load-open lid at 300 degree or ?something else?

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