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I've been holding my 18" plates for about 45 minutes at 960 to anneal. I go AFAP from slump or fuse temp to 1050 and then about 250/hr to 960 hold. Is this enough time? I had someone tell me their large plate broke in two for no apparant reason. Sounds like an annealing problem to me. It's an older plate that I don't think I annealed as long as I should have at the time and it's the first time this has ever happened.

A bit worried... Marc

Hi Marc-

It is my understanding that a hold at 960 is not enough for proper annealing, but rather is more for making sure the temp through out the piece is uniform before descending further thru the strain point/range. For a piece that size with varying thickness, I would hold for at least 1&1/2hrs at 960 and then descend slowly, usually 60dph, til I get to 750. I believe that proper annealing occurs as a result of controlling temps in this range rather than holding at any one temp.

My 2, Lisa

Marc Demian wrote:I've been holding my 18" plates for about 45 minutes at 960 to anneal. I go AFAP from slump or fuse temp to 1050 and then about 250/hr to 960 hold. Is this enough time? I had someone tell me their large plate broke in two for no apparant reason. Sounds like an annealing problem to me. It's an older plate that I don't think I annealed as long as I should have at the time and it's the first time this has ever happened.

A bit worried... Marc

Marc - The important thing to consider when figuring out a proper annealing schedule is the thickness, not the diameter, of your piece. It's hard to grasp, at least it was for me, but diameter doesn't really come into play, just the thickness. On the Bullseye site you'll find a chart to help you figure this out, or re-post with the thickness information.

Jackie

Marc Demian wrote:I've been holding my 18" plates for about 45 minutes at 960 to anneal. I go AFAP from slump or fuse temp to 1050 and then about 250/hr to 960 hold. Is this enough time? I had someone tell me their large plate broke in two for no apparant reason. Sounds like an annealing problem to me. It's an older plate that I don't think I annealed as long as I should have at the time and it's the first time this has ever happened.

A bit worried... Marc

It does sound like an annealing problem.

IF it's 1/4" thick, then 45 minutes should be plenty long enough for the temp to equalize, but then you have to ramp down to below the lower strain point (for BE I believe it's 750, so I go to 700) at around 150 dph in order for it to be annealed properly as Lisa suggested.

Like Jackie pointed out, you are annealing for the thickness and not the diameter, but if your kiln heats unevenly, then you will want slow things down to accomodate for uneven heat distribution when firing larger diameter pieces (not such an issue for smaller diameter work). So in that respect, you do want to take into consideration the diameter as well as the thickness. You have to know your kiln and how it heats.

If your kiln has hot or cool spots, you aren't cooling through the annealing range slowly enough...or a little of both, or if your pieces are or have places where the thickness is greater than 1/4", you might want to revisit and rethink your schedule.

Thanks everyone for your help.

The peices are generally two layers thick (1/4") with some added elements. I've been letting the kiln cool naturally from 960 to 750 and my 1414 Skutt does cool faster than my smaller Paragon. I'll start cooling at 150 degrees per hour from 960 to 750. I don't think the kiln cools a lot faster than this by itself so I'll stop worrying too much about the pieces I've already done. Marc