Question on speeding up cooling below 750°F

[BillsBayou]

Paragon CS14D clamshell kiln (top or bottom loading lid). Bullseye COE 90 glass.

My schedules all use a 400°F/hour rate for the last stage below 750°. At some point below that, the cooling rate is much slower and gets exponentially slower as time passes (6 - 7 hours and longer to get it to room temperature) I want to speed things up.

Since my kiln is top-firing and the rate is 400°/hour, how far can I open the top part of the lid (the part that allows for top-loading) to get the cooling rate down near the one I've programed?

The top lid has an inset brick layer that settles down between the walls. Cracking the lid 1/2" just barely gives me a view beneath the lid.

I've assumed that opening the lid in the bottom-loading configuration is a very bad approach.

[DonMcClennen]

It depends on what size and thickness your projects are... Small (2"0 pcs) will be forgiving.. but the larger and thicker projects..HURRAY KILLS!!

[Brad Walker]

How thick are your pieces? In general for a typical two layer piece you can open 1" at around 300F and about 2" at 200F. More conservative than that for thicker pieces.

Also, I would open from the bottom (clamshell) not the top, a lot of the heat stays up in the clamshell so opening from the top loses heat more quickly.

I don't program a step below 750F. Just turn the kiln off and let it cool on its own.

[Marty]

" Cracking the lid 1/2" just barely gives me a view beneath the lid."

There's nothing to see, move along now.
If you're in that much of a hurry (hurray?) then you need to buy another kiln.

[BillsBayou]

Thanks for the replies. I'm just going to suck it up and wait for the projects to complete with a closed lid.

For now.

After the holidays, I'm going to be doing some tests with scrap glass. I'll test on 3-4 layer tack fuses, 2-layer full fuse, 1-layer polishes. How fast can I cool until the glass cracks?

Things I'll keep in mind during the tests:
The thermocouple measures the air, not the glass. Air cools faster than glass.
A cooling rate just below the rate that cracks the glass will likely produce stressed glass. Ready to break for almost any reason.
Eye protection, gloves, remove all shards after each crack/shatter.

I'll make notes.

[Marty]

maybe Santa will bring you another kiln.

[Kevin Midgley]

I would not bother doing those tests.
Cheaper and easier to get another kiln.
You have covered off some variables in what may cause glass to crack from exposure to rapid cooling but there will be many more to be discovered.
Plus you should know in advance that those variables will invariably show up in a directly inverse relationship to the value of the glass being fired.

Some of the unforeseen variables may not evident until you have completed thousands of similar firings.
Only then will you fully understand why "Speed Kills" is such a mantra to be believed in while making glass.

I managed to blow up some glass the other day, not thinking that speed would be an issue.
It was.
I've also done the thousands of firings.

Why did the cat go to the beach? Because he heard Sandy Claws was coming to town and he wanted to ask for a new kiln.

[jim simmons]

GROAN!!!!!!!!

[Kevin Midgley]

Well those sorts of jokes would formerly go to Spab but nothing is there any more.

[JestersBaubles]

I agree with all the others, Turn off the kiln (I turn it off at 700 deg F), and walk away. I may open the kiln at 200... maybe. That involves cracking the lid 1" to 2" and... walking away.

If it is important enough to fire, it's important enough to let it cool on its own, IMO. I have a day job and often plan my firings so the kiln has reached 700 by the time I leave for work, and then it cools while I am away for 9 hours.

Dana

[Franzeska]

I agree with all the others, Turn off the kiln (I turn it off at 700 deg F), and walk away. I may open the kiln at 200... maybe. That involves cracking the lid 1" to 2" and... walking away.

If it is important enough to fire, it's important enough to let it cool on its own, IMO. I have a day job and often plan my firings so the kiln has reached 700 by the time I leave for work, and then it cools while I am away for 9 hours.

Dana

But what if the kiln takes longer than 9 hours to cool down to 100? My kiln is sooooo sloooow dropping from 700 to 100, sometimes 12+ hours. In my last house I ran a fan breeze across the body of the kiln but that didn't seem to make a difference. My Olympic clamshell/top loader is 14" deep and 18" square. There is a lot of hot air in there, and bricks seem to do a great job insulating. At what temperature is it safe to crack open the top or bottom an inch or so to bring the temperature down? It's not that I am overly curious, although we are all tempted to peek. With such a long cool down, it is hard to keep the work flow going when I am in the mood.

Maybe I am over-reacting. How long does it take everyone's kiln to cool from 700 or 800 to 100?? Maybe my kiln is not an outlier.

Thanks.

F.

[Marty]

Reread the entire thread. All the guidelines you need are there.

Everyone's kiln and practice is different. You'll find out what your parameters are when your work starts cracking on cooldown.

[Franzeska]

Reread the entire thread. All the guidelines you need are there.

Everyone's kiln and practice is different. You'll find out what your parameters are when your work starts cracking on cooldown.

I am trying to avoid cracking on cooldown without having almost a 24 hour cycle. Back when I was working, I could leave the house at 6:30 a.m. with the kiln around 700. Of course I turned it off. When I returned at 6:00 p.m. the kiln would be in the upper 100s. It might not get down to 100 until after my bed time. It is just frustrating.

Of course I read the entire thread before I posted. The original poster's kiln takes 7 hours to cool. Dana says she might crack open her lid at 200 degrees. I've read Brad's book and a bunch of other books, but "typical" cooldown is not covered. I suppose that is because there are so many kinds of kilns, sizes, etc. that there is no typical. Twelve+ hours to cool seems excessive. It is doubtful that I will buy another kiln just because it takes so long to cool. However, if I do, I will research the cooldown cycle so I don't experience this. Or maybe I'll have to move to the frigid north.

Thanks all.

F.

[Marty]

Franzeska- My biggest (7'x 3'x 16") kiln will take 12 to 18 hours to cool from 700 to room temp, depending on what's in it. The Paragon GLs are much quicker. If I don't have anything really valuable or risky in the big kiln and I'm getting antsy, I can crack it ½" at 250F. That's at the front and since the wall is 4" thick, that's probably a ¼" opening in the kiln. I'll open it a little more as it cools but not much and not often.
Someone else with the same kiln and work might be more aggressive. There are no easy answers to this as to so much else in fusing.
I still say that if you're making that much work that you need to hurry the cooling, you need another kiln. Moving won't help.
Marty