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temp for opening kiln?


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#41 Jime

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Posted 20 April 2013 - 12:46 PM

This is a really useful thread, as I'm sitting here waiting to peek in the kiln.
I have a pretty basic setup, so I don't have a way to measure the temperature inside the kiln. Does anyone have tricks for gauging the temperature inside?
When the kiln was pitch black inside I took out the second peep.
I've heard of people doing the paper test, but I'm not too sure what temperature is represented by which results. I just took some paper and left it in for 10 seconds, and got a tiiiiiny bit of color change, barely tan, not brown.
I have a small electric cress 23. Any idea what temp it might be if the top of the lid is warm? cool?
thanks!

#42 neilestrick

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Posted 20 April 2013 - 02:11 PM

Paper will smolder above 400 degrees. Just stick a rolled up piece in the peep hole and see what happens.

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#43 Roger Gilmour

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Posted 03 March 2014 - 06:33 PM

Hi all...

 

I have heard that opening the kiln between 200°F and 100°F is bad for the elements, causing them to wear out prematurely. Same for pulling the plugs or cracking the lid. Regardless if it's bisque or glaze.

I can't find any data to back that up. 

 

I can understand the care for porcelain, as that material would need careful cooling. but if one is quickly fetching out pieces, not leaving the lid open, I fail to see the harm in opening the lid versus the life of the elements.

In reading this thread, I see none has mentioned the elements even once. 

I can respect the concern (where I first heard it) they have about waiting to give the elements a good run for the money, but if its truly moot and has no impact on the elements, then it would be really nice to clear that up.

 

Any one know?

 

Thanks

RG



#44 High Bridge Pottery

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Posted 06 March 2014 - 03:24 PM

You probably have a lot more pieces in a bisque firing to hold the heat in the kiln compared to the air in a glaze firing.

 

My kiln shuts itself off usually late afternoon early evening (4-6:00pm) and I don't open it until the morning. I have noticed that my bisque firings are warm to touch in the morning and my glazed firings are usually cool to touch even though I expected them to be hotter since they get up to a higher temperature. I am assuming it's due to the glaze being less absorbent of the temperature.
I dont have a temperature on my kiln and I rely completely on the cones. So I have to wait until the next morning because I don't want to take a chance.

 

I only open my kiln under 150degC after reading articles saying glazes are more about what happens after the kiln is turned off.

 

I usually forget how hot 150 is and burn my fingers on the pots. I think too relatively.

 

No idea about element life, I mean they go from room temps to very hot quite quickly so is it any worse the other way round?


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#45 neilestrick

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Posted 07 March 2014 - 09:17 AM

Hi all...

 

I have heard that opening the kiln between 200°F and 100°F is bad for the elements, causing them to wear out prematurely. Same for pulling the plugs or cracking the lid. Regardless if it's bisque or glaze.

I can't find any data to back that up. 

 

I can understand the care for porcelain, as that material would need careful cooling. but if one is quickly fetching out pieces, not leaving the lid open, I fail to see the harm in opening the lid versus the life of the elements.

In reading this thread, I see none has mentioned the elements even once. 

I can respect the concern (where I first heard it) they have about waiting to give the elements a good run for the money, but if its truly moot and has no impact on the elements, then it would be really nice to clear that up.

 

Any one know?

 

Thanks

RG

 

Nope, never heard that. If you waited for the kiln to get below 100F  before opening, it would take days. You've got to get the lid open at some point.


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#46 kdavitt

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Posted 06 February 2016 - 11:58 AM

For 4 years now I've been opening the lid of a glaze firing and looking in a number of times from 600F on down. Around 450 I prop the lid a couple of inches open and at 400 I open all the way. I remove the pots at around 220. I do about 2 full loads of 2 or 3 kilns 2 or 3 times weekly and I've had no problems. The attached (if it shows) was taken with the kiln around 430. By the way, that particular kiln has had about 250 firings with the same elements.



#47 perkolator

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Posted 10 February 2016 - 08:37 PM

For crash cooling I usually let the students pull spy plugs below 600*.  Crack the lid with a piece of soft brick when it's below maybe 400*.  Fully open lids at 250* or lower and unload with gloves if need be.  Typically leave vent on until room temp.



#48 Marcia Selsor

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Posted 10 February 2016 - 08:56 PM

I always used the paper test. fahrenheit 451 is the temperature at which paper burns. The movie by the same name written by Ray Bradbury is interesting if you get the chance.
I start cracking doors or lids at that temperature but wait til 250 or so to open completely.
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#49 elaine clapper

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Posted 11 February 2016 - 08:24 AM

I fire cone 5 with and electric kiln, leave all the plugs in and wait until the kiln is room temperature. i put too much time into my pieces to ruin the glaze just because of my impatience.  When I was teaching, the kids who procrastinated and did not get their work in on schedule where up against grade deadlines. I would warn them if I opened the kiln early they risked fine cracks in the glaze.  The times that I gave in and unloaded at 120 degrees almost ended with the "pings" of cracking glaze.



#50 Joseph F

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Posted 11 February 2016 - 08:59 AM

I am with the 250F folks. Anything more and I feel like I am just wasting time. I open at 250F let it cool to room temp, then take the pots out. Takes about an hour or so after I open it. 



#51 Babs

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Posted 11 February 2016 - 04:44 PM

My new kiln takes a day and a bit to cool to 200C so slow in fact that a number of my glazes have changed significantly and some not for the better.. I haven't the recipe here but a blue/green has become so metallic and matte that I will have to play to get it where I want it or give it the flick.

Unless one of the readers of this post has any ideas.....taking plugs out and crash cooling at the top end?? What harm would this do to elements and bricks?



#52 perkolator

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Posted 11 February 2016 - 06:14 PM

I have no science behind this, but if you're crash cooling at the top end of your temp you're going to end up pulling in significantly cooler air through your peep holes - could possibly thermally shock hot elements and brick local to the peeps.  I do it because I already know I'll be working on my kilns continuously through the year, some home ceramicists might not ever touch their equipment until it breaks.

 

Sometimes you just gotta do what you gotta do.  I've been known to crash cool the student's work in a big gas kiln firing - just leave the damper and burner ports fully open and remove the spys.  Below maybe 500* I'll crack the door open and put on the blowers.  Usually this is only when we are on a time restriction, usually for critique.



#53 glazenerd

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Posted 11 February 2016 - 06:58 PM

 

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Posted 06 March 2014 - 02:24 PM

You probably have a lot more pieces in a bisque firing to hold the heat in the kiln compared to the air in a glaze firing.

Great point, it all plays a roll in how fast the kiln cools. The scientific term is "thermal mass" for those who want to know in technical terms. The simple illustration is: two pots of water boiling on the stove covered. One has one quart of water, the other has 1 gallon of water; obviously the one gallon will take a lot longer to cool. Simple premise- but you get the point.

A cheap way to track temps on the low side of cooling (400F and under) is using an oven thermometer. Just stick it in a peep hole or under the lid. Can buy them most anywhere for $3-5 and most have a 3-5" probe.

Nerd

 

Note: Was just reading the technical specs on K-23 IFB. Very low thermal conductivity 0.17% @ 725F. Basically what that is saying is: at 725F the brick is storing little heat- everything else in the kiln however is.






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