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-   -   firing up a crucible (http://talk.craftweb.com/showthread.php?t=11595)

Pete VanderLaan 06-22-2017 07:41 AM

firing up a crucible
 
Your pot should have a reasonable clearance from the side wall of an electric kiln, preferably at least an inch and a half on each side. The crucible should be brought up to temperature at a rate of 50F per hour until you reach 1000F. The hold at 1000F for four hours. Then, advance at 25 F per hour to 1100F and hold again for four hours. This is not just for your pot, it's also for your kiln. This is known as the quartz inversion range and it's when silica flips and a huge amount of expansion occurs. Once through this range, proceed at fifty degrees per hour again until the kiln is really beginning to glow. At this point, you can pretty much just turn it up.

DO NOT FILL THE POT WITH CULLET UNTIL IT'S 2100F! Filling it when it's cold is the single best way to break your pot quickly we can think of. Fill it slowly- about five lbs per charge until the charge is flat.

Don't leave the kiln door open admiring your pot of glass. It encourages thermal shock to do that.

Should one of your elements fail, try to remove all of the glass from the pot and this will be difficult. Leaving glass in the pot causes the glass to shrink away from the wall, pulling in stones at the best, and at the worst, it will cause very uneven heating of the pot when it is refired, likely causing failure.

If you do plan to turn your kiln on and off, it normally reduces the life expectancy of the pot about 35%. Saying how long a pot should last is impossible to do since there are too many variables in how it was used. They include how many times the pot was filled, was it turned on and off? What kind of glass was melted? What temperature was it fired at? Did anything bang into the pot, even once? Did you follow a ramp up procedure?

When you do want to turn a kiln off, just empty the pot and turn it off. Don't open the door during this period. Those crunchy sounds are shrinkage
sounds.

Larger pots require longer schedules and it is best to contact us with schedules for 28 and 34 inch pots which are only used in gas fired equipment. In gas equipment, bottom fired furnaces consistently have shorter pot life spans than do side fired above glass line furnaces. Flame impingement is death on a crucible.

Even with this information, pots are half art/ half science. They are not meant to be permanent fixtures in your kiln. Keep a spare on the shelf. We don't offer any type warranty on crucibles. They are sold "As Is". If it's damaged on arrival, that's another issue entirely.

Mark Rosenbaum 06-22-2017 11:06 AM

You probably need a disclaimer that says that the manufacturer is not responsible for any failures due to negligence and/or not following directions.

Scott Dunahee 06-22-2017 11:46 AM

And that even under closely and scrupulously followed instructions, a pot my still crack or fail at any time. It is the nature of the beast.

BSD

Brad Smith 06-23-2019 01:24 PM

Pot fire up
 
Thank you for this guide Pete,

I was curious, when firing up a pot that has already been fired/charged/worked out of, would you advise using the same schedule as a fresh one?

Pete VanderLaan 06-24-2019 08:16 AM

Quote:

Originally Posted by Brad Smith (Post 144434)
Thank you for this guide Pete,

I was curious, when firing up a pot that has already been fired/charged/worked out of, would you advise using the same schedule as a fresh one?

****
Yes, Quartz inversion is an event.


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