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crash cooling vermiculite board

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crash cooling vermiculite board

Postby marie » Sun Sep 03, 2017 6:52 am

I Just had a little mis-hap with crash cooling some vermiculite board. It Is new board so I pre-fired cut up pieces apx.10"x10" in My 22" Pearl kiln at The rate Of 500 f p/hr to 1580 f And held for 30 min. Then I opened The lid apx 2" And turned off The kiln And left The room. When I returned ,hours later, My 22" kiln shelf had broken right DOWN The middle. My question Is...What blunder Did I do? I do NOT usually crash cool anything ha..Now I know why.
Can Someone please Tell me How to crash cool vermiculite board?
I Feel so embarrassed right about now. Thanks for Your help,Marie
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Re: crash cooling vermiculite board

Postby marykaynitchie » Tue Sep 05, 2017 9:53 am

Oh no!

I have a question: Your kiln shelf that broke down the middle--what is it made of? Is it mullite, vermiculite board, or some other material?

You may already have this article, but just in case:
http://www.bullseyeglass.com/images/sto ... _board.pdf

Looking forward to helping you with some info about this unlucky incident. Sorry it happened to you!

Mary Kay
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Re: crash cooling vermiculite board

Postby marie » Tue Sep 05, 2017 2:13 pm

Hi Mary Kay,
The shelf Is made Of mullite And I've had It forever(came with The kiln.) I had cut The vermiculite board into two pieces and placed Them 1/4" apart from each other which made them hang over the edge of the shelf a little. I Also centered These on The shelf directly (no risers). Also no pictures .... I've already cut up The shelf,sorry. I Did NOT use risers because I thought The boards would be better flat to the shelf.
Thankyou so much for your speedy reply :) ,Marie
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Re: crash cooling vermiculite board

Postby marykaynitchie » Fri Sep 15, 2017 2:57 pm

I wonder if risers would have helped the air circulate under the shelf (making the temperature more uniform.)
So sorry about the loss of your shelf!

Mary Kay
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Re: crash cooling vermiculite board

Postby jestersbaubles » Sat Sep 16, 2017 9:42 pm

Kiln shelves (and kiln lids!) can thermal shock just like glass given rapid enough temperature changes.

My opinion is there is very little need to crash cool anything except when you are stopping a drop or some other process where the glass is moving and you want to stop it.

If crash cooling is just a way to speed things up, well... impatience never serves anyone well when working with glass :mrgreen: .

Best, Dana
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Re: crash cooling vermiculite board

Postby martykremer » Wed Sep 20, 2017 5:29 pm

I'd like to know the rationale for pre-firing vermiculite. I've been using the 2" thick stuff for a very long time, got it from Skamol originally and they said NOT to bother pre-firing, that it was ready to go.
I just got another batch of bigger boards, 1.25" thick, from Jim Wiles and he reiterated- no need to prefire.
The stuff does get brittle with use; I've had full (24"x39") boards crack on occasion but it's usually from a combination of old age and uneven coverage- exposed areas of boards in conjunction with work on other parts- or operator error (I dropped it). The smaller pieces (say 18" diam.) never crack. I put the shelves directly on the floor of the kiln, no furniture.

And Dana is absolutely right about crash cooling. If you're that impatient, get more kilns.
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Re: crash cooling vermiculite board

Postby marykaynitchie » Tue Sep 26, 2017 8:45 am

The first firing is to burn out binders and moisture that can seed devitrification and/or vapor bubbles in the glass. The fine people at Skamol may not have the same concerns as we glass people.

Mary Kay
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