[ATM] Re: 40" mirror Pyrex anneal rates

["Mike Conran" <mike@guidesys.com>]

I was always curious about this.

Mike Conron 


 From site: 

http://www.megspace.com/science/sfe/i_fa_cir.html#cooking 

 

"Cool the glass to 375 degC at a constant rate. The cooldown from 575 to 375 
degC should take 60 hours per inch of thickness. At 375 degC, the glass is 
hard and will crack from thermal shock, so don't open the oven door below 
500! 

Cool the glass from 375 degC to room temperature at a constant rate. I have 
found that 24 hours per inch of thickness is safe for this final cooling. 

Open the furnace and put your hand on the glass; if it feels warm, leave it 
in place with the furnace door open until it is at room temperature. Warm 
glass that is comfortable to handle can crack when removed from the furnace. 
Haste makes waste! 

All of the above times assume that heat is entering the glass from both 
sides. If the glass is on an insulating platform such as firebrick, double 
these times. " 


Jerry B. Hillman writes: 

> Hi Matt,
> I am looking into Cas, coude, etc. designs, but haven't learned enough about
> them to make a decision to go that route. This is only my third mirror.
> Succeeding on the simplest terms, ie. a Dob/Newt is probably going to be a
> challenge as it is without trying the exotic designs. 
> 
> Clear skies,
> Jerry 
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
 


Mike Conron 
_______________________________________________
ATM mailing list http://www.atmlist.net/