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Old 11-04-2003, 06:30 PM
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Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
Join Date: Apr 2002
Location: Chocorua New Hampshire
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drop or raise the quantity of soda by one pound to move the C.O.E. about one full point - based on a 100 lb batch.
You will have to play with it but it's ballpark.

The corning protocol is simply that you want to melt as cold as you can get away with and then to turn it up after the mass has melted. The notion is that the lower the temperature, the less attack on the refractories which yields less pot wear and less cords ( up to a point). It's relative to the cording potential and general meltability of the glass. Sometimes melting cold means 2200 F and that's where I melt SP87. I have fluorine glasses I melt at 1900F. You have to be willing to experiment, and to have a few genuine disasters.

As to franklin's question. the lumps Dave saw were perilously close to staying lumps, and they were unmelted silica. I would not melt it that cold or if I did, the quantities would be tiny. The tendency in a large batch pile, say fifty or sixty pounds is for the outside to melt first and for the core to gradually heat up and fuse. You don't want that fusion to go on too slowly or you will get agglomerated big honking piles of snot- ( a highly technical phenomena well worth avoiding..)
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