January 13, 1997 at 19:47

by: John M. Hill

I'm pleased to announce that at 20:30 MST on Sunday January 12, 1997 we began heating the furnace for the casting of the first 8.4 meter diameter borosilicate honeycomb mirror. The mirror blank produced in this casting is destined to become the first of two primary mirrors for the Large Binocular Telescope on Mt. Graham.

On January 2-3, the casting crew loaded 41,942 pounds of Ohara E6 borosilicate glass into the honeycomb mold. The finished mirror will weigh a bit over 16 metric tons. At the moment the oven is at 140 °C and the control system is working nicely. We will heat slowly up to 500 ° C by Thursday. If all systems are go, we'll then proceed with the actual melting of the glass into the mold on Saturday and Sunday. An approximate schedule is listed below:

• Saturday, January 18
  • 08:10 MST Furnace starts turning (750 ° C)
  • 09:00 MST Furnace rotating at 6.8 RPM (762 ° C)
  • Noon MST Noticeable glass softening (810 °C)
  • 14:30 MST Glass blocks slumping (850 ° C)
  • 17:30 MST Glass melting (900 ° C)
  • 23:00 MST Smoothing of glass surface (980 °C)
• Sunday, January 19
  • 03:30 MST Glass clear (1070 ° C)
  • 11:00 MST Maximum Temeperature (1180 ° C)
  • 13:30 MST Start cooling (1180 ° C)

Don't be surprised if the schedule moves around by a few hours. We don't know the exact thermal time constant of the more than 70 tons of glass and ceramics in the mold and the furnace.

You can find more information on the Mirror Lab web pages at:
http://mirrorlab.as.arizona.edu//.html

or the Large Binocular Telescope web pages at:
http://mirrorlab.as.arizona.edu/lbtwww/lbt.html

We will have images from the video cameras that look through small holes in the wall of the rotating furnace so you can watch the progress of the melting glass.

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