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October 14, 2019


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History - Industry - PPG Tarentum

Casting and Rolling Sheets of Plate Glass

Here we see one of the most interesting processes in the manufacture of glass. That huge clay pot, poised above the casting-table, has just come from the furnace and contains the fluid glass. The man on the platform of the electric cranes will release the levers in such a way that the pot will be tapped to allow the glass to fall upon the mold. That roller at the further end of the casting-table is then passed rapidly over the mold to reduce the glass to a uniform thickness.

The mold will then go through a series of furnaces called a "lehr." This "lehr" is generally about 200 feet long and consists essentially of a continuous, covered, smooth, level bed of specially prepared clay, which, beginning at the first furnace, heated to about the melting point of glass, passes through five "stations," or furnaces, each in succession, having a somewhat lower temperature.

The mold after resting in the first, or hottest furnace, for a sufficient period, is slowly moved along through the four succeeding stations, gradually losing its heat until the red "lehr" is reached, when it is withdrawn. This entire process consumes only three hours, while in former days by the old method it took three days. When it leaves the "lehr," the plate is thoroughly set and ready to be taken off, ground and polished.

Next - Revolving Iron Disks Grinding Surface of Plate Glass

Previous - Drawing a Pot of Liquid Glass from the Furnace

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