Float Glass

Broken glass to be recycled piles up at the mixing or "batching" end of PPG's float-glass factory in Wichita Falls, Texas. Conveyors in the background carry sand and other materials from storage to the plant's furnaces.

Batching begins when raw materials are combined on a conveyor belt to be weighed, blended, and carried to storage silos.

Then they travel, by a different conveyor belt, to the main factory building (the gray structure visible in the background), then enter the melter.

A hopper feeds the mixed materials into the front end of the 36-foot-wide melting furnace, where temperatures reach 3,000 F.

The melting process is completed in the refiner, where air bubbles are removed before the molten glass is poured onto a tin bath.

On the red-hot forming line, the glass is poured in a thin layer atop a bath of molten tin, from which it stays separate as it takes shape. T-shaped electrodes hang above to convey heat, and a guide wheel controls the stream's width, which in turn determines the glass's thickness.

Because of the terrific heat of the glassmaking process, operators on the forming line work largely on computers in airconditioned consoles, yet wear protective clothing in case they need to approach the machinery. Even packing-line operators wear protective gear to shield them from broken glass.

After exiting the lehr, or cooling chamber, at about 300 F, a "ribbon" of fully formed glass drops in temperature further as it moves down the cooling line. As it cools, a laser checks it for flaws.

Next, it passes under automated cutters that score it into preprogrammed widths before cutting it lengthwise. The cutting blades are computer-adjusted to fulfill the specified dimensions for different sizes of prefabricated glass sheets.

The finished product: Workers in the wareroom transport bulk loads of Azuria aqua-blue glass (made at PPG's Wichita Falls plant, though not in Carlisle). Each load weighs about 16,000 pounds.

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