A LIQUID for packaging and architecture, engineering and art! Essential to automobiles, radio, television and satellites, it is indispensable in hospitals, factories and homes. It can be as strong as steel, hard as gems, heavy as iron; or fragile as eggshells, soft as silk, light as cork. Supplied in abundance surpassed by few other materials, it is the liquid of antiquity--glass.

'Glass--a liquid?' you may ask in disbelief. Yes, when glass is formed from a white-hot mixture of molten ingredients its atoms and molecules retain the random pattern of a liquid even though it becomes as rigid as ordinary solids. A liquid that looks, feels and behaves like a solid seems fantastic, but the peculiar properties of its unique state make glass one of your most versatile and valuable servants.

Glassmaking is one of the most ancient industries. It is also very modern. Man has used glass for more than thirty-five centuries, but he barely 'scratched the surface' of its versatility until about seventy-five years ago. In fact, it was not until 1903 that a glass bottle was produced entirely by automation, and a machine for flat-drawing window glass was not a commercial reality until about 1916. Since then increased knowledge and better means to utilize this amazing liquid have allowed mass production to transform glass from a treasured luxury to a servant in myriads of forms.

Continuous Production

The basic ingredients of glass have remained unchanged for thousands of years. Silica sand, lime and soda still make about 90 percent of the world's glass, but the production scale has been considerably increased to meet modern demands. Today's glassmakers scrupulously select tons of pure raw materials, weigh them to the ounce, thoroughly mix them and then feed the mixture, or batch, to gigantic tank furnaces that can hold more than 1,000 tons of molten glass. Although added cullet, or scrap glass of the same formula to be manufactured, speeds the melting process, the furnace must be heated to about 2,800 degrees Fahrenheit! So corrosive is molten glass at this temperature that the process has been compared to melting a block of ice in a container of sugar. The heat-resistant furnace walls must usually be replaced every two to four years.

However, once the process is in operation it continues day and night, week after week, until repairs or changes in formula force a shutdown. The batch is continuously fed into one end of the furnace while workable glass, mixed and refined to uniform viscosity, free of bubbles and impurities, is drawn from the other. The red-hot liquid is then ready to be drawn, pressed or blown into your service.

Window Glass

Although some fashionable Roman homes during the first century C.E. boasted almost transparent glass windows, little more than a century ago they were still considered a luxury. Today the annual production of window glass would stretch for thousands of miles as the ancient liquid is drawn, cut and framed to provide light, reduce noise, keep heat in and cold out.

Ordinary window glass is drawn from the drawing kiln, a small extension of the furnace. To begin production an iron grill bait is lowered into the melt and slowly raised. The molten glass is fluid enough to flow, yet viscous enough to adhere to the bait so that it rises vertically in a continuous sheet! The bait is knocked off as electrically driven rollers carry the hardened liquid some thirty feet straight up to a cutting loft where the fire-polished sheet is cut into standard lengths.

The surfaces of sheet glass produced by this method are not perfectly parallel, causing slight visual distortion through the glass. For optically superior windows and mirrors, flat glass, drawn from the furnace, moves horizontally as a continuous ribbon a thousand feet long through gigantic grinders. It is ground on both sides simultaneously to near perfect flatness. The plate glass is then cut into sections and polished to provide an undistorted view of the road for some motorist, or to fascinate a little child with his flawless rosy-checked image in the glass.

Float Glass

A revolutionary new process for the manufacture of quality plate glass was announced in 1959. Called the float process, it eliminates entirely the costly grinding and polishing procedures.

Molten glass flows from the furnace in a continuous strip directly onto the surface of an enclosed pool of molten tin. The glass is kept hot enough for all irregularities to melt out while the surfaces become perfectly flat and parallel. The glass is carefully cooled as it progresses along the float bath to emerge distortion free with hard fire-polished surfaces.

Float glass has been met with enthusiasm, especially by the automobile industry, which gobbles up about 50 percent of all the flat glass manufactured annually.

Author: Flor Ayag

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