Building Edison’s Bulb

Edison gets credit for inventing the incandescent light bulb, but few of us would own one were it not for the Corning Ribbon Machine. For more than 70 years, this machine and its successors have churned out the bulbous glass shells that house fragile filaments. Not the most glamorous of tasks, but by performing it cheaply and quickly this machine revolutionized an industry and, ultimately, helped light our world.

For years after Edison built the first electric light bulb in 1879, his favorite invention served only as a laboratory device. Large-scale manufacture of Edison’s contraption was impossible because the glass had to be blown by hand-a time-consuming and prohibitively expensive process. Though glass companies spent decades of research and development to automate the process, progress was disappointingly slow. Then, in 1926, Corning Glass Works introduced the Ribbon Machine and put an end to the bulb production problem. Today, modern versions of the machine make more than 2 billion glass shells each year. A mere 15 ribbon machines would be enough to fill the entire world’s need for regular-sized incandescent bulbs and ensure that, wherever electricity flows, there can be light.

The machine’s design is ingenious. A melting tank above one end feeds a continuous stream of molten glass down between two water-cooled steel cylinders. The cylinders rotate and flatten the glass into a ribbon-only one-eighth of an inch thick-extruded onto a horizontal metal conveyor belt. Still about 1100C, the glass begins to fall through regularly spaced holes in the belt. Then plungers drop onto the ribbon from above and blast pressurized air into each sagging bulge, forcing it to expand. At the same time, rotating split molds below the conveyor belt briefly clamp together around the forming bulbs, ensuring the proper size and shape. Finally, a small metal tool breaks each newly formed bulb from the ribbon, and the excess glass is fed back into the melting tank.