Electricity in Glass
The dawn of the 20th century witnessed a period of profound transformation. The invention of the incandescent light bulb by Thomas Edison in 1880 revolutionized how we work, play, and live. While the glassmaking industry of that era bore some resemblance to its medieval counterpart, it was on the cusp of significant change. The advent of electric power played a crucial role in shaping the glass industry into the multi-billion-dollar behemoth it is today.
In 1867, German industrialist Friedrich Siemens, drawing inspiration from the British steel industry, patented a continuous regenerative furnace. This innovation, preceding Edison's lightbulb by over a decade, laid the groundwork for modern industrial glassmaking. Electric melting would also become a major factor in the advance of glass making. However, the widespread adoption of electricity was not without its challenges. The "War of Currents" erupted, pitting proponents of alternating current (AC) against those of direct current (DC) power.
The War of Currents pitted Thomas Edison, champion of direct current (DC) power, against Nikola Tesla and George Westinghouse, proponents of alternating current (AC). Edison, holding patents on DC technology, fiercely opposed AC. He publicly demonstrated its supposed dangers by electrocuting animals and even influencing the design of the electric chair for a convicted murder in 1890. However, Tesla's AC system, with its ability to transmit power over long distances at high voltages, ultimately prevailed. Key victories for AC included powering the 1893 World's Fair in Chicago and the successful electrification of Buffalo, New York, using hydropower from Niagara Falls and Tesla's innovative AC induction motors. Despite Edison's initial resistance, his company, General Electric, eventually embraced AC technology.
Why is this important for Glass makers?
The electric melting of glass began to be explored in the 1920s. A significant breakthrough occurred in 1952 with the introduction of molybdenum electrodes for Joule heating glass furnaces. This innovation has revolutionized the industry, leading to widespread adoption of electric heating, with many furnaces now operating entirely on electricity. The latest low-carbon hybrid melters utilize electricity for up to 80% of their energy needs.
However, one can't help but wonder: what might the state of the glass industry be today if Nikola Tesla had lost the "War of Currents" and direct current (DC) power had become the dominant technology? It would not have worked near as well.
I have witnessed three times what happens when DC current runs through the electrodes on a glass furnace. This occurs when a SCR (Silicon Controlled Rectifier) stops delivering AC power and instead , due to failed thyristors, delivers DC power. If the thyristors fail they stop switching every 60 Hz. and instead the power just runs in one direction. In molten glass, Joule heating works because the alkali atoms vibrate back and forth about 5 microns every 1/60th from the AC current. If the SCR stops switching the current only goes in one direction which is DC. In glass this means that all the sodium atoms in a tank will run from one electrode to its partner. This creates a stream of hot sodium that can dissolve almost anything. It is also a very very low viscosity glass. The result of this can be glass leaks through very small cracks or even dissolution of fused cast electrode blocks. It is not pretty,
Would it be possible to have the modern glass world without AC current? Maybe, but it was a lot easier with Tesla’s current.
