Thermal processing has played a key role in making Industrial Heating’s home city of Pittsburgh great. I know you’re thinking of steel, and you would certainly be right. But did you know that almost a century before steel began its run in Pittsburgh, the Pittsburgh Glassworks was established in 1797? By 1900, there were more than 100 glass factories in western Pennsylvania.
It is believed that glass was first discovered in ancient Egypt as a byproduct of ceramic firing. According to experts, glass was first produced independently of ceramics around 1,500 B.C. From then until the late 1820s, all glass was handmade. Beginning in 1827, the first machine technologies were introduced. Little more than a decade later, Pittsburgh was the pressed-glass capital of the world. By 1920, 80% of America’s glass was made in western Pennsylvania.
Some Pittsburgh craftsmen, and others around the world, still make glass the old-fashioned way. One such glass blower even makes plates this way. Each plate takes almost an hour to make and sells for about $100. Glass blowing is a very heat-intensive process with heating furnaces running at 2400°F.
Glass is actually made by combining raw materials at temperatures of 2800°F. For a process such as bottle making, this molten glass is carefully cooled as it moves into a feeder and is cut into “gobs,” which are fed into mold cavities. Once the bottle is formed, it is then annealed by being reheated to 1050°F and cooled slowly to reduce internal stresses. Tempered glass, on the other hand, is reheated to 1200°F and immediately quenched with cold air to 400-600°F, which produces the temper.
Three basic types of tempering furnaces are used to fabricate tempered glass: vertical, horizontal (on rollers) and gas-hearth style. The third actually transports the glass in a horizontal position on a sloped bed of gas being guided with edge rollers. Tempered glass is four to five times stronger than annealed glass. Due to the quenching process, the exterior surfaces are in compression, and the center is in tension. This causes tempered glass to shatter into small oval-shaped pebbles when it breaks. It has been given the name of safety glass for this reason.
Tempered glass is common in our homes and automobiles. It is used in all doors, all tub and shower enclosures and all auto glass (with the exception of the windshield, which is laminated). In this process, a sheet of plastic is sandwiched between two glass panels. Harkening back to Pittsburgh, it was Pittsburgh Plate Glass (PPG) that revolutionized auto glassmaking in the U.S.
So far, this discussion of glass sounds much like the ferrous thermal processing with which we are more familiar. One of the differences between metal and glass is that glass is a metal wannabe. It wants to become a crystallized solid like a metal, but the atoms in glass can’t become a crystal because they are “jammed up” in a nearly random arrangement. This state of matter actually moves very slowly as it attempts to get unjammed.
Although glass is literally a prehistoric material, it is used in some very high-tech applications such as flat-panel displays and fiber optics. In the early 1970s, researchers at Corning produced an optical fiber with low enough attenuation to usher in optical-fiber telecommunication, which enabled the Internet. In 1981, General Electric first produced fused-quartz ingots that can be drawn into fiber-optic strands 25 miles long. Did you know that enough fiber-optic cable has been installed to go to and from the moon over 160 times?
Another impact that glass has had on our world is in the insulation market. It is estimated that fiberglass house insulation has conserved more than 25 quadrillion BTUs. Now that’s a lot of green. In the area of medicine, glass microspheres smaller than a human hair are providing a promising new liver cancer treatment.
Now you know how thermal processing has played a role in our lives in a way we may not have thought, and Pittsburgh was on the cutting edge of most of this development.