Up through 1959, sheets of glass were made in one of two ways: either by casting large puddles of glass onto an iron surface and then polishing both sides once it cooled or by using rollers to draw a thin sheet of molten glass up vertically, which then cooled and stiffened as it rose. Both processes produced glass sheets that were nowhere near as smooth as the glass of today. In 1959, Alastair Pilkington introduced the process, now known as the Pilkington Process, that revolutionized the way glass was made. Read on to learn more about the way your windows, mirrors, and other sheet glass is manufactured.
- The raw materials are mixed and heated to 1,500 degrees C in a furnace. The raw materials vary, but commonly include sand, sodium carbonate, dolomite, limestone, sodium sulfate, and crushed, recycled glass. Other materials can be mixed in to add color to the glass or change other physical properties.
- Once all the ingredients have become molten, the glass may be kept at high temperatures for as long as 50 hours, which helps ensure it will be free of bubbles and other imperfections.
- The glass is then brought down to a temperature of approximately 1,200 degrees C and flows onto a table of molten tin. This is where the real genius of the Pilkington Process lies. The main barrier to making perfectly smooth glass prior to 1959 was finding a perfectly smooth surface on which to pour and cool it. Alastair Pilkington found that molten tin worked because it is more dense than glass and remains molten at temperatures that cause glass to cool, meaning the glass won't sink and the surface of the tin remains perfectly smooth.
- At this point, the glass can receive various coatings. For instance, it may be coated to reflect certain wavelengths of light.
- The fifth step is called "annealing." It involves cooling the glass down and subsequently relieving any stresses that formed in the glass during its production.
- The final step in forming sheet glass is cutting it to specified shapes and sizes. Manufacturers typically use diamond-tipped or tungsten carbide wheels to score the glass. Oil is used to lubricate the wheel and glass. The glass then breaks along the score.
Thanks to the Pilkington Process, the glass at places like Suburban Trim & Glass Corp of today is cheaper and practically perfect, featuring uniform thickness and unparalleled smoothness. The next time you look out a window, drive your car, or check your hair in the mirror, thank Sir Alastair Pilkington.