How to Make Tempered Glass
Tempered glass is made with controlled cooling to make it much stronger than ordinary glass. Glass normally has a breaking stress of about 6,000 pounds per square inch (psi) whereas tempered glass requires a stress of approximately 24,000 psi to break. Tempered glass is also safer because it breaks into dull pieces, which makes it especially useful in automobiles. Tempered glass also has a variety of other applications that require high strength such as cookware and glass furniture.
Instructions
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1
Examine the effect of heating and then cooling glass rapidly. The surface of the glass will cool more quickly than the center, which creates an initial compression on the glass's surface. Once the glass cools, the initial stress will need to be overcome before the glass will break.
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2
Combine the ingredients for the glass. The specific proportions vary somewhat but a typical recipe for glass includes 15 percent limestone, 22 percent soda and 63 percent silica sand. Heat the mixture to a temperature of about 1,200 degrees Celsius and mix them thoroughly.
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3
Make sheets of ordinary glass using the float process. Pour the molten glass onto a bed of molten tin so the surface of the glass is extremely smooth and flat. Cool the molten glass on top of the tin gradually from a temperature of approximately 1,100 degrees Celsius to about 600 degrees Celsius.
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4
Remove the solid glass from the tin bath and allow it to cool to room temperature. Cut the glass into sheets of the desired size and drill any needed holes. Tempered glass is extremely brittle and can't be easily cut.
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5
Heat the glass to more than 1,200 degrees Fahrenheit in a kiln and remove it from the kiln. Blast cool air from nozzles immediately onto the glass sheets to cool the glass to 300 degrees Celsius as quickly as possible.
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