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How does heat-treating glass make it stronger?

April 26, 2017glass stronger

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How does heat-treating glass make it stronger?

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Heat-treating, either heat strengthening or tempering, requires reheating the annealed glass to 1100-1500 F. and rapid cooling it so that a compression envelope develops around the glass surfaces and edges and a balanced tension stress within the glass itself. The equilibrium of stresses causes the strength of glass to increase 2x or 4x that of the original glass. Heat strengthened glass has a surface compression between 3500-7500 psi (2x strength increase). Tempered glass has a minimum surface compression of 10,000 psi (4x strength increase).