Glass can be heat-treated in the following two ways, heat-strengthened or tempered glass. Both processes use the same tempering furnace which heats the glass to about 1200 degrees Fahrenheit. The rate in which the glass is forced to cool down determines the surface and edge compression. Depending on the final use of the glass the required treatment is applied. Optical distortion is a characteristic found in high performance glazing such as heat-strengthened and tempered glass. Glass with increased strength will look distorted in the way of a wave or bend due to higher surface compression and is not a defect.
The cooling process is slower with HS glass, meaning the compression strength is higher than annealed, approximately twice as much, and lower than tempered glass. The required surface compression for HS glass is 3,500 to 7,500 psi. While HS glass alone is stronger than annealed and cannot be cut it is not considered safety glass, unless laminated. This type of glass treatment is required when additional resistance to heat and/or wind is needed. Laminated heat-strengthened glass is commonly used for doors, sliding doors, and windows.
Tempered glass also known as safety glass is force cooled at a faster rate resulting in a surface compression of 10,000 psi. Tempered glass cannot be cut and when broken it will shatter into many tiny pieces, preventing an injury. It is widely used for shower glass, sliding doors, railing, storefronts, etc. Tempered glass will fall out of its glazing system leaving unwanted areas exposed. To prevent the unit from falling apart and further safety and protection, laminated glass is highly recommended.
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