Types Of Glass
As mentioned in “The Origins of Glass Making” section, the amount of heat used in the glass manufacturing process determines the final glass product. The greater the heat used, the stronger the glass produced. Below, we have listed different glass types in order, starting from the one with the lowest amount of heat used, and ending with the one that uses the highest amount of heat (tempered glass).
Annealed Glass – This is the most commonly used glass type today and is used in most home windows. It is manufactured using the float method, wherein molten glass is continuously poured onto a bed of molten tin. The tin has a lower melting point than glass, which causes the glass to solidify as it cools on top of the tin. The thickness of the glass can be controlled by adjusting the flow of molten glass onto the tin. Once the glass solidifies, it is then cooled in an annealing oven to remove any residual stress. Annealed glass is relatively fragile because it has a low amount of surface heat compression. When it breaks, it shatters into small and irregularly shaped pieces.
Heat-Treated Glass – This glass type is twice as strong as annealed glass. It is produced by heating the annealed glass to its softening point (1200 degrees F), then cooling it quickly using water. The water cools the glass surface faster than the interior, which creates an extra degree of surface compression. Increasing the rate of cooling produces a stronger surface compression. Heat-treated glass is more resistant to stress caused by heat, wind, and flying objects than standard annealed glass, but not as strong as safety glazing products.
Thermally Tempered Glass – This glass type is four times as strong as annealed glass and is highly resistant to temperature changes that cause cracking. It is produced by increasing the heat-treatment method to provide the highest amount of surface compression. When tempered glass breaks, it shatters into smaller pieces (shards) that are less dangerous than larger fragments created by annealed glass. Tempered glass is ideal for areas prone to glass breakage, such as car windshields and commercial storefronts. Most tempered glass has an etching label on the corner to ensure that it is fully tempered.
Laminated Glass – Any of the above glass types can be laminated. The most common finished product is two sheets of toughened glass laminated together with a 1.52mm thick Polyvinyl Butyral (PVB) interlayer. Laminated glass offers many advantages, such as safety and security. When laminated glass breaks, it does not shatter into pieces but is held together by the interlayer, reducing the safety hazard associated with shattered glass fragments and, to some extent, the security risks associated with easy penetration.