The windshields of automobiles are made of a specialized form of glass, specifically designed for this purpose. This glass is composed of silica, fine sand, soda ash, dolomite, waste glass and limestone, with some formulations containing small amounts of potassium oxide and aluminum oxide. Laminated glass is created by sandwiching a thin layer of vinyl between two layers of glass, resulting in a thicker and stronger window. This type of glass is considered one of the safest, as it is not easily broken or shattered.
Most vehicle windshields are made from laminated glass, making them effective in preventing break-ins due to the effort required to break them. Rear glass, also known as rear window glass, rear windshield or rear glass, is the piece of glass opposite a vehicle's windshield. This type of glass is made from tempered glass, also known as safety glass. When broken, it shatters into small round pieces, unlike the front windshield which is made from laminated glass. Laminated glass consists of two pieces of glass with a layer of polyvinyl butyral (PVB) between them.
The two pieces of glass and the PVB are sealed together by a series of pressure rollers and then heated. This combination of pressure and heat chemically and mechanically bonds the PVB to the glass. Mechanical bonding occurs through the adhesiveness of PVB while chemical bonding is created through hydrogen bonding between the PVB and the glass. Safety glass is used in all automotive glass due to its ability to reduce the likelihood of injury should it break. Windshields are manufactured through a lamination process which involves sandwiching a layer of PVB between two pieces of float glass and then heating them together.
This combination creates a laminated windshield which is much stronger than simple float glass. When laminated glass breaks, it breaks into small pieces instead of large fragments. Molten plastic is then injected into the mold and after cooling, a plastic frame is formed around the glass so that it can be shipped to car or glass manufacturers. In 1903, French chemist Edouard Benedictus discovered shatter-resistant glass when he dropped a jar filled with dry collodion film. The float glass used to create laminated windshields is then tempered to improve its strength by rapidly heating it and then blasting it with cold air. This “tempering process” makes the glass many times stronger than untempered glass of the same thickness.
When tempered safety glass breaks, it breaks into small pieces instead of large fragments which makes it safer than other types of automotive glasses. Some companies that manufacture automotive glasses include AGC Glass Company North America, Guardian Industries, PGW Glass, Pilkington North America and Vitro. Ellen Rogers has been involved with the automotive industry for nearly 20 years and is the editor of USGlass Magazine and Architects' Guide to Glass magazine. However, in severe impact situations, the tempered safety glass “breaks” but usually does not separate because broken pieces generally adhere to the vinyl inner liner.
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