![]() Note also that a blow with a sharp object, such as an awl or prick punch, can shatter tempered glass with very little energy input. It takes more than three times the kinetic energy of a blunt object to penetrate through a typical laminated glazing than to shatter and penetrate through tempered glass. The laminated glazing may be cracked but the plastic interlayer holds the glass pieces together and keeps the window closed. But when the tempered glass is fractured, it shatters, scattering the glass fragments and opening out the window. This makes tempered glass have a harder surface, resisting fracture when struck by a blunt object under loads that crack the annealed glass of windshield type laminated glazing. The glass is reheated, given the needed curvature in a mold, then blasted on both sides by cool air, causing a shrinkage or compression of the surfaces. The glass is cut to the window size and any necessary holes are cut. In today’s manufacture, molten glass floating on a hot bath of liquid tin, “float glass,” is drawn off on rollers then cooled slowly to become annealed glass. In the United States, the windshield remained of laminated glass, with its ability to prevent the penetration into the occupant compartment of a heavy object that would shatter tempered glass. Tempered glass side and rear windows were gradually introduced in other models and by other manufacturers, essentially replacing laminated side and rear windows by 1961, with contested arguments that tempered glass was better for side windows than laminated glazing. It was first introduced in the United States in a Chrysler model in 1936. Tempered glass for automobiles was developed in Europe, and soon was considerably less expensive than laminated glazing. The plastic interlayer holds together the pieces of glass when broken, greatly reducing the danger. Henry Ford introduced the laminated windshield, first developed in Europe, for the Model T in 1927, and soon after the windows were also with laminated glazing. ![]() The first windshields, about 1903 in the United States, and soon after the first glass windows, were of plate glass, which breaks into long, sharp, dangerous shards. Automobile glazing in the United States is primarily the three ply (annealed glass/polyvinyl butyral or PVB plastic interlayer/annealed glass) laminated windshield, and tempered glass side, rear, and roof windows.
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