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safety glass[′sāf·tē ‚glas]
(in Russian, tripleks), a three-ply shatterproof glass composed of two sheets of organic or silicate glass, or combinations of the two, and a connecting (adhesive) layer. The organic glass may be polymethyl methacrylate or polycarbonate, and the silicate glass may contain sodium or calcium, or it may be of the aluminoborosilicate type.
If an adhesive polymer film—for example, polyvinyl butyral —is used as the connecting layer, safety glass is prepared in the following manner. The film is placed between the glass plates, then the resulting intermediate product is glued together by such means as pressure molding at 1.8–2 meganewtons per sq m, or 18–20 kilograms-force per sq cm, and a temperature of 40°–50°C higher than the flow point of the film. Safety glass does not shatter on impact but only cracks. It is used for windows in automobiles, airplanes, helicopters, ships, and railroad rolling stock.
A unitary structure formed of two or more sheets of glass between each of which is interposed a sheet of plastic, usually polyvinyl butyral. In usual manufacture, two clean and dry sheets of plate glass and a sheet of plastic are preliminarily assembled as a sandwich under slight pressure to produce a void-free bond. The laminate is then pressed under heat long enough to unite. For use in surface vehicles the finished laminated glass is approximately ¼ in. (6 mm) thick; for aircraft it is thicker. See Glass