Automotive Products Processes
Laminated Glass
Plies of glass are bonded together with a layer of polymer film in between. Heat and pressure eliminate air bubbles from the laminate so that it appears optically as a single sheet of glass. If the laminate is fractured, the glass plies are held together and are less likely to cause injury. Laminated glass for building use is also made in this way.
Car windscreens and increasingly side windows, are made from laminated glass. Multi-layer laminates are used in locomotive windows, in security glazing for cars and in bullet resistant glazing.
Tempered (toughened) Glass
Float glass is heated to about 650ºC, then quenched with air jets so that the surfaces are cooled quickly, and the inside core more slowly. At room temperature, the core continues to cool. The surfaces go into compression and the core goes into tension.
If the glass breaks, the core releases tensile energy resulting in the formation of small blunt glass particles. This toughened glass is used in side and rear car windows and in safety glazing in buildings.
Shaping
Glass has to be bent into shape for vehicle windows. Between 500°C and 600°C the viscosity of glass falls by a factor of 10,000 as it transforms from a brittle solid to a plastic substance. This plastic phase allows the manufacture of complex shapes, free from wrinkles and other optical defects.
Sag-bending is the most widely used process for windscreens. The glass is heated to the plastic phase and allowed to sag under its own weight to the required shape. Alternatively, a press-bending process can be used where a greater surface accuracy is required. Once in the plastic phase, glass is pressed into the desired shape between male and female dies.