Float glass comes off manufacturing lines in the form of a flat sheet. In some instances, it may however be required that the glass be bent or curved, depending on its end uses. This includes glass for vehicles such as windshields or some backlights which may be curved on their edges, or glass for architectural uses, such as curved doors or windows, glass domes, or display counters. Various methods exist to provide for such bent or curved glass sheets. To date, the known methods for bending glass are: 1.hot bending; 2.cold bending; 3.lamination cold bending. 1) Hot bending is the most common process for bending monolithic glass. It consists of slowly heating the glass above its softening point (~720 °C for soda lime silica glass) and then shaping it into a mould (Figure 1). Gravity suffices to slump the glass over the mould for single curvature bending, whilst pressing is required for doubly curved shapes. Once the glass takes the shape of the mould, slow cooling must be done to ensure annealing. No residual stresses are generated on the glass and small radius of curvature can be achieved (for reference, 100 mm of radius of curvature for 6 mm glass). Hot bending is effective for all the thickness range. If strengthening is required thermal tempering or chemical tempering are both possible. Thermal tempering can be made by means of a special furnace equipped with adjustable rollers and quenching nozzles at once. Chemical tempering can be performed as usual, but as a separate process after bending. Lamination of curved hot bent glass is also possible, but tight tolerances arc required. For each curved geometry a specific mould ought to be manufactured.
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