Glass Manufacturing - Building Products Processing
Semi-Finished Processing
The following types of processing are high volume and predominantly performed by glass manufacturers.
Coating (Off-line)
Off-line processes use a vacuum coating technology called sputtering. A ‘target’ material is bombarded to produce atoms which are deposited on the glass. This process is used to make products such as Pilkington Optitherm™ S3 and Pilkington Suncool™.
Laminating
Plies of glass are bonded or laminated together with a layer of polymer film in between. By using heat and pressure, air bubbles are eliminated from the laminate so that it appears optically as a single sheet of glass. Mechanically, however, it is more robust: if the laminate is fractured, the broken glass fragments are held together and are less likely to cause injury. Laminated glass is used in safety and security applications.
Silvering
Float glass is made into mirrors in a process which deposits a thin film of high purity silver on one surface of the glass. A further thin film is then deposited to protect the silver from oxidation. Finally, a ceramic paint is applied. This is the process by which Pilkington Optimirror™ Plus is made.
Downstream Processing
The following types of processing are performed by glass manufacturers and also by other companies.
Multiple Glazed Units
Multiple glazed units incorporate two (or more) panes, separated by spacers to create a hermetically sealed gap between each successive pane in the unit, e.g. Pilkington Insulight™. This gap can be filled with air, which is subsequently desiccant dried, low conductivity gases such as argon can be used instead of air in the cavities or, in the case of the Group’s Spacia™ product, the layer of dry air is replaced by a vacuum to achieve higher performance.
Heat Treatment
Toughened glass, or tempered glass as it also known, is produced when float glass is heated to around 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. When the glass breaks, the core releases tensile energy resulting in the formation of small, safer glass particles. Toughened glass is used in safety glazing in buildings.
Shaping
Glass can be bent into shape for some building applications. Between 500ºC and 600ºC the viscosity - or syrupy nature - of glass falls by a factor of 10,000 as it transforms from a brittle solid to a plastic substance. The science of glass bending is to use this plastic phase to produce shapes that are free from wrinkles and other optical defects. Sag-bending is the most widely used process. The glass is heated to the plastic phase and allowed to sag under its own weight to the required shape.
Surface Working
ine surface textures can be applied using sand blasting and acid etching.