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Glass (Lime-soda glass- made from a mixture of sand, lime and sodium…
Glass
Lime-soda glass- made from a mixture of sand, lime and sodium carbonate that’s heated to 1500°C in a furnace.
Sheet is annealed to reduce stresses. Material is cut at the end of the process to required size with diamond wheel cutters.
Resulting molten material is then tapped off forming a continuous flow that can be ‘floated’ on a tank of molten tin to form plate glass.
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Glass vs polymers- ready-made meals containers made from thermoplastic polymer (PET or PVC). Bottles- glass bottles= wine, sauces and jams. Many of these now in plastic bottles.
Advantages (polymers instead of glass): Lightweight (transportation), low melting point (recycling), screw tops can be used, squash without breaking.
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Glass blowing- used to manufacture hollow objects like bottles. For everyday products- automated process used where a ‘gob’ of glass is formed by pressing and blowing into a mould.
Slumping is where glass is heated until soft meaning that it takes the shape of the mould. Car windscreens are produced this way.
Slumping involves filling ceramic mould with clear and coloured glass fragments. Then placed in a furnace so that it can take shape of the mould.
Annealing glass- contracts on cooling, creating internal stresses. Glass is cooled slowly in a 'lehr'.
Properties- brittle (mechanical shock will break glass: dropping, a cricket ball hitting glass, thermal shock- hot glass in cold water)
Toughened glass- properties can be modified. Toughened by heating glass to 400°C then rapid cooling with air blasts. Used for vehicle windows and glass doors.
Coloured glass- adding oxides of metals (iron, copper and nickel). E.g. stained glass windows, wine/beer bottles, tinted windscreens for cars.
Lead crystal and Pyrex- lead oxide increases the way material reflects light. Used for 'cut glass' wine glasses and vases. Pyrex= heat-resistant products made from boro-silicate glass. Used for cookware applications and laboratory equipment.
Laminated glass- tough composite material, 2 thin sheets of plate glass between tough clear polymer. If glass breaks, polymer holds fragments together. Used for security applications.
Thermal insulator- 'K' glass. Allows heat (sunlight) into building while reducing amount of heat escaping.
Self-cleaning glass- Special coating applied to outer glass surface. This prevents droplets settling on the surface by forcing water to spread out into a sheet.