Building Materials Glass

Glass Major Ingredient Composition Glass – an amorphous (without any shape) substance having homogeneous texture Glasses are typically brittle, and often optically transparent. Glass consists mainly of silica (pure sands) This sand is washed and sifted to remove shells, stones and exceptionally large grains of sand, before it is mixed with other materials which control the colour and other properties, and lower the 1730ºC melting point of pure silica. Between 10 and 80% of the finished product is from recycled glass (known as cullet) Major Ingredient Composition Sand 96 - 98 % SiO2 Soda ash Na2CO3 Limestone CaCO3 Cullet Glass

Glass The mix of raw materials is dependent on the type of glass desired. Window glass is made from 72% SiO2, 13% Na2CO3 and 12% CaCO3 Bottle glass has more SiO2 and less CaCO3. Crystal is made from 45% SiO2 and 44% PbO with 9% K2CO3

Manufacture of Glass

Commercial types of Glass Sheet glass Used for glazing doors, windows and partitions Obtained by blowing the molten glass into the shape of a cylinder The cylinder is flattened over a plane tray Sheet glass Plate glass Tempered glass Wired glass Obscured glass Laminated glass Coloured glass

Commercial types of Glass Plate glass Superior to sheet glass Produced by poring the molten glass on casting tables and leveling it into a uniform thickness Used for all engineering purposes Tempered glass Made from plate glass by reheating and sudden cooling 3-5 times stronger than plate glass Resists bending stress than plate glass Used in sport arenas, sliding doors and curtain walls

Commercial types of Glass Wired glass Produced by embedding wire nets 0.4 -0.5 mm into the centre of sheet glass during casting. The minimum thickness of wired glass is 6mm When broken, it does not fall into pieces Used for fire resisting doors and windows, for skylights and roofs

Commercial types of Glass Obscured glass Comparatively opaque to sunlight Also known as patterned glass Classified as frosted glass, rolled glass, ribbed glass Frosted glass – the polished face of the glass is subjected to sand blast which grinds off the surface Rolled glass – series of waves of desired pattern on the surface Ribbed glass – series of triangular ribs produced during casting

Commercial types of Glass Laminated glass Made by sandwiching a layer of poly-vinyl-butyral between two layers of sheet or plate glass Known as safety glass Eg. Heat proof glass, sound proof glass, bullet proof glass

Commercial types of Glass Coloured glass Produced by adding oxides of metals to molten glass Red glass – oxide of iron added Blue glass – cobalt oxide added Yellow glass – alkali uranate added