DEFINITION Glass is an amorphous, hard, brittle, transparent or translucent super cooled liquid of infinite viscosity, having no definite melting point obtained by fusing a mixture of a number of metallic silicates or borates of Sodium, Potassium, Calcium, and Lead.It possess no definite formula or crystalline structure: “An inorganic product of fusion which has cooled to a rigid condition without crystallizing” Does not have a specific melting point Softens over a temperature range
PROPERTIES OF GLASS Amorphous Brittle Transparent / Translucent Good electrical insulator Unaffected by air, water, acid or chemical reagents except HF No definite crystal structure means glass has high Compressive strength Can absorb, transmit and reflect light
RAW MATERIALS USED IN MANUFACTURING GLASSRaw Materials Sodium as Na2Co3 . Potassium as K2Co3 . Calcium as lime stone, and lime. Lead as litharge, red lead (flint glass). Silica arc quartz, white sand and ignited flint. Zinc is zinc oxide (Heat and shock proof glass). Borates are borax, Boric acid (Heat and shock proof glass). Culets or pieces of broken glass to increase fusibility.
MANUFACTURING STEPS Melting Forming and Shaping Annealing Finishing
MELTING PROCESS1). Raw materials in proper proportions are mixed with culets.2).It is finely powdered and intimate mixture called batch is fused in furnace at high temperature of 1800°C this charge melts and fuses into a viscous fluid. CaCO3 + SiO2 CaSiO3 + CO2 Na2CO3 + SiO2 Na2SiO3 + CO23).After removal of CO2 decolorizes like MnO2 are added to remove traces of ferrous compounds and Carbon. Heating is continued till clear molten mass is free from bubbles is obtained and it is then cooled to about 800°C.
FORMING, SHAPING, AND ANNEALING Forming and Shaping. The viscous mass obtained from melting is poured into moulds to get different types of articles of desired shape by either blowing or pressing between the rollers. Annealing. Glass articles are then allowed to cool gradually at room temperature by passing through different chambers with descending temperatures. This reduces the internal Strain in the glass.
FINISHINGFinishing is the last step in glass manufacturing.It involves following steps. Cleaning. Grinding. Polishing. Cutting. Sand Blasting.
SODA LIME OR SOFT GLASS About 90% of all glass is soda-lime glass made with silica (sand), Calcium carbonate and soda ash. The approximate composition is Na2CO3.CaO.6SiO2. They are low cost, resistant to water but not to acids. They can melt easily and hence can be hot worked. Uses: Window glass, Electric bulbs, Plate glass, Bottles, Jars, cheaper table wares, test tubes, reagent bottles etc
POTASH LIME OR HARD GLASS Potash lime glass is made with silica (sand), Calcium carbonate and potassium carbonate. The approximate composition is K2CO3.CaO.6SiO2 . They posses high melting point, fuse with difficulty and are less acted upon by acids, alkaline and other solvents than ordinary glass. Uses: These glasses are costlier than soda lime glass and are used for chemical apparatus, combustion tubes and glassware which are used for heating operations.
LEAD GLASS OR FLINT GLASS It is made up of lead oxide fluxed with silica and K2CO3 is used instead of sodium oxide. Its approximate composition is K2Co3.PbO.SiO2. Uses: High quality table wares, optical lenses, neon sign tubing, cathode ray tubes, electrical insulators, crystal art objects or cut glass, Windows and Shields for protection against X-rays and Gamma rays in medical and atomic energy fields etc.
BOROSILICATE It contains SiO2(80.5%), B2O3(13%), Al2O3(03%), K2O(3%) and Na2O(0.5%). These glass have low thermal coefficient of expansion, and high chemical resistance i.e..shock proof. It is common hard glass containing silica and boron with small amount of alumina and less alkaline solids.
ALUMINO-SILICATE GLASS The typical approximate composition of this type of glass SiO2(55%), Al2O3(23%), MgO(090, B2O3(07%), CaO(05%) and Na2O, K2O(01%). This type of glass possess exceptionally high softening temperature. Uses: It is used for high pressure mercury discharge tubes, chemical combustion tube and certain domestic equipments.
99.5% VITREOSIL GLASS It contains pure silica heated to its melting point. It is translucent, the coefficient of thermal expansion is very low hence it has high resistance to thermal shock, have high chemical resistance to corrosive agents. If Vitreosil glass is heated above its melting point, it becomes transparent and is known as clear silica glass. Uses: They are used in construction of chemical plants, laboratory crucibles, induction furnace lining, electrical insulators and heaters and have high light transmission properties.
SAFETY GLASS It is made by fusing two to three flat sheets of glass and in between them alternate thin layer of vinyl plastic is introduced. It is heated where both the layers merge together and glass is toughened. Uses: It is used as wind shield in automobiles and airplanes. On breaking it pieces does not fly apart because of the presence of the plastic layer in between the glass layers.
OPTICAL OR CROOK’S GLASS It contains Phosphorus, PbCO3, silicates and Cerium oxide which has the property to absorb harmful ultra-violet light. This glass is given through homogeneity by heating it for a prolonged period of time. These glasses have low melting point and are relatively soft. Uses: They are used for making optical lenses.
COLOURED GLASSAddition of transition metal compounds to glass gives color to the glass. They are outlined below. Yellow: Ferric Salts Green: Ferrous and Purple: Magnese dioxide Chromium salts saltRed: Nickel and cuprous Lemon Yellow: Cadmium Fluorescent greenish salts Cu2O sulphide yellow: Uranium oxideBlue: Cobalt Salts, CuO Greenish Blue Color: Brown: Iron Copper SulphateOpaque milky white: Ruby : Auric ChlorideCryolite of Calcium
WIRED GLASS Wired glass does not fall apart into splinters when it breaks and is fire resistant. It is made by fusing wire in between the two glass layers.Uses: For making fire resistant doors, roofs, skylights and windows
FIBER GLASS It is transformed into a fine thread of filament and has got a high tensile strength.Uses: Found extensive use for the manufacture of fabric, reinforcing plastics and production of thermal insulation materials etc
NEUTRAL GLASS These glasses are highly resistant to chemical attacks and they are specialized soda lime glass where alkali has been replaced by alumina, boron oxide and zinc oxide. Uses: Making Syringes, Injection Ampoules and vials etc.
LAMINATED GLASS The sheets of glass fiber or glass wool are soaked in a solution of thermosetting plastic like phenol formaldehyde resin and placed one above the other and then cured under heat or pressure. It is strong as steel. Non flammable and insulating. In bullet resistant glass vinyl resins are added in alternate layers. Uses: Shatter, shock andBullet proof Glass
INSULATING GLASS Two or more plates of glass are filled with dehydrated air and the edges are sealed air-tightly. Uses: Provides thermal insulating and so houses remain cool in summer and warm in winter.
FRACTURE / FAILURE OFGLASS Glass does not have crystal lattice structure hence it breaks. Fracture is caused by small imperfections, flaws and irregularity on the surface of the glass. Flaws are very fine cracks cause concentration of stress and the crack proceeds quickly causing a fracture….
IT IS CLEAR THAT GLASS PLAYSA VITAL ROLE IN OURLIFE…GLASS COVERS A VERYLONG JOURNEY BEFORE ITCOME TO US..AND IT’S REALLYHARD TO MAKE GLASS. SO BETTERWATCH BEFORE CRACKING ONE.