Glass production and applications

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Introduction:

Glass is any substance or mixture of substances that has solidified from the liquid state without crystallization. It may be defined as a hard, transparent, or translucent material chiefly compound of silica, combined with varying proportions of oxides of sodium, potassium, calcium, magnesia, iron, and other minerals. It has a random arrangement of molecules, the great majority of which are oxygen ions bounded together with the network forming ions of silicon, boron or phosphorous.

Glass Composition:

  1. It is obtained from fusion of silica, chalk (lime) and potash or soda at over 1000°C.
  2. Silica is the main constituent which fuses at high temperature, so alkaline admixture is added to lower down the fusion temperature.
  3. Potash gives fire resistant properties to glass.
  4. Soda quickens fusion of glass.
  5. Lime imparts durability and toughness.
  6. Lead oxide provides color.
  7. Cullet, broken glass of the same type added to bring down cost of production.

Properties of glass:

  1. No definite crystalline structure.
  2. No sharp melting point.
  3. Absorbs, refracts, or transmits light.
  4. Affected by alkalis.
  5. An excellent electrical insulator at elevated temperatures.
  6. Extremely brittle.
  7. Available in beautiful colors.
  8. Not affected by water or air.
  9. Possible to weld pieces of glass by fusion.
  10. Not easily attacked by ordinary chemical reagents. A reagent is a substance or compound that is added to a system in order to bring about a chemical reaction or is added to see if a reaction occurs.

Glass Manufacturing:

  1. All constituents are separately ground, sieved and mixed in definite proportions.
  2. The mixture is fused in tank furnace or pot furnace.
  3. Charge is fed at one end and molten glass is tapped at the other end continuously.
  4. Molten glass is shaped by following methods:
  5. Blowing: articles of various shapes by blowing pipe
  6. Flat drawing: plate of glass pressed between rollers to form sheet glass
  7. Rolling: molten glass poured over flat iron table rolled into sheet
  8. Compression molding: irregular shape articles using molds
  9. Spinning: glass fibers produced by spinning action

Glass Classification:

  • Soda lime glass:
  • Fusion of silica, lime, soda, and alumina mixture.
  • Also called soda-ash glass, soda glass or soft glass.
  • Used for glazing doors, windows, common glassware.
  • Lead glass:
  • Fusion of silica, lead, and potash.
  • Also called flint glass.
  • Boro-silicate glass:
  • Fusion of silica, borax, lime, and feldspar.
  • Withstands high temperature.
  • Lab equipment and cookware made with it.
  • Soda glass or soda-lime glass:
  • It is the most common variety of glass. It is prepared by heating sodium carbonate and silica.
  • It is used for making windowpanes, tableware, bottles, and bulbs.
  • Available in thickness of 2.0 to 12.0 mm.
  • Plate glass:
  • Plate glass is thicker than ordinary glass. It has a very smooth surface.
  • Available in thickness of 3.0 to 32.0 mm.
  • It is made by floating a layer of molten glass over a layer of molten tin. It is used in shop windows and doors.
  • Ground and polished.
  • GG quality: cabinets, show cases, shelves, counters, etc.
  • SG quality: mirrors
  • SQ quality: superior quality for high class work
  • Colored glass:
  • Small amounts of metallic oxides are mixed with the hot molten mixture of sand, sodium carbonate and limestone.
  • The desired color determines the choice of the metallic oxide to be added, as different metallic oxides give different colors to the glass.
  • Colored glass is much in demand. It is used for decorating walls, making sunglasses, and for making light signals for automobiles, trains, and aero planes.
  • Tempered plate glass:
  • Glass plate is heated and suddenly cooled to give it a temper.
  • Much stronger than ordinary glass.
  • Used for glazing entrance doors, tabletops, shelves, counters.
  • Laminated glass:
  • Two or more glass plates with intervening layers of transparent plastic bound under heat and pressure
  • It can also be called bulletproof glass. Several layers of safety glass are bound together with a transparent adhesive. The larger the number of layers used the greater is the strength of the glass.
  • It is used in aero planes and windshields of cars.
  • Safety glass:
  • It can also be called shatterproof glass. It is made by placing a sheet of plastic such as celluloid between sheets of glass.
  • The special quality of this glass is that in case of breakage the broken pieces stick to the plastic and do not fly off. You must have noticed a broken windowpane of a bus or a car still in its place. It is used in automobiles and bulletproof screens.

Muhammad Fawad
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