Glass Industries

• Glass

  Physically, it is a rigid, undercooled liquid having no definite melting point and a sufficiently high viscosity (greater than 10 Pa · s) to prevent crystallization.
• Glass

  Chemically, it is formed by combining nonvolatile inorganic oxides through the decomposition and fusion of alkali and alkaline earth compounds, sand, and other ingredients. The resulting product has a random atomic structure.
• Glass

  • is a completely vitrified product/suspended with a small amount of nonvitreous material.
  • has properties such as: transparency, hardness, and the ability to be molded or shaped when heated.
  • has high resistance to chemical attack.
  • is a good electrical insulator.
  • is a brittle material.
  • exhibits much greater compressive strength than tensile strength.
• Uses of Glass

  • Window and doors
  • Food and drinks packaging
  • Tableware
  • Insulation
  • Conservatory
  • Flacon for cosmetics and pharmaceutical
  • Interior design and furniture
  • Automotive and transport
  • Medical technology, optical glass, biotechnology, etc.
• Composition of Glass

  • over 90% lime, silica, and soda
  • Major Ingredients: Sand Lime Soda ash
  • Minor Ingredients: other raw materials
• Important factors to make glass:

  • Viscosity of molten oxides
  • Relation  between  viscosity  and composition
• CLASSES OF COMMERCIAL GLASSES

  Fused Silica or Vitreous Silica

  • Made by pyrolysis of silicon tetrachloride or fusion of quartz and sand.
  • Sometimes called quartz glass.
  • Has  low  expansion  and  can  handle  high temperatures.
  • Stays strong in heat better than other glasses.
  • Exceptionally transparent with ultraviolet light.
• CLASSES OF COMMERCIAL GLASSES

  Alkali Silicates

  • Made by melting sand and soda ash.
  • Composition ranges from Na2O-SiO2 to Na2O-4SiO2
  • Understanding them helps understand more complex systems
  • Silicate of soda solution (or water glass) used as paper adhesives and for fireproofing.
  • Higher alkaline types used in laundering and soap making.
• CLASSES OF COMMERCIAL GLASSES

  Soda-Lime Glass or Soft Glass

  • Constitutes 95% of all manufactured glass.
  • Used  for  containers,  flat  glass,  automobile  and other windows, tumblers, and tableware.
  • Chemical composition: 70-74% SiO2, 8-13% CaO, 13-18% Na2O.
  • In the liquor trade, glassware was made with high alumina and lime, low alkali, resulting in difficult melting  yet  chemically  resistant  glass;  selenium was used as a decolorizer for better color
• CLASSES OF COMMERCIAL GLASSES

  Lead Glass or Flint Gas

  • Derived  from  replacing  calcium  oxide  with  lead oxide.
  • Utilized in optics for its high refractive index and dispersion.
  • High lead (PbO) content yields superior "cut glass."
  • Employed in electric light bulbs, neon signs, and radiotrons for its high electrical resistance.
  • Ideal for nuclear radiation shielding.
• CLASSES OF COMMERCIAL GLASSES

  Borosilicate or Hard Glass

  • Chemical  composition:  10-20%  B2O3,  80-87% silica, less than 10% Na2O.
  • Has low expansion coefficient, superior resistance to  shock,  excellent  chemical  stability,  and  high electrical resistance.
  • “Pyrex” laboratory glassware
• CLASSES OF COMMERCIAL GLASSES

  Special Glasses

  • Colored  and  coated,  opal,  translucent,  safety, optical, photochromic glasses, and glass ceramics.
  • Have  varying  compositions  depending  on  final product desired.
• CLASSES OF COMMERCIAL GLASSES

  Glass Fibers

  • Produced from special glass compositions that are resistant to weather conditions.
  • Have  large  surface  area  which  makes  them vulnerable to moisture in air.
  • Low in silica (55%), low in alkali
• RAW MATERIALS

  Sand

  
  

  • Should consist of nearly pure quartz.
  • Determines the glass factory's location.
  • Iron content should be below 0.45% for tableware; below 0.015% for optical glass.
• RAW MATERIALS

  Soda (Na2O)

  • Supplied by dense soda ash.
  • Other   sources   include   sodium bicarbonate,  salt  cake,  and  sodium nitrate  (latter  aids  in  oxidizing  iron and speeding up melting).
• RAW MATERIALS

  Lime

  • Sourced from limestone and burnt lime  from  dolomite  (the  latter introduces MgO into the batch).
• RAW MATERIALS

  Feldspars

  • General  formula  is R2O⋅Al2O3⋅6SiO2
  • Cheap, pure, and fusible
  • Composed  entirely  of  glass-forming oxides.
  • Alumina  content  lowers  the  melting point and retard devitrification.
• RAW MATERIALS

  Salt Cake

  • Said  to  remove  troublesome  scum from tank furnaces.
  • Acts as oxidizing agent by removing impurities  such  as  iron  oxide  and convert it to a form that can be easily removed from the molten glass.
• RAW MATERIALS

  Borax

  • Supplies glass with Na2O and boric oxide.
  • Has  high  fluxing  power,  lowers expansion coefficient, and increases chemical durability.
• RAW MATERIALS

  Cullet

  • Crushed  glass  from  imperfect articles, trim, and other waste.
  • Facilitates melting and utilizes waste.
  • Can  constitute  10%  to  80%  of  the charge.
• RAW MATERIALS

  Refractory Blocks

  • Sintered zircon, alumina, mullite, mullite- alumina, and electrocast zirconia-alumina- silica,  alumina,  and  chrome-alumina  are some examples seen in glass tanks.
  • Used  for  their  ability  to  withstand  high temperatures    without    melting    or deforming
• METHODS OF MANUFACTURE

  1. Melting
  2. Shaping or forming
  3. Annealing
  4. Finishing
• Melting

  Pot Furnace

  • Capacity: 2t or less.
  • Used for small-scale production of special glasses (optical and art glass by casting process).
  • Protects the melting batch from combustion byproducts.
  • Pots are crucibles made of selected clay and platinum, latter is chosen to minimize product contamination and ensure furnace durability and longevity.
• Melting

  Tank Furnace

  • Capacity: 1350t
  • Dimensions: Approximately 38 x 9 x 1.5 m
  • Batch  materials  charged  at  one  end,  built  from  refractory blocks.
  • Glass forms a pool in the hearth of the furnace.
  • Refined glass exits from the opposite end through continuous operation.
• Shaping or Forming

  • Machine or hand molding
  • In  a  short  time,  glass  changes  shape  from  viscous  liquid  to clear solid.
  • Should consider flow of heat, stability of metals, clearance of bearings
  • Most common types of machine-shaped glass:

  1. Window Glass
  2. Plate Glass
  3. Float Glass
  4. Wired and Patterned Glass
  5. Blown Glass
  6. Light Bulbs
  7. Television Tubes
  8. Glass Tubing
• Annealing

  • Should be done to reduce strain.
  • Involves 2 operations:

  1. Holding a mass of glass above a certain critical temperature long enough to reduce internal strain by plastic flow to less than a predetermined maximum
  2. Cooling  the  mass  to  room  temperature  slowly  enough  to hold the strain below this maximum
  3. Annealing  lehr  -  designed  heated  chamber  which  rate  of cooling can be controlled
• Finishing

  • Includes cleaning, grinding, polishing, cutting, sandblasting, enameling, grading, and gaging.