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Glass & its types

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  1. 1. 1WEC
  2. 2. 2 Ceramic materials divide into three categories: 1.Glasses – melting & solidification processing 2.Traditional ceramics – particulate processing 3.New ceramics – particulate processing Introduction of Ceramics WEC
  3. 3. Classification + Applications of Ceramics Glasses Clay products Refractories Abrasives Cement Functional ceramics - optical - composite - reinforce - containers/ - household - wares - bricks - bricks for high T (furnaces) - sandpaper - cutting wheel - polishing materials - composites - structural as construction - engine - rotor -valve -bearing - sensors - windshield Traditional or Classical Ceramics Advanced Ceramics - thermal protection materials 3WEC
  4. 4. 4 Glass  Glass is one of three basic types of ceramics. Glass is distinguished by its amorphous (non crystalline) structure.  Structure : Network formers Molecules that link up with each other to form long chains and networks. Hot glass cools, chains unable to organize into a pattern. Solidification has short-range order only.  Amorphous structure occurs by adding impurities (Na+,Mg2+,Ca2+, Al3+).  Impurities: interfere with formation of crystalline structure WEC
  5. 5. 5 Glass  Raw Materials 1. Glass forming oxides: usually the dominant constituent SiO2, B2O3, P2O5, etc. 2. Fluxes: reduce melting temperatures Na2O, PbO, K2O, Li2O, etc. 3. Property modifiers: added to tailor chemical durability, expansion, viscosity, etc. CaO, Al2O3, etc. 4. Colorants: oxides with 3d, 4f electron structures; minor additives (<1 wt%) 5. Fining agents: minor additives (<1 wt%) to help promote bubble removal As-, Sb-oxides, KNO3, NaNO3, NaCl, fluorides, sulfates WEC
  6. 6. What is Glass? • Fusion of sand (SiO2), soda (Na2CO3) & lime (CaO) that produces a transparent solid when cooled. • A 3D network of atoms which lacks the repeated, orderly arrangement typical of crystalline materials. • Physical Properties: hard, elastic, brittle, non- conductor of electricity, density, refractive index, etc. • Chemical: resistant to all but fluorine and very strong bases.
  7. 7. The primary uses for glass are in windows, containers, light bulbs and eyewear. • Borosilicate Glass (pyrex): 5% borax (Na2B4O7) is added to resist breaking when heated or cooled. • Colored Glass: metal oxides or colloidal iron (Fe) & sulfur (S) are added to change its color. • Lead Glass: Pb increases refractive index & density What Types of Glass Are There?
  8. 8. What Types of Glass Are There? • Flat glass: made by a “float glass process”; molten glass is floated on a pool of tin while cooling. Commonly found in doors and windows. • Laminated glass: used in windshields, two sheets of glass with plastic between them. • Tempered safety glass: used in car side windows and designed to break into tiny pieces; potassium (K) replaces sodium (Na) on the surface.
  9. 9. • Each force causes a deformation that may leave a visible mark or fracture the glass. This can be used to determine the direction and amount of force. • Glass acts initially as an elastic surface and bends away when a force is applied. When the force increases beyond its tensile strength, it cracks. How Do Glass Windows Break?
  10. 10. 10 Glassmaking 1. The ingredients for glass are mixed, and along with a proportion of cullet (broken glass), are added to a bath furnace, where they are heated to about 1500 C and fused together. 2. Molten glass is fed as „gobs‟ to an automatic bottle or jar making machine. 3. A hot gob is first made into a parison or blank shape (by either pressing or blowing), which is then blown to the final bottle or jar shape. Surface coatings (sc) may be applied while hot. WEC
  11. 11. 11 4. The bottles or jars pass into a lehr (an annealing oven), where they are first reheated to soften the glass to remove stresses, and then cooled gradually to prevent stresses developing. 5. The bottles or jars are inspected and tested to meet quality standards. Bottles not passing the quality checks are broken and returned to the furnace as cullet. Cullet reduces the amount of energy required to melt the glass ingredients. 6. Bottles passing inspection and testing are packed for dispatch to where they will be filled, capped, and labeled. WEC
  12. 12. WEC 12
  13. 13. 13 Shaping Processes in Glassmaking  Shaping processes to fabricate these products can be grouped into three categories: 1. Discrete processes for piece ware (bottles, jars, plates, light bulbs) 2. Continuous processes for making flat glass (sheet and plate glass) and tubing (laboratory ware, fluorescent lights) 3. Fiber-making processes to produce fibers (for insulation and fiber optics) WEC
  14. 14. 14 Shaping of Piece Ware  Ancient methods of hand-working glass included glass blowing.  Handicraft methods are still used today for making glassware items of high value in small quantities. However, most modern glass shaping processes are highly mechanized technologies for producing discrete pieces in high quantities.  Piece Ware Shaping Processes 1. Spinning – similar to centrifugal casting of metals 2. Pressing – for mass production of flat products such as dishes, bake ware, and TV tube faceplates 3. Press-and-blow – for production of wide-mouth containers such as jars 4. Blow-and-blow - for production of smaller-mouth containers such as beverage bottles and incandescent light bulbs 5. Casting – for large items such as large astronomical lenses that must cool very slowly to avoid cracking. WEC
  15. 15. 15 Spinning of funnel-shaped glass parts such as back sections of cathode ray tubes for TVs and computer monitors: (1) gob of glass dropped into mold; and (2) rotation of mold to cause spreading of molten glass on mold surface WEC
  16. 16. 16 Pressing of flat glass pieces: (1) glass gob is fed into mold from furnace; (2) pressing into shape by plunger; and (3) plunger is retracted and finished product is removed (symbols v and F indicate motion (velocity) and applied force) WEC
  17. 17. 17 1. A gob of hot glass drops into the blank (parison) mould. 2. The mould is sealed shut by a „base‟ part and a plunger pushes the glass into the mould (made from iron). 3. The glass is shaped into a „blank‟ and also pushed into the neck finish by the plunger. This part of a jar or bottle is finished to its final shape at this stage. 4. The blank shape (parison) is removed, rotated 180 , and transferred to the blow (finishing) mould. 5. This mould is in two halves, made from fine-grain cast iron, and is highly polished. 6. Air is blown into the hot parison to expand it tightly against the mould walls. 7. The mould opens, the bottle is removed, annealed in the lehr, inspected and tested, and shipped for filling. WEC
  18. 18. 18 1. A gob of hot glass drops into the blank (parison) mould. 2. The end is sealed and a puff of air pushes glass into the neck (finish). 3. A puff of air from below pushes glass into the mould and shapes it into a „blank‟ or parison, a thick-walled bottle looking vaguely like the final bottle shape. 4. The blank shape (parison) is removed, rotated 180 , and transferred to the blow (finishing) mould. 5. This mould is in two halves, made from fine-grain cast iron, and is highly polished. 6. Air is blown into the hot parison to expand it tightly against the mould walls. 7. The mould opens, the bottle is removed, annealed in the lehr, inspected and tested, and shipped for filling. WEC
  19. 19. 19 Casting  If molten glass is sufficiently fluid, it can be poured into a mold.  Relatively massive objects, such as astronomical lenses and mirrors, are made by this method.  After cooling and solidifying, the piece must be finished by lapping and polishing.  Casting of glass is not often used except for special jobs.  Smaller lenses are usually made by pressing. WEC
  20. 20. 20 Shaping of Flat and Tubular Glass  Processes for producing flat glass such as sheet and plate glass: Rolling of Flat Plate Starting glass from melting furnace is squeezed through opposing rolls whose gap determines sheet thickness, followed by grinding and polishing for parallelism and smoothness WEC
  21. 21. 21 Float Process Molten glass flows onto the surface of a molten tin bath, where it spreads evenly across the surface, achieving a uniform thickness and smoothness - no grinding or polishing is needed. WEC
  22. 22. 22 Danner Process Molten glass flows around a rotating hollow mandrel through which air is blown while the glass is drawn. WEC
  23. 23. Thanks WEC 23