GLASS Glass is an Amorphous substance having Homogenous Texture - PowerPoint Presentation

1. GLASSGlass is an Amorphous substance having Homogenous TextureIt is a Hard, Brittle, Transparent or Translucent Material Most Common Material Glazed into Frames forDoorsWindowsCurtain Walls 11Because of demand for more Natural Day Light in Offices Commercial ComplexesIndustriesEducational InstitutionsResidential BuildingsThe most common Types used in Building Construction are:SheetPlateLaminatedInsulatingTemperedWired Patterened 1

2. The most Ordinary Colourless Glasses are:Alkali – Lime Silicate andAlkali – Lead Silicate The Tensile strength is in the range of 30 – 60 N/mm2The Compressive Strength is in the range of 700 – 1000 N/mm2 The Modulus of Elasticity is in the range of 0.45 x 105 to 0.8 x 105 N/mm2The main Shortcoming of the Glass is its Brittleness which mainly depends upon The Ratio of Modulus of Elasticity to Tensile Strength of MaterialA Quality Glass Should be Clear Free from Blisters Free from ScratchesFree from Bubbles Free from Waviness2

3. Constituents of GlassThe Raw materials used are:SandLime (Chalk)Soda or Potash These Raw materials are fused together at a temperature of about 1000C Oxides of Iron, Lead and Borax are added to modify Hardness, Brilliance and Colour The Functions of the various Ingredients are as follows :SILICAUsed in the form of Pure Quartz, Crushed Sandstone and Pulverized Flint Should be free from Iron Content for best quality Glass Since Silica Melts at 1710C, Carbonates of Sodium or Potassium are added to lower the fusing temperature to 800 C These Carbonates also make Liquid Silica more Viscous and Workable.LIMEUsed in the form of Limestone, Chalk or Pure Marble. Addition of Lime makes the glass Fluid and suitable for Blowing, Drawing, Pressing or Spinning Also imparts Durability & Toughness to GlassExcess of Lime makes the molten mass too thin for Fabrication 3

4. SODA Acts as an Accelerator for the Fusion of Glass but Excess is harmfulPOTASH Renders Glass Infusible and Fire Resistant LEAD OXIDE Imparts Colour, Brightness and Shine When 15 to 30% is added to Substitute Lime, it lowers the Melting Point, Imparts Good WorkabilityBut Transparency is lost and Glass becomes Brittle and Crystalline NOTE Iron is not Desirable as a Constituent However if present it Imparts Bottle Green Colour to the Glass Manganese Dioxide known as Glass Maker’s Soap is added which washes the Liquid Glass and removes the Colour 4

5. Glass is manufactured in the following steps:-MELTINGThe Raw Materials – LIME SODA & SAND – Separately Cleaned, Ground and Sieved in Definite Proportions i.e. BatchedThen Mixed with Water Then Fused in a Furnace The Material in the First Stage Melts Forming a Bubbly Sticky Mass at about 1000C As the Temperature is Raised to 1100C - 1200C the Material turns to a more Watery Liquid and the Bubbles rise to the surfaceThe Melting Process involves the following series of Reactions:CaCO3 + SiO2  CO2Na2CO3 + SiO2  CO2Manufacturing5

6. When all the Carbon Dioxide has escaped Decolourisers such as MnO2 or Nitre are added to do away with the Ferrous Compounds and CarbonThe Colouring Salts are added at this stageHeating is continued till the Molten Mass is Free from BubblesAs the Glass Cools upto 800C, it is ready to be Drawn or Floated to its desired Thickness & Size at the other end of the Furnace [Fig 1]FORMING & SHAPINGThe Molten Glass can be Fabricated to desired Shapes by any of the following Methods:BLOWINGA 2 m long and 12 mm dia pipe is dipped in molten glass and taken outIt is held vertically and Blown vigorously by the OperatorThe sticking molten glass takes the shape of a hollow ballOn cooling it is Reheated and the Blowing Operation Repeated till the Desired Articles are readyFLAT DRAWINGThis method is used to manufacture Sheet or Plate Glass The Sheet Glass made by Flat Drawing when Ground or Polished is called Flat Glass6

7. In this process a Grille or Bait is lowered into the Molten Glass in a KilnThe molten Liquid Glass then sticks to the Bait As the Bait is slowly lifted then it draws a Sheet of Glass along with it The Bait along with Molten Glass is then passed through RollersThe bait cracks up and continuous Sheet of Glass is ObtainedThis sheet is then slowly cooled in a Chamber and Annealed for cutting into Proper SizeA Machine for Vertical Drawing of Glass is shown in [Fig 2]This Method is Now being replaced by Float Glass Process FLOAT METHODThe Principle used in this method is that when a Lighter Fluid Floats over a heavier Fluid, the Surface of the Lighter Fluid becomes Flat and ParallelThe Molten Glass from the Furnace is Floated over Molten Tin in Float bath where it is formed into thin layer assuming the perfect parallel surface of the Molten TinHeaters are fitted into the Bath which provided heat to polish the surface of the GlassThe Glass in Plastic State is passed through rollers and simultaneously cooledThis Introduces Internal Stresses which are then relieved by Annealing ProcessThe Plate Glass so produced is distortion free and of superior quality7

8. Fig 1 Glass Manufacturing Process 8

9. Fig 2 Machine for Vertical Drawing of Glass 9

10. COMPRESSION MOULDINGIn this Process Moulds are Used to Obtain the Articles of Desired ShapesSPINNINGA Machine is Used to spin the Molten Glass. The Fibres so produced are very fine and are used for Heat and Sound Insulation ANNEALINGGlass Articles are allowed to cool under Room Temperature by Passing through Different Chambers with Descending Temperatures. If Cooled Rapidly the Glass being Bad Conductor of heat, the Superficial Layer Cools down First and Strain Develops in the Interior Portions, which Causes unequal expansion and the articles are likely to crack.FINISHING After Annealing the Glass Articles are Cleaned, Ground, Polished, Cut and Sand Blasted 10

11. ClassificationDepending Upon the Constituents Glasses are Classified as Soda – Lime Glass Lead GlassBoro – Silicate Glass SODA - LIME GLASS Also Known as Soda – Ash Glass, Soda Glass or Soft Glass It is Obtained by Fusing a Mixture of Silica, Lime and Soda It has a softening point of 600CSoft Glass has the following Approximate Composition73% Silicon Dioxide10% Calcium Oxide17% Sodium Oxide It has Lower Softening TemperatureLess Resistance to Thermal ShocksBut More FlexibleThe quality can be improved by adding Alumina and Magnesium Oxide and glass is then called Crown Glass Used in Doors Windows and for making Glass Wares such as Bottles11

12. LEAD GLASS Also Known as Flint GlassIt is Obtained by Fusing a Mixture of Silica, Lead and Potash It is free from Iron Impurities and is Colourless Has high Shining Appearance and can take PolishIt is not affected by Temperature Used to Manufacture :Electric BulbOptical GlassesCut GlassesOrnamental Glass WorksRadio ValvesBORO – SILICATE GLASSAlso Known as Pyrex or Heat Resistance GlassIt is Obtained by Fusing a Mixture of Silica, Borax, Lime and Felspar.Has the following Approximate Composition13% Boric Acid or Borax80% Silicon Dioxide4.5% Sodium Oxide0.5% Potassium Oxide12

13. The Softening point is about 800C Boro-Silicate Glass can withstand high temperatures and is most suitable for making Laboratory Equipments and Cooking Utensils Commercial Forms of GlassesSHEET GLASSUsed for Glazing Doors, Windows and PartitionsObtained by Blowing the Molten Glass into the Shape of the Cylinder The ends of the Cylinder are Cur away and the Cylinder is Flattened over a Plane TrayAvailable in Thicknesses of 2, 2.5, 3, 4, 5, 5.5, and 6.5 mm and upto 1750 x 1100 mm Size Classified as:TYPESUSESOrdinary Glazing Quality General Engineering Purposes Selected Glazing QualityClass Works Special Selected QualitySuperior Quality Works such as Show Cases, Cabinets etc.13

14. PLATE GLASSUsed for all Engineering Purposes and is Superior to Sheet GlassProduced by Pouring the Molten Glass on Casting Tables and Levelled to a Uniform Thickness Both the Surfaces are then Ground, Smoothened and PolishedGlass so Produced is Clear and Contains Unblemished True Plane SurfacesIt has Parallel, Distortion-Free Surface obtained by Grinding or Floating MethodAvailable in Thicknesses of 3 to 32 mm and Sizes upto 2750 x 900 mmClassified as:TYPESUSESGround Glass Quality Showcases, Cabinets, Counters, Shop Fronts etc. Selected Glazing QualityMaking MirrorsSpecial Selected QualityHigh Class Works, Wind Screens of Vehicles14

15. TEMPERED GLASSProduced by Reheating Plate Glass it in its Finished Shape at 650C It is then Rapidly CooledBy doing so both Sides get permanent Compressive Stress without stressing the Interior of the Glass, which still remains in a Fluid StateIt is 3 to 5 times stronger than Plate GlassAlthough Not Unbreakable, it resists Bending Stresses Better than Plate Glass. When Broken Pieces are Relatively Smaller in SizeUSESSports ArenasSliding DoorsCurtain WallsWhere People are Likely to Come in Bodily Contact with Glass15

16. WIRED GLASSProduced by Embedding Wire Nets 0.46 to 0.56 mm into the Center of the Sheet Glass during CastingMinimum Thickness of Wired Glass is 6 mmWhen Broken it Does not Fall into PiecesHas higher melting Point than ordinary GlassUSESFire Resisting Doors and WindowsSky Lights and RoofsA Special kind of this Glass is Wired – Refrax Glass which Transmits 100% more Light than other Glasses OBSCURED GLASSIs Made Comparatively Opaque to SunlightAlso known as patterned GlassClassified as:Frosted GlassRolled GlassRibbed GlassUsed in Doors & Widows of Bedrooms, Bathrooms, Lavatories 16

17. Frosted GlassProduced by Subjecting the Polished Surface of the Glass to a Sand Blast, which Grinds off the SurfaceIt can also be produced by Etching on Glass by Hydrofluoric Acid Rolled GlassHas a Series of Waves of Desired Pattern on the Surface and is also known as Figured Rolled GlassRibbed GlassA Series of Triangular Ribs are Produced in the Glass During Casting LAMINATED GLASSIs Made Sandwiching a layer of Polyvinyle Butyral Between Two or more Layers of Plate or Sheet GlassIt is also Known as Safety GlassExamples are:Heat Proof GlassSound Proof GlassBullet Proof GlassInsulating Glass17

18. Heat and Sound Proof GlassTwo or more Glass Plates are Sandwiched by a Tinted Plastic Inner Layer It provides high Resistance to Heat and GlareBy increasing the thickness of the Plastic layer the Glass can be made more Sound ResistantBullet Proof GlassProduced by Placing Vinyl Plastic and Glass in Several Alternate Layers and Pressing them with outer layers of glassUSESIn BanksJewellery StoresDisplay WindowsInsulating GlassProduced by Sealing a Layer of 6 – 13 mm thick Dehydrated Air between Two Glass Plates These Glasses Reduce the Heat Transmission by 30 – 60 per cent 18

19. COLOURED GLASSProduced by Adding Oxides of Metals to Molten Glass:S. NTYPES OF GLASSESMETAL OXIDES1Ruby Red GlassLead Glass, 1% Cupric Oxide & 1% Magnetic Oxide of Iron2Ruby Rose GlassGold Chloride is used as Colouring AgentBrownish Red Colour is obtained by adding Oxide of Iron Bluish Red Shade is Obtained by Adding 2% MnO2 & 4% Nitre (KnO3 )3Blue Glass0.1% of Cobalt Oxide in Ordinary Glass4Yellow GlassUranium Glass (Greenish Yellow)Selenium Glass ( Orange) 2 – 3% of Alkali Uranate Selenite or Reducing Agent or Ferric Oxide & MnO2 5Green Glass (Emerald Green)Oxide of Chromium Cr2O76Violet Glass (Violet)MnO27Black Glass Oxide of Co and Mn19

20. GLASS WOOLSilicate Rock or Flint is Melted (1650C) with a small quantity of Calcareous MatterThe resulting Liquid is Blown by Steam Jet [Fig 3], it Splashed out in the form of small Globules These Globules are Hurled in a large Container at a great Speed This Causes them to be Converted into very Soft and Flexible Fibres of not more than 10 Microns in DiameterAlso known as Rock Wool it can be Packed into small Pads or formed into (5 -6 ) Boards or Blankets The Fibres are Chemically Inert and a low Coefficient of heat ConductivityGlass Wool has :High Tensile StrengthChemical ResistanceLow Sound & Heat ConductivitiesUSESUsed as Filter Media for Air Conditioners Insulating Material for Heat and SoundAs Aggregate in the Manufacturing of Asbestos – Cement ItemsAs Fine Aggregate for Plastering and Finishing MortarsUsed to Produce Glass Reinforced Plastics by Mixing it with PolymersUsed in Water-Proofing of RoofsIn the Manufacturing of Water Tanks 20

21. Fig 3 Manufacturing of Glass Wool by Blowing21