GLASSGLASSGlass is obtained by fusion of silica, chalk(lime) and potash or soda at over10000C.In order to modify its properties ofhardness, brittleness and colour ,otheringredients like iron oxide, leadoxide,borax,etc are added in varyingproportions.Functions of various important constituentsof glass are given below.
(1) Silica (SiO2):It is the major constituent of all types ofglass. As it fuses at very hightemperatures some alkaline admixtureslike sodium carbonate or potassiumcarbonate is added to it so as to make itfuse at lower temperature. Theadmixtures added to lower the fusiontemperature also make the liquid silicaviscous and better workable.
(2) Potash:It renders glass infusible andgives fire resisting properties to it.(3) Soda:It accelerates fusion of glass; assuch excess of it is harmful.
(4) Lime (CaO):It gives durability and toughness(hardness) to glass.(5) Lead oxide:It gives colour to glass.(6) Cullet:It is broken glass, which is used as araw material to reduce to its cost.
All the constituents of glass discussed above areseparately ground, sieved and mixed in definiteproportions. The mix is then fused in a tank furnaceor in a pot furnace.Tank Furnace:It is used for large scale productions.Pot Furnace:It is used for smaller production but of superiorquality.In the furnace all the ingredients are turned intomolten state and then desired shape of glass isobtained by Blowing, Flat drawing, Rolling,Compression moulding and Spinning (pulling), etc.
CLASSIFICATION OF GLASS:BASED UPON ITSCOMPOSITION:Glass is generally classified in to threecategories.(1) Soda lime/soda ash/softGlass:It is obtained from the fusion of amixture of silica, lime, soda andalumina. Powdered glass too may beadded.
(2) Lead Glass:It is obtained from the fusion of amixture of silica, lead and potash.Powdered glass is added.It has shining appearance and takesgood polish. It is not affected bytemperature.It is used for cut glass work, electricbulbs.
(3) Boro-silicate Glass:It is obtained from the fusion of amixture of silica, borax, lime, etc.Powdered glass too may be added.It can with stand high temperature.It is used for manufacturing oflaboratory equipments and cookingutensils.
SPECIAL COMMERCIALFORMS OF GLASS:For various engineering andindustrial requirements specialvarieties of glass with thedesired specifications are made.These include the following:
(1) Sheet Glass:Sheet glass is made by blowing.It is available within 2 to 6 mmthicknesses.It is mainly used as door andwindow panels and for all kindsof glazing works.
(2) Plate Glass:Molten glass is rolled into plateglass with thicknesses varying from6 to 25mm. It is also suitable forglazing works, as table tops,windows, train carriages, buses,cars, the windscreens and superiorquality mirrors.
(3) Coloured Glass:It is prepared by mixing differentpigments at the fusion stage. Itdiffuses the light passing throughit. It is also called as stainedglass.It is used in decorative works.
(4) Wired Glass:This is the plate and sheet glass inwhich steel wires or mesh isembedded during the rolling process.The steel wire acts as reinforcement.It is also called as reinforced glass.It is used for sky-lights, high classroofing works and fire proof doorsand windows.
(5) Structural Glass:This type of glass is used in constructionalworks and can be embedded anywhere withinthe walls and ceilings. It is made in the form ofhollow square blocks, tiles, bricks and lenses.It is light in weight. It can be easily cut anddrilled.It is used for transparent face work, partitionwalls, roofing and flooring works where everlight is desired to pass through. It is also usedfor heat and sound insulation works.
(6) Laminated Glass:This is also safety glass; itconsists of sheets of glass gluedtogether with a celluloid layerbetween them.It is used for the wind screensand rear glass in the automobilesetc.
(7) Bullet-Proof Glass:This is bullet-resistant glass. It consists of anumber of glass layers alternating with vinyl-resin plastic layers, pressed together. Theinner glass plates are thick and coolingprocess is carried out under speciallycontrolled manner. It is made in variablethicknesses, varying from 15mm to 80mm.This glass is used when extra safetymeasures are required. It is used in aircrafts,bullet proof automobiles, cabins, offices andenclosures.
(8) Fibre Glass:This is also described as glasswool; it is in the form of glassfibres which are soft and flexible.It is highly resistant to wear andtear.It is mainly used for all kinds ofthermal and sound insulationworks.
(9) Foam Glass:It is porous or cellular variety of glass, lightin weight but rigid in form. It is water proof.Also it is good heat insulator. It can besawn or cut into any shape or size likewood. It is prepared by heating the mixtureof a finely ground glass and carbon.It is used for all kinds of thermal and soundinsulation works. It is also used forrefrigeration and air conditioning works.
(10) Flint Glass:It is the glass containing lead whichmakes it highly shining and capable ofhigh polish. It is costly glass. It is alsoknown as shielding glass as it stopsdifferent kinds of radiations. It is widelyused for high-class glass ware like cutglass, table glass, as optical glass forlenses, prisms and slabs, electric bulbs,electric tubes, radio valves, etc.
(11) Soluble Glass:It is that type of glass which issoluble in water. It may be kept in theform of small chips or pieces or inliquid glass. It is prepared by meltinga mixture of silica and sodiumsulphate or potassium carbonate.The soluble glass is used for mixingwith cement to make it resistant tothe acids.
PROPERTIES (OR) CHARACTERISTICS OFGLASS:(1) It has highly shining appearance and takes goodpolish.(2) It is not affected by temperature except in someexceptional cases.(3) It is fire retardant.(4) It provides heat insulation.(5) It also ensures transmission of light.(6) It is available in various varieties.(7) It transmits light but also provide privacy byobstructing vision.(8) Glass blocks provide heat and sound proofproperties.
USES OF GLASS:(1) Glass is extensively used in building constructionsince long time for glazing doors and windows.(2) It is also used for decoration.(3) It is also used for sound insulation purposes.(4) It is used for cut glass work, electric bulbs (leadglass).(5) It is used for manufacturing of laboratoryequipments and cooking utensils (Boro-silicateglass).(6) It is used for partition walls.(7) It is used for cabinets, show cases, shop fronts.(8) It is also used as fire retarder.
ANNOUNCEMENTSESSIONAL TESTDate : 13 April, 2012Day : FridayTime : During CEM Class