Presented By:Engineer Ghulam Shabir SolangiMehran University College of Engg: & Technology Khairpur Civil Engineering Materials1st Term 1st Year B.E.Civil

GLASS AND ITS MANUFACTURING

GLASSGlass is obtained by fusion of silica, chalk (lime) and potash or soda at over 10000C.In order to modify its properties of hardness, brittleness and colour ,other ingredients like iron oxide, lead oxide,borax,etc are added in varying proportions. Functions of various important constituents of glass are given below.

(1) Silica (SiO2):It is the major constituent of all types of glass. As it fuses at very high temperatures some alkaline admixtures like sodium carbonate or potassium carbonate is added to it so as to make it fuse at lower temperature. The admixtures added to lower the fusion temperature also make the liquid silica viscous and better workable.

(2) Potash:It renders glass infusible and gives fire resisting properties to it.(3) Soda:It accelerates fusion of glass; as such 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 a raw material to reduce to its cost.

All the constituents of glass discussed above are separately ground, sieved and mixed in definite proportions. The mix is then fused in a tank furnace or in a pot furnace.Tank Furnace:It is used for large scale productions. Pot Furnace:It is used for smaller production but of superior quality.In the furnace all the ingredients are turned into molten state and then desired shape of glass is obtained by Blowing, Flat drawing, Rolling, Compression moulding and Spinning (pulling), etc.

CLASSIFICATION OF GLASS:BASED UPON ITS COMPOSITION:Glass is generally classified in to three categories.(1) Soda lime/soda ash/soft Glass:It is obtained from the fusion of a mixture of silica, lime, soda and alumina. Powdered glass too may be added.

(2) Lead Glass:It is obtained from the fusion of a mixture of silica, lead and potash. Powdered glass is added.It has shining appearance and takes good polish. It is not affected by temperature. It is used for cut glass work, electric bulbs.

(3) Boro-silicate Glass:It is obtained from the fusion of a mixture of silica, borax, lime, etc. Powdered glass too may be added. It can with stand high temperature.It is used for manufacturing of laboratory equipments and cooking utensils.

SPECIAL COMMERCIAL FORMS OF GLASS:For various engineering and industrial requirements special varieties of glass with the desired specifications are made. These include the following:

(1) Sheet Glass:Sheet glass is made by blowing. It is available within 2 to 6 mm thicknesses.It is mainly used as door and window panels and for all kinds of glazing works.

(2) Plate Glass:Molten glass is rolled into plate glass with thicknesses varying from 6 to 25mm. It is also suitable for glazing works, as table tops, windows, train carriages, buses, cars, the windscreens and superior quality mirrors.

(3) Coloured Glass:It is prepared by mixing different pigments at the fusion stage. It diffuses the light passing through it. It is also called as stained glass.It is used in decorative works.

(4) Wired Glass:This is the plate and sheet glass in which steel wires or mesh is embedded during the rolling process. The steel wire acts as reinforcement. It is also called as reinforced glass.It is used for sky-lights, high class roofing works and fire proof doors and windows.

(5) Structural Glass:This type of glass is used in constructional works and can be embedded anywhere within the walls and ceilings. It is made in the form of hollow square blocks, tiles, bricks and lenses. It is light in weight. It can be easily cut and drilled.It is used for transparent face work, partition walls, roofing and flooring works where ever light is desired to pass through. It is also used for heat and sound insulation works.

(6) Laminated Glass:This is also safety glass; it consists of sheets of glass glued together with a celluloid layer between them. It is used for the wind screens and rear glass in the automobiles etc.

(7) Bullet-Proof Glass:This is bullet-resistant glass. It consists of a number of glass layers alternating with vinyl-resin plastic layers, pressed together. The inner glass plates are thick and cooling process is carried out under specially controlled manner. It is made in variable thicknesses, varying from 15mm to 80mm.This glass is used when extra safety measures are required. It is used in aircrafts, bullet proof automobiles, cabins, offices and enclosures.

(8) Fibre Glass:This is also described as glass wool; it is in the form of glass fibres which are soft and flexible. It is highly resistant to wear and tear. It is mainly used for all kinds of thermal and sound insulation works.

(9) Foam Glass:It is porous or cellular variety of glass, light in weight but rigid in form. It is water proof. Also it is good heat insulator. It can be sawn or cut into any shape or size like wood. It is prepared by heating the mixture of a finely ground glass and carbon.It is used for all kinds of thermal and sound insulation works. It is also used for refrigeration and air conditioning works.

(10) Flint Glass:It is the glass containing lead which makes it highly shining and capable of high polish. It is costly glass. It is also known as shielding glass as it stops different kinds of radiations. It is widely used for high-class glass ware like cut glass, table glass, as optical glass for lenses, prisms and slabs, electric bulbs, electric tubes, radio valves, etc.

(11) Soluble Glass:It is that type of glass which is soluble in water. It may be kept in the form of small chips or pieces or in liquid glass. It is prepared by melting a mixture of silica and sodium sulphate or potassium carbonate. The soluble glass is used for mixing with cement to make it resistant to the acids.

PROPERTIES (OR) CHARACTERISTICS OF GLASS:(1) It has highly shining appearance and takes good polish.(2) It is not affected by temperature except in some exceptional 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 by obstructing vision.(8) Glass blocks provide heat and sound proof properties.

USES OF GLASS:(1) Glass is extensively used in building construction since 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 (lead glass).(5) It is used for manufacturing of laboratory equipments and cooking utensils (Boro-silicate glass).(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 : 1st(OR) 2nd April, 2011Day : Friday (OR)SaturdayTime : During CEM Class

TEST TOPICSBricksStonesTilesCementAggregatesConcrete