GLASS

UNIT V - GLASS

Composition of glass

Manufacture, Treatment, Properties, Uses of glass.

Types of glass - Float glass, Cast glass, Glass blocks, Foamed glass. Decorative glass, Solar control, Toughened glass, Wired glass, Laminated glass, Fire-resistant glass, Glass blocks, Structural glass

Properties and Application in building industry, Glazing and Energy Conservation Measures

DefinitionGlass is an amorphous, hard, brittle, transparent or translucent super cooled liquid of infinite viscosity, having no definite melting point obtained by fusing a mixture of a number of metallic silicates or borates of Sodium, Potassium, Calcium, and Lead. I

It possess no definite formula or crystalline structure.

• “An inorganic product of fusion which has cooled to a rigid condition without crystallizing”

• Does not have a specific melting point• Softens over a temperature range

Properties of glassGlass is:

• Amorphous• Brittle• Transparent / Translucent• Good electrical insulator• Unaffected by air, water, acid or chemical

reagents except HF• No definite crystal structure means glass

has high Compressive strength• Can absorb, transmit and reflect light

Raw materials used in manufacturing glass

Raw Materials• Sodium as Na2Co3 (used in soft glass).• Potassium as K2Co3 (used in Hard Glass).• Calcium as lime stone, chalk and lime.• Lead as litharge, red lead (flint glass).• Silica arc quartz, white sand and ignited flint.• Zinc is zinc oxide (Heat and shock proof glass).• Borates are borax, Boric acid (Heat and shock

proof glass).• Cullets or pieces of broken glass to increase

fusibility.

Manufacturing stepsFIVE STAGES OF MANUFACTURE

1. Collection of Raw materials

2. Preparation of the Batch

3. Melting in Furnace

4. Fabrication

5. Annealing

Cullet –

1. Indicates waste glass or pieces of broken glass, They increases the

fusibility of glass

2. Prevent loss of alkali by vitalization during the reaction in forming new

glass

3. They also reduce the cost.

• The raw materials , cullet and de-colouriser are finely

powdered in grinding machines.

• They are accurately weighed in correct proportions before

they are mixed together.

• The uniform mixture is called Batch or Frit

Preparation of Batch

Melting process Raw materials in proper proportions

are mixed with cullets. It is finely powdered and intimate mixture called batch is fused in furnace at high temperature of 1800°C this charge melts and fuses into a viscous fluid.

POT FURNACE

TANK FURNACE

POT FURNACE TANK FURNACE

Fabrication of GlassBLOWING- 12mm dia and 1.8m long blow-pipe is used. One end is dipped in to molten glass and 50N of wt. of glass is taken out. CASTING – Pouring into moulds-allowed to cool slowlyDRAWING – Iron bar dipped in molten glass sideways and sheets of glass are drawn to spread in the form of thin sheet.PRESSING- molten glass is pressed into moulds- mechanically or manuallyROLLING- either passed between heavy iron rollers and flat glass is obtained or poured on a flat ironcasting table and turned flat with heavy iron rollers.SPINNING – the molten glass is spun at high speed to obtain fine glass fibres.It does not allow fade, decay and shrink

AnnealingGlass articles are then allowed to cool gradually at room temperature by passing through different chambers with descending temperatures.

• This reduces the internal Strain in the glass. Sudden drops in temp is highly not recommendable.

1. Flue Treatment – large scale production.2. Oven Treatment – small scale production.

Treatment of Glass1. Bending – to rods, sheets or tubes2. Cutting – cut using diamond/rough

glass/steel wheels3. Opaque Making- grinding the surface

with emery or chemically treated (hydrofluoric acid)

4. Silvering- a thin coat of tin is applied to the surface. Silver is deposited on this layer of tin. A suitable paint is applied on top to give protection against the atmospheric effects.

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Varieties of glassSoda lime

or soft glass

Potash lime or hard glass

Lead glass or flint glass

Borosilicate or Pyrex

glassAlumino- Silicate glass

Silica glass Soluble glass

Safety glass

Optical or Crook’s

glass

Poly-crystalline

glass

Toughened glass

Colored glass

Wired Glass

Glass Wool Fiber glass Photosensitive

glassPhoto-

chromic glass

Neutral glass

Laminated glass

Insulating glass

Float glass, Cast glass, Glass blocks, Foamed glass. Decorative glass, Solar control, Toughened glass, Wired glass, Laminated glass, Fire-resistant glass, Glass blocks, Structural glass

Soda lime or soft glass• About 90% of all glass is soda-lime glass

made with silica (sand), Calcium carbonate and soda ash.

• They are low cost, resistant to water but not to acids.

• They can melt easily and hence can be hot worked.

• Uses: Window glass, Electric bulbs, Plate glass, Bottles, Jars, cheaper table wares, test tubes, reagent bottles etc

Borosilicate / pyrex glass• It is common hard glass

containing silica and boron.

• These glass have low thermal coefficient of expansion, and high chemical resistance i.e..shock proof.

• Uses: Industrially used for pipeline of corrosive liquids, gauge glasses, superior laboratory apparatus, kitchen wares, chemical plants, television tubes, electrical insulators etc.

Lead glass or flint glass• It is made up of lead oxide fluxed

with silica and K2CO3• To get dense optical glasses about

80% lead oxide is used.• It is bright lustrous and possess

high specific gravity.

• Uses: High quality table wares, optical lenses, neon sign tubing, cathode ray tubes, electrical insulators, crystal art objects or cut glass, Windows and Shields for protection against X-rays and Gamma rays in medical and atomic energy fields etc.

Coloured glassAddition of transition metal compounds to glass gives

color to the glass. They are outlined below.Yellow: Ferric Salts Green: Ferrous and

Chromium saltsPurple: Magnese

dioxide salt

Red: Nickel and cuprous salts Cu2O

Lemon Yellow: Cadmium sulphide

Fluorescent greenish yellow: Uranium oxide

Blue: Cobalt Salts, CuO

Greenish Blue Color:Copper Sulphate

Brown: Iron

Opaque milky white: Cryolite of Calcium

phosphate

Ruby : Auric Chloride

Safety glass• Tempered Glass: The side and rear windows in most

consumer automobiles are customarily made of tempered glass due to its high impact resistance and safe shattering qualities-commercial building doors, bathtub and shower enclosures, sliding doors

•  Laminated Glass: Laminated glass provides improved safety features .It can also be used for added security in windows or balconies, aircraft windshields, and tank viewing windows.

• Armed Glass: Armed glass is most commonly used in the roofing of industrial building or other outdoor structures. This type of glass can provide additional light from above, but its metal grill lowers overall visibility. 

• Tempered glass is a glass that has been subjected to an additional heat treatment after annealing in order to increase its mechanical strength •

• The tempering process lies on the controlled creation of permanent stresses in the glass

• Tempered glass can be as much as 4 to 5 times stronger than annealed glass (without tempering) • When fracturing, tempered glass breaks into small fragments. It is often referred to as “safety glass

Tempered glass

Toughened glass• It is made by dipping

articles still hot in an oil bath, so that chilling takes place. This results in outer layer of articles shrink and acquire a state of compression while inner layer are in state of tension. Such glass is more elastic to mechanical and thermal shock. It breaks into a fine powder.

• Uses: For making window shields of fast moving vehicles, windows of furnace and automatic opening doors.

Laminated glass• The sheets of glass fiber or glass wool are

soaked in a solution of thermosetting plastic like phenol formaldehyde resin and placed one above the other and then cured under heat or pressure. It is strong as steel. Non flammable and insulating. In bullet resistant glass vinyl resins are added in alternate layers.

• Uses: Shatter, shock and Bullet proof Glass

Wired glass• Wired glass does not fall apart into splinters when it

breaks and is fire resistant. It is made by fusing wire in between the two glass layers.

Uses: For making fire resistant doors, roofs, skylights and windows

Fibre glass• It is transformed into a fine thread of filament and

has got a high tensile strength.

Uses: Found extensive use for the manufacture of fabric, reinforcing plastics and production of thermal insulation materials etc

Glass wool• Glass wool consists of tiny

fibers formed by action of steam jets on dripping molten glass down from very fine hole.

• Uses: Heat Insulation, for filtration of Corrosive chemicals, sound insulation etc

Float Glass – The molten glass coming out of furnace is allowed to float on the molten tin. This is annealed to remove all the stresses. It is superior to ordinary glass in many ways

1. Environmental friendly2. Aesthetically appealing3. Available in larger sizes4. Cost-effective compared to bricks, paints etc5. Suitable for solar applications due to high light transmission6. Tougher and more scratch resistant7. Mirrors that give true mirrors8. For ideal window9. Optical clarity, superior saftey10. No refraction defect due to uniform thickness and superior

optical clarity( eye lenses)

Foam Glass :

They are in the form of rectangular blocks. The finely ground glass and carbon are thoroughly mixed and melted. At the time of melting the mixture expands and assumes the form of a black foam.

This floats in water and it can be cut like wood. It is fore proof, rigid and excellent heat insulator. It is a substitute for cork.

Glass Blocks

Fracture / failure of glass• Glass does not have crystal lattice structure hence

it breaks. Fracture is caused by small imperfections, flaws and irregularity on the surface of the glass. Flaws are very fine cracks cause concentration of stress and the crack proceeds quickly causing a fracture.

Potash lime or hard glass• Potash lime glass is made with silica (sand),

Calcium carbonate and potassium carbonate. • The approximate composition is K2CO3.CaO.6SiO2. • They posses high melting point, fuse with difficulty

and are less acted upon by acids, alkaline and other solvents than ordinary glass.

• Uses: These glasses are costlier than soda lime glass and are used for chemical apparatus, combustion tubes and glassware which are used for heating operations.

Alumino-silicate glass

• This type of glass possess exceptionally high softening temperature.

• Uses: It is used for high pressure mercury discharge tubes, chemical combustion tubes and certain domestic equipments.

silica glass / vitreosil• It contains pure silica heated

to its melting point. It is translucent, the coefficient of thermal expansion is very low hence it has high resistance to thermal shock, have high chemical resistance to corrosive agents.

• If Vitreosil glass is heated above its melting point, it becomes transparent and is known as clear silica glass.

• Uses: They are used in construction of chemical plants, laboratory crucibles, induction furnace lining, electrical insulators and heaters and have high light transmission properties.

Optical or crook’s glass• It has the property to absorb harmful

ultra-violet light. This glass is given through homogeneity by heating it for a prolonged period of time. These glasses have low melting point and are relatively soft.

• Uses: They are used for making optical lenses.

Photosensitive glass• These are glasses by

which a colored picture may be developed by exposing the glass to black and white negative in ultra violet light. The appropriate proportions of potash-alumina glass, mixed with LiSO3, cerium and Silver salts have also been used as photosensitive glass.

• Uses: Photographic development

Photo-chromic glass• The three dimensional silicate

network contains large no. of microscopic particles of silver halide which on exposure to light produce color.

• Uses: In making tinted car glasses and goggles.

Insulating glass• Two or more plates of glass are filled with

dehydrated air and the edges are sealed air-tightly.

• Uses: Provides thermal insulating and so houses remain cool in summer and warm in winter.

Mitigate climate changeIn many of its application glass can help to save energy. It is most obvious in the case for insulating glass for windows and facades but also for less known products such as weight-lightening reinforcement glass fibre used in automotive, aviation and other transport modes to reduce the weight of vehicle and their fuel consumption.

Save natural resourcesGlass is a resource efficient material which is made of abundant natural raw material such as sand and glass waste (cullets). Glass is a fully recyclable material that can be recycled in close loop over and over again.

Safeguard people’s health and well-beingGlass is among the preferred materials not only for its aesthetics but also for its own characteristics. Glass preserves taste and vitamins.

Sustainability & the Environment