GlassIndustries

ByB.Sandeep

What is Glass ?Glass is a substance which is made by high fluxes which is heated to high temperature and its is completely vitrified product.Glass is an amorphous (non-crystalline) solid material. Glasses aretypically brittle and optically transparent.The following are the properties that are exhibited by the glass1. Capacity to absorb different colors without

effecting transparency

2. Hardness3. Chemically inert4. High refractive index5. High dispersion6. High refractive index7. Transparent and translucent8. Low thermal conductivity9. Electrical insulator10. Brittle11. Amorphous Natural glass formed

from12. High viscous meteorite13. Supper Cooled liquid

Physical properties of glass :

Amorphous : In condensed matter physics, an amorphous (from the Greek a, without, morphe, shape, form) or non-crystalline solid is a solid that lacks the long-range order characteristic of a crystal.

Brittleness : A material is brittle if, when subjected to stress, it breaks without significant deformation (strain). Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound

Brittle fracture in glass

Difference between brittle material and ductile material :

Graph comparing stress-strain curves for brittle and ductile materials

Transparency and translucence : In the field of optics, transparency (also called pellucidity or diaphaneity) is the physical property of allowing light to pass through a material; translucency (also called translucence or translucidity )only allows light to pass through diffusely.

Capacity to absorb different colours without affecting

transparency

Dispersion : In optics, dispersion is the phenomenon in which thephase velocity of a wave depends on its frequency, or alternatively when the group velocity depends on the frequency. Media having such a property are termed dispersive media.

In a prism, material dispersion (a wavelength-dependent refractive index) causes different colors to refract at different angles, splitting white light into a rainbow.

Vitrification : It is a word (from Latin vitreum, "glass" via French vitrifier) is the transformation of a substance into a glass. Usually, it is achieved by rapidly cooling a liquid through the glass transition. Certain chemical reactions also result in glasses. An important application is the vitrification of an antifreeze-like liquid in cryopreservation.

A vitirfied glass cook top

Glass colouring : Glass coloring and color marking may be obtained by addition of coloring ions, by precipitation of nanometer sized colloids (so-called striking glasses such as "ruby gold" or red "selenium ruby"), by colored inclusions (as in milk glass and smoked glass), by light scattering (as in phase separated glass), by dichroic coatings or by colored coatings.

The formula of the glass

x R2O y MO 6Sio2WhereR=Mono valent ions such as Na KM=Bi valent ions such as Ca Zn MgRaw Materials used for glass

1. Sand2. Soda Ash Forms basic part of glass3. Sodium nitrate Accelerates melting4. Cao Forms basic part of glass5. Silica Forms acidic part of glass6. Barium Sulphate To remove impurities in the

form of the Scum7. Feldspar Retards de vitrification8. Potassium Oxide Used as softening agent9. Borax Increase hardness or refractive

index10. Boric Oxide Improves chemical or corrosive

resistivity11. Phosphoric Oxide To impart bright appearance12. Magnesia In manufacture of electric

bulbs

13. Lead Oxide Increases insulation14. Selenium Used as Decolorizer

Coloring Agents :

1. Cadmium Oxide Red color2. Copper Oxide Ruby red3. Titanium Oxide Light yellow4. Cobalt Oxide Deep blue5. Cuprous Oxide Greenish Blue6. Chromium Oxide Emerald green7. Manganese Oxide Black

While fused quartz (primarily composed of SiO2) is used for somespecial applications, it is not very common due to its high glasstransition temperature of over 1200 °C (2192 °F).

Normally, other substances are added to simplify processing. One is sodium carbonate (Na2CO3), which lowers the glass transition temperature. However, the soda makes the glass water soluble, which is usually undesirable, so lime (calcium oxide (CaO), generally obtained from limestone), some magnesium oxide (MgO) and aluminum oxide

Quartz sand (silica) is the main raw material in commercial glass production

(Al2O3) are added to provide for a better chemical durability. The resulting glass contains about 70 to 74% silica by weight and is called a soda-lime glass.Soda-lime glasses account for about 90% of manufactured glass.

Glass is an amorphous solid. It exhibits an atomic structure close to that observed in the super cooled liquid phase but displays all the mechanical properties of a solid.

The amorphous structure of glassy Silica (SiO2) in two dimensions. No long range order is present, however there is local ordering withrespect to the tetrahedral arrangement of Oxygen(O) atoms around the Silicon (Si) atoms

Major steps in glass manufacture

1.Selection of raw materials2.Size reduction3.Melting of Raw materials4.Shaping5.Anealing

Double click on the diagram to view full screen

Process :

Based on the type of the glass suitable glass manufacture materials are selected . Raw materials are reduced to 100-200 Mesh by crushing and grinding. Raw materials are now subjected to melting in Pot furnace or monkey furnace.

Pot furnace :

For special glasses like optical glass raw materials are melted in pot (monkey shaped pots) made of ceramic material capacities varying from 1-2 tons.

Tank Furnace :

Molten glass is obtained by melting the raw materials in 150-200 ton capacity regenerative tank furnace. During melting of raw materials various reactions occur at various temperatures .

Reactions :

100 C Surface moisture loss500 C Body moisture loss500-600 C Na2CO3 ---------> Na2O + CO2

Pb3O4 --------> 3PbO + [O]

600-800 C PbO + SiO2 ---------> PbSiO2 Na2SO4 + 2C ---------> Na2S + 2CO2 K2CO3 ---------> K2O+ CO2 K2O + SiO2 ---------> K2SiO3

800- 900 C Na2SO4 ---------> Na2O +SO3 Na2S + SO3 ----------> Na2O+SO2+[S] Na2O+SiO2 ----------> Na2SiO3

900- 960 C CaCO3 ----------> CaO + CO2

1010 C CaO+SiO2 ---------->

CaSiO3

1120 - 1400 C Vitrification

Shaping :

Completely vitrified glass from tank furnace is shaped on the type of the finished product.

Shaping Methods :

1. Colburn Horizontal drawing2. Float/Asahi Vertical drawing3. Pilkington Glass float over tin4. Forcault

Parison mould process :

Glass products produced / shaped by this process are narrow neck and wide neck products. Gob of glass is transferred to parison mould. Plunger is lowered as a result parison is obtained and transferred to blowing mode.

Shaping of narrow / wide neck product :

Transfer glass gob to parison mould blow air from top where gob rests on narrow neck. Air is blown from bottom until it should fill the neck. Obtain parison after Demoulding . Transfer the parison to the narrow neck blowing mould. Blow air from the top. Demould to obtain narrow neck product.

The above shaping process is a batch process and used for continuous manufacture o the products. It consists of two rotating tables. One table is mounted with parison moulds and the other with the blowing moulds. As a result the shaping operation is carried in a continuous process and increases the productivity.

Shaping of window glass or plate glass :

Molten glass from tank furnace is shaped from plate glass by following method. Molten glass at 980 C is transferred to a rectangular tank line with refractory bricks. A refractory brick with a slot in center called as debituse is made to float over molten glass. Molten glass emerges in the form of tongue through the slot which is hold firmly by metallic baits. This is followed by continuous drawing of glass through the slot by the water cooled rollers cooling the external surface of the glass leaving the core of glass under stresses. The glass which is drawn horizontally or vertically in next stage as per following.

Colburn :

Glass is drawn horizontally producing 1-2 mm thick window glass.

Asahi :

Glass is drawn vertically to produce 0.05 to 0.2 mm. It is the glass that is specially required for the microscopes.

Forcault : Similar to colburn process (horizontal)

Pilkington :

In this process molten glass is allowed to flow over a molten tin because of close melting point range. After cooling hardened glass floating over molten tin is cut into desired specification.

Annealing :

During roiling and also cooling only surface of glass cools leaving core of glass under heavy stresses which make glass highly brittle. Hence it is subjected to annealing process in a annealing tunnel which is horizontal or vertical where temperature of core of glass is brought to ambident temperature and as the entire length of annealing tunnel increases then the temperature decreases . This variation can be given by the following graph given below.

Glass making in laboratory :

Types of Glass : 1. Quartz glass : When silicon dioxide SiO2 is cooled

rapidly enough, it does not crystallize but solidifies as a glass. The glass transition temperature of pure SiO2 is about 1600 K (1330 °C or 2420 °F). Like most of the crystalline polymorphs the local atomic structure in pure silica glass is regular tetra hedra of oxygen atoms around silicon atoms forming quartz glass.

Optical fibers made from quartz glass play a major role in communication.

2. Soda-lime glass : It is also called soda-lime-silica glass, is the most prevalent type of glass, used for windowpanes, and glasscontainers (bottles and jars) for beverages, food, and somecommodity items. Glass bake ware is often made of temperedsoda-lime glass. Soda-lime glass is prepared by melting the raw materials, such as sodium carbonate (soda), lime, dolomite, silicon dioxide (silica),aluminum oxide (alumina), and small quantities of fining agents(e.g., sodium sulfate, sodium chloride) in a glass furnace at temperatures locally up to 1675 °C.

3. Bullet-resistant glass : It is a type of strong but optically transparent material that is particularly resistant to being penetrated when struck by bullets, but is not completely impenetrable. It is usually made from a combination of two or more types of glass, one hard and one soft. The softer layer makes the glass more elastic, so it can flex instead of shatter. The index of refraction for both of the glasses used in the bulletproof layers must be almost the same to keep the glass transparent and allow a clear view (not distorted) through the glass. Bulletproof glass varies in thickness from three-quarter inch to three inches.

4. Flat glass : It is a sheet glass, or plate glass is a type of glass, initiallyproduced in plane form, commonly used for windows, glass doors,transparent walls, and windshields. For modern architectural andautomotive applications, the flat glass is sometimes bent afterproduction of the plane sheet. Most flat glass is soda-lime glass, produced by Forcault process.

5. Fiberglass : Fiberglass is a lightweight, extremely strong, and robust material. Although strength properties are somewhat lower than carbon fiber and it is less stiff, the material is typically far less brittle, and the raw materials are much less expensive. Its bulk strength and weight properties are also very favorable when compared to metals, and it can be easily formed using molding processes. The plastic matrix may be epoxy, a thermosetting plastic (most often polyester or vinylester) or thermoplastic. Common uses of fiber glass include boats, automobiles, baths, hot tubs, water tanks, roofing, pipes, cladding and external door skins.Storage tanks can be made of fiberglass with capacities up to about 300 tones. The smaller tanks can be made with chopped strand mat cast over a thermoplastic inner tank which acts as a preform during construction.

6.Studio glass : Studio glass or glass sculpture is the modern use of glass as an artistic medium to produce sculptures or three-dimensionalartworks. Specific approaches include working glass at room temperature cold working, stained glass, working glass in a torch flame (lampworking), glass bead making, glass casting, glass fusing, and,most notably, glass blowing.

7.Lead glass : It is a variety of glass in which lead replaces the calcium content of a typical potash glass.[1] Lead glass contains typically 18–40 weight% lead(II) oxide (PbO), while modern lead crystal, historically also known as flint glass due to the original silica source, contains a minimum of 24% PbO.[2] Lead glass is desirable owing to its decorative properties.

Glass beads made up of lead glass

8. Flint glass : It is a optical glass that has relatively high refractive index and low Abbe number. Flint glasses are arbitrarily defined as having an Abbe number of 50 to 55 or less. The currently known flint glasses have refractive indices ranging between 1.45 and 2.00. A concave lens of flint glass is commonly combined with a convex lens of crown glass to produce an achromatic doublet lens because of their compensating optical properties, which reduces chromatic aberration (color defects). Flint glass can be fashioned into rhinestones which are used as diamond stimulants.An achromatic doublet, which combines crownglass and flint glass.

9.Float glass : I Glass is a sheet of glass made by floating molten glass on a bed of molten metal, typically tin, although lead and various low melting point alloys were used in the past. This method gives the sheet uniform thickness and very flat surfaces. Modern windows are made from float glass. Most float glass is soda-lime glass, but relatively minor quantities of specialty borosilicate and flat panel display glass are also produced using the float glass process. The float glass process is also known as the Pilkington process,

10. Chalcogenide glass : It is a glass containing one or more chalcogenide elements. These are Group 16 in the periodic table e.g. sulfur, selenium or tellurium. Such glasses are covalently bonded materials and may be classified as network solids. In effect, the entire glass matrix acts like an infinitely bonded molecule. The classical chalcogenide glasses are strong glass-formers (mainly sulphur based ones) such as systems As-S, Ge-S possess glasses within large concentration regions.

A CD-RW (CD). Amorphous chalcogenidematerials form the basis of re-writable CD and DVD solid-state memory technology....

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