GLASS

• 1. Glass is an amorphous, hard, brittle, transparent or translucent, super cooled liquid of infinite viscosity.

• 2. Produced by fusing a mixture of a number of metallic silicates, most commonly of Na, K, Ca and Pb.

• 3. It possesses no sharp melting point, definite formula or crystalline structure

FEED CHARGE(Kgs)

• 1. SAND: 45.4• 2. SODA ASH(DENSE): 16• SALT CAKE: 4.5• POWDERED COAL: 0.2• LIME: 6.8• CULLETS: 22.7• OTHERS: 0.5-1.0

• 4. Approximately represented as: xR2O .yMO. 6SiO2 , where R is atom of monovalent alkali metal like Na, K, ete., M is an atom of a bivalent metal like Ca, Pb, Zn, etc., x and y are whole numbers.

• 5. Approximate composition of ordinary glass (Soda lime glass) is: Na2O.CaO. 6SiO2

• 6. In some glasses SiO2 may be replaced by Al2O3, B2O3 ,P2O5

Manufacture of Glass

• The manufacturing procedure can be divided into 4 major phases:

• 1.Melting,2.Shaping or forming,3.Annealing and 4.Finishing

1.Melting:• The charge entering into the glass furnace

consisting of sand, dense soda ash, salt cake, powdered coal, lime, Culetts, and other ingredients mixed as per the quality of the glass being manufactured, are added into the tank furnace.

• The size of the furnace is 38 X9 X 1.5 mts in size and has a capacity of 1350 MT.

• The glass forms as a pool in the heart of the furnace, across which the flames play alternatively from one side to the other.

• The product (Fined) glass is worked out of the opposite end of the tank.

• The quality of the glass and the life of the tank are dependent upon the quality of the construction glass.

• The furnace is usually lined with refractory bricks. • The furnace is heated either electro thermally or by

gas, as a regenerative furnace.• It operates in two cycles with two sets of checker

work chambers.

• The flame gases after giving up some of their heat in passing across the furnace containing the molten glass, and then

• go-downward through one set of chambers stacked with open brick work or checker work.

• A great deal of sensible heat content of the gases is removed thereby the checker

work reaching the temperatures ranging from 1500 C near the furnace to 650 C on the exit side. Simultaneously, air is preheated by being passed up through the other previously heated regenerative chamber and is mixed with the burned fuel gas.

• the resulting flame being of a higher temperature than would have been possible if the air had not been preheated.

• At regular intervals of 20-30 minutes, the flow of the air- fuel mixture, or the cycle, is reversed

and it enters the furnace from the opposite side through the previously heated checker work.

• Much of heat is saved by this regenerative principle, and a higher temperature is reached.

• The temperature of the furnace be raised only certain increments each day till the furnace

reaches temperature of at-least 1200 C is maintained at all times. Most of the heat is lost by radiation from the furnace, and a much smaller amount is actually used in the Melting.

• To reduce the action of the melting glass, water cooling pipes are frequently placed inthe furnace walls.

2.Shaping or Forming:• The glass now is shaped by either machine or hand

molding. • In machine molding, the design of the glass mission should

be such that the article is completed in a very few seconds. • During this relatively short time, the glass changes from a

viscous liquid to a clear solid.• Hence, design of machine to meet the parameters of flow

of heat, stability of metals and clearance of bearings are very

complicated.• Now, with the advent of the technology the glass engineer

is able to accomplish on the said tasks.

3.Annealing:• Reduction of strains during the glass formation

either by machine or hand molding method is very important

• It is accomplished by the process of annealing. Annealing involves two operations:

• 1. Holding the mass of glass above a certain critical temperature long enough to reduce internal strain by plastic flow to less than a pre-determined maximum and

• 2. Cooling the mass to room temperature slowly enough to hold the strain below this maximum.

4.Finishing:

• All types of annealed glass must undergo certain physical operations such as

cleaning ,grinding, polishing, cutting, sandblasting, enameling, grinding andglazing.

REFRACTORY BLOCKS• Severe conditions encountered in Glass

manufacture operation calls us to Select suitable Refractory blocks.

• FURNACE(TANK): • i) sintered Zircon, Alumina, Mullite, Mullite-Alumina• Ii) Electrocast Zirconia-Alumina-Silica, Alumina and Chrome-

AluminaREGENERATORS: requires Basic Refractories(alkali dust, alkali

vapors)i) Magnesite(MgO) and Dolamite(MgO + CaO) refractories

REACTIONS

• Na2CO3 + a SiO2 -------- Na2O.a SiO2 + CO2

• CaCO3 + b SiO2 ---------- CaO.b SiO2 + CO2

• Na2SO4 +c SiO2 + C ---- Na2O.c SiO2 + SO2 + CO