GLASS a hard, amorphous (non- crystralline) solid material made by melting sand, lime, and varying amounts of calcium oxide and silicon dioxide, at very high temperatures. typically brittle and optically transparent.
HISTORY OF GLASS MAKING
History It started on 3500 BCE in Mesopotamiain the Roman glass making center at Trier. Comes from a German word ‘glesum’ which means transparent or lustrous substance.
Silica(Quartz Sand) It is the main raw material in commercial glass production. Obtained from beds of fine sand or from pulverized sandstone.
Soda Ash (sodium carbonate Na2CO3) another main ingredient in manufacture of glass which lowers the glass transition.
Lime (calcium oxide(CaO) generally obtained from limestone, is added to provide for a better chemical durability.
Cullet (Recycled glass) Another common glass ingredient coming from waste glass which saves on raw material and energy.
Additional Substances Lead – brilliance and weight Boron – thermal and electrical resistance Barium – to increase refractive index Lanthanum oxide – for optical glasses Iron and cerium – infrared rays and UV wavelengths Metallic oxides – to impart color Manganese – decolorizing Sodium sulfate and sodium chloride – finishing agents
GLASS MAKING PROCESS
Glass Making Process Modern glass factories are three-part operations: Batch House Hot End Cold End
The Batch House handles the raw materials from the storage silos glass batching is used to determine the correct mix of raw materials (batch) for to achieve the desired glass composition.
Batch Diagram Charging of Raw material in to Storage Hoppers: Batching, Mixing and cullet addition Storage for raw materials Storage Hoppers Batching Hoppers Batching and mixing takes place Batched materials are discharged to the furnace Furnace
The Hot End handles the main part of manufacture with the furnaces, annealing ovens, and forming machines.
Furnace a device used for heating. The name derives from Latin fornax, oven. The heat energy to fuel a furnace may be supplied directly by fuel combustion, by electricity such as the electric arc furnace. The furnaces operate at temperatures up to 1,575°C.
Glass Forming Once glass has been melted, it can be shaped and used in various ways. The Blowing Pressing Drawing.
Glassblowing A glass forming technique that involves inflating molten glass into a bubble, or parison, with the aid of a blowpipe, or blow tube. Air can be blown in manually or by machine
Pressing In the pressing method of glass making, the liquid glass is poured into a mold and then pressed into shape by either a machine or a special tool.
Glass Drawing is used to make flat and tubular pieces, such as glass for windows and test tubes. To make the glass flat, it is placed into a tank along with melted tin. Tube-shaped glass is poured into a spinning mold
Annealing Once the glass is finished, it goes through an annealing or tempering process to increase its strength.
Annealing is a process of slowly cooling glass to relieve internal stresses after it was formed. The process may be carried out in a temperature-controlled kiln known as a Lehr.
The Cold End its role is to inspect the products for defects, package the glass for shipment and label the glass. Automatic machines, or sometimes persons, inspect every container for a variety of faults.
TYPES OF GLASS, ITS USES AND APPLICATIONS
1. Soda glass it is the cheapest & most common glass. it is prepared by fusing soda ash, sand , limestone. it is also called soft glass soda glass is used for the manufacture of window glass, common glassware, bottles and jars, etc. it is easily attacked by chemcials.
2. Hard glass Toughened glass are best choice for areas where safety is the highest consideration. Used for window panes of automobile, glass roofs, furniture and shelves, partitions etc. It is obtained by fusing potassium carbonate & limestone .
3. Lead crystal glass lead glass has high refractive index. Ordinary glass has a refractive index of n = 1.5, while the addition of lead produces a range up to 1.7 it, therefore, sparkles & is used for making expensive glass ware.
4. Pyrex glass Pyrex was made from borosilicate glass. It has a high mechanical strength so is less vulnerable to breakage when dropped. it is used in chemical laboratory apparatus, ampoules, pharmaceutical containers, et. in home, it is familiar with oven ware.
5. Optical glass This glass is formulated very precisely so that its properties are knownand specially made so as to be free of strains & defects. it is used for making lenses for spectacles, microscopes, cameras, telescopes & other optical instruments.
6. Laminated glass it is prepared by placing a layer of transparent plastic between the two layers of glass by means of suitable adhesive. The 3 layers are joined together by the action of heat & pressure. . It is used in making wind screens of airplanes, automobiles, bulletproof glass etc…
7. Glass fibres: Fiberglass, (also called fibreglass and glass fibre), is a material consisting of numerous extremely fine fibers of glass. Glass fibers are useful thermal insulators because of their high ratio of surface area to weight. Glass fibre has varied applications in most of the industries.
Glass wool Glass wool is a bundle of loose glass fibres, which is an excellent heat insulator. It is used as insulating material in refrigerators, ovens etc.
Other uses of fibreglass electrical insulation pole vault poles crossbows hockey sticks surfboards boat hulls paper honeycomb for medical purposes in casts.
8. Energy efficient glass Is a high quality clear glass with a specially formulated, permanent, transparent Low E coating applied pyrolitically to one surface during glass manufacture the Low E coating is to reflect the long wavelength energy (generated by heating systems, lighting and building occupants) back into the building
Low E glass The radiation coming from your heating system and your furniture and furnishings is long wave radiation. This type of radiation should be contained in your room as best as possible, while the radiation from the sun should be shielded and reflected back outside.
9. Mirrors Mirrors are manufactured by applying a reflective coating such as tin(II) chloride or silver to the glass. The tin (II) chloride is applied because silver will not bond with the glass. The chemical activator causes the tin/silver to harden. Copper is added for long-term durability and paint to protect the coating on the back of the mirror from scratches and other accidental damage.
DEBATE The status of glass as a liquid, versus a solid, has been hotly debated. The short story is that glass is a supercooled liquid, meaning that it is rigid and static but does not change molecularly between melting and solidification into a desired shape. Glass is one the most versatile substances on Earth, used in many applications and in a wide variety of forms, from plain clear glass to tempered and tinted varieties, and so forth.