HOW IS PLATE GLASS MADE?


Plate glass is thick, good quality glass made in huge sheets for shop windows. It’s very smooth surface is made by floating the molten glass onto a bath of molten tin. Tin melts at a lower temperature than glass, so the glass begins to set on the tin and is then passed over rollers as it finishes cooling. The larger the bath of molten tin the larger the glass that can be made.



Plate glass, flat glass or sheet glass is a type of glass, initially produced in plane form, commonly used for windows, glass doors, transparent walls, and windscreens. For modern architectural and automotive applications, the flat glass is sometimes bent after production of the plane sheet. Flat glass stands in contrast to container glass (used for bottles, jars, cups) and glass fiber (used for thermal insulation, in fiberglass composites, and optical communication).



Flat glass has a higher magnesium oxide and sodium oxide content than container glass, and lower silica, calcium oxide, and aluminum oxide content. (From the lower soluble oxide content comes the better chemical durability of container glass against water, which is required especially for storage of beverages and food). Most flat glass is soda-lime glass, produced by the float glass process (1950s). Other processes for making flat glass include:



Scratches can occur on sheet glass from accidental causes. In glass trade terminology these include “block reek” produced in polishing, “runner-cut” or “over/under grind” caused by edge grinding, or a “sleek” or hairline scratch, as well as “crush” or “rub” on the surface.



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WHAT IS GLASS MADE OF?


Glass is an extraordinarily useful material. The substances from which it is made are easy to find and very cheap. Glass is mainly melted, cooled sand, but other ingredients are added, such as sodium carbonate (soda ash) and limestone. Although it appears solid to us, glass is in fact a liquid, flowing incredibly slowly. When windows that are hundreds of years old are measured, they are found to be slightly thicker at the bottom than at the top, as the glass very gradually flows downwards.



In a commercial glass plant, sand is mixed with waste glass (from recycling collections), soda ash (sodium carbonate), and limestone (calcium carbonate) and heated in a furnace. The soda reduces the sand's melting point, which helps to save energy during manufacture, but it has an unfortunate drawback: it produces a kind of glass that would dissolve in water! The limestone is added to stop that happening. The end-product is called soda-lime-silica glass. It's the ordinary glass we can see all around us.



Once the sand is melted, it is either poured into molds to make bottles, glasses, and other containers, or "floated" (poured on top of a big vat of molten tin metal) to make perfectly flat sheets of glass for windows. Unusual glass containers are still sometimes made by "blowing" them. A "gob" (lump) of molten glass is wrapped around an open pipe, which is slowly rotated. Air is blown through the pipe's open end, causing the glass to blow up like a balloon. With skillful blowing and turning, all kinds of amazing shapes can be made.



Glass makers use a slightly different process depending on the type of glass they want to make. Usually, other chemicals are added to change the appearance or properties of the finished glass. For example, iron and chromium-based chemicals are added to the molten sand to make green-tinted glass. Oven-proof borosilicate glass (widely sold under the trademark PYREX®) is made by adding boron oxide to the molten mixture. Adding lead oxide makes a fine crystal glass that can be cut more easily; highly prized cut lead crystal sparkles with color as it refracts (bends) the light passing through it. Some special types of glass are made by a different manufacturing process. Bulletproof glass is made from a sandwich or laminate of multiple layers of glass and plastic bonded together. Toughened glass used in car windshields is made by cooling molten glass very quickly to make it much harder. Stained (colored) glass is made by adding metallic compounds to glass while it is molten; different metals give the separate segments of glass their different colors.



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What is safety glass?


            Safety glass is glass that has been strengthened. There are two kinds of this protective glass-laminated and toughened-and both were discovered by accident.



             In the early 1900s EdouardBenedictus, a French chemist knocked a glass flask on to the floor. Although the glass starred and cracked, it did not break. After examining the flask he realized that a coating of dried celluloid on the inside had held the fragments together.



             Some years later, when injuries from broken car windscreens increased, Benedictus recalled this incident. Using glass sheets and celluloid bonded together in an old letter press, he produced the world’s first sheet of laminated, or layered, glass. Since then the clarity of the glass has been improved to equal that of ordinary glass. But it will withstand the impact of a half-pound steel ball dropped from a height of 16 feet. Toughened glass was developed later, although in the 17th century, Prince Rupert, nephew of king Charles I of England, discovered that molten glass was turned into immensely strong pear-shaped drops when tipped into cold water. Prince Ruport’s drops, as they are called, can be hammered on an anvil without breaking, but if the tail of the drop is broken they crumble into dust.



             In 1874 a French scientist, de la Bastie, heated small sheets of glass and then quenched them in oil, increasing their strength dramatically. However these sheets of toughened glass were very small and it was not until the 1930s that sheets large enough for use in cars could be toughened.



            Laminated or toughened safety glass is now used all over the world in cars, buses, trains, aircraft, ships and shops and has proved its safety value.




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What is a glass made from?


Glass is made naturally from a fusion of silica (sand), soda and lime. This fusion can be achieved merely by lightning striking in a place where the right ingredients happen to be adjacent to each other. When glass is made by man, other ingredients are added, such as potash, lead oxide and boric oxide. Some of these ingredients are used to make glass clear, some to colour it, and others to give it a frosted effect.



      Glass was made by potters in Egypt for glazing stone beads as early as 12,000 B.C. As Egyptian culture progressed, craftsmen used glass for the manufacture of personal ornaments and bottles.



    A tremendous step forward in the use of glass was made by the Phoenicians in about 300 to 200 B.C. by the invention of the blow-pipe. The blowpipe is a hallow iron tube with a mouthpiece at one end and a knob shape at the other. The knob-shaped end is dipped into hot, viscous glass. A “gather” of molten glass can be blown by the worker into a hollow ball. The more he blows, the larger the ball.



    During the Roman civilization the art of glass-making reached near perfection. In the 3rd Century, the Romans cast glass on flat stones and produced the first window panes. The break-up of the Roman Empire and the ensuring Dark Ages brought an end to such cultural developments. The glazing of windows did not become wide spread over the whole of Europe until the 15th and 16th Centuries.



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What is glass fiber?


Glass fiber is a mass of very fine strands of glass. When ordinary glass is spun into thin threads it is strong and bendable, unlike normal glass objects, which are brittle and break easily.



       These silky strands of glass can be woven into a material or massed together like cotton-wool. Glass fiber does not decay or corrode. It is a good insulator and a poor conductor of electricity. Curtains made of this material do not rot in damp conditions or in sunlight. Now that technical dyeing problems have been overcome, glass Fiber can be patterned.



    Many plastics tend to crack or bend under stress or impact, but  combining them with strands of glass fiber results in very light, strong and useful materials. Glass fibre increases their strength in much the same way as concrete is reinforced with steel rods. These mixtures are moulded to make such things as aircraft parts, car bodies mats of glass fiber are used for filters and washers, and blankets of the material provide good in solution for houses.



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