Making of the glass!! A mixture of large amount of silica combined with alkali and lime result in a wonderful element called Glass. Sodium bicarbonate(soda),potash or other alkali is used to lower the melting point and lime is used to stabilize the mixture,it also makes the glass water resistant and stronger. Silica,soda and lime form the main components.The properties of glass can be altered by the addition of other substances during the process.The way it is heated and cooled also effects on the nature of the glass. To begin with,the mixture of silica,soda and lime is heated for as long as 24 hours in melting furnaces to approximately 2,500° Fahrenheit.This molten glass is cooled to a temperature at which it can be worked.Glass looks like a thick liquid at this stage and is of an orange-red colour. Once glass cools,it becomes hard hence it has to be worked quickly to form the desired shape.Now the glass can be blown,pressed,drawn or even rolled.Then it is annealed.This eliminates areas of stress in the glass and strengthens it. To blow glass, a blob of molten glass is placed at the end of a long, hollow iron blowpipe. Air is blown in and causes the glass to form into a pear-shaped bulb, which is then rolled on an oiled slab, shaped with tools and sometimes re-blown into a mold. To keep the glass from hardening during this process, it is periodically re-heated in small ovens. Pressed glass is worked by taking the molten glass from the furnace and dividing it up into small sections. These would be placed in molds made of iron or brass. A plunger would press the glass down into the mold, and after a few seconds it would be ready. Drawn glass is used to make tubes and rods.To make tubes, the molten glass gets drawn over a hollow cylinder or cone that has air blowing through it, to keep it from collapsing until the glass hardens around it. The tube can be drawn out horizontally, vertically, or at an angle.To make glass rods, the air inside the cylinder or cone is eliminated. Rolled glass is used for flat glass,the sheet of glass rolls along the assembly line as it is manufactured.Hence they are not damaged by the heat of molten glass. To cut the glass,first it must be scored with a glass-cutter wheel. Pressure is then applied across the score to force a break.Another way to cut glass is to heat a narrow strip of glass by a focused flame or a ring of such flames to heat a particular area of the glass till it becomes soft enough to pull apart. Glass is categorized by its composition. The most common – ninety percent of manufactured glass – is so-called soda glass, the combination of silica, soda and lime. Although it’s the cheapest to make, it is also the least resistant to high temperature, or sudden changes in temperature, or chemicals. Fiberglass and foam glass are mostly used for insulation purposes. To make fiberglass, the molten glass is formed into continuous, hair-like glass filaments. Foam glass is made by trapping gas bubbles in the glass, creating an almost spongy consistency. Colored glass is made by adding chemicals into the mix, with particular chemicals creating specific colors. For example, the amber or brown glass you see used in beer bottles gets its color from iron sulphide. Iron-chromite creates shades of green, while cobalt makes beautiful shades of blue.
Posted on: Wed, 11 Sep 2013 08:29:15 +0000