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Architectural glass
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Architectural glass has been used in buildings since the 11th
century. Glass is typically used in buildings as a transparent
glazing material for windows in the building envelope. Glass is also
used in glazed internal partitions and as an architectural feature. Glass in buildings is often of a safety type, including toughened and laminated glasses. Before the invention of the float glass method of manufacture, flat glass panels were generally made via the cylinder, sheet or rolled plate processes. Optical distortions could be reduced at substantial cost by grinding the glass to produce polished plate glass. In this manufacturing process glass is blown into a cylindrical iron mould. The ends are cut off and a cut is made down the side of the cylinder. The cut cylinder is then placed in an oven where the cylinder unrolls into a flat glass sheet. William J. Blenko used this method in the early 1900s to make stained glass. These imperfect panes have led to the misconception that glass is actually a high-viscosity liquid at room temperature, which is not the case. |
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Sheet glassSheet glass (sometimes called window glass or drawn glass) was made by dipping a leader into a vat of molten glass then pulling that leader straight up while a film of glass hardened just out of the vat. This film or ribbon was pulled up continuously held by tractors on both edges while it cooled. After 12 meters or so it was cut off the vertical ribbon and tipped down to be further cut. This glass is clear but has thickness variations due to small temperature changes just out of the vat as it was hardening. These variations cause lines of slight distortions. You may still see this glass in older houses. Float glass replaced this process.Rolled plate glassThe glass is taken from the furnace in large iron ladles, which are carried upon slings running on overhead rails; from the ladle the glass is thrown upon the cast-iron bed of a rolling-table; and is rolled into sheet by an iron roller, the process being similar to that employed in making plate-glass, but on a smaller scale. The sheet thus rolled is roughly trimmed while hot and soft, so as to remove those portions of glass which have been spoilt by immediate contact with the ladle, and the sheet, still soft, is pushed into the open mouth of an annealing tunnel or lehr, down which it is carried by a system of rollers.Polished plate glassThe plate glass process starts with sheet or rolled plate glass. This glass is dimensionally inaccurate and often created visual distortions. These rough panes were ground flat then polished clear. This was a fairly expensive process.Before the float process, mirrors were plate glass as sheet glass had visual distortions that were akin to those seen in amusement park or fun-fair mirrors. Float (annealed) glass90% of the world's flat glass is produced by the float glass process invented in the 1950s by Sir Alastair Pilkington of Pilkington Glass, in which molten glass is poured onto one end of a molten tin bath. The glass floats on the tin, and levels out as it spreads along the bath, giving a smooth face to both sides. The glass cools and slowly solidifies as it travels over the molten tin and leaves the tin bath in a continuous ribbon. The glass is then annealed by cooling in a temperature controlled oven called a "lehr". The finished product has near-perfect parallel surfaces.A very small amount of the tin is imbedded in the glass on the side it touched. The tin side is easier to make into a mirror. This "feature" quickened the switch from plate to float glass. The tin side of glass is also softer and easier to scratch. Glass is produced in standard metric thicknesses of 2, 3, 4, 5, 6, 8, 10, 12, 15, 19 and 22 mm. Molten glass floating on tin in a nitrogen/hydrogen atmosphere will spread out to a thickness of about 6 mm and stop due to surface tension. Thinner glass is made by stretching the glass while it floats on the tin and cools. Similarly, thicker glass is pushed back and not permitted to expand as it cools on the tin. Annealed glass is considered a hazard in architectural applications as it breaks in large, jagged shards that can cause serious injury. Building codes across the world restrict the use of annealed glass in areas where there is a high risk of breakage and injury, for example in bathrooms, in door panels, fire exits and at low heights in schools. The elaborate patterns found on figure rolled glass are produced by in a similar fashion to the rolled plate glass process except that the plate is cast between two moving rollers. The pattern is impressed upon the sheet by a printing roller which is brought down upon the glass as it leaves the main rolls while still soft. This glass shows a pattern in high relief. The glass is then annealed in a lehr. The glass used for this purpose is typically whiter in colour than the clear glasses used for other applications. This glass can be laminated or toughened depending on the depth of the pattern to produce a safety glass. Laminated glass is a type of safety glass that holds together when shattered. In the event of breakage, it is held in place by an interlayer, typically of PVB, between its two or more layers of glass. The interlayer keeps the layers of glass bonded even when broken, and its high strength prevents the glass from breaking up into large sharp pieces. This produces a characteristic "spider web" cracking pattern when the impact is not enough to completely pierce the glass. Laminated glass is normally used when there is a possibility of human impact or where the glass could fall if shattered. Shopfront glazing and windshields are typically laminated glasses. The PVB interlayer also gives the glass a much higher sound insulation rating, due to the damping effect, and also blocks 99% of transmitted UV light. Using toughened glass on windshields would be a problem when a small stone hits the windshield at speed, if it were toughened and the stone hit with enough force the whole windshield would shatter into the small squares making visibility difficult and it would also be likely that the wind would blow the small squares into the driver and passengers. Laminated glass was invented in 1903 by the French chemist Edouard Benedictus, inspired by a laboratory accident. A glass flask had become coated with the plastic cellulose nitrate and when dropped shattered but did not break into pieces. Benedictus fabricated a glass-plastic composite to reduce injuries in car accidents. However, it was not immediately adopted by automobile manufacturers, and the first widespread use of laminated glass was in the eyepieces of gas masks during World War I. Today, laminated glass is produced by bonding two or more layers of ordinary annealed glass together with a plastic interlayer, usually polyvinyl butyral (PVB). The PVB is sandwiched by the glass which is passed through rollers to expel any air pockets and form the initial bond then heated to around 70 °C in a pressurized oil bath. The tint at the top of some car windshields is in the PVB. A typical laminated makeup would be 3 mm glass / 0.38 mm interlayer / 3 mm glass. This gives a final product that would be referred to as 6.38 laminated glass. Multiple laminates and thicker glass increases the strength. Bulletproof glass is often made of several float glass, toughened glass and Perspex panels, and can be as thick as 100 mm. A similar glass is often used in airliners on the front windows, often three sheets of 6 mm toughened glass with thick PVB between them |
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Jul 23, 2010 ... Tea, today, has become an integral part of our life. Right from
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