(c) 2018 BOE, used with permission
One of today’s modern technological wonders is the flat-panel liquid crystal display (LCD) screen, which is the key component we find inside televisions, computer monitors, smartphones, and an ever-proliferating range of gadgets that display information electronically. What most people don’t realize is how complex and sophisticated the manufacturing process is. The entire world’s supply is made within two time zones in East Asia. Unless, of course, the factory proposed by Foxconn for Wisconsin actually gets built.
Last week I had the opportunity to tour BOE Technology Group’s Gen 10.5 factory in Hefei, the capital of China’s Anhui Province. This was the third factory, or “fab” that Beijing-based BOE built in Hefei alone, and in terms of capability, it is now the most advanced in the world. BOE has a total of 12 fabs in Beijing, Chongqing, and several other major cities across China; this particular factory was named Fab 9.
Liquid crystal display (LCD) screens are manufactured by assembling a sandwich of two thin sheets of glass. On one of the sheets are transistor “cells” formed by first depositing a layer of indium tin oxide (ITO), an unusual metal alloy that you can actually see through. That’s how you can get electrical signals to the middle of a screen. Then you deposit a layer of silicon, followed by a process that builds millions of precisely shaped transistor parts. This patterning step is repeated to build up tiny little cells, one for each dot (known as a pixel) on the screen. Each step has to be precisely aligned to the previous one within a few microns. Remember, the average human hair is 40 microns in diameter.
On the other sheet of glass, you make an array of millions of red, green, and blue dots in a black matrix, called a color filter array (CFA). This is how you produce the colors when you shine light through it. Then you drop tiny amounts of liquid crystal material into the cells on the first sheet and glue the two sheets together. You have to align the two sheets so the colored dots sit right on top of the cells, and you can’t be off by more than a few microns in each direction anywhere on the sheet. The sandwich is next covered with special sheets of polarizing film, and the sheets are cut into individual “panels” – a term that is used to describe the subassembly that actually goes into a TV.
For the sake of efficiency, you would like to make as many panels on a sheet as possible, within the practical limitations of how big a sheet you can handle at a time. The first modern LCD Fabs built in the early 1990s made sheets the size of a single notebook computer screen, and the size grew over time. A Gen 5 sheet, from around 2003, is 1100 x 1300 mm, while a Gen 10.5 sheet is 2940 x 3370 mm (9.6 x 11 ft). The sheets of glass are only 0.5 - 0.7 mm thick or sometimes even thinner, so as you can imagine they are extremely fragile and can really only be handled by robots. The Hefei Gen 10.5 fab is designed to produce the panels for either eight 65 inch or six 75 inch TVs on a single mother glass. If you wanted to make 110 inch TVs, you could make two of them at a time.
(c) 2018 BOE, used with permission
The fab is enormous, 1.3 km from one end to the other, divided into three large buildings connected by bridges. LCD fabs are multi-story affairs. The main equipment floor is sandwiched between a ground floor that is filled with chemical pipelines, power distribution, and air handling equipment, and a third floor that also has a lot of air handling and other mechanical equipment. The main equipment floor has to provide a very stable environment with no vibrations, so an LCD fab typically uses far more structural steel in its construction than a typical skyscraper. I visited a Gen 5 fab in Taiwan in 2003, and the plant manager there told me they used three times as much structural steel as Taipei 101, which was the world’s tallest building from 2004- 2010. Since the equipment floor is usually one or two stories up, there are large loading docks on the outside of the building. When they bring the manufacturing equipment in, they load it onto a platform and hoist it with a crane on the outside of the building. That’s one way to recognize an LCD fab from the outside – loading docks on high floors that just open to the outdoors.
LCD fabs have to maintain strict standards of cleanliness inside. Any dust particles in the air could cause defects in the finished displays – tiny dark spots or uneven intensities on your screen. That means the air is passed through elaborate filtration systems and pushed downwards from the ceiling constantly. Workers have to wear special clean room protective clothing and scrub before entering to minimize dust particles or other contamination. People are the largest source of particles, from shedding dead skin cells, dust from cosmetic powders, or smoke particles exhaled from the lungs of workers who smoke. Clean rooms are rated by the number of particles per cubic meter of air. A class 100 cleanroom has less than 100 particles less than 0.3 microns in diameter per cubic meter of air, Class 10 has less than 10 particles, and so on. Fab 9 has hundeds of thousands of square meters of Class 100 cleanroom, and many critical areas like photolithography are Class 10. In comparison, the air in Harvard Square in Cambridge, MA is roughly Class 8,000,000, and probably gets substantially worse when an MBTA bus passes through.
Since most display manufacturing has to be done in a cleanroom and handling the glass requires such precision, the factory is heavily automated. As you watch the glass come in, it is placed into giant cassettes by robot handlers, and the cassettes are moved around throughout the factory. At each step, robots lift a piece of glass out of the cassette, and position it for the processing machines. Some of the machines, like the ones that deposit silicon or ITO, orient the glass vertically, and put them inside an enormous vacuum chamber where all the air is first pumped out before they can go to work. And then they somehow manage to deposit micrometer thin layers that are extremely uniform. It is a miracle that any of this stuff actually works.
(c) 2018 BOE, used with permission
It obviously costs a lot to equip and run such a fab. Including all of the specialized production tools, press reports say BOE spent RMB 46 billion (US$6.95 billion). Even though you don’t see a lot of people on the floor, it takes thousands of engineers to keep the place running.
The Hefei Gen 10.5 is one of the most sophisticated manufacturing plants in the world. On opening day for the fab, BOE shipped panels to Sony, Samsung Electronics, LG Electronics, Vizio, and Haier. So if you have a new 65 or 75-inch TV, there is some chance the LCD panel came from here.
A window screen (also known as insect screen, bug screen, fly screen, flywire, wire mesh, or window net) is designed to cover the opening of a window. It is usually a mesh made of metal, fibreglass, plastic wire, or other pieces of plastic and stretched in a frame of wood or metal. It serves to keep leaves, debris, bugs, birds, and other animals from entering a building or a screened structure such as a porch, without blocking fresh air-flow.
Most houses in Australia, the United States and Canada and other parts of the world have screens on windows to prevent entry of flying insects such as mosquitoes, flies and wasps. In some regions such as the northern United States and Canada, screens were required to be replaced by glass storm windows in the winter, but now combination storm and screen windows are available, which allow glass and screen panels to slide up and down.
For screens installed on aluminium frames, the material is cut slightly larger than the frame, then laid over it, and a flexible vinyl cord, called a spline, is pressed over the screen into a groove (spline channel) in the frame. The excess screen is then trimmed close to the spline with a sharp utility knife. Common spline sizes range from 3.6 mm (0.140 in) to 4.8 mm (0.190 in), in increments of 0.25 mm (0.010 in).
The spline is often manufactured with parallel ridges running along the length of the spline to provide a better grip and compression when it is pressed into the spline channel. A spline roller — a special tool that consists of a metal (or plastic) wheel on a handle — is used to press the spline into the frame. The wheel edge is concave, to help it hold the spline and not slip off to the side. Some spline rollers are double-ended and have both convex and concave rollers; the convex roller can be used to seat the spline deeper into the channel without risk of cutting the screen. Driving the spline into the channel tends to tension the screen on the frame, so the installer must avoid pre-tensioning the screen excessively to prevent the frame from becoming warped.
History
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"Wove wire for window screens" are referenced in the American Farmer in 1823. Advertisement for wire window screens also appeared in Boyd's Blue Book in 1836. Two wire window screens were exhibited at Quincy Hall in Boston in 1839.
In 1861 Gilbert, Bennett and Company was manufacturing wire mesh sieves for food processing. An employee realized that the wire cloth could be painted gray and sold as window screens and the product became an immediate success. On July 7, 1868, Bayley and McCluskey filed a U.S. Patent, number 79541 for screened roof-top rail-car windows, allowing ventilation, while preventing "sparks, cinders, dust, etc." from entering the passenger compartment. By 1874, E.T. Barnum Company of Detroit, Michigan advertised screens that were sold by the square foot.[1]
Window screens designed specifically to prevent insect entry were not patented in the United States, although by 1900 several patents were awarded for particular innovations related to window screen design. By the 1950s, parasitic diseases were largely eradicated in the United States in part due to the widespread use of window screens.[2] Today many houses in Australia, the United States and Canada have screens on operable windows.[3]
Uses
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A window screen prevents insects flying or crawling into a house without obstructing the view or airflow through the window. It is not generally intended to prevent young children from falling out of the window, stop home intruders, or defend against larger animals.
Collecting water
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Screen mesh may collect condensation. This effect has been used to collect water from fog.[4]
Decoration
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Screen painting is a folk art consisting of paintings on window screens. It is also possible to print images directly onto fiberglass screen cloth using specially designed inkjet printers.
Fabric types
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The most common materials used for the mesh of window screens are aluminum and fiberglass. Aluminum is generally available in natural aluminum or in an applied black or charcoal color, which make the screening less visible. Fiberglass is available in light gray as well as charcoal colors, the charcoal again offering better viewing and appearance. Fiberglass is less expensive, and has the advantage of not "denting" when hit or pushed, but it is somewhat more opaque than aluminum. For this reason, dark aluminum allows a better view of windows from the exterior, detracting less than fiberglass from the architectural effect of traditional divided-light window styles.
For applications requiring greater strength, such as screened doors (which have a larger area than windows), nylon and polyester screening is often used. However, these materials are not generally used for smaller applications such as window screens.[5]
Bronze insect screening is much more expensive, but gives much longer service than either aluminum or fiberglass. When first installed, it has a bright gold color; this weathers to an unobtrusive dark charcoal within a year or less. Weathered bronze darkens the external appearance of windows to approximately the same degree as charcoal or black aluminum. Bronze is somewhat more resistant to denting than aluminum. Less common screen fabrics include copper, brass, stainless steel, and galvanized steel. For coastal locations, corrosion resistance usually requires the use of bronze or synthetic screening fabric.
Some manufacturers offer screening that promise to substantially reduce the visibility of the screening. Several manufacturers offer screens that roll into a pocket when not in use. These are available for casement windows as well as other types of window and door openings.
Do-it-yourself screen and frame replacement kits are widely available at hardware and home improvement stores. One kind is composed of straight aluminum sides (which can be cut to size) and plastic corner inserts. Screen replacement kits usually consist of a roll of nylon screening fabric and a generous supply of rubber spline.
In addition to insect screening, denser screen types that also reduce sunlight and heat gain are available. These offer significant potential energy savings in hot climates.[citation needed] Other manufacturers offer screens designed to filter for pollen and dust.
Temporary, removable screens that fit within window tracks of double-hung windows are a common expedient widely available in hardware and home improvement stores. Typically 30 to 76 centimetres (12 to 30 in) high, these screens are wedged beneath the lower sash of a double-hung window and secured laterally by the tracks of the window. A sliding mechanism allows the screen to be adjusted laterally to fit the width of most windows, which also allows the screen to fit securely within the tracks below the open sash.
Screen sizes
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Typically, metal screen frames (roll form) are 6.4 mm (1⁄4 in), 7.9 mm (5⁄16 in), 9.5 mm (3⁄8 in) or 11 mm (7⁄16 in) in thickness by 19 mm (3⁄4 in) and 25 mm (1 in). The most common sizes are 7.9 mm (5⁄16 in) and 11 mm (7⁄16 in) by 19 mm (3⁄4 in). The 6.4 mm (1⁄4 in) and 7.9 mm (5⁄16 in) sizes are generally used for single hung windows, while the two larger sizes are used for double hung windows. As 9.5 mm (3⁄8 in) is not a common size, the 7.9 mm (5⁄16 in) thickness may be used instead and shimmed as needed. They come in a variety of colors including unpainted, white, bronze, tan, black, desert sand, etc. The screen may also include a crossbar for added strength.
Fiberglass screen material is typically available in 30 m (100 ft) rolls in varying widths, from 46 to 305 cm (18 to 120 in) wide. Aluminum screen material is available in 30 m (100 ft) rolls except the range of available widths is less than for the more commonly used fiberglass. The fineness of a screen mesh is measured in wires per inch on the warp (length) and the weft or filler (width). An 18×14 mesh has become standard; 16×16 was formerly common and other common sizes are 18×18 and 20×20. For comparison, a typical screen in a clothes dryer has a nylon 23x23 mesh screen.
Fiberglass solar screens provide over 75% of UV protection, by using thicker strands and a closer mesh than regular 18x14 fiberglass window screening. There is some reduction in visibility, but this can be advantageous, since solar screens are difficult to see through from the outside, while easier to see through from the inside.
Finer meshes have been developed to prevent very small insects, often called "noseeums" from flying through. The finer mesh screens are also used to prevent pollens and allergens from entering homes in order to control allergic reactions.
Gallery
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A pierced window screen brings light into the mandapa at Manikesvara Temple in Lakkundi, Lakkundi
A window with an insect screen
Sailors assigned to the dock landing ship USS Tortuga (LSD 46) replace a protective window screen at Kalalake Elementary School during a community service project
See also
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Notes
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