- Window screen
A window screen, insect screen or bug screen is a metal wire, fiberglass, or other synthetic fiber mesh, stretched in a frame of wood or metal, designed to cover the opening of an open window. Its primary purpose is to keep leaves, debris, insects, birds, and other animals from entering a building or a screened structure such as a porch, while permitting fresh air-flow. Most houses in Australia, the United States and Canada have screens on all operable windows, which are most useful in areas that have large mosquito populations. Formerly, screens in North America were usually replaced with glass storm windows in the winter, but now the two functions are usually combined in combination storm and screen windows, which allow glass and screen panels to slide up and down.
Types of screening fabric
The most common materials used for insect screening material are aluminum and fiberglass. Aluminum is generally available in natural aluminium or in an applied charcoal color; the charcoal is much 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. However, the fiberglass mesh is somewhat more opaque than aluminum mesh, which darkens the external appearance of the window and reduces the amount of light transmitted from outside. In addition, fiberglass screen degrades rapidly with exposure to UV light, leading to it fraying and breaking after just a few years, unlike aluminum which lasts considerably longer.
For applications requiring greater strength, such as screened doors, nylon and polyester screening are also available.
Bronze insect screening is much more expensive, but gives much longer service than either aluminium or fiberglass. When first installed, it has a bright gold color; this weathers to an unobtrusive dark charcoal within a year or less. Bronze is somewhat more resistant to denting than aluminium. Less common screen fabrics include copper, brass, stainless steel, and galvanized steel.
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.
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. These frames are usually 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.
Fiberglass screen material is typically available in 100 foot rolls in varying widths, from 18 inches to 120 inches wide. Aluminum screen material is available in 100 foot 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.
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.
"Wove wire for window screens" were referenced in the American Farmer in 1823. Advertisement for wire window screens appeared in Boyd's Blue Book in 1836. Two wire window screens were exhibited at Quincy Hall in Boston in 1839. In 1861 Gilberr, 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. Apparently, 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. Today most houses in Australia, the United States and Canada have screens on all operable windows.
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 .140″ to .190″, in increments of .010″.
The spline is often manufactured with parallel ridges running along the length of the spline to provide a better grip and compliance when it is pressed into the 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.
When installed using wooden frames, the screen fabric is tacked or stapled onto the frame. A narrow wooden molding is then nailed over the ragged edge. The screening fabric needs to be stretched tightly before nailing, but not so tightly as to deform the fabric.
Because of corrosion problems with dissimilar metals, metal screening fabrics other than aluminium are not used in aluminium frames.
Screen mesh may collect condensation. This effect has been used to collect water from fog.
- ^ "The Busy Brush Decorative Art - The History of Screen Painting". 2005. http://www.busybrushart.com/historyofscreenpainting.htm. Retrieved 2008-08-12.
- ^ Ted and Mary, Fried (1978). "America’s Forgotten Folk Arts". Pantheon Books. http://members.aol.com/_ht_a/neddybee/folkart.html. Retrieved 2008-08-12.
- ^ Meador, MD, Clifton K. (22 April 2004). "From Med School: Shoes, Window Screens, and Meat". Med School (Medscape from WebMD). PMC 1395801. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1395801.
- ^ Particle Size Conversion Table: wovenwire.com
- ^ "Screen Collecting water in Nepal" wateraid.org; "Screen collecting water system design" designboom.com
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