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If it is true that one luck a hundred failures would chip, the opening of the technology of pulling the tungsten filament, may serve as evidence of this. Method of production of tungsten filament, the victim as a failure, was a turning point in the development of powder metallurgy technology.
Incandescent bulbs, such as we know them, appeared in 1904. Prior to this, the light source in the lamps served as carbon electrodes, More than a quarter century went searching for a suitable material, since, when the Swan in 1878 first introduced in Newcastle invented carbon lamp brightness eight and sixteen candles. At the end of the NINETEENTH century von welsbach from osmium (t°PL = 2700° C) produced a metal filament. Osmium lamp was 6 times better and brighter coal, however, the price of osmium, the element of the platinum group, doing these lamps are extremely expensive.
In 1903 von Bolton from the company «Siemens and Halske» offered for filaments of tantalum with t°PL 2996 °C. for Tantalum lamp was 15% more efficient osmium and even started to infiltrate the production, but could not compete with appeared a year later, a tungsten filament. Lamps with tungsten filaments pushed out of the market all the other lamps to 1911. The light output of tungsten was 2 times higher than that of osmium, and high voltage is almost 4 times higher. Modern fluorescent lamps with cathode made of tungsten is almost 9 times more efficient and brighter osmium the end of the NINETEENTH century.
Development of technology for tungsten filament
For a long time, due to the considerable brittleness of tungsten at normal temperature could not pull the delicate fabric. At the beginning HH century «Siemens Halske» tried to apply the technology of extrusion, developed for tantalum. However, for tungsten, it was not enough malleable. Was later patented the original method, when in a hydrogen atmosphere excitation of an electric arc between tungsten electrodes tungsten billet melted in a graphite crucible, coated inside with tungsten powder. It turned out droplets of molten tungsten Ø 10 mm up to 30 mm long, which after cooling was subjected to further processing. Another patent was mixing the tungsten powder with an organic paste, the resulting mass is extruded through a die and under an inert atmosphere annealed. Was quite a thin tungsten filament. One of the promising developments looked like. Heated carbon filament in an atmosphere of hydrogen and vapor WCl4. On the surface of the filament to form tungsten that was sintered with carbon in the form of carbide WC in white. The thread is re-heated in a stream of hydrogen, which is «washed» carbon, leaving a pure tungsten filament similar to the filament obtained by extrusion. All these technologies tried to protect the tungsten from oxidation during the heating, since otherwise the grain structure of the thread made it very brittle. In 1909 the American Coolidge managed to select the ideal mode of thermal and mechanical processing of tungsten without the use of filler.
The starting material is tungsten powder of high purity. Special mills grind raw materials to fine powder in a nitrogen atmosphere to avoid oxidation of the surface heated by the friction of the particles. Further, in steel molds pressed blanks under pressure of 5−25 kg/mm2. If the raw materials are of poor quality, the blank obtained is fragile. To avoid this, in the feedstock is readily oxidizable organic component. The next stage is the sintering. Extruded billet, also called rods, have the specific weight is about 2/3 of the density of metal tungsten, so they are sintered at very high temperatures. They are placed between the contacts, water-cooled, and in an atmosphere of dry N2 flow, electric discharge, warming almost to the point of melting. This increases the size of crystal grains and the workpiece reaches 95% density of the casting. Billet prokovyvayut at a temperature of 1200−1500°C. At a special mill sintered rods compressed by the hammer, with each time flat out 12%. Tungsten grains are elongated and due to this acquired a fibrillar structure. After forging the stretch thread through the diamond mesh. The diameter of the resulting filament ~13 µm.
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Advantages of tungsten filament
Tungsten — the most refractory of the metals, it t° melting +3422°C. tungsten filament heat-resistant, has a minimum coefficient of thermal expansion, it has a very high electrical resistivity and luminous efficiency, high resistance to temperature creep, good thermal conductivity.
Tungsten belongs to the rare elements in the earth’s crust. The difficulty of obtaining it in its pure form and the capriciousness of tungsten in the processing all affect the cost of tungsten filament.
The tungsten filament in demand in electrical and electronics due to the low vapor pressure of tungsten at high temperatures up to 2500 °C. Refractoriness and exceptional output, make this an indispensable thread in the incandescent lamps, television tubes and other vacuum tubes. Tungsten filament (GOST 19 671−91) stamps VA, HF, VRN is designed not only for spirals and bodies glow. From it produce a spiral and respiratoorse the cathodes of electronic devices and parts semiconductor devices, loop heaters, nets, targets of x-ray tubes. From brand VRN doing the bushings, beams and details that do not require doped tungsten.
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In stock, LLC «Electrocentury-steel» wide range of high quality tungsten filament and a tungsten wire of various brands at a price that will satisfy any customer. We offer good conditions for wholesale and retail buyers. If necessary, advise you experienced managers. All products are certified Quality is guaranteed by strict observance of technological norms of production. Delivery in the shortest possible time. At wholesale orders are provided preferential discount.
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