Tungsten is chemically resistant metal. Does not respond to the presence of moisture, the concentrated solutions of alkalis and acids. To 400 °C in oxygen, Aqua Regia. Up to 600 °C in hydrogen chloride, hydrogen 700 °C for ammonia to 800 °C in carbon monoxide, nitrogen boiling mercury. He reacts with a mixture of nitric and hydrofluoric acids, a mixture of hydrogen peroxide with ammonia at t° red heat, and hydrogen sulfide and chlorine — about 250 °C, boiling sulfur hot Aqua Regia, nitric acid, melts nitrite, potassium chlorate and nitrate, lead dioxide, sodium nitrite, bromine, iodine, fluorine. Carbide WC is obtained by reaction with carbon at 1400 °C and oxide WO2 — by reacting with sulfur dioxide, water vapor (at t° red heat), or oxides of Mg, Th, Al, carbon dioxide (t° 1200 °C and above).
Exceptional heat resistance (t° PL. of tungsten is +3422°C), high temperature creep resistance, high elastic modulus, the minimum coefficient of thermal expansion in comparison with other metals, resistance to aggressive agents and corrosion resistance, strength, durability and reliability. A steel after aging at the temperature of red heat lose their hardness, but tungsten — no. This quality is called the red hardness. Alloy tungsten tool steel makes possible the most intense metal processing with the speed of tens meters per second. This metal is due to refractoriness, is one of the most durable and heat-resistant alloys. Higher melting point among all the simple substances has only carbon.
|The temperature at which the obtained data the features of t°C||20°C|
|The linear thermal expansion coefficient α [1/Deg]||43x10-6|
|The density of the alloy [g/cm3]||19,3|
|Tensile strength tensile kg/mm2||35|
|Specific heat at 20 °C [kJ/(kg·deg)]||0,134|
|The thermal conductivity K [W/(m·K)]||300,173|
|Electrical resistivity R, Mhmm2/m||0,054|
The drawbacks include the difficulty of obtaining tungsten in its pure form, great weight, and brittleness at low temperature. Tungsten rod not sufficiently plastic at ordinary temperatures, because of its exceptional properties to process (rolling, drawing and forging) only with considerable heat.
Rod is the most popular products with a standard cross-sectional dimension. The complexity of manufacturing tungsten rod is connected with low technological plasticity of tungsten at normal temperatures. When heated increases its plasticity and strength remains high, so it is produced using heat treatment under pressure. Fort (original stock) obtained by methods of powder metallurgy. The rod is heated, after which Raskulinecz on a rotary forging machine. Bars are produced with a diameter of 2 — 3 mm and supply usually in the form of straight line segments.
Rod, wire used as a semi-finished product for the most critical components that operate in extreme conditions, heavy loads and higher temperatures. Machinery, military, metal working, petrochemical industry, metallurgy, mining industry today can not do without tungsten rod. It is an indispensable material in hot working of metals under pressure (mandrel piercing mills, matrices, presstampa) and alloying of tool steels. It uses the glass industry in the form of a mixer for the melting of glass melting electrodes and other nodes furnaces. It serves for the production of molds and cores used in casting machines under pressure for alloys. Tungsten electrodes are widely demanded for welding of creep resisting and low alloy steels. Electronics and electrical engineers uses a tungsten filament coils for incandescent and cathodes in cathode ray tubes, lamps and other vacuum tubes.
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