Tungsten
Ramisa Sas handles semi-finished products in Tungsten (Wolfram) and its main alloys. We supply material to specification for industry, from standard semi-finished products to custom parts to drawing.
Wire in coil, wire on spools
Round bars, square bars, small bars, cylinders
Flat bars, foils, strips, sheets, plates and platelets
Round tubes, square tubes, tubes to drawing, seamless tubes, welded tubes, fittings
Electrodes, welding wire
Fasteners, screws, bolts, nuts, discs
Metal meshes and nets, custom parts and components (turned or CAD-machined), forged parts
TUNGSTEN PRODUCT RANGE
Tungsten semi-finished products
Tungsten anodes
Custom tungsten anodes to drawing
Tungsten carbide
Tungsten wire on spool
Thick tungsten wire
Tungsten needles W 99.95% electropolished diam. 0.5 (+/-0.01) x 23 (+/-0.1) mm
Tungsten small bars
Round tungsten small bars W 99.95% diameter 1 mm; 1.5 mm; 2 mm; 2.5 mm; 3 mm
Tungsten bars
Tungsten flat bars
Welded tungsten wire
Tungsten foils
Tungsten strips
Tungsten sheets
Tungsten sheet 0.5 x 100 x 100
Tungsten tubes
Tungsten filaments
Tungsten screws and nuts
Custom tungsten components to drawing
Custom tungsten parts to drawing
Tungsten parts W99.95% - Dim. 2 x 24 x 24 mm + 10 x 24 x 24 mm + 68 x 24 x 24 mm
Custom tungsten platelets 99.95% to drawing
Tungsten carbide small bars diam. 6x330 mm ground h5
Tungsten wire for glass wool
Tungsten wire
Round tungsten bars W99.95% diam. 16x200 mm
Round tungsten bars W99.95% diam. 16x35 mm
Tungsten small bar 6 x 6 x 500 mm
Tungsten electrodes in wires and bars
Small tungsten electrodes W 99.95
Tungsten discs
Tungsten flat bars
Welded tungsten wire
Tungsten strips
Tungsten sheets
Tungsten tubes
Tungsten filaments
Tungsten screws and nuts
Blue tungsten oxide
Yellow tungsten oxide
Tungsten powder
Consultancy and design. Ramisa can offer consultancy and design for finished parts and machining in tungsten.
TUNGSTEN ALLOYS
Ramisa supplies all the main alloys based on Tungsten (Wolfram).
WLa (Tungsten-Lanthanum), WRe (Tungsten-Rhenium), WCu (Tungsten-Copper), WNiCu (Tungsten-Nickel-Copper), WNiFe (Tungsten-Nickel-Iron) and hard metal.
Copper-Tungsten (CuW)
Hardness and wear resistance of tungsten combined with the conductivity of copper. Erosion electrodes, contacts, sheets and bars.
Silver-Tungsten (AgW)
Material for electrical contacts at very high switching currents: power switches, current switches, earthing switches.
Rhenium-Tungsten (WRe)
Greater ductility and heat resistance than pure tungsten. High-temperature thermocouples, filaments, X-ray anodes.
HISTORY AND CHEMICAL PROPERTIES
Atomic number 74
Atomic weight 183.85
Melting temperature 3410 ±20 °C
Boiling temperature 5660 °C
Density 19.3 g/cm3 at 20 °C
Tungsten or Wolfram is a very heavy metal; it appears as a grey powder or as a shiny white metal. It has the highest boiling and melting point of all metals, a low coefficient of thermal expansion, high tensile strength at high temperatures, high resistance to corrosion and chemical attack at room temperature and a very high conductivity. It is extracted mainly from wolframite (iron and scheelite, (FeMn) WO 4) and scheelite (CaWO4). The largest reserves of raw materials are in China, with other deposits in the CIS countries, Austria, Australia, Korea, Bolivia, Malaysia, etc. About 70% of the metal is used as a hardener (tungsten carbide), tungsten alloys and pure tungsten, about 10-25% as an alloying element in steel products and the rest as tungsten-based chemicals or other chemicals.
The name derives from Swedish and means heavy stone, a name initially attributed to its mineral scheelite (from the Swedish chemist Scheele). Tungstic acid was isolated as early as the mid-1700s, while in 1781 Tobern Bergman argued that the metal could be obtained from the acid, without however being able to prove it. In the same years two Spanish chemists, the d’Elhuyar brothers, obtained the same acid from wolframite. The first metal obtained by reducing the acid was produced in 1783 from a wolframite from Zinnwald. In 1785 Rudolf Erich Raspe, among other things author of “The Adventures of Baron Munchausen”, demonstrated that the metal obtained from scheelite is identical to that obtained from wolframite and that this metal had a hardening power on steel.
Chemical properties of Tungsten or Wolfram
Tungsten has a remarkable resistance to the corrosion of many acids. It is resistant to hydrofluoric acid and to hydrochloric acid and is only slightly attacked by hot hydrochloric acid and by sulphuric acid. Nitric acid and aqua regia only slightly attack tungsten, while solutions of hydrofluoric acid and nitric acid can rapidly dissolve the material.
Tungsten is stable in alkaline solution, provided it does not contain oxidising agents. Molten caustic soda strongly attacks tungsten in the presence of oxidising agents.
Tungsten is also attacked by fluorine at room temperature, by chlorine at a temperature of 250 °C (523K) and by bromine and iodine at around 500 °C (773 K).
Tungsten has a remarkable resistance to corrosion by many molten metals.
CHARACTERISTICS, APPLICATIONS AND PROCESSING
very high melting point
very high density and good corrosion resistance in many acids, alkalis and molten metals
from 500 °C rapid oxidation in air and from 800 °C sublimation of tungsten oxide
under vacuum or inert gas, resistant to exceptionally high temperatures
It is used in the form of pure tungsten, tungsten alloys and tungsten composite materials for: incandescent lamps, filaments, anodes for X-ray tubes, electrical switch contacts, heat conductors, shielding, erosion electrodes, welding electrodes, friction stir tools for welding, thermocouples, tool holders.
Processing of Tungsten or Wolfram
Forming and stamping. Tungsten can be bent, curved, formed, spun, flow-turned, sheared, stamped, drilled and riveted. Tungsten is a strong, hard metal that is sensitive to cracking, usually brittle at room temperature. It requires special processing and greater attention than most metals and alloys.
The most important rule to remember when working with tungsten is that it must be formed or cut at temperatures well above its transition temperature. Failure to follow this rule generally leads to cracked or laminated parts. It should be ensured that the metal remains at this temperature for the entire forming process. The use of cold tools that rapidly cool the metal can be as harmful as not preheating the material.
The following basic rules apply to almost all production techniques:
| Tungsten should be produced at a temperature above the transition temperature. |
| Tungsten must not be heated to a crystallisation temperature above its own, unless the resulting brittle structure is without consequences. |
| Tungsten is a shear-sensitive material. It is good practice to eliminate all stresses before production. |
| Tungsten has directional properties related to the rolling direction. When possible, bends should be made perpendicular to the rolling direction of the sheet. |
| Cut edges should always be kept sharp, and cleaning should be kept to a minimum. |
| Bend radii should be as generous as possible. |
Welding. Welding of tungsten with tungsten or with other metals should be undertaken with caution and bearing in mind the inherent limitations. Tungsten can be welded to tungsten. However, the resulting weld is always recrystallised and therefore brittle. Even the use of W/Re filler bars does not eliminate the brittleness of the metal adjacent to the heat-affected zone.
In welds where there must be no narrow cracks, but good mechanical strength at high temperature is required, the use of tungsten or tantalum rivets has proven very satisfactory. Tantalum rivets, which are no stronger than tungsten ones, are much easier to insert. Tungsten rivets require more insertion skill, but are more satisfactory.
If tungsten parts that do not require exposure to very high temperatures must be joined, brazing is preferable to welding. As long as the brazing material has a melting point lower than the recrystallisation temperature of tungsten (below 2200°F), embrittlement can be avoided. Copper or silver alloys containing small proportions of nickel or iron are suitable for these applications.
Machining and grinding. Tungsten can be machined by grinding, milling or drilling. For thick parts, a slight preheating of the piece to 400°F is sometimes helpful, otherwise a highly chlorinated oil such as trichloroethylene is used.
Using a C-2 carbide-type tool, the suggested geometry is: side angle 10°; cutting angle from 3° up to 10°; back clearance angle 0°; bottom clearance angle from 3° up to 5°; front radius from 1/32'' up to 1/16''; cutting speed from 100 to 200 RPM.
The final shaping of tungsten parts is frequently done by grinding. Since tungsten is hard and brittle, surface control can be a problem if an adequate coolant is not used. An oil-emulsion type coolant is recommended.
Surface treatments. The surface of tungsten can be cleaned with chemical treatments using aqueous alkaline solutions or caustic soda mixed with sodium nitrate. Electrochemical polishing of tungsten can be completed in an aqueous alkaline solution containing oxidisers, with the tungsten coating as the anodes.
REFERENCE STANDARDS
ASTM B760 — tungsten plates, sheets and foils
ASTM F288 — tungsten wire for electronic devices and lights
ASTM F73 — tungsten-rhenium wires for electronic devices and lights
ASTM E696 — tungsten-rhenium wires for thermocouples
ASTM F269 — determination of the deflection of tungsten wire
ASTM B702 — tungsten-copper, contact materials
ASTM B631 — silver-tungsten, electrical contact materials
ASTM B777 — tungsten heavy metals
