The composition performance of tungsten copper points on electrical life experiment table

A TDR-40A vacuum single-grains furnace can be employed to measure the electrical erosion. Tungsten copper points is used for a contact material, which act as a cathode material, and has been polishing after being processed into metallographic sample, pure tungsten of Φ = 2mm is acting as a anode material, placing the two electrodes into a vacuum furnace. Then energize DC (Direct Current) voltage between the anode and the cathode, which is 8000V to get higher stability. Therefore, with the speed of 0.2mm / min, the cathode will rise slowly to make it close to the anode until the arc between the anode and the cathode can ignite, a precision of 0.1mg analytical balance is used for weight loss measurement of samples, arc each 30 times, and the total number of arc times is 300 times around.
A 1000-B-type scanning electron microscope is used for scanning electrical erosion of morphology, and a electron spectroscopy for changes analysis on sample composition.

 

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Tungsten copper contacts composition performance table of electrical life experiment

Electrical erosion can be measured in a TDR-40A vacuum single-crystal furnace. Cathode material is tungsten copper contacts, a contact material, which has been processed into metallographic sample after polishing, anode material is pure tungsten (Φ = 2mm), they are placed in a vacuum furnace. Plus DC voltage of 8000V (in order to obtain a higher stability) between the anode and the cathode, so that the cathode can rise slowly with the speed of 0.2mm / min, let it close the anode until arc ignite between the anode and the cathode, arc every 30 times, using a precision (0.1mg) analytical balance to measure weight loss of a sample, total arc times is 300 times.

Employ 1000-B-type scanning electron microscope to scan morphology electrical erosion, and electron spectroscopy to analyze changes in the sample composition.



 

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Sample 1: WCu30, prepared by powder metallurgy, size of 10mm * 10mm * 10mm;
Sample 2: Fibrous structure tungsten copper points, Φ = 0.12mm, size of 10mm * 10mm * 10mm;

The arc erosion of WCu30 and fibrous structure tungsten copper points, which increase with the arcing erosion increase. Along with the increase of arcing time, mass loss of both points’ arc erosion increase rapidly at first; then during 15-20 times, it increases slowly; and then after 30 times, it increases quickly. What is more, sample 2’s mass loss is less than sample 1’s. The reason why mass loss of the two samples increasing rapidly lies that: original burr, unevenness and impurities on the surface of cathode material are subject to strong electron and ion sputtering under thermal action of discharge arc, leading to a large loss of material; Because sample 2’s raw material is tungsten fiber(can enhance mechanical properties), therefore, its hardness and strength of the sample will increase, and whose loss can be reduced; At the same time, due to capillary suction, the molten copper can make melt filling in tungsten skeleton under the action of arc, so that splash and losses of cathode materials can also be reduced. Since the mass loss of Sample 2 is less than sample 1’s, so sample 2 owns lower arc corrosion resistance.



 

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New tungsten copper contacts material: tungsten copper contacts (with fibrous structure)
Sample 1: WCu30 prepared by mixing, sintering and other process;
Sample 2: fiber structure of tungsten copper contacts (Φ = 0.12mm);
Sample size: 10mm * 10mm * 10mm.

The arc erosion of new tungsten copper contacts material and WCu30 are increasing with the increase of arcing erosion. In the beginning, quality loss of arc erosion of both samples increase rapidly with the number of arcing time, then slowly increasing during 15-20 times, and then quickly increase after 30 times, besides, the quality loss of sample 2 is less than sample 1. The reason of quality loss increased rapidly of the two samples is: under the thermal action of discharge arc, the original burr, unevenness and impurities of the cathode material’s surface are suffering from strongly electron and ion sputtering, resulting in a large loss of material; since sample 2 is using tungsten fibers as its materials, which enhance its mechanical properties, so the strength and hardness of the material increases, and the loss can be reduced; the arc has played a role in it at the same time, the molten copper, due to capillary suction, can make melt filling in tungsten skeleton, such splash and losses of cathode materials can be reduced. Because the quality loss of Sample 2 is less than sample 1, so sample 1 with higher arc resistance to corrosion.

 

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Tungsten ores

Tungsten does not occur naturally in its pure metallic state; rather, it is found in several ores, but only two kinds of tungsten-bearing mineral rocks, called wolframite and scheelite, are mined commercially. Wolframite accounts for about 70% of the total tungsten resources in the world, and scheelite accounts for about 30%.

Scheelite

Scheelite is a calcium tungstate mineral that forms a series with the rarer mineral powellite, which contains molybdenum in place of the tungsten. Colors include golden yellow, brownish green to dark brown, pinkish to reddish gray, orange and colorless. Transparency ranges from translucent to transparent and crystal faces are highly lustrous. Its gravity is high and its hardness is low. It also fluoresces under shortwave ultraviolet.

Scheelite occurs in contact metamorphic skarns, in high-temperature hydrothermal veins and greisens, and less commonly in granite pegmatites. Notable occurrences include Hollinger Mine, Ontario, Canada; Saxony, Germany; Tong Wha, Korea; Sonora, Mexico; Cornwall, England; New South Wales and Queensland, Australia; Mill City, Nevada, Atolia, San Bernardino Co., California, Cochise Co., Arizona, Utah and Colorado, all in the USA; and Jiangxi, Hunan and Yunnan provinces, China.

Scheelite is a subordinate ore of tungsten, with wolframite supplying a greater quantity on a worldwide basis. Scheelite is synthesized via the Czochralski process to produce the material that is used to imitate diamond, as a scintillator, or as a solid state lasing medium.



 

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Tungsten ores

Tungsten does not occur naturally in its pure metallic state; rather, it is found in several ores, but only two kinds of tungsten-bearing mineral rocks, called wolframite and scheelite, are mined commercially. Wolframite accounts for about 70% of the total tungsten resources in the world, and scheelite accounts for about 30%.

Wolframite

Wolframite is not scientifically classified as an individual mineral species by the International Mineralogical Association (IMA). However, it is widely recognized as a mineral series, with the minerals huebnerite and ferberite being its end members. Huebnerite is the manganese rich end member while ferberite is the iron rich end member. Wolframite is a reddish-brown to grayish-black lustrous mineral which is the chief ore of the metal tungsten.

Wolframite mainly occurs in quartz veins and pegmatites associated with granitic intrusive rock. Notable occurrences include the Nanling Range, China; southwestern states and Colorado in the USA; Russia; Korea; England; Bolivia; Portugal; Australia; Myanmar and the Malay Peninsula. Wolframite ore can be concentrated by gravity (spirals, cones, tables), sometimes in combination with magnetic separation.

Because Wolframite is a strong and quite dense material with a high melting temperature, it is an ideal material for electric filaments and armor-piercing ammunition, as well as hard tungsten carbide machine tools.


 

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Wolfram is kind of essential mineral to get tungsten, and it is usually inlayed in granite and quartz together with cassiterite. Wolfram is weak magnetic with its density of 7.2-7.5g/cm³ and mohs hardness of 4-4.5.

The process of wolfram dressing is mainly gravity separation while sometime intensity magnetic separation can be involved. Wolfram tungsten ore is usually inlayed with coarse granules with big density and small hardness, so the specific separation or concentration of wolframite tungsten can be pre-selection, gravity separation after screening & classifying, intensity magnetic separation and treatment of fine tungsten mud.

The big density difference between wolfram and gangue makes gravity separation workable if the wolframite tungsten granules can be liberated or dissociated from the impurities. For the coarse tungsten or blocky tungsten separation, gravity separation can be used to get the coarse wolframite granules. Here the main wolfram dressing plant is jigging machine. The wolfram ore concentration machine can deal with ore of +80 meshes to 30mm. For some finer tungsten ore, shaking table or other equipment can be used to get the fine wolframite grains.

In the gravity separation of wolramite tungsten, the common processing plant can be jig separator and shaking table. Jigging machine is especially important to beneficiate wolfram tungsten of coarse and medium granules. The raw wolframite tungsten needs crushing and screening before jigging processing to gain high grade tungsten.

As kind of wolfram beneficiation machine, jig has been added to the circle of milling in order to reduce the pelitization of tungsten. The tungsten concentrate from jigging gravity concentration occupies a big part of the whole concentrate.

Shaking table is to separate wolfram of fine grains with its good enrichment ratio, great beneficiation efficiency. So the classifying of raw wolfram ore is necessary before separation.



 

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Tungsten collimators are used in linear accelerators used for radiotherapy treatments. Tungsten collimators help to shape the beam of radiation emerging from the machine, they can limit the maximum field size of a beam. The treatment head of a linear accelerator consists of both a primary and secondary collimator. The primary collimator is positioned after the electron beam has reached a vertical orientation. When using photons, it is placed after the beam has passed through the X-ray tungsten target. The secondary collimator is positioned after either a flattening filter (for photon therapy) or a scattering foil (for electron therapy). The secondary collimator consists of two jaws which can be moved to either enlarge or minimize the size of the treatment field.

New systems involving multileaf collimators (MLCs) are used to further shape a beam to localize treatment fields in radiotherapy. MLCs consist of approximately 50–120 leaves of heavy, metal tungsten collimator plates which slide into place to form the desired field shape.

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For industrial radiography using gamma radiation sources such as Iridium-192 or Cobalt-60, a collimator allows the radiographer to control the exposure of radiation to expose a film and create a radiographic "negative", a.k.a., a radiograph, to inspect materials for defects. A collimator in this instance is most commonly made of tungsten, and is rated according to how many half value layers tungsten material contains, i.e., how many times tungsten material reduces undesirable radiation by half. For instance, the thinnest walls on the sides of a 4 HVL tungsten collimator 0.52" thick will reduce the intensity of radiation passing through them by 88.5%. The shape of these collimators allows the radiographer to direct the radiation to the film and away from other workers.

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The main component of tungsten ore is tungsten.Tungsten is a dull silver-colored metal with the highest melting point of any pure metal.Also known as wolfram, from which the element takes its symbol, W, tungsten is more resistant to fracturing than diamond and is much harder than steel. It is the refractory metal's unique properties - its strength and ability to withstand high temperatures - that make it ideal for many commercial and industrial applications.

Applications:

Tungsten's primary application for over 100 years has been as the filament in incandescent light bulbs. Doped with small amounts of potassium-aluminum silicate, tungsten powder is sintered at high temperature to produce the wire filament that is in the center of light bulbs that light millions of homes around the world.

Due to tungsten's ability to keep its shape at high temperatures, tungsten filaments are now also used in a variety of household applications, including lamps, floodlights, heating elements in electrical furnaces, microwave ovens, x-ray tubes and cathode-ray tubes (CRTs) in computer monitors and television sets. The metal's tolerance to intense heat also makes it ideal for thermocouples and electrical contacts in electric arc furnaces and welding equipment. Applications that require a concentrated mass, or weight, such as counterweights, fishing sinkers and darts often use tungsten because of its density.




 

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