The following will tell something about specification for tungsten and oxide dispersed tungsten electrodes for arc welding and cutting rounding-off procedure.

For purposes of determining compliance with the requirements of this Standard, the actual test values obtained shall be subjected to the rounding-off rules of ISO 31-0:1992, Annex B, Rule A or ASTM E 29. If the measured values are obtained by equipment calibrated in units other than those of this Standard, the measured values shall be converted to the units of this Standard before rounding off. If an average value is to be compared to the requirements of this Standard, rounding-off shall be done only after calculating the average. In the case where the testing standard cited in the normative references of this Standard contains instructions for rounding off that conflict with the instructions of this Standard, the rounding-off requirements of the testing standard shall apply. The rounded-off results shall fulfill the requirements of the appropriate table for the classification under test.



 

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1. Electrode diameters, lengths and tolerances

Standard electrode diameters, lengths and tolerance are given in Table 1. Other diameters, lengths, and tolerances may be as agreed on between the supplier and the purchaser.

2. Electrode roundness

Electrode shall fit through ring gages sized for their maximum allowable diameter in accordance with Table 1.

3. Finish

Tungsten electrodes shall be supplied with a ground finish. The ground finish designates that the electrodes have been cleaned of impurities after they have been center-less ground to a uniform size. It shall be supplied with a bright, polished surface. The maximum surface roughness shall be 0.8 μm Ra[32 μmin AARH].

4. Electrode straightness

The electrodes shall be straight such that any element of its surface, over a specified length, must lie between two parallel lines of a specified spacing where the two lines and the nominal axis of the electrode of the electrode share a common plane. The specified spacing is 0.5mm[0.020 in] over a length of 100mm[4 in].



 

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In accordance with the following table, tungsten electrodes shall be marked on the basis of their chemical composition, with one color ring near one end of the electrode. The width of the color ring shall be at least 3mm [1/8 in]. Such color coding shall have no adverse effect on the operation or use of the electrode. Alternatively, tungsten electrodes may have their classification symbols marked on the surface of the electrode near at least one end of the electrode.

The ‘Chemical composition requirements for tungsten electrodes’ table is shown as bellow




 

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Domestic heavy fuel always has high viscosity, high colloid, it will directly affect the combustion performance, such as decreases the quality of fuel atomization, leads to incomplete combustion of harmful gases contained in the flue gas increases and so on. In order to improve the quality of atomization and the combustion efficiency, some researchers consider energy conservation as their main goal. For the nozzle, to obtain droplets as fine as possible in the coverage of requirements is beneficial for accelerating the combustion. With the rapid development of science and technology, more suitable for fuel atomization technology, ultrasonic atomizing nozzles appeared. Ultrasonic atomization technology has smaller particle size (typically less than 100μm), the uniformity of the droplet is also excellent (N value is usually greater than 2, compared with ordinary burner N value 1.1-1.7).

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Recently, so many successes of high performance ceramics research provide new thinking for new nozzle developing. The new high-performance ceramic mostly apply submicron and nano powders, whiskers, fibers, chips, so that the grains and grain boundaries in combination between them have reached the nanometer level, and can be sintered at a lower temperature to achieve high density and high strength. In terms of sintering temperature, the products has lower 400 ° C sintering temperature than coarse-grained material and can withstand bending deformation without cracks at 180℃ sintering temperature.

In addition, some easy solution, immiscible components on the nanoscale composite can form a new composite material, which can improve the performance of hardness, toughness and wear resistance and other properties to a certain extent. When these techniques are widely in grinding compound nozzle, it will make a progress in jet flow nozzle and get a new breakthrough.

















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At present, there are two coating materials have bright prospects in application. One is artificial diamond PCD coating, which American scientists invent a method for producing nano-diamond immediately under 1.01×10Pa and decreases the production cost of traditional diamond coating. The other is cubic boron carbide CBN coating, its hardness only lower than diamond, which has similar structure with diamond and hardness reach 60Gpa.

Owing to the unique structure and high coherent of nonmaterial, shows a variety of features such as surface effect, size effect, super plasticity and so on. Although tungsten carbide and ceramics have great hardness and toughness, they are all belonging to brittle materials. Especially ceramic materials have been hampered in application because of its own high brittleness.
















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Among these kinds of new technology, surface coating is the most direct, which applies a harder layer on basis for enhancing the anti-abrasion and erosion wear. So the mechanical property will be improved and reduce the abrasion. Apply surface coating to nozzle process, which is unfamiliar in domestic, but it had some applications abroad already. After coating, the roughness of internal surface of the nozzle is remarkably decreasing, which improves the precision and extends the lifespan. For instance, coating on the substrate of tungsten carbide or pottery by 10-30mm diamond film will make the material physical and chemical properties are close to the natural diamond. And improve the lifespan up to 3-10 times compared to un-coating material.



















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Although most of the world wide production of tungsten comes from the mineral wolframite, Scheelite is especially abundant in the US and provides the United States with most of its supply. The word "Tungsten" was probably first used by A. F. Cronstedt in 1755, who applied it to the mineral subsequently known as "Scheelite," which is the natural form of calcium tungstate.

C. C. Leonhard named this mineral Scheelite in 1821 in recognition of the discovery made by K. W. Scheele, in 1781. He believed that the mineral was a compound of lime and a previously unknown acid, which he called "Tungstic Acid. Tungsten was first isolated from tungstic aci in 1783 by the de Elhuyar brothers. Before Scheele made his discovery, the mineral was generally regarded as containing tin.

The word tungsten denotes a substance of high density and is derived from the Swedish language, "tung," meaning heavy, and "sten," meaning stone. The metal is known as tungsten in some countries and as wolfram in others, including Sweden, the country of origin of the name tungsten. The chemical symbol W, which is universally used to denote tungsten, suggests that wolfram was formerly the more generally accepted name for the element. In Britain the mineral wolframite is also known as wolfram.



 

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The element is resistant to ordinary acids and aqua regia but dissolves in a mixture of hydrofluoric and nitric acids. It forms compounds with carbon, chlorine, oxygen, sulfur, and some other elements. It forms tungstic acid (H2WO4), or wolframic acid, which is the basis of a series of salts called tungstates, or wolframates.

Tungsten metal is used extensively for filaments for light bulbs and electronic tubes. Carboloy, stellite, and tungsten steels are of importance in industry because they retain their hardness and strength at high temperatures. Tungsten is usually added to steel in the form of ferrotungsten, obtained by the reduction of ferrous tungstate in an electric furnace.

Tungsten carbide is used in place of diamond for dies and as an abrasive. Sodium wolframate is used in the fireproofing of fabrics, in the weighting of silk, and as a mordant in dyeing. Tungsten does not occur uncombined in nature. Large deposits of its ores are found in various parts of the world. The trioxide occurs in nature as the mineral wolfram ochre. Scheelite and wolframite are the chief wolframate minerals. Tungsten is usually prepared from the trioxide by reduction with hydrogen or carbon.



 

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Uses of Scheelite:

Scheelite is an important source of tungsten,which is a strategically important metal. Scheelite is rarely cut as gemstones. But it is considered as a rare mineral specimen by collectors and good specimens can command very high prices.

Since Scheelite is a primary ore of tungsten we will add some information about tungsten. Tungsten is a very hard, silver-white to steel-gray metal with a body-centered cubic crystalline structure. In its chemical properties it resembles molybdenum.

It is sometimes called wolfram, and it's chemical symbol "W" is taken from this name. When naming compounds of tungsten, use of the name wolfram as a root is preferred. Tungsten is one of the most dense metals and has a higher melting point than any other metal. It melts at about 3,410 deg C and boils around 5,660 deg C. Pure tungsten is ductile, and wires made of it, even those of very small diameter, have a very high tensile strength. 



 

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