Appearance and size requirements of tungsten contacts in cut-out:
The appearance of tungsten contacts should look smooth, there are without the existence of burr, rust, discoloration, cold solder joint and other defects; Moreover, its electrodeposition must not have leak plating layer, peeling, de-plating and other issues.
Welds should be uniform. The thickness of the weld is thinner than a quarter of the thickness of tungsten sheet.

Contact surface of tungsten contacts do not exist depressions or remaining machining marks, its roughness Ra is less than 0.4μm.
The size requirements of tungsten contacts should be according to customer-supplied drawings, and specifications, or the dimension agreed by customer and supplier.

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Technical requirements of tungsten contacts in cut-out:

Brazing material purity: ≥99.9%;

Weld seam strength of tungsten contacts : ≥78.45MPa;

Tungsten contacts are composed of the sit nails, tungsten sheet, and the solder, which are welding and manufacturing in the condition of hydrogen and nitrogen gas;

Tungsten sheet material must be according to JB / T9860.2 standards and its inspection of products is up to the aforementioned standard, its main technical parameters are as follows:

Purity: ≥99.95%;

Hardness: ≥70HRA;

Crystal grain number: 7500-25000 points / mm²;

Sit nail material is low carbon steel, whose carbon content is about 0.15% -0.20%, can also adopt other materials which own similar performance and composition and can be easily used for caulking.

 

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The following standards contain provisions in this standard by reference in the provisions of this standard.

Reference standard of tungsten contacts in cut-out:

Chemical analysis of tungsten ------ GB / T 4324.1-4324.30 --- 1984

Metallic Vickers hardness test method------ GB / T 4340 --- 1984

Metallic Rockwell hardness test method------ GB / T 230 --- 1991

Cut-out in Magneto test method------ JB / T 9864.2 --- 1999

Tungsten rod in cut-out contacts technical conditions ------ JB / T 9860.2 --- 1999

Sintered bar, rod crystal grain size of tungsten, molybdenum and alloys test method ------ GB / T 4197 --- 1984

Batch inspection Sampling procedures and sample forms (for continuous batch of checks) ------ GB / T 2828 --- 1987

 

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The thermal decomposition of ammonium paratungstate tetrahydrate (APT·4H₂O), (NH₄)₁₀[H₂W₁₂O₄₂]·4H₂O, in air to tungsten trioxide, WO₃, was investigated under non-isothermal conditions using thermal analysis coupled on-line by a skimmer system to a quadrupole mass spectrometer (TA-MS) for evolved gas analysis (EGA), with X-ray powder diffraction (XRD), with Fourier transform infrared (FT-IR) and raman spectroscopy.

The decomposition is characterized by three endothermic and one exothermic step. The first endothermic step comprises the release of crystal water resulting in the formation of crystal-water-free ammonium paratungstate. During the second endothermic step ammonia is released leaving behind ammonium hydrogen paratungstate, (NH₄)₆H₄[H₂W₁₂O₄₂. The presence of protons in the “roasted” APT was supported by ex situ and in situ FT-IR spectroscopy (vibration bands at 1100 and 2160 cm⁻¹). Ammonium hydrogen paratungstate is the precursor for the metatungstate anion, [H₂W₁₂O₄₀]⁶⁻, which is formed during the digestion of “roasted” APT with hot water.


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Ammonium metatungstate producing method includes neutralization method, tungstic acid method, thermal decomposition method, solvent extraction method and ion exchange method.

Neutralization method uses secondary ammonium metatungstate and nitrate as the raw material to produce metatungstate.

Tungstic acid method using ammonia tungstate tungstic acid dissolved, add a boil deionized water in the stirring, heating by ammonia, Ph=8, in the boiling solution by adding acetic acid.

Thermal decomposition method combines ammonium paratungstate and a small amount of citric acid catalyst after mixing into the far infrared, rotary furnace, controlled thermal decomposition temperature 200 ～ 280 ℃, decomposition of about 1 h.

Solvent extraction using ammonium tungstate solution and organic extractant phosphoric acid: two (2- ethylhexyl) ester (D2EHPA) or phosphoric acid butyl ester three (TBP) and kerosene solvent to form organic phase, extract ammonium ion from ammonium tungstate solution.

Ion exchange method uses ammonium paratungstate as raw material, heating ammonium paratungstate from 1 to 8 h at 130 ~ 140 ℃, the resultant tune into a paste, to 80 ~ 100 ℃ boiling for 2 ~ 6 h, generates ammonium metatungstate solution. And then obtain the product through concentrating crystallization, filtration and drying.


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Ammonium paratungstate producing method includes evaporation crystal method, neutralization crystal method and lyophilization crystal method.

Evaporation crystal method is the most widely applied in industry. Reduction evaporation is common used in the producing process. Vacuum pressure is maintained around 40kpa, evaporation temperature is between 353-363k, producing the strip of crystallization and the component of which is 5(NH4)2O•12WO3•5H2O3.

Neutralization crystal method neutralizes hydrochloric acid with concentration of 10%-20% and ammonium tungstate solution to ph value 7. If neutralizing acid under temperature 363-368k, after an hour ammonium paratungstate is produced by crystallization. If adding acid under room temperature, the solution needs to be stewing for 8-12 hours, sometimes even 24 hours, the finished ammonium paratungstate is of shape like needle and the component of which is 5(NH4)2O•12WO3•11H2O.

Lyophilization crystal method freezes ammonium tungstate solution first and heat it under vacuum low pressure environment which can obtain polyporous and drying ammonium paratungstate.


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Using a coupling process of neutralization–nanofiltration–crystallization, pure ammonium metatungstate (AMT) was prepared. The effects of chemical neutralization of ammonium paratungstate (APT) by nitric acid, operating pressure, AMT concentration, the volume of washing water on the coupling process were systematically discussed.

It was found that the better conditions of AMT preparation were as follows: the neutralization temperature was 80–95 °C, pH value was 2.0–3.5; the operating pressure of HDS-12-2, nanofiltration was 1.5–2.0 MPa, the density of AMT crystallization solution was 2.39 kg/L, and then cooling. APT conversion efficiency (δ) to AMT was more than 97.62%. The removal ratio of nitrate ion (NO₃⁻) was more than 99% while AMT rejection (R_AMT) was 99.9%. Besides, small-grained, even-proportioned, white-colored and high-purified AMT crystal was be obtained and analyzed. This method has several advantages such as simple technological process, short production cycle, lower environmental pollution and high quality.


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Several techniques have been used to study the structure of the Keggin-type polyoxometalate salt ammonium metatungstate (AMT)—(NH₄)₆[H₂W₁₂O₄₀]*nH₂O, a potential fuel cell catalyst. The dehydrated salt is comprised of a mixture of crystallites of different unit cells in a centered eutactic cubic configuration. Varied orientations of the Keggin ions in the cubic arrangement create the differences, and orientational variation within each unit cell size represents an energy well. Progressive hydration of each crystallite leads to expansion of the lattice, with the degree of expansion depending on the locations of the water added in relation to the Keggin ion, which is influenced by cation location and hydrogen bonding. The structural hypothesis is supported by electron diffraction of single and multicrystal samples, by powder density measurements, X-ray powder diffraction studies, synchrotron powder X-ray diffraction, anda priori structural modeling studies. Based on the structure, projected active site densities are compared with nanostructured platinum catalysts for fuel cell application.

The structure of ammonium metatungstate powders are highly dependent on hydration and POM molecule rotation, with cation and hydrogen bonding forces directing a mixture of structures that have been studied with bulk and single-crystal methods. The illustration shows Monte Carlo simulated anion structural disorder for the fully dehydrated form of the title compound.


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Installation method of tungsten contacts in automotive relay described below:

To maximize the performance of the automotive relay, the mounting direction should be consistent with the impact resistance direction of the automotive relay. That is, in order to effectively improve the anti-shock and impact resistance performance of the normally closed tungsten contacts in the non-energized state, impact direction should be perpendicular to the direction of movement of the armature and the tungsten contacts.

When it is installed, in order to improve contact reliability, the axial of tungsten contacts of automotive relay should parallel to the ground, to avoid spatter tungsten contacts, tungsten carbide falling on tungsten contacts surfaces.

If installing multiple sets of automotive relay, you should avoid large load tungsten contacts on the top of small load tungsten contacts.

If install large volume of relays, in order to prevent the mounting feet will damage in the condition of shock and vibration, you can choose housing mounting method.


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Working principle of tungsten contacts in automotive relay:
Automotive relay can be thought of as been made up of main circuit which tungsten contacts are working and the control circuit which the coil works. In the relay control circuit, it can only be controlled by tungsten contacts, in order to control its on-off, because the capacity of tungsten contacts  which is used for controlling switch are smaller, therefore, the operating current is small, and it can not be used to directly control the larger load on the power consumption.

Coupled with a certain current or voltage at both ends of the coil of electromagnetic relay, magnetic flux will generate by the coil through the magnetic circuit (its compositions are the armature, yoke, core, working air gap magnetic circuit).

Under the influence of a magnetic field, armature will be attracted to the pole face of the core, thus promoting the normally open tungsten contacts are closed, and normally closed tungsten contacts open;

When the voltage or current across the coil is less than a certain value, the electromagnetic attraction is less than mechanical counterforce, the armature will return to its initial state, normally open tungsten contacts will disconnect, and normally closed tungsten contacts will connect.


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