Manufacturer's quality inspection department must inspect tungsten contacts and fill quality certificate to ensure that products conform to relevant standards.

Customers can test received tungsten contacts, if the test results does not conform to the mark of label, you can raise this problem to the manufacturer within three months, and after the two sides of mutual identification, if these tungsten contacts still not meet the requirements, the products failed.

Each batch of product sample in accordance with the following provisions:
The sample testing of the hardness, purity and the number of crystals of tungsten: Customers can directly make the sample preparation to measure tungsten contacts; or extracting a batch of products from the tungsten rods and sampling at its ¼. If the results fail, then double sampling retest. If there is still a failure, then the product failed.

In accordance with the provisions of GB / T 2828, check the size of the tungsten contacts, weld strength, appearance and the roughness of contact surface of tungsten contacts.
Specific check and accept programs can agree by manufacturers and customers.


 

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In the turning operation, coatings on the tungsten carbide inserts have been approved to make efforts in  cutting forces reduction and extending the tool life to provide greater productivity. It should be noticed that, if these coating architectures could be well accepted, the tungsten carbide inserts are likely to make some significant cost reductions in this area, and to enable higher turning speeds and lower frictional losses during machining.

However, due to the technology limitation and inherent coating processes shortcomings, it still difficult to balance all the factors and which results, so far no single layer, multi-layer or multicomponent coating has been developed yet to meet satisfactorily meet all these requirements.


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In actual practice, when employing coated tungsten carbide inserts on turning operations, there are several typical factors are likely to be involved, such as huge strains, high interface temperature, and newly generated chemically reactive surface. Specially, the interface temperature between tool and chip or tool and workpiece could be leveled up to 700-1250 ℃ and in the cutting zone the energy consumption due to the frictional losses varied from 25-35%.



In order to withstand such harsh condition, an ideal coating architecture of tungsten carbide inserts is required to meet high wear resistance, outstanding chemical stability, hot hardness, low friction and excellent adhesion to the substrate, as well as compressive residual stresses.


Tungsten Carbide Manufacturer & Supplier: Chinatungsten Online - http://www.tungsten-carbide.com.cn
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During the machining operations , the chemical vapour deposition (CVD) coatings as a traditional way have been widely applied in tungsten carbide inserts to enhance the tool life. Only in USA and Europe, there are over 60% of the cutting tools are applied by the CVD process.

However, the CVD coatings due to inherent disadvantages, have been examined several limitations which include the relative higher deposition temperature (950~1050℃） compared to other coating method, tensile stresses increasing between layers,  inability to achieve thin coating layers as well as multicomponent coating layers, and due to the brittle formation, sometimes the adhesion of coating to the substrate is poor.
 

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It is known that since the using hard coating on tungsten carbide cutting tools, some huge improvements in productivity of machining operations have been achieved. The physical vapour deposition (PVD) method, which has several advantages over the chemical vapour deposition, has been employed for coatings like TiN, TiCN on tungsten carbide cutting tools.

The inherent advantages of PVD coatings over CVD ones have been revealed as the improvement of wear resistance of tungsten carbide cutting tools and the better performance in machining operations. In addition, since the coatings deposited by the PVD process, its film growth occurs at the atomic level, single or multiple thin layers of single or multicomponent structures could be employed on the tungsten carbide cutting tools, by using different reactive atmospheres and cathode materials.


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After studies we found the difference between vanadium dioxide (VO₂) films and tungsten-doped vanadium oxide films. Which are tungsten-doped vanadium oxide films has low phase transition temperature. But comparing XRD atlas of tungsten-doped vanadium oxide films which use microwave plasma with doping nitrogen to producing and VO2 found there has little different between both. Mainly tungsten doping is small and V^{4 +} and W^{4 +} ionic radius is very close. On the other hand VO₂ by nitrogen doping can effectively reduce the phase transition temperature, when certain tungsten content, the phase transition temperature of the sample is the incorporation of the role of nitrogen. With the reduction of plasma reaction enhanced and doping nitrogen flow change, and the great changes of phase transition temperature indicating that nitrogen ions have been incorporated into the crystal lattice of V_0.98W_0.02O₂-XNY undermine the VO₂ The stability of the semiconductor, so that the phase transition temperature changes. The experiment found that when H₂ flow of 10ml / min, N₂ was 10ml / min, the reaction of the total power of 1kPa, the reaction time was 10min, the resulting thin film phase transition temperature can be reduced to 35 ℃.

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Firstly, the analysis of vanadium dioxide (VO₂) XRD and the phase transition temperature. After analysis XRD patterns found VO₂ film crystallinity is not high and smaller particle size. According to the nature of VO₂ which is when the phase changing will cause sudden change of resistivity found vanadium dioxide film will cause phase changing in temperature about 62 ℃.And the resistance change in this process very largely which showed significant calorific value phase change performance, compared to the powder, the phase transition temperature is reduced by about 6 ℃. After many researches the scholars find using microwave plasma method with doping nitrogen to produce tungsten-doped vanadium oxide films has good performance which compare to VO₂ film. On one hand, tungsten-doped vanadium oxide films have low phase transition temperature. On the other hand doping also will reduce the phase transition temperature .so doping nitrogen will good for tungsten-doped vanadium oxide films performance. But analysis the XRD found litter different with VO₂. 

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Mark of tungsten contacts
Each batch of tungsten contacts must be identified and marked:
The type of tungsten contacts and the number of the standard;
Specifications;
Production batch;
Quality;
Production Date;
With manufacturers and related inspection department mark.

Package of tungsten contacts
Firstly packaging tungsten contacts with plastic bags, and then putting them in plastic boxes or metal boxes.
Tungsten contacts with the same batch number, size and type mount on the same box.

Transport of tungsten contacts
Boxes used to hold tungsten contacts need to reinforce and in which put the moisture-proof of paper.
Tungsten contacts in transit should prevent violent impact, corrosion, and must not expose them in acid rain and snow.

Storage of tungsten contacts
Tungsten contacts storage location should be dry and free of acid, alkali and other corrosive gases.

 

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Ammonium tungstate is also called ammonium wolframate, its molecular formula is (NH4)6W7O24·6H2O. It is colorless trapezius crystal which is soluble in water and insoluble in alcohol. Under 100℃ it loses four molecular crystal water. Ammonium tungstate can be used as the raw material for ammonium phosphotungstate and other tungstate compound. It can also be applied in producing metallic tungsten and catalyst.

Ammonium paratungstate is a white crystalline salt of ammonium and tungsten, it is insoluble in water. Its shape is like sheet or needle. Ammonium paratungstate is used as a source for high-purity tungsten oxides, tungsten metal powders, carbides, or as a laboratory reagent. Also used in the manufacture ammonium metatungstate and other tungsten compounds as additives for the petrochemical industry.

Ammonium metatungstate is a tungsten chemical in the form of highly soluble hydrated crystals, solubility is 303.99/loogH:O when 20℃. It is white or slightly yellow crystals which has no harmful components and slightly acidic. Ammonium metatungstate is very versatile and can be used as catalysts, capacitors, nuclear shielding, flame retardants, corrosion inhibitors raw materials, but also excellent raw materials in the preparation of ultra fine tungsten powder, tungsten heavy alloy powder, phosphotungstic acid, arsenic acid, silicon tungstate.



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The structure and morphology of ammonium metatungstate (AMT), (NH4)6[H2W12O40]⋅4H2O, and its thermal decomposition in air and nitrogen atmospheres were investigated by SEM, FTIR, XRD, and TG/DTA-MS.

The thermal decomposition of ammonium metatungstate involved several steps in inert atmosphere: (i) release of crystal water between 25 and 200 °C resulting in dehydrated ammonium metatungstate; (ii) formation of an amorphous phase between 200 and 380 °C, (iii) from which hexagonal WO3 formed between 380 and 500 °C, and (iv) which then transformed into the more stable m-WO3 between 500 and 600 °C. As a difference in air, the as-formed NH3 ignited with an exothermic heat effect, and nitrous oxides formed as combustion products. The thermal behavior of ammonium metatungstate was similar to ammonium paratungstate (APT), (NH4)10[H2W12O42]⋅4H2O, the only main difference being the lack of dry NH3 evolution between 170 and 240 °C in the case of AMT.



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