Tungsten carbide tools wear process is divided into early wear, normal wear and severe wear of three phases.

1. Wear the early stages
Tungsten carbide cutting tools and the workpiece during the fourth year, as the new tools sharpening surface roughness and micro-cracks, defects such as oxidation or decarbonization layer, so that the actual contact area is small, the contact point bonding serious, so the tools wear faster. As the cutting proceeds, the tools surface micro peak peak gradually rubbed off, the surface roughness values decrease, the actual contact area increases, increased number of contact points, so tungsten carbide tools wear rate decreased. Coated tungsten carbide cutting tools at low speed, the wear more evenly. When the speed increases, the wear and tear is beginning to show a parabolic band.

2. Normal wear stage
After the initial worn, rough surfaces and polished tungsten carbide cutting tools gradually phase into the normal wear and tear. This stage is relatively slow uniform wear, with the growth of the amount of wear and the cutting time is approximately proportional to the increase. This stage is the stage of effective working tool. When the tools wear stage into the normal wear and tear, wear, Deputy Regional flank wear was uniform phenomenon. Especially coated tungsten carbide cutting tools, wear range presents a uniform wear strip. Compared with uncoated tungsten carbide cutting tools, wear it more slowly into the normal wear stage.

3. Severe wear stage
When the amount of wear tungsten carbide cutting force reaches a certain value will increase sharply, cutting temperature rises rapidly, the flank wear values will increase significantly decreased mechanical efficiency, precision loss, abnormal vibration and noise, the final result cutting tools fall, resulting in the loss of tungsten carbide cutting ability.

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Swaged rods final diameter of about 3 mm. Available swaging draw blank drawing production, but also the production of usable rolling method; rolling billet production pass deformation large, relatively homogeneous, in favor of subsequent processing. Drawn tungsten tungsten blanks with "warm brushed" method. First, pull on the chain stretching machine to a diameter of 1.3 mm, respectively, and then pull through coarse, medium and fine pull pull so diameter of less than 0.06 mm 0.2,0.06.

With the reduced diameter, so that the heating temperature should drop, drawing speed. Pass deformation is generally between 10 to 20%. Drawing coal gas - air mixture is heated at a temperature of 900 ~ 400 ℃. Pull thick wire with carbide dies, diamond mold is used to pull the filaments. Mold material, pass, grinding technology has a great influence on the quality of the wire, graphite lubricant quality, particle size, proportion, coating methods also affect the quality of the wire. Inhomogeneity wire diameter is one of the most important reason of broken wires when used, there are 0.2 to 0.4 micron deviation will cause a vacuum in the tungsten filament life is greatly reduced.

Diameter filament material can be used gravimetric method or vacuum measurement standard current law. In the drawing process, as the diameter decreases, the deformation resistance is increased (e.g., fracture strength tungsten wire diameter of 0.1 to 0.3 mm can be up to 350 kgf / mm 2), the plastic is reduced accordingly. In order to further improve the processing performance, generally eliminate the need for intermediate stress annealing. In addition, the electrolytic etching can be processed into a wire filament diameter of less than 0.01 mm.

Plate Rolling

Tungsten can be divided into hot-rolled plate rolling, warm rolling and cold rolling. Due to the large deformation resistance of tungsten, ordinary rolls not fully meet the requirements of the tungsten plate rolling, you should use special materials roll. When rolling, the roll is preheated, depending on rolling conditions, preheating temperature of 100 ~ 350 ℃.




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 Process for the continuous preparation of ammonium paratungstate hydrate directly in the reextraction of a tungsten-laden organic phase with an ammonia-containing aqueous solution in a mixer-settler apparatus, which comprises carrying out the reextraction at an NH3:W molar ratio of from 0.83 to 1.30, and a volume feed ratio of the tungsten-laden organic phase to the ammonia-containing aqueous solution of from 5 to 25 wherein the reextraction in the mixer is carried out so that a solids concentration of the ammonium paratungstate hydrate, based on the ammonia-containing aqueous phase in the mixer, of from 100 to 1200 g/l, is established and wherein the tungsten-laden organic phase and the ammonia-containing aqueous solution are introduced into a stirrer region of the mixer and in that that a three-phase mixture is formed and is taken off both from the upper region, via a free overflow, and from the stirrer region, of the mixer, so that a stationary ratio of tungsten-laden organic phase (OP) and ammonia-containing aqueous solution (AP) in a phase ratio (OP:AP) in the range from 1:5 to 1:70 is established in the mixer.

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Ammonium paratungstate is normally prepared by any one of several well known techniques. One technique involves the dissolution of tungstic acid in ammonium hydroxide to produce ammonium tungstate followed by filtration and evaporation to crystallize ammonium paratungstate. Another technique involves addition of ammonium chloride to sodium tungstate solution to precipitate ammonium paratungstate and leave sodium chloride in solution. Still another technique involves the extraction of a metatungstate species with an organic extracting agent followed by stripping with ammonium hydroxide to produce ammonium tungstate which is evaporated to produce ammonium paratungstate crystals. Another technique involves addition of ammonium hydroxide to ammonium metatungstate solution to precipitate ammonium paratungstate crystals.

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Cobalt doped ammonium paratungstate (Co-doped APT) precursors for the fabrication of cemented carbides were synthesized by co-precipitation, where W and Co are mixed on the atomic scale. The effect of cobalt content on the reduction of W–Co precursor was studied. W–Co precursors with different ratios of tungsten to cobalt were prepared and calcined at 220 °C for 5 h in air, followed by a reduction in hydrogen gas at 600 and 650 °C for different times. The resulting powders were characterized with respect to phase constituent, specific surface area, particle size, density, and morphology of the reduced powders. It has been found that the addition of cobalt results in a higher reduction rate toward the metallic phases. However, the particle size of the reduced powders increases with increasing cobalt content, while its relative density decreases. The specific surface area of reduced powders at 650 °C increases for short reduction times, due to reduction of oxides to metal powder, and decreases for long reduction time due to agglomeration of metal powder. Cobalt plays the role as a catalyst during the reduction processing. On the other hand, it promotes the agglomeration of small particles. However, the completely reduced powders were well nanostructured with an average particle size between 20–50 nm.

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Ammonium paratungstate hydrates (hereinafter referred to as APTs) are known intermediates for producing tungsten metal, tungsten-containing catalysts or hard materials based on tungsten, for example tungsten carbides.

A process for the continuous preparation of ammonium paratungstate hydrate directly in the reextraction of a tungsten-laden organic phase with an ammonia-containing aqueous solution in a mixer-settler apparatus, which comprises carrying out the reextraction at an NH3:W molar ratio of from 0.83 to 1.30, and a volume feed ratio of the tungsten-laden organic phase to the ammonia-containing aqueous solution of from 5 to 25. Directing ammonium paratungstate decahydrate containing at least 75% of crystals having a length of at least 200 μm and having a ratio of length to width of less than 4.5:1.

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The possibility of mechanochemical decomposition of ammonium paratungstate (APT) has been studied, and compared with thermal decomposition method. For this purpose, APT powders were milled using a planetary ball mill up to 36 h and under air atmosphere. For thermal decomposition, APT powders were heated for 30 minutes at 300 and 450 °C in air atmosphere. X-ray diffraction (XRD), differential scanning calorimeter (DSC), and thermo gravimetric analyzer (TGA) were used to study the decomposition progress, and products. The XRD results showed that APT completely decomposed to WO₃ by thermal decomposition, while the final product of mechanochemical decomposition was WO₃ (H₂O)_0.5. According to DSC and TGA results, during thermal decomposition, ammonia and water released in four steps, and leaved WO₃. By mechanochemical decomposition crystal water and ammonia liberated from APT structure, but structural water of APT remained. In both methods, an X-ray amorphous phase was the intermediate product of APT decomposition.

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Thermal plasma process has been applied to the synthesis of nanosized tungsten carbide powder with ammonium paratungstate (APT) as the precursor. The reduction and carburization of vaporized APT produced nanosized tungsten carbide (WC1−x) powder, which sometimes contained a small amount of W2C phase. The effects of reactant gas composition, plasma torch power, the flow rate of plasma gas, and the addition of secondary plasma gas (H2) on the product composition and particle size were investigated. The produced tungsten carbide (WC1−x) powder was <20 nm in particle size. The synthesized powders were also subjected to a hydrogen heat treatment to fully carburize the WC1−x and W2C phases to the WC phase as well as to remove excess carbon. Finally, WC powder of particle size <100 nm was obtained.

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Violet tungsten oxide was prepared with pure ammonium paratungstate in argon gas. Tungsten powder was obtained from violet tungsten oxide through deoxidation in hydrogen gas (rate of purity: 99.99%, dew point: –40 °C), and tungsten powder was oxidized in the air. Tungsten oxide was reduced to tungsten powder in hydrogen gas. The samples were characterized with the laser particle size distribution measuring instrument and the electron probe scan instrument. The results show that submicron tungsten powder can be obtained through circulatory oxidation twice and reduction three times. The percentage of the particle size distribution of submicron spherical tungsten powder is 95.73% between 0.1 μm and 1.0 μm, and its BET is 1.082 m2/g.

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After decades of development, the hardness of tungsten carbide cutting tools has reached 89 ~ 93HRA, at a high temperature of 1000 ℃ still has good red hardness, durability is several times its high speed steel cutting tools. tungsten carbide cutting tools material is WC, TiC, TaC, NbC, VC and other refractory metal tungsten carbides and prepared by powder metallurgy from iron group metals as a binder. Compared with the high-speed steel, it has high hardness, wear resistance and red hardness; compared with super hard material, it has a higher toughness. Because of tungsten carbide cutting tools has a good overall performance, so in the tools industry has been widely used.

However, under certain circumstances, tungsten carbide cutting tools diffusion wear occurs. Diffusion wear occurs at high temperature effects. tungsten carbide at the time of cutting temperature 800 ~ 900 ℃, W and C atoms will diffuse to chip in, chip in Ti and Al atoms will diffuse into the tool, after mutual displacement between atoms, it will reduce the tools interatomic bonding strength and wear resistance and the formation of diffusion wear. When cutting titanium, due to the high temperature of the cutting area, and the surface is always in contact with each other just cutting out a fresh surface, chip, before the workpiece and tools flank greater chemical activity, so the tools material and titanium tungsten carbide element alloy contact surfaces will spread to the other side to each other, and cause diffusion wear, changing the chemical composition of both the direct impact on its performance.




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