When applying tungsten carbide cutting tools in natural wood cutting processes, a fast increase in power consumption and surface roughness is indicated.



Specially if the natural wood is wet Western Red Cedar, within 15 minutes, the tungsten carbide cutting tools blunt would occur. The tests of the reactivity of cobalt and tungsten carbide in solutions of Western Red Cedar extractives at temperatures of 20°C and 60°C showed that the cobalt binder is preferentially attacked while the carbide grains remained relatively unaffected since they retained their sharp edges. The corrosive nature was found to be temperature dependent where the metals lost 35% more weight at 60°C than at 20°C. This indicates that the increase in temperature accelerated the dissolution process and may control the rate of chelation. Both worn and unworn tool inserts were investigated and the unworn carbide inserts showed very little dissolution of the carbides, while the worn inserts showed a higher amount of carbide dissolution. This indicates that lattice damage due to wear facilitates chemical access resulting in higher wear rates. They further proposed that carbide grains are held in position by the cobalt and when this cobalt is removed then the carbide grains either fall out or are removed.

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The intense contact will be generated between tungsten carbide woodcutting tool and wood, during the wood cutting processes, and the high temperature and stresses are also involves. As hardness, toughness and chemical stability would change with increasing temperature, cutting temperature is a vital factor.



Many previous experimental investigations has been set up to discuss the problem of determining tungsten carbide tools’ cutting temperature and how to theoretically to calculate it. It is likely that the accuracy of the calculation depends on the assumptions made concerning boundary conditions and the proportion of the cutting energy which is converted into heat at the tool/wood interface. The cutting tool temperature is dependent on factors such as speed, feed rate, depth of cut and wood type, with speed being the most important.

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Crystalline tungsten powder have the characteristics of high purity,coarse particle size,good mobility and low oxygen content, which is the material of diamond. For satisfy the need of foreign, we develop crystalline tungsten powder all by ourselves according to international standard.  

The main material to produce crystalline tungsten powder is blue tungsten oxide. Blue tungsten oxide was adopted in the experiment. Hydrogen reduction in molybdenum wire furnace was going on after mixing the ingredients. And then get the tungsten powder ball milling, with quantitative solution washed, which finally drying, sieving, batching. So we get what we want eventually.

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Although superfine tungsten powder has universally used in a variety of important functional and constructional materials which acts as a kind of principal raw material, that most of the tungsten powders prepared by conventional processes are the precursory composited oxides powders which should be reduced under hydrogen atmosphere before using for preparing the superfine composites or composited materials.

As a result, in the presented paper, the reduction process and mechanism of tungsten oxide and the characteristics of the reduced powder in different conditions are summarized, the effect on properties of the reduced powder prepared with different raw materials are overviewed, and the effect factors of powder grain sizes and the distributional uniformity during H2-reduction process are discussed in detail.

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Take advantage of the characteristics of tungsten powder, we often get it coated by metals for the new characteristics we want.

The tungsten powder coated by copper could be prepared by chemical plating with selfmade equipments. The microstructure and component of coating powder was recorded by the scanning electronic microscopy and x-ray diffraction instrument. It is shown that chemical plating method can be used to prepare the copper coated tungsten powder, and the coating is uniform as well as the thickness achieves 0.45 μm. The optimum technological parameters of chemical plating on the tungsten powder surface are that copper sulfate is 20 g/L, sodium potassium tart rate is 13.6 g/L, dis-odium ethylene diamine tetra acetate is 27.3 g/L, formaldehyde is 15 ml/L, pH value equals 12,temperature is 60 ℃,and the grain size of tungsten powder is 10 μm.

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Nanosized tungsten powder with a particle size of 60 nm was used as raw material, which was prepared by catalysis-gel process. By means of compacting with a steel die, the green compact was sintered in hydrogen so as to look into its shrinkage kinetic curve. By these methods the changes of grain size and relative density during sintering at different temperatures and different sintering time were tested. Now we could clearly see that the compact of nanosized tungsten powder begins to shrink at the temperature of 200 ℃ and stops shrinking at 1 300 ℃.And we can also se that  the highest shrinkage rate comes out  at 1 225 ℃. From 1 000 ℃ to 1 200 ℃, the relative density increases by 24%. After sintered at 1 200 ℃ for 120 min, the average grain size is 5 μm, and the relative density is 95% at the same time.

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In addition the blue tungsten oxide form affects tungsten powder particle size the process parameters also affect the size of tungsten powder. Influence of Process Parameters on the tungsten powder particle size is mainly hydrogen mode, heating systems and hydrogen influence humidity. There has two kinds of hydrogen mode one is cis hydrogen mode and the other is inverse hydrogen, the study found that cis hydrogen mode reduction of tungsten powder particle size is significantly thinner than the inverse hydrogen mode. ATB phase blue tungsten powder at low temperature with cis hydrogen mode can producing tungsten powder particle size thinner, narrow distribution, and the nature the better. In heating system, the researchers found that heating from a low temperature and the heating process more gentle process are good for the producing fine tungsten powder. At the same time hydrogen humidity also impact on the tungsten powder particle size, at the same other process parameters, continuously push the boat and single boat reduction effect is not the same, which is mainly due to different hydrogen humidity. Cis hydrogen mode is good for retrain tungsten powder grow up so producing of fine particles tungsten powder should be used cis hydrogen mode.

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Blue tungsten oxide forms including composition, phase composition, surface area, particle size and oxygen index and so on. Blue tungsten oxide particle size has a significant impact at the tungsten powder reduction on tungsten powder particle size, which the coarse blue tungsten is good for producing fine tungsten powder, because coarse blue tungsten oxide particles in the process of reduction has good permeability can exclusion vapor water which have a greater advantage. To a certain extent, blue tungsten oxide specific surface area also affect tungsten powder particle size having a large specific surface area of ​​blue tungsten oxide in favor of   producing fine tungsten powder. Because the more advanced blue tungsten oxide surface area, the greater its reaction interface, reducing activity, the better. In the study also found the relative composition of blue tungsten oxide will effect tungsten powder particle size this is also can not be ignored. After comparing the different components of blue tungsten oxide along with the effect of hydrogen reduction found that phase component ATB and W20O58 blue tungsten oxide reduction fine tungsten powder better than other blue tungsten oxide which containing more tungsten trioxide. And with ATB basic phase of blue tungsten, reducing effect at low temperatures is good than other blue-phase component of tungsten. ATB Blue Tungsten is hexagonal structure, because this structure is unstable, having a large number of lattice defects, developed specific surface area, with a high reduction activity.

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Blue tungsten oxide forms including composition, phase composition, surface area, fisher particle size, oxygen index and residual volatiles. The calcine temperature and atmosphere of process parameters is the main factors influence blue tungsten oxide forms. Calcine temperature influence bule tungsten oxide specific surface area size. After the different calcine temperature we found that specific surface area also different. It is reported that blue tungsten surface area will decreased with calcine temperature increases. calcine temperature is 400 ℃, blue tungsten oxide surface area will reach 16.31㎡ / g, and when the calcine temperature is to 500 ℃, the specific surface area decreased to 10.07m³ / g. From the study can found in order to make blue tungsten oxide has developed specific surface area, APT calcine temper should at a lower temperature. Although the high calcine temperature help to improve the size distribution of the tungsten oxide particles, and it will lead to the sharp of tungsten powder decrease intense and in products will generate large aggregates. Therefore, the results from this study can be found to make the blue tungsten oxide holding developed specific surface area, APT should calcine at a lower temperature.

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Reduction of tungsten trioxide with hydrogen chemical reaction is: WO3 + 3H2 = W + 3H20. Tungsten has four relatively stable oxides, and the reduction reaction actually is following the sequence which is from tungsten trioxide, blue tungsten oxide, tungsten dioxide to tungsten powder. In the course of these reactions are endothermic reactions, thus raising the reaction temperature conducive to the reaction. In the hydrogen reduction process of tungsten trioxide, tungsten powder particle size usually growing up. Because during the restore process, with the reduction temperature growing high, tungsten trioxide volatility increases, its vapor deposited on the surface of the particles which has been reduced cheap tungsten oxide or tungsten metal powder. If that time tungsten trioxide reduction again, then tungsten powder particles will grow. Study found that tungsten dioxide volatile low than tungsten trioxide, so in the industries they use a two-stage reduction method to take tungsten powder. The first step will use low temperature restore tungsten trioxide. At this step reduction temperature is low so tungsten oxide particles do not grow too much. The second step use tungsten dioxide to making metallic tungsten powder, with higher temperatures. Because at this step particle growth trend compared with the first stage is small. The advantage of using a two-stage reduction of tungsten powder can give a fine, middle size of the tungsten powder, tungsten powder to improve the quality of uniformity. To obtain coarse particles of tungsten powder, it can be used a high-temperature phase reduction method to achieve.

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