New Improvement Plan for Spherical Tungsten Carbide Powder

Spherical tungsten carbide powder is an important raw material for thermal spraying. Some scholars have proposed an improved method for the manufacture of spherical tungsten powder:

(1) Establish stable operation of argon plasma torch: Input argon gas flow of main working gas to the plasma reactor at 0.5MPa, 0.6MPa or 0.8MPa. The hydrogen input pressure of the auxiliary working gas is 0.5MPa, 0.6MPa or 0.8MPa. The induction coil is loaded to a certain power, and the power can be 20 KW, 30 KW or 50 KW. At the same time, the igniter discharges, the high voltage coil inductively couples and the igniter corona triggers, so that the argon ionization produces an argon plasma torch. At this time, the entire plasma reactor is maintained in a negative pressure state to ensure stable operation of the plasma torch.

(2) The tungsten carbide powder (raw powder) was injected into the high temperature zone of the core of the argon plasma torch with nitrogen gas to heat. The heating time ends with the gas powder "flying away" from the plasma torch and lasts for only 140 to 170 milliseconds. The cast tungsten carbide powder is fed into the high temperature zone of the core of the plasma torch and absorbs a lot of heat. The pellet surface begins to melt. When the weight of the pellet is 50% (at least) melted, the spherical shape is high due to surface tension.

(3) The heated molten tungsten carbide powder droplets are cooled and solidified to form spherical tungsten carbide powder. Under the action of four heating mechanisms: radiation, convection, conduction, and chemistry, they are rapidly heated and melted. When the particles are melted to at least 50%, the melted particles form droplets of very high sphericity under surface tension and rapidly cool at very high temperature gradients (10‐6 K/m) into the heat exchange chamber. Cold solidifies to form spherical particles. This spheroidizing process can achieve a spheroidization rate of nearly 100% as long as the process parameters are set appropriately.

(4) The gas is removed and a spherical tungsten carbide powder is collected. After the spheronization process is completed, the gas is extracted, treated and discharged, and the spheronized powder enters the collection tank and is automatically collected.

In the entire spheroidization method, it is important to adjust and set the argon plasma parameters. The small differences in raw material powder properties, such as the particle size of the powder particles, can have very different process parameters. In general, this scheme has the advantages of low cost, stable quality, and easy scale-up compared to the spherical tungsten powder preparation abroad.
 

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