After ball milling, crushing, shaping, and rough purification, the next key step for diamond micropowder is particle size classification. The main goal of this process is to ensure that the particle size distribution is as concentrated as possible and to completely eliminate oversized particles.
Due to the extremely fine particles of diamond micropowder, traditional sieve classification methods cannot achieve precise classification. Therefore, it is especially important to use scientific, efficient, and precise classification methods.
As the applications of diamond micropowder continue to expand and the market’s quality requirements gradually increase, the commonly used classification methods in diamond micropowder companies at present mainly include: natural sedimentation, centrifugal classification, overflow method, and hydraulic cyclone method.
Natural Sedimentation Classification
Diamond particles, under the same specific gravity, have different settling rates in water based on their particle size. The natural sedimentation method uses this principle. It controls the settling height and time to classify particles by size.
Particles in a liquid are influenced by three forces: the gravitational force from the particle’s mass, the buoyant force of the liquid, and the resistance of the medium against the particle. The settling speed depends on several factors. These include the contact area between the particle and the medium, the viscosity of the liquid, and the frictional resistance the particle faces while moving through the medium.
Centrifugal Classification
Centrifugal classification follows the same principle as natural sedimentation, but with a key difference. In centrifugal classification, centrifugal force generated by a centrifuge replaces gravity for classifying diamond micropowder products.
For coarser particles, the mass is larger, and the settling time is short. Natural sedimentation stretches the settling distance of particles with similar sizes. This method is suitable for fine classification of diamond micropowders with similar specifications.
For finer particles, their small mass means they settle very slowly in a gravitational field. Using natural sedimentation would extend the production cycle significantly. It would occupy a lot of classification containers and space. Furthermore, ultrafine particles may not be effectively classified due to Brownian motion and particle interference.
In a centrifugal field, the centripetal acceleration is much higher than gravity. This greatly increases the speed of particle movement and accelerates the classification process.
As a result, many diamond micropowder manufacturers combine natural sedimentation and centrifugal methods. This approach produces a full range of micropowders from fine to coarse. It is efficient and yields high-quality results.
Overflow Classification
The overflow method can be understood as a reverse sedimentation classification method. In an overflow classification container, water enters from the bottom into the lower conical section of the container. As the cross-sectional area of the container gradually increases, the upward velocity of the fluid slows down and eventually stabilizes in the upper cylindrical part.
Diamond particles settle against the rising water flow. When the flow speed stabilizes, particles of a certain size are affected by both gravity and the reverse buoyant force of the water. When these two forces reach equilibrium, the particles remain in a suspended state, neither rising nor sinking.
Very fine particles overflow from the container with the water flow, while coarser particles settle into the lower conical section. As the fluid velocity increases in this part, particles will suspend at different heights based on their size. By adjusting the flow rate, products of the desired particle size can be obtained.
Hydrocyclone Classification
The hydrocyclone method uses the principle of centrifugal sedimentation. It accelerates the separation of coarse and fine particles by the high-speed rotation of the slurry inside the hydrocyclone. This process is widely used in coarse classification and product dehydration in various fields. Its main advantages are fast speed, ease of operation, good repeatability, and continuous feeding capability. It is effective for classifying the full range of diamond micropowders, except for ultrafine particles smaller than 2 microns. However, it also has the disadvantage of lower classification accuracy.
Conclusion
Since each method has its inherent characteristics, practical production can benefit from flexibility. Depending on the specific circumstances, one method can be used for diamond micropowder classification, or two or more methods can be combined for more effective classification.
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