Technical knowledge

Technical knowledge

Nano Color Paste (Ⅲ)

Nano Color Paste (Ⅲ)

  • April 27,2020.

Nano Color Paste ()

-- PUHLER nano grinding technology exchange

Author: LiMeng Lei.

(Germany PUHLER Group, Puhler International Holding Group-PUHLER (Guangdong) Smart Nano Technology Co.,Ltd - General Manager)


2.4 The method to determine the average particle size (D50)

If the slurry formulation is fixed and the operating conditions of the grinding machine are also fixed, the average particle size will be determined by the specific energy value.

The specific energy E value is defined as follows:

E: Specific energy, unit is kWh/t

P: Power consumption, unit is kW

P0: Invalid consumption of power. The power consumption of starting the grinding machine when the grinding ball has not been added, the unit is kW

m': Flow rate,unit is ton/hr

Cm: Solid content, unit is percent

From the above, the physical meaning of specific energy is the power consumed per hour per ton of powder.

As shown in Figure (4), taking calcium carbonate as an example, the author changed six different grinding machine's rotor speed (6.4-14.4 m/s), seven different flow rate, the X axis as specific energy value, the Y axis as the average particle size, known from the figure, no matter how flow rate or stirring shaft speed changes within the allowable range, as long as the specific energy value is fixed, the average particle size obtained by grinding will be fixed. Therefore, in order to produce the same product quality, as long as the same specific energy value is under controlled, the same average particle size value can be obtained.

FIG (4) The relationship between the specific energy value consumed by the grinding machine and the average particle size of the slurry

2.5 Effect of grinding bead size on grinding results

Different sizes of grinding beads will affect the required specific energy value. According to FIG (5), when using a 1.0-1.4mm grinding bead to grind calcium carbonate, 320 kWh/t is needed to reach the particle size as D80<2μm. However, when the specific energy E value reaches 96 kWh/t, 0.6-0.8mm grinding bead is used to continue grinding, and only the specific energy value of 180 kWh/t is needed to achieve the same particle size as D80<2μm. If the initial particle size of the slurry can be pretreated smaller, for example, less than 20μm, then the grinding bead used can be 0.2-0.6mm, it is believed that the specific energy value required will be greatly reduced. According to the above research and explanation, the smaller the grinding bead, the better the grinding effect, and the smaller the specific energy value required.

FIG (5) Same slurry particle size requirement, the relationship between different grinding bead size and the speicific energy value consumption

2.6 Method of determining Particle size distribution

FIG (6) Movement mode of slurry in grinding machine

FIG (7) Determination rules of slurry particle size distribution

As shown in FIG (6) and FIG (7), the particle size distribution determined by the size of the Peclet number. The larger the Peclet number, the wider the particle size distribution.

Peclet is defined as follows:

Pe: Peclet number

V: Axial velocity

l: Length of grinding chamber

D: Diffusion coefficient

Therefore, when the slurry is pumped into the grinding chamber, the faster the axial velocity is, the greater the axial force is, the smaller the slurry diffusion coefficient is, and the larger the Peclet number will be, so as to obtain a narrower particle size distribution.

In actual application, during the grinding process, the flow rate can be increased as much as possible within the allowable range of the grinding chamber pressure, so that the Peclet number can be increased to obtain a narrower particle size distribution. As shown in IFG (8), the larger the Peclet number is, the narrower the particle size distribution will be.

FIG (8) The relation between Peclet Number and the determination rules of slurry particle size distribution

(To be continued)

© Copyright: 2020 PUHLER (Guangdong)Smart Nano Technology Co.,Ltd. All Rights Reserved.

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