JPH06343890A - Pulverizing method by wet process - Google Patents

Abstract

PURPOSE:To prevent the degradation in pulverizability by co-rotating by stepwise diluting a mixture composed of a material to be pulverized and a dispersion medium according to progression of pulverization of the material to be pulverized. CONSTITUTION:Siliceous stone (pulverized) and water (dispersion media) are first fed so as to attain about 75% slurry concn. in a stage 1 and are then pulverized in a stage 1. The slurry concn. increases and corotating arises to successively decrease a grain size reducing speed according to progression of pulverization. The water is slightly added to lower the slurry concn. to about 65% as a stage 3 and thereafter the stage is returned to the stage 2. The stages 2, 3 are repeated in such a manner and the target grain size is attained when the slurry is diluted to about 45%. The pulverized slurry is thereafter delivered in a stage 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet grinding method in an ultrafine powder manufacturing facility.

[0002]

2. Description of the Related Art FIG. 4 is a vertical sectional view showing an example of a conventional wet continuous mill, and FIG. 5 is a view showing a wet continuous crushing condition by the mill of FIG. An outer cylinder (2) having a stirring blade (4) on the inner wall
An inner cylinder (1) having an agitating blade (3) on the outer wall is disposed therein so that they rotate in opposite directions. A grinding medium (ball) (6) is filled in the grinding chamber (5) formed between the inner cylinder (1) and the outer cylinder (2). Raw material supply hole (7) provided through the rotating shaft of the inner cylinder (1)
Thus, a coarse-grained slurry composed of a crushed material (material to be crushed) and a dispersion medium such as water is continuously supplied into the crushing chamber (5) and crushed by the crushing medium (6). The finely divided slurry is separated from the grinding medium by the discharge eye plate (8) installed at the opposite end, and only the finely divided slurry is continuously discharged from the ground product outlet (9). In this case, the concentration of the coarse-grained slurry supplied is constant throughout.

Next, FIG. 6 is a diagram showing a conventional wet batch (batch) grinding process. First, in the step, a specific amount of the crushing material and the dispersion medium are charged into the mill filled with the crushing medium (6), then crushed in the step, and the crushed product is discharged from the inside of the mill in the step. Therefore, also in this case, the concentration of the slurry is constant throughout the entire pulverization process.

[0004]

FIG. 7 is a diagram showing the correlation between the viscosity and the average particle diameter of the powder contained when the concentration of the slurry is constant. The viscosity of the slurry increases as the average particle size of the contained powder decreases. When the viscosity of the slurry exceeds a certain value, the movement of the ball will be governed by the viscosity rather than the effect of the shearing force and gravity received from the stirring blade, and the ball, the slurry and the stirring blade of the crusher will work together. A so-called co-rotation phenomenon occurs, which begins to rotate. When this phenomenon occurs, the kinetic energy of the ball hardly acts as the crushing energy for the particles, and the crushability is significantly reduced.

FIG. 8 is a diagram showing an example in which the ultrafine pulverization becomes difficult because the viscosity of the slurry increases and co-rotation occurs to deteriorate the pulverizability. When the slurry viscosity indicated by Δ in the figure exceeds the upper limit value at which co-rotation does not occur, the particle size indicated by ○ in the figure decreases at a reduced rate and hardly decreases from a constant value. As described above, when the wet ultra-fine pulverization is performed, the pulverization speed decreases as the atomization progresses, and a great amount of pulverizing energy and time are consumed to obtain the target fine powder.

[0006]

In order to solve the above-mentioned conventional problems, the present invention provides a method for finely pulverizing an object to be pulverized by stirring a mixture of an object to be pulverized and a dispersion medium together with a pulverizing medium, As the atomization of the pulverized material progresses,
The present invention proposes a wet pulverization method characterized by diluting the mixture with the dispersion medium stepwise.

[0007]

FIG. 9 is a diagram showing the correlation between the slurry concentration and the viscosity, with the average particle size of the powder contained in the slurry as a parameter. Even if the average particle size of the powder is the same,
The higher the concentration, the higher the viscosity.

In the method of the present invention, the slurry viscosity is maintained in an appropriate range and the slurry viscosity is high by diluting the mixed slurry of the material to be ground and the dispersion medium with the dispersion medium to appropriately reduce the slurry concentration. This is to suppress the co-rotation phenomenon that occurs due to this.

[0009]

EXAMPLE FIG. 1 is a view showing a state in which silica stone was pulverized by wet batch pulverization as an example of the method of the present invention. First, in a step, silica stone (crushed material) and water (dispersion medium) are charged so that the slurry concentration becomes 75%. Next, crushing is performed in the process. As the pulverization progresses, the viscosity of the slurry increases, co-rotation occurs, and the particle size reduction rate decreases. Therefore, as a process, a small amount of water is added to reduce the viscosity by decreasing the slurry concentration to 65%, and the process is returned to the process again. The process was repeated in this way, and the target particle size was reached when diluted to 45%. Then, the crushed slurry was discharged in the process.

FIG. 2 is a diagram showing changes in powder particle diameter, slurry viscosity, and slurry concentration in the silica stone crushing test. When pulverization was started, the slurry viscosity increased with atomization, and as the upper limit value of 5000 cp was approached, co-rotation began to occur and the particle size reduction rate decreased. Therefore, when water was added to reduce the concentration to 65% to reduce the viscosity, the particle size reduction rate increased. When the pulverization was further continued, the decreasing rate of the particle size was decreased again, so that the concentration was further diluted to 55%. By repeating such steps, 1
Atomization of less than μm could be achieved. If the above-mentioned dilution is not carried out, the average particle size will eventually be about 2 μm.
Did not get smaller than.

FIG. 3 is a correlation diagram in which the lower limit value of the viscosity (concentration) is defined from the processing amount and the upper limit value is defined from the viewpoint of preventing co-rotation. In particular, the lower limit value will be described. When the dilution proceeds excessively and the concentration becomes 40% or less, the processing rate on a dry powder base decreases to 100 kg / hr or less, and the economical limit is reached. Therefore, it can be said that it is desirable to maintain the slurry concentration (viscosity) at 40% or more during pulverization. In this way, it is important to keep the concentration within an appropriate pulverization concentration range, considering both economical efficiency and pulverizability.

As described above, in this embodiment, by performing the multi-stage dilution, it was possible to achieve fine pulverization which could not be achieved by the conventional wet pulverization method.

[0013]

In the method of the present invention, when performing wet pulverization using a pulverizing medium, the slurry viscosity is controlled within a proper range by gradually diluting the slurry and reducing the concentration in accordance with atomization of the material to be pulverized. Since the co-rotation phenomenon of the keeping pulverizing medium is suppressed, it is possible to pulverize much finer than the conventional wet pulverizing method. Further, the grinding power and the grinding time required to obtain the target fine powder can be significantly reduced as compared with the conventional method.

[Brief description of drawings]

FIG. 1 is a view showing a state in which silica stone is trially pulverized by wet batch pulverization as one embodiment of the method of the present invention.

FIG. 2 is a diagram showing changes in powder particle size, slurry viscosity, and slurry concentration in the above-mentioned silica crushing test.

FIG. 3 is a diagram showing an upper limit value and a lower limit value of viscosity (concentration).

FIG. 4 is a vertical cross-sectional view showing an example of a conventional wet continuous mill.

5 is a diagram showing a wet continuous pulverization situation by the mill of FIG. 4;

FIG. 6 is a diagram showing a conventional wet batch pulverization process.

FIG. 7 is a diagram showing the correlation between the viscosity of the slurry and the average particle diameter of the powder contained therein.

FIG. 8 is a diagram showing an example in which ultrafine pulverization is difficult due to an increase in slurry viscosity.

FIG. 9 is a diagram showing a correlation between slurry concentration and viscosity with an average particle diameter of powder as a parameter.

[Explanation of symbols]

 (1) Inner cylinder (2) Outer cylinder (3), (4) Stirring blade (5) Grinding chamber (6) Grinding medium (ball) (7) Raw material supply hole (8) Discharge plate (9) Grinded product outlet

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuyuki Ueda 1-1 No. 1 Atsunoura-machi, Nagasaki-shi Nagasaki Shipyard Co., Ltd. Inside the shipyard

Claims (1)

[Claims] 1. A method of finely pulverizing a material to be pulverized by stirring a mixture of the material to be pulverized and a dispersion medium together with a pulverizing medium, wherein the mixture is stepwise added as atomization of the material to be pulverized progresses. A wet pulverization method, which comprises diluting with the dispersion medium.