# Experiment on Wet Superfine Grinding of Zirconia Ball in Heavy Calcium Carbonate

The effects of zirconia ball diameter, ball filling rate, slurry concentration, rotation speed of ball mill and grinding time on particle size distribution and median diameter of heavy calcium were studied. The experimental results show that the technological conditions of wet ultrafine grinding are as follows: the diameter of zirconium ball is 0.7 mm, the concentration of slurry is 50%, the filling rate of medium is 6O %, the rotation speed of ball mill is 425r/min, and the grinding time is 84min. The particle size of crushed calcium is 98% below 1.2um and D50 is 0.36m.

Calcium carbonate is widely used as filler in rubber TAk, coating industry, paper industry, plastic industry, ink industry and other industries. Superfine heavy calcium carbonate is mainly using the method of dry crushing or grinding, craft production in the dry method is suitable for the production, the average particle size is greater than 3 um fine calcium carbonate wet grinding to used in the production of the average particle size less than 2 um, maximum particle size of less than 10 um filler and coating grade calcium carbonate, the wet ultrafine grinding and dry grinding is from the coarse grinding process, Mixer is one of the most studied wet grinding equipment for heavy calcium.

Using zirconia ball as grinding medium, this paper mainly studies the influence of the technological conditions of wet crushing of heavy calcium by planetary ball machine on particle size distribution and median diameter 50, and obtains the technological conditions of preparing super heavy calcium by star grinding. The research results can be used as the base data of single grinding wet crushing of superfine powder for forming heavy calcium carbonate.

## Ⅰ. The Experimental Part

The raw materials for the experiment were selected from the 200-day heavy carbon produced by a common Chinese curioso, the content of calcium carbonate was more than 99% and the whiteness was more than 94 degrees. Its original grain size composition was shown in Table 1.

The ultrafine crushing equipment of heavy calcium is QMs4 star high-energy ball mill, the ball grinding tank is 250M1 agate tank, the grinding medium is zirconia ball, the density of the medium is 5.4g/cm, the specifications are 0.trAM, 1.9mm, 3.0mm, 5.OMM respectively.

The particle distribution of halo calcium before and after comminution was analyzed and measured by NSKC – 1 plow light transmission particle size analyzer. Dispersion preparation is 0.5% sodium polyacrylate solution, dosage of 0.001% 0.1% (halo). In this experiment, the particle size distribution obtained under different experimental conditions was selected respectively before testing dispersant dosage.

## Ⅱ. Experimental Results and Discussion

*1. Influence of Grinding Medium Size*

In order to determine the influence of grinding medium size, zirconium balls with diameters of 5mm, 3mm, 1.9mm and 0.7mm were used for experiments with the same slurry concentration of 50%, medium filling rate of 55%, ball mill speed of 425r/min and ball grinding time of 24min. FIG. 2 shows the particle size distribution and median diameters of ca2 + with different zirconium ball diameters.

In the process of ball grinding grinding, extrusion, impact foot grinding ball on the powder of the most important force mode, and different grinding equipment grinding ball main force mode there are differences. Planetary ball mill is mainly through the grinding of the ball powder and rub and other effects to achieve the refinement of the powder in the ultrafine grinding process. The number of large balls at the filling rate is less (the number of balls is inversely proportional to the square of the ball diameter at the same filling rate), the specific surface area is small, and the collision point between balls is less. When the powder is refined to a certain extent, the probability of catching powder becomes smaller, so the large ball is conducive to the rapid crushing of granular materials, but conducive to the ultrafine grinding of small particles. Although the energy carried by the ball is small, the grinding efficiency of coarse powder is lower than that of the large ball, but the filling rate is the same, the surface area of the ball is large and the number of balls is large, the collision point between the ball and the ball is more, the probability of catching fine powder is hot, and the grinding effect of fine powder is stronger than that of the large ball. That is, it is more favorable for grinding medium with small diameter. Therefore, as the diameter of the zirconium ball decreases in Figure 2, the content of heavy calcium with small particle size increases and the median diameter decreases after grinding.

*2. Influence of Slurry Concentration on Comminution Effect*

When the zirconium ball diameter is 0.7mm, the medium filling rate is 55%, the ball mill speed is 425r/min, and the ball grinding time is 24min, the particle size distribution and median diameter of heavy calcium under different slurry concentrations are shown in FIG. 3.

It can be seen from Figure 3 that the particle size distribution of the crushed heavy calcium is different when the slurry concentration is different under the same cleaning condition of other crushed pieces. It can be seen that with the increase of slurry concentration, the content of small particle size powder increases first and then decreases, and reaches a maximum value when the concentration is 50%. The median diameter of heavy calcium decreases first and then increases with the slurry concentration, and reaches a maximum value of D, O. 44um when the concentration is 50%. The main reason is that when the slurry concentration is low, the slurry rheology is good, which is conducive to improving the grinding efficiency, but with the continuous decrease of the concentration, the collision chance between the particles and the grinding medium becomes smaller, which is not conducive to improving the grinding efficiency. However, with the slurry concentration, although the density of the suspension composed of powder and water increases, which is conducive to the improvement of the grinding efficiency, the viscosity of the slurry also increases, and the fluidity becomes poor, thus reducing the grinding efficiency.

*3. Influence of Medium Filling Rate on Comminution Effect*

When the zirconium ball diameter is 0.7mm, the slurry concentration is 50%, the ball mill speed is 425r/min, and the ball grinding time is 24min, the particle size distribution and median diameter of heavy calcium are shown in FIG. 4 under different medium filling rates.

The effect of medium filling rate on grinding effect is the reflection of the contact chance between medium and the effective action degree of material. Medium filling rate is small, medium impact, crushing and used for materials less opportunity, crushing effect is poor. On the contrary, the medium filling rate is large, the grinding effect is good, but when the medium material ratio increases to too much media, more than the ball mill in the ball grinding tank of the effective load, the effective contact of the medium will also decline, reducing the grinding efficiency. Therefore, the median diameter of heavy calcium decreases first and then increases with the increase of medium filling rate, and the minimum value is 0.41um when the filling rate reaches 60%. The content of heavy calcium carbonate with small particle size also increases first and then decreases with the increase of zirconium ball filling rate, and reaches a maximum value when the filling rate is 60%.

*4. Influence of Rotation Speed of Ball Mill on Grinding Effect*

The diameter of the fixed zirconium ball was 0.7mm, the slurry concentration was 50%, the medium filling rate was 60%, and the ball grinding time was 24min. Figure 5 shows the particle size distribution and median diameter of the heavy calcium at different ball mill speeds.

Figure 5 ball mill speed under different particle size distribution of coarse whiting and median diameter Chen Shizhu and gong Yao Teng etc. The crushing mechanism of planetary mill for study in planetary high-energy ball mill, grinding medium and concluded from the point of only related to the size, and design and has nothing to do with the ball mill speed, so the planet type ball mill is not there exists a critical speed, This is also the planet type ball mill than other forms of ball mill shows the superiority. Increasing the speed of ball mill can increase the impact frequency and the number of impact between the ball and the material, so as to improve the grinding efficiency. Therefore, in this experiment, with the increase of the rotation speed of the ball mill, the cumulative distribution value of the particle size of heavy calcium under small particle size increases, while the median diameter decreases, reaching 0.41um at 425r/min. Since the rotation speed limit of the planetary mill used in the experiment is 530r/mi, the rotation speed of the ball mill selected in this experiment is 425r/min.

*5. Influence of ball grinding time on comminution effect*

Ball grinding time is a very important factor in the process of ultrafine grinding. When the zirconium ball diameter is 0.7mm, the slurry concentration is 50%, the medium filling rate is 60%, and the ball mill speed is 425r/min, FIG. 6 shows the relationship between particle size distribution and median diameter of heavy calcium and ball milling time.

It can be seen from Figure 6 that, with the extension of time, the content of powder with small particle size gradually increases, but the increasing trend gradually slows down. It can be seen that there is little difference between the experimental values of particle size distribution at 84min and 120min: The median diameter of the heavy calcium decreased with the increase of time, and it was the minimum at 84min, and the median diameter was 0.36um at 84min. This is because brittle fracture and crystal splitting require two processes, first the generation of cracks, then the propagation of cracks until the final fracture crushing. Cracks in the material can be places of stress concentration and surface separation during fracture occurs gradually rather than simultaneously along the entire cross section. Therefore, in the initial stage of crushing, there are tiny cracks in the particles, and these cracks are places of relatively concentrated stress. The strength of the actual particles is much smaller than the strength of J crystal. With the extension of crushing time, the particles are smaller and smaller, the structural defects are less and less, the strength of the body is constantly improving, and the difficulty of crushing is also sharply increased. In addition, with the prolongation of grinding time, grinding medium wear, medium filling rate decreases, powder can not be fully crushed, manifested as the grinding fineness increases slowly. So in zirconium ball diameter, pulp concentration, medium filling rate, rotating speed of ball mill given conditions, with the extension of time, the powder particle size is reduced gradually, and fineness increased more and more difficult, the excessive extension of time, a few small powder is the reunion phenomenon, exists in the super fine crushing of powder grinding reunion balance.

## Ⅲ. Conclusions

This paper mainly studies the influence of superfine grinding process of planetary grinding wet method on the median diameter of heavy calcium, and the following conclusions can be obtained within the experimental scope:

1. Reducing the diameter of zirconium ball, increasing the speed of ball mill and increasing the grinding time can increase the content of small particle size of heavy calcium and reduce the median diameter of heavy calcium. With the increase of slurry concentration and medium filling rate, the content of small particle size of heavy calcium increases first and then decreases, while the median diameter decreases first and then increases.

2. The optimum technological conditions for wet ultrafine grinding of heavy calcium in planetary mill are as follows: the diameter of zirconium ball is 0.7mm, the slurry concentration is 50%, the filling rate of medium is 60%, the rotation speed of ball mill is 425r/min, and the grinding time is 84min. The particle size of crushed heavy calcium is 98% below 1.2um, ds0= 0.36um.

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