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Application of bead mill in the production of titanium dioxide

Application of bead mill in the production of titanium dioxide

  • August 20,2020.

Application of bead mill in titanium dioxide production


Foreword


Titanium dioxide, molecular formula is TiO2. Titanium dioxide has high refractive index, ideal particle size distribution, good covering power and coloring power, is a kind of white chemical pigment with excellent performance, widely used in coating, rubber, plastic, paper making, printing ink, daily-use chemical industry and so on.


In general, the development of titanium dioxide production technology mainly consists of sulfuric acid method and chlorination method. Because a large number of scar particles are produced during the production process of chlorination titanium dioxide gas phase oxidation, they cannot be completely dispersed during the beating process. If this part of scar particles is not grinded, the scar particles will be directly coated in the enveloping process. After being crushed by the air jet mill, the membrane of this part of scar particles will not be completed, and the particle shape is irregular, affecting the quality of the product, which is an important reason for the low dispersion and color difference of the product. In view of this situation, we have carried on the sieving experiment to the oxidized incoming material and the slurry after grinding, to determine the number of scar particles, and to study the role of bead mill in the titanium dioxide post-treatment process.


1. Developing process of titanium dioxide production technology


FIG.1 Production process of titanium dioxide


The development of titanium dioxide production technology in China has gone through three stages:

The first stage was from the mid-1950s to the end of 1970s, the annual capacity of titanium dioxide in China was only 20,000 T, and most were low-grade varieties.  This stage is characterized by backward technology and slow development.


The second stage began in the late 1970s to the end of the 1980s, sulfuric acid titanium dioxide production technology level has been rapid development, anatase products and rutile products have been produced, the national production capacity of titanium dioxide increased from 20,000 T to 100,000 T. During this period, due to the scientific and technological breakthrough of "comprehensive utilization of vanadium-titanium magnetite resources in Panzhihua", the production technology of sulfuric acid titanium dioxide was made new breakthroughs, which promoted the rapid improvement of the technical level of sulfuric acid titanium dioxide production equipment in the mid-1980s.


The third stage is from the 1990s to present, the production capacity and output have been expanding year by year. At the same time, new breakthroughs have been made in production technology. The large production facility of sulfuric acid rutile titanium dioxide imported from abroad has been put into production successively, and the imported large production facility of titanium dioxide chloridehas been digested and absorbed in China and has also been put into production smoothly. The introduction and use of titanium dioxide production facility has not only improve the production technology of titanium dioxide in China, but also change the production mode of small-scale sulfuric acid method and can only produce low-grade anatase titanium dioxide backward situation.


2. Working principle of bead mill


Bead mill is mainly composed of machine body, grinding chamber, grinding disc, grinding medium, motor and feeding pump.

FIG.2 Structure of horizontal bead mill


Bead mill is an important process of titanium dioxide post-treatment, which is not only required for sulfuric acid method but also chlorination method. Bead mill is a kind of wet continuous production of superfine particle dispersing machine. Grinding is to further crushed the aggregated particles, the agglomerated particles and flocculation particles produced in the previous process. Because of the binding force between particles is very weak, it is easy to dispart them by means of mechanical grinding, under the action of dispersant, to prevent them from agglomerating again, so that some of the coarser particles can be grinded to a particle size range with application properties.


FIG.3 Working principle of bead mill


Use a pump to transfer the dispersed solid - liquid phase mixture into the grinding chamber, the mixed material and the grinding medium are stirred together by the high-speed rotating disperser, so that the particles of the material and the grinding medium are mutually produce more intense collision, friction and shear action, to achieve the purpose of accelerating the grinding fine particles and dispersing aggregates. After grinding and dispersing, when going through the separator, the grinding media is intercepted, the finished material flows out of the discharge pipe, and the product meets the granularity requirements is obtained. After grinding, the particle size of titanium dioxide is usually controlled to <5μm.


3. Application of bead mill in production of titanium dioxide


In the production of high-grade rutile titanium dioxide, the grinding process is an important process that cannot be ignored. In overseas countries, to use the bead mill to grind the material before coating, and it is very common.


In the production of rutile titanium dioxide, the reason why the bead mill can not be underestimated is that it can disperse the agglomerated large particles, moreover, after grinding, the titanium dioxide particles are spherical with no edges and corners, the particle size is less than 1μm, and the particle size distribution is relatively concentrated. Therefore, the coated products have excellent pigment properties and optical properties.


FIG.4 Horizontal bead mill


3.1 Advantages of horizontal bead mill

3.1.1 Low height of horizontal bead mill

Due to the compact structure, the motor is placed above the grinding chamber, and the grinding chamber is in lower place, which not only makes the operation stable, but also greatly reduces the overall height of the equipment. The large bead mill also has a chamber dismounting slideway for easy maintenance.


3.1.2 Grinding medium is evenly distributed

The new structure and horizontal type of the grinding disc of the bead mill overcome the shortcoming of the non-uniform distribution of grinding medium in the traditional vertical bead mill, thus greatly improving the grinding efficiency. With the uniform distribution of the grinding medium, the grinding medium and the grinding material could be fullly contacted, avoids the collision and friction between the particles of grinding medium in the high density place due to the uneven distribution of grinding medium. This not only affects the grinding efficiency, but also reduce the service life of the grinding medium.


3.1.3 The agitator shaft adopts double mechanical seal

The double mechanical seal system with forced cooling liquid circulation ensures the cleanness of the mechanical seal liquid, avoids the wear of the mechanical seal system, has good sealing effect, and extends the service life of the mechanical seal system.


3.2 Material of grinding chamber and grinding disc

According to the specific materials to be grinded, grinding chamber and agitating disc can choose stainless steel, ceramics, polyurethane and other materials. These materials not only have a certain strength, but also have good abrasion resistance, and will not cause pollution to the grinding materials.


3.3 Grinding process

According to different production process requirements, the grinding process of bead mill is also different.


3.3.1 Continuous grinding process

The grinding slurry is fed quantitatively into the bead mill by the feed pump. After the grinding material is separated by the dynamic classified rotor separator, it is discharged from the outlet. The continuous grinding process can be single or multiple continuous grinding processes according to the different fineness requirements of the materials. Continuous grinding process is shown in FIG 5.

FIG.5 Continuous grinding process


3.3.2 Circulation grinding process

The slurry to be grind is quantitatively fed to the grinding chamber of the bead mill by the feed pump. After the grinded material is separated by the dynamic classifier, the material is returned to the feed storage tank of the bead mill through the return pipe, to grind again. The circulation grinding time can be determined according to the required fineness of the material. This process is suitable for situations where the fineness requirement of materials is high. The circulation grinding process is shown in FIG.6.

FIG.6 Circulation grinding process


Conclusion


In the application of titanium dioxide industry, bead mill has its unique function and position. The bead mill is used to grind the intermediate material of titanium dioxide powder which is going to be coated, so that the particles of the grinded material are fine and uniform, with concentrated particle size distribution and the particle shape is geometric spherical shape, thus improving the pigment performance, optical properties and dispersion of the final product of titanium dioxide. The grinding effect of bead mill is irreplaceable in a sense.


The competition of titanium dioxide market is becoming increasingly fierce, facing the pressure of high-grade products from large foreign titanium dioxide manufacturers, we should try to adopt advanced technology and equipment, improve product quality, build up our own brand, make the quality of the titanium dioxide product of China gradually rank among the international advanced level, and reach the level of approaching, catching up with or competing with, and walk out of the development road of titanium dioxide industry with Chinese characteristics, among which the application of bead mill will play a more positive role in promoting.


PHE SuperMaxFlow Agitator Disk Bead Mill


By CNPOWDER and PUHLER


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

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