Introduction and application of non-metallic powder - mica powder

Mica is a general term for mica group minerals. It is an aluminosilicate of metals such as potassium, magnesium, iron, and lithium. The structure is all layered. From the perspective of formation, it can be divided into two types: natural mica and artificial mica. Natural mica mines mainly include biotite, phlogopite, muscovite, lepidolite, sericite, green mica, iron lepidolite, etc. Muscovite, sericite, phlogopite and lepidolite are the most widely used in industry. Synthetic mica is a component that people imitate mica. Metal oxides are mixed according to a certain proportion and then melted at high temperature. During the cooling process, they recrystallize to form pure mica crystals.

1. Muscovite

Muscovite is the most used in industry. Ultrafine mica powder can be used as functional fillers in plastics, paints, paints, rubbers, etc., which can improve their mechanical strength, enhance toughness, adhesion, anti-aging and corrosion resistance. In the industry, it is mainly used for its insulation and heat resistance, as well as acid resistance, alkali resistance, compression resistance and peeling properties, and is used as an insulating material for electrical equipment and electrical equipment; secondly, it is used to manufacture steam boilers and furnaces for smelting furnaces Windows and mechanical parts. Mica chips and mica powder can be processed into mica paper, and can also replace mica sheets to produce various insulating materials with low cost and uniform thickness.

2. Sericite

The mineral aggregates of sericite are rose, flesh red, gray green, light gray purple, gray-dark gray and so on. But the powder is all white. When iron enters the lattice, the powder is white with gray, and the whiteness decreases accordingly. Sericite is in the form of fine scales (generally <0.01mm) and has a distinct slippery feel. Sericite has a strong silk luster, transparent to translucent. It has moderate light transmittance and covering rate, and has the ability to reflect ultraviolet rays. The above properties determine the uniqueness of sericite application. Because sericite is generally in the shape of small scales, it is widely used in the coating industry, paper industry, daily chemical industry and rubber and plastic industry.

3. Phlogopite

Natural phlogopite has dark phlogopite and light phlogopite. Phlogopite is characterized by complete cleavage of the mica, a yellow-brown color and golden-like reflections. It is widely used in building material industry, fire protection industry, fire extinguishing agent, welding rod, plastic, electrical insulation, paper making, asphalt paper, rubber, pearlescent pigment and other chemical industries.

4. Synthetic mica

Synthetic mica, also known as fluorine phlogopite, is made by imitating the composition and structure of natural mica and using quartz and other raw materials through high temperature melting and constant temperature crystallization. Compared with natural mica, synthetic mica is less restricted by natural resource conditions, its structure is similar to natural mica, and its purity, transparency, insulation and high temperature resistance are better than natural mica, so it can be completely used in some industrial applications. Replacing or even surpassing natural mica, it has strong vitality and development prospects. It is a new material of artificially synthesized flaky non-metallic crystals with strategic significance. The current main purpose of synthetic mica is to crush mica into mica powder of various particle sizes. Its application industries include coatings, rubber, plastics, mica paper, mica ceramics, special synthetic wave-absorbing materials, synthetic mica electric heating plates, machinable ceramics and Synthetic mica pearlescent pigments and other applications.

Advantages of dry grinding

1. The production process is simple, without excessive equipment and long production lines;

2. No need for water and heat energy, less energy demand;

3. Compared with the wet method, the price of the final product is low, and the cost performance is higher for some less demanding filler grade products;

4. The production efficiency is relatively higher than that of the wet method.

by ALPA

Medical ultrafine grinding equipment - jet mill

The micronization of raw materials can significantly improve the solubility of poorly soluble drugs, and the dissolution rate of solid preparations prepared from ultrafine powdered poorly soluble drugs can meet the requirements of domestic consistency evaluation. The jet mill is one of the most important components in the ultrafine pulverization equipment, which can pulverize the material to a few micron powder. Jet mill, also known as jet mill or flow energy mill, uses high-speed airflow or superheated steam to collide, grind and shear materials to crush them.

The working principle of jet mill in the process of powder preparation

After compressed air or inert gas is pressurized in the nozzle, the injection force of high-speed elastic fluid is used to make strong impact, shear, collision and friction between particles, gas and particles, particles and wall and other components. And so on. At the same time, under the action of the centrifugal force of the airflow rotation, or combined with a classifier, the coarse and fine particles are classified to achieve ultrafine pulverization.

(1) Flat jet mill

The flat jet mill is also called the disc jet mill. The working principle of this type of equipment is that the compressed air enters the air distribution chamber through the inlet, which will generate negative pressure, and the material enters the mixing chamber, and then is sprayed into the crushing chamber by the high-speed airflow ejected from the nozzle. room. The radial direction of the nozzle and the crushing chamber has a certain angle, so the material rotates at a very high speed under the high-speed airflow ejected from the nozzle, and performs circular motion. The materials collide with each other, and the inner wall of the crushing chamber collides, grinds, etc., so the materials are crushed. Coarse materials that do not meet the requirements are thrown to the wall to continue crushing under the action of centrifugal force, and fine powder enters the collection system of the jet mill from the outlet pipe of the crusher to collect the crushed products.

(2) Fluidized bed (counter-spray) jet mill

Fluidized bed (opposite jet) jet mill is a newer jet mill. The working principle of the fluidized bed counter-jet jet mill is that the air flow passes through a group of nozzles (number > 2) to form a counter-jet flow field in the mill, and the material is fluidized. The materials in the jet mill will have strong collision, friction and impact between the particles at the intersection point of the nozzle jet, and then be crushed. The pulverized powder passes through the classifier under the action of negative pressure, and the products that meet the requirements are collected by the cyclone separator and dust collector, while the coarser particles that do not meet the requirements are returned to the crushing area for pulverization under the influence of gravity.

The characteristics of jet mill for medicine grinding

1. The particle size distribution range is narrow, and the average particle size is fine

Through the high-pressure airflow pulverization process and the centrifugal force of the airflow rotation of the precision classifier, automatic classification of different particle sizes is realized. The particle size distribution of the obtained products is narrow, the average particle size is fine, and the D50 particle size is between 5 and 10 μm.

2. Powder shape is good, product purity is high

The appearance of the powder produced by the jet mill is spherical, the surface of the particles is smooth, the shape is regular, the dispersion is good, the mechanical wear is small during the crushing process, and the product purity is high.

3.Suitable for low melting point and thermosensitive drugs

The jet pulverizer is powered by compressed air, and the high-speed jet pneumatically produces the Joule Thomson effect. The pneumatically adiabatic collision at the nozzle reduces the temperature of the crushing system and offsets the heat generated by drug collision and friction.

4. Good sealing, no pollution

Due to the good sealing performance of the jet mill, the product yield is high; the whole crushing process is carried out under negative pressure, without leakage, no pollution to the environment, and can be operated aseptically.

5. Crushing-mixing-drying online operation

The jet mill can realize online operations such as crushing, mixing, and drying, and can also simultaneously modify drug powder. For example, some drugs are sprayed into a liquid during pulverization, covering and modifying the particles.

The jet mill has become the first choice for the development of various high-performance micro-powder materials.

by ALPA

Ceramic impact pulverizer, pollution-free production of ultra-fine powder

For traditional mechanical crushing, it is generally a process of crushing materials by mechanically applying forces such as shearing, extrusion, impact, and grinding. The crushed materials need to be in direct contact with grinding bodies or grinding media, while traditional grinding bodies are mostly made of various metal materials, and it is inevitable to introduce metal impurities due to abrasion. Therefore, the application of mechanical pulverizers is greatly limited in fields such as lithium batteries, medicines, health products, and food that require pollution-free pulverization.

If you want to use the mechanical mill in an industry without magnetic pollution, it is necessary in the design of the crushing machine. The part in contact with the material during the crushing process must be a ceramic structural part. Shenfei Powder (Hangsheng Industry) has developed and produced a ceramic mechanical ultra-fine pulverizer according to the needs of customers during the research on the pulverization process of lithium battery materials. The feed particle size of this type of equipment is < 3 mm, and the product particle size can be adjusted from 5-100 μm. The whole set of equipment has high system integration, low fine powder rate, high yield, good particle shape, and strict control of large particles. It is deeply loved by lithium battery users.

The working principle of ceramic mechanical ultrafine pulverizer is that the material is evenly sent into the pulverization chamber by the feeding system, and is subjected to centrifugal force under the impact of the pulverization disc, collides with the pulverization ring gear, and is pulverized by various forces such as shearing, friction, and collision; the product moves to the classification area with the airflow, and is separated by the classification wheel controlled by frequency conversion.

At present, the ceramic mechanical ultrafine pulverizer developed and produced by alpa powder has 20 years of application experience in the lithium battery industry. This equipment is especially suitable for pulverizing materials with a particle size of more than 5 microns, and has the characteristics of high efficiency and energy saving. With the explosive growth of the lithium battery new energy industry in recent years, this equipment will become a powerful supplement for the application of jet milling equipment and sand mills in lithium battery materials. Customers can choose more economical and practical crushing processes and equipment according to their own requirements for material crushing and processing with diversified particle sizes.

Of course, in the crushing processing of medicine, health care products, food, chemical industry, etc. that require no magnetic pollution, the ceramic mechanical ultrafine grinder is also a very good choice.

by ALPA

Application and equipment selection of jet mill

In recent years, as the superior performance of ultrafine particles has been continuously affirmed, more and more researchers have begun to pay attention to the research work of fine powder manufacturing. As an important preparation method of ultrafine powder, jet milling technology has become one of the preferred methods for developing various high-performance micropowder materials.

The jet mill, also known as jet mill or flow energy mill, uses high-speed airflow to make the material collide with the impact parts, impact, shear and other effects to pulverize. The product obtained by pulverizing the material with a jet mill has uniform fineness, narrow particle size distribution, high purity, smooth particle surface, regular shape, and good dispersibility. During the crushing process, the material is less polluted, and even a pollution-free and sterile environment can be achieved, so it can be applied to ultra-fine crushing in fields such as food and medicine that are not allowed to be contaminated by foreign objects. The jet mill does not release a lot of heat during the crushing process, so it is more suitable for crushing materials with low melting point or heat sensitivity than other crushing equipment. The degree of automation in the production process is high and can be used for large-scale industrial production. Jet milling can also realize the joint operation of crushing and subsequent production steps. For example, the crushing and drying of materials can be realized at the same time, and the solution can also be sprayed during crushing to coat or modify the surface of the powder. But there are disadvantages such as large energy consumption.

Types of Jet Mills

Spiral Jet Mill

Spiral Jet Mill, also known as horizontal disc jet mill, is the earliest and most widely used jet mill in industry. It has the advantages of simple structure, convenient operation, self-grading, etc., but the impact kinetic energy of the equipment is not large, and the crushing strength is low. When processing materials with high hardness, the inner wall of the body will collide and rub violently with the inner wall of the grinding chamber due to the action of the material with the high-speed airflow, which will aggravate the pollution of the grinding chamber and cause certain pollution to the product. It is suitable for a wide range of materials, especially materials composed of various aggregates or aggregates.

Counter-jet jet mill

Counter-jet jet mill, also known as counter-jet jet mill and reverse jet mill, is a kind of equipment with high energy utilization rate. Since the crushing process mainly relies on the high-speed collision between particles, it can effectively avoid the wear of the impacting parts by the high-speed airflow, and at the same time improve the problem of material contamination, and the product particle size is finer; but the equipment occupies a large area, high energy consumption, and wide particle size distribution. It is often used to crush hard, brittle and viscous materials.

Fluidized bed jet mill

Fluidized bed jet mill is a new type of jet mill, which has the advantages of narrow particle size distribution, high crushing efficiency, low energy consumption, less product pollution, and less wear and tear of accessories, but the cost of equipment is relatively high. Since the material needs to be treated in a fluidized state before it can be collided and crushed by the air stream, the fluidized bed jet mill usually requires the crushed material to have sufficient fineness, and the requirement for high-density materials is more obvious. It is often used for superfine crushing, dispersing and shaping of materials in synthetic resin, phenolic resin, medicine, cosmetics, advanced ceramics, magnetic powder, battery materials and other industries.

In the future, the mainstream development trend of ultra-fine jet milling equipment will be mainly manifested in increasing the output of a single machine and reducing energy consumption per unit of product; improving product fineness and strengthening the crushing limit of equipment; online regulation of product fineness and particle size distribution, etc.

by ALPA

14 methods of surface coating treatment of ultrafine powder

Ultrafine powder usually refers to particles with a particle size of micron or nanometer. Compared with bulk conventional materials, it has larger specific surface area, surface activity and higher surface energy, so it exhibits excellent optical, thermal, electrical, magnetic, catalytic and other properties. As a functional material, ultrafine powder has been extensively studied in recent years, and has been more and more widely used in various fields of national economic development.

1. Mechanical mixing method. Using extrusion, impact, shearing, friction and other mechanical forces, the modifier is evenly distributed on the outer surface of the powder particles, so that various components can penetrate and diffuse each other to form a coating.

2. Solid phase reaction method. Fully mix and grind several metal salts or metal oxides according to the formula, then calcinate, and directly obtain superfine coating powder through solid-state reaction.

3. Hydrothermal method. In a closed system of high temperature and high pressure, water is used as a medium to obtain a special physical and chemical environment that cannot be obtained under normal pressure conditions, so that the reaction precursor is fully dissolved and reaches a certain degree of supersaturation, thereby forming growth elements, and then Nucleation and crystallization make composite powder.

4. Sol-gel method. First, the modifier precursor is dissolved in water (or organic solvent) to form a uniform solution, and the solute and the solvent undergo hydrolysis or alcoholysis to obtain the modifier (or its precursor) sol; then the pretreated coated particles Uniformly mixed with the sol, so that the particles are uniformly dispersed in the sol, the sol is transformed into a gel after treatment, and calcined at a high temperature to obtain a powder coated with a modifier on the outer surface, thereby realizing the surface modification of the powder.

5. Precipitation method. Add a precipitant to the solution containing powder particles, or add a substance that can trigger the formation of a precipitant in the reaction system, so that the modified ions undergo a precipitation reaction and precipitate on the surface of the particles, thereby coating the particles.

6. Heterogeneous coagulation method (also known as "miscellaneous flocculation method"). A method based on the principle that particles with opposite charges on the surface can attract each other and agglomerate. If the diameter of one type of particle is much smaller than the diameter of another charged particle, then during the agglomeration process, the small particle will adsorb on the outer surface of the large particle to form a coating.

7. Microemulsion coating method. First, the micro-water core provided by W/O (water-in-oil) microemulsion is used to prepare the ultrafine powder to be coated, and then the powder is coated and modified by microemulsion polymerization.

8. Non-uniform nucleation method. According to the LAMER crystallization process theory, the coating layer is formed by using the heterogeneous nucleation and growth of modifier particles on the coated particle matrix.

9. Electroless plating method. It refers to the process of metal precipitation by chemical method without external current, including displacement method, contact plating method and reduction method.

10. Supercritical fluid method. It is a new technology still under study. In supercritical conditions, reducing the pressure can lead to supersaturation, and high supersaturation rates can be achieved, allowing solid solutes to crystallize out of supercritical solutions.

11. Chemical vapor deposition method. At a relatively high temperature, the mixed gas interacts with the surface of the substrate, decomposing some components in the mixed gas, and forming a metal or compound coating on the substrate.

12. High energy method. The method of coating nanoparticles by using infrared rays, ultraviolet rays, γ-rays, corona discharge, plasma, etc., is collectively referred to as high-energy methods. The high-energy method usually uses some substances with active functional groups to achieve coating on the surface of nanoparticles under the action of high-energy particles.

13. Spray pyrolysis method. The process principle is to spray the mixed solution of several salts containing the required positive ions into mist, and send it into the reaction chamber heated to the set temperature, and generate fine composite powder particles through the reaction.

by ALPA

What are the classification techniques for ultrafine powders?

Ultrafine powder is not only the basis for preparing structural materials, but also a material with special functions. field is required. With the application of ultra-fine powder in modern industry more and more widely, the position of powder classification technology in powder processing becomes more and more important.

1. The meaning of classification

In the pulverization process, only a part of the powder usually meets the particle size requirements. If the products that have reached the requirements are not separated in time, and then pulverized together with the products that do not meet the particle size requirements, it will cause energy waste and over-crushing of some products.
In addition, after the particles are refined to a certain extent, the phenomenon of crushing and agglomeration will appear, and even the crushing process will deteriorate due to the larger particle agglomeration. For this reason, in the process of ultrafine powder preparation, it is necessary to classify the product. On the one hand, the particle size of the product is controlled to be within the required distribution range; Then crush to improve the crushing efficiency and reduce energy consumption.

With the improvement of the required powder fineness and the increase of output, the difficulty of classification technology is getting higher and higher. The problem of powder classification has become the key to restrict the development of powder technology, and it is one of the most important basic technologies in powder technology. one. Therefore, the research on ultrafine powder classification technology and equipment is very necessary.

2. The principle of classification

Classification in a broad sense is to divide the particles into several different parts by using the different characteristics of particle size, density, color, shape, chemical composition, magnetism, and radioactivity. Classification in a narrow sense is based on the fact that particles of different particle sizes are subjected to centrifugal force, gravity, inertial force, etc. in the medium (usually air and water), resulting in different motion trajectories, so as to realize the classification of particles of different particle sizes.

3. Classification of classifiers

According to the medium used, it can be divided into dry classification (the medium is air) and wet classification (the medium is water or other liquids). The characteristic of dry classification is that air is used as fluid, which is relatively cheap and convenient, but it has two disadvantages. One is that it is easy to cause air pollution, and the other is that the classification accuracy is not high. Wet classification uses liquid as the classification medium, and there are many post-processing problems, that is, the classified powder needs to be dehydrated, dried, dispersed, and waste water treatment, etc., but it has the characteristics of high classification accuracy and no explosive dust.

According to whether it has moving parts, it can be divided into two categories:

(1) Static classifier: There are no moving parts in the classifier, such as gravity classifier, inertia classifier, cyclone separator, spiral airflow classifier and jet classifier, etc. This type of classifier has a simple structure, does not require power, and has low operating costs. The operation and maintenance are more convenient, but the classification accuracy is not high, so it is not suitable for precision classification.

(2) Dynamic classifier: There are moving parts in the classifier, mainly referring to various turbine classifiers. This type of classifier is complex in structure, requires power, and consumes a lot of energy, but it has high classification accuracy and is easy to adjust the particle size of the classifier. As long as the rotation speed of the impeller is adjusted, the cutting particle size of the classifier can be changed, which is suitable for precision classification.

by ALPA

Application of talcum powder in engineering plastics

Talc powder is a white, flaky, high aspect ratio, inorganic and inert natural mineral. It is widely used in PP, PA, PC/ABS alloy, PBT, LCP and other engineering plastics. It has similar calcium carbonate filling cost reduction And near glass fiber reinforced dual function. Talc powder has the ability to increase the HDT temperature of products, the flexural modulus of thin-walled products, and reduce the coefficient of linear expansion CLTE, etc. It is widely used in industries such as automobiles, home appliances, and food containers.

The crystalline structure of talc is layered, which tends to be easily split into scales, and has special properties such as lubricity, anti-sticking, flow aid, non-absorbent, and chemical inertness. Ultra-fine talc powder is processed from natural minerals through multiple processes such as mining, rough selection, fine selection, crushing, coarse grinding, airflow grinding, etc. The key factor for high-quality talc powder products is to retain the flaky structure of talc powder to the highest degree .

1) Ultrafine talc powder filled products have high flexural modulus and are suitable for high rigid parts.
2) Filling modification has better dimensional stability, better aspect ratio control ability, and anti-warping performance is obviously better than glass fiber.
3) Talc micropowder can be used as an inorganic nucleating agent, assisting with an organic nucleating agent to achieve a nucleating effect and increase the HDT temperature.
4) Comply with the requirements of FDA, ROHS and other regulations, and meet the limit that talcum powder does not contain asbestos (the International Cancer Research Center IARC lists "asbestos-containing talc" as a carcinogen)

Application of talcum powder in TPO

Under the same experimental conditions, change the type of EPDM/POE, the content of the toughening agent, and select talc powder products of different thicknesses to evaluate the complete strength of the modified TPO, the notched impact strength at room temperature and low temperature, and HDT temperature and The performance of the linear shrinkage of the material. The following is the particle size index of Yimifabi talcum powder products that are routinely used in the market.

Ultra-fine talc powder has more flaky structure, which can better strengthen TPO plastics, endow TPO products with low shrinkage rate, improve the dimensional stability of products, and be used to produce "thin-walled" products, so that products can be designed Thinner and more precise dimensions.

by ALPA

Effect of Powder on Thermal Conductivity of Alumina Ceramics

In the preparation process of ceramic materials, the preparation of powder is a very important link, and the performance of the powder directly determines the performance of the finished ceramic product. The performance of the powder mainly depends on the particle size distribution and microscopic morphology of the powder.

The particle size distribution of powder mainly affects the grain size and sintering performance of ceramic materials. The researchers studied the effect of the particle size distribution of the powder on the density of the alumina ceramic material, and the results showed that the alumina ceramic with a density of nearly 99% can be prepared regardless of the use of a wide or narrow particle size distribution powder, and its grain size can be maintained. At about 1 μm, however, a wider particle size distribution can increase the density of the powder compacted green body, enabling the material to undergo a densification process with a smaller shrinkage rate. The main reason is that the large particles in the powder with a wide particle size distribution will More voids are formed, which are filled with fine particles during the molding process.

The researchers conducted a more in-depth study on this. They divided the sintering into three stages: initial, middle, and late stages. The powder with a wider particle size distribution increases the density of the green body and accelerates the densification rate of the ceramic in the early stage of sintering. In addition, in the middle stage of sintering, the powder with wide particle size distribution increases the rate of grain growth, and the closed isolation pores in the material are embedded in the larger granular matrix, so it has better sinterability and helps To maintain a high sintering speed in the later stage of sintering. However, a wider particle size distribution will lead to a difference in densification due to the accumulation of local particles of the material. Even when the particle size distribution exceeds a certain size, the grain size of the sintered body will be too large and the pore structure will become coarser. In order to obtain highly densified alumina ceramics, the selection of molding and sintering methods plays a key role in the selection of powder particle size distribution. Therefore, the particle size distribution of the powder has a great influence on the density of the ceramic material, which in turn determines the thermal conductivity of the ceramic.

The alumina powder with regular shape will have a great impact on the performance of ceramic materials during the sintering process. The researchers believe that the powder with reasonable particle size and particle gradation can be granulated by adding a binder to the powder. Making it more fluid will have a positive impact on subsequent molding and sintering. Among them, the granulation process is to make the powder form a spherical shape under the action of the binder, which also indirectly shows that spherical alumina plays a positive role in improving the density of ceramics during the molding and sintering process.

Therefore, it can be found that the performance (morphology and particle size) of the powder affects the performance of ceramic sintering, which also means that the thermal conductivity of ceramics is inseparable from it. After molding and sintering, the flake powder has a lower density and a higher porosity. , the researchers preliminarily speculated that its thermal conductivity is not high; and spherical alumina powder can produce high-density transparent ceramics, so it can be judged that using spherical powder to prepare thermally conductive ceramics is a suitable choice.

by ALPA

Superfine Powder Classification Process

Ultrafine powder raw materials are not only the basis for preparing structural materials, With the application of ultra-fine powder in modern industry more and more widely, the position of ultra-fine powder classification technology in powder processing becomes more and more important.

At present, it is difficult for the ultrafine powder produced by mechanical methods to achieve the required particle size through mechanical crushing at one time, and the product is often in a large particle size distribution range. In the use of various modern industrial fields, it is often required that ultrafine powder products be in a certain particle size distribution range.

At present, the more common grading method is based on the gravitational field and the centrifugal force field.

Gravity field grading principle is the oldest, most classic and relatively perfect theory, and its theoretical basis is based on Stokes' law in laminar flow state. In the classification process, it is assumed that the flow field is carried out in a laminar flow state, and the ultrafine solid particles are assumed to be spherical and free to settle in the medium. These are quite different from the actual situation. In the centrifugal force field, the particles can obtain much greater centrifugal acceleration than the gravity acceleration, so the sedimentation velocity of the same particle in the centrifugal field is much higher than that in the gravity field, in other words, even smaller particles can obtain a larger sedimentation velocity .

In addition, ultrafine powder classification can be divided into dry classification and wet classification according to the medium used. The characteristic of dry classification is that air is used as fluid, which is cheap and convenient, but it has two disadvantages. One is that it is easy to cause air pollution, and the other is that the classification accuracy is not high. Wet classification uses liquid as the classification medium, and there are many post-processing problems, that is, the classified powder needs to be dehydrated, dried, and dispersed for wastewater treatment, etc., but it has the characteristics of high classification accuracy and no explosive dust.

According to different fluid media, it can be divided into dry classification and wet classification. In dry classification, it can be divided into gravity type, centrifugal type and inertial type according to different classification principles.

1. Gravity super fine classifier

Gravity ultra-fine classifier is used to classify particles with different particle sizes in the gravitational field at different sedimentation velocities. There are two types of gravity classifiers: horizontal flow type and vertical flow type.

2. Inertia classifier

Particles have a certain amount of kinetic energy when moving, and when the moving speed is the same, the larger the mass, the larger the kinetic energy, that is, the larger the inertia of motion. When they are subjected to the action of changing their motion direction, different motion trajectories will be formed due to the difference in inertia, so as to realize the classification of large and small particles. At present, the classification particle size of this classifier can reach 1 μm. If the particle agglomeration and the existence of eddy current in the classification chamber can be effectively avoided, the classification particle size is expected to reach submicron level, and the classification accuracy and classification efficiency will be significantly improved.

3. Centrifugal classifier

Centrifugal classifiers are a type of ultra-fine classifiers that have been developed so far because they are easy to generate a centrifugal force field that is much stronger than the gravitational field. According to the different flow patterns in the centrifugal force field, it can be divided into two types: free vortex type and forced vortex type.

4. Jet classifier

Compared with other classifiers, the jet classifier has the following characteristics:

(1) There are no moving parts in the grading part, the maintenance workload is small, and the work is reliable.

(2) Jet jet can make the powder get good pre-dispersion.

(3) Once the particles are dispersed, they immediately enter the classifier for rapid classification, avoiding the secondary agglomeration of the particles to the greatest extent.

(4) Multi-level products can be obtained, and the particle size of each level can be flexibly adjusted through the angle of the grading blade and the outlet pressure.

(5) High classification efficiency and classification granularity.

by ALPA