Air classifier technology is becoming more and more important in the powder processing industry
The raw material of the air classifier is not only the basis for the preparation of structural materials, it is also a material with special functions, such as fine ceramics, electronic components, biological engineering treatment, new copy materials, high-quality refractory materials, and materials related to fine chemicals. Required by the field. With the more and more widespread application of air classifiers in modern industry, the status of air classifier classification technology in powder processing is becoming more and more important.
Main research trends of super subdivision
(1) Research and develop new powerful dispersion devices. At present, physical methods and chemical methods have been applied. In the chemical method, it is commonly used to add a dispersing aid to the material before classification in the previous pulverization process, but this method will increase the production cost, and the dispersant may pollute the material, so it is only used in special circumstances. Commonly used physical methods are mechanical or high-speed compressed air dispersion devices, of which high-speed compressed air is the most used. In addition, the chemical method of surface modification to disperse particles is another important way for ultrafine dispersion.
(2) Research on hierarchical flow field. Analyze the flow characteristics of the classification flow field of the turbo-type air classifier and the movement of the classification particles (mainly the movement characteristics of the gas-solid two-phase flow), clarify the influencing factors of the classification flow field, design a reasonable structure form, and reduce local vortices The generation of the grading flow field makes the flow state of the graded flow field as uniform as possible.
(3) The design of the grading force field and the exploration of new grading principles. Through the study of particle surface characteristics, interface states, and the behavior differences of particles in different media and different force fields, new principles, methods and approaches are found, stable and adjustable force fields are designed, and a new and more refined superfine level is developed. machine.
(4) Research on performance parameters and system operating parameters. Through the study of the characteristic parameters of the classifier and the analysis of the operating parameters of the classification system (or crushing-classification system), the classification equipment of reasonable specifications is designed, and the structural parameters and system operating parameters are optimized to make the classification equipment in an ideal working state, that is, high efficiency. , Energy saving and low consumption.
(5) Research on corresponding measures for other problems in the super-subdivision process. For example, in view of the explosion hazard of ultra-fine powder, research on inert gas as a grading medium is carried out; for the tensile test of ultra-fine powder, the development and research of testing devices with good dispersion performance and standard operation can be carried out.
Jet mill has become the first choice for the preparation of cathode materials
Many kinds of equipment can be used to crush the positive electrode material, such as: grinder, pin sand mill, jet mill, etc. Compared with other crushing equipment, the average particle size of the material processed by the jet mill is fine, the particle size distribution is narrower, the particle surface is smooth, the particle shape is regular, the purity is high, the activity is high, and the dispersion is good, which fully meets the preparation requirements of electrode materials. Therefore, jet mills are widely used.
At present, the preparation of cathode materials using jet mills has become the industry's first choice. Jet mill is a kind of equipment that uses high-speed airflow to achieve ultra-fine grinding of dry materials. It consists of a crushing nozzle, a grading rotor, a screw feeder and so on. The material enters the crushing chamber through the screw feeder, and the compressed air is jetted into the crushing chamber at a high speed through a specially configured supersonic nozzle. The material is accelerated in the supersonic jet and repeatedly impacts and collides at the intersection of the nozzles to achieve crushing. The pulverized material enters the classification chamber with the ascending airflow. Due to the high-speed rotation of the grading rotor, the particles are subjected to the centrifugal force generated by the grading rotor and the centripetal force generated by the viscous action of the airflow. When the centrifugal force is greater than the centripetal force, the coarse particles above the grading diameter return to be crushed. The chamber continues to be impacted and crushed, and the fine particles below the classification diameter enter the cyclone separator and collector with the air flow for collection, and the gas is discharged by the induced draft fan.
There are many advantages of using a jet mill to prepare cathode materials, which can be summarized as follows:
1. The jet mill has the ability to shape, the finished particles have excellent morphology, and can obtain spherical (potato-like) particles.
2. Narrow particle size distribution and high tap density of the finished product.
3. The over-crushing is low, and the finished product rate can reach 75%-95% or more.
4. The inside of the equipment can be lined with wear-resistant materials, and the finished product has high purity and low equipment wear.
5. The air flow classifier adopts frequency conversion adjustment, which can be adjusted arbitrarily between 0.5μm and 100μm.
6. The equipment runs stably, and there is no difference or change when it is turned on continuously for a long time.
7. Fully enclosed negative pressure operation, automatic control, low noise and no dust pollution.
The jet mill for positive electrode material uses precision ceramics and polyurethane lining, which can 100% prevent metal pollution caused by the crushing process of materials and ensure the purity of crushed products. It is especially suitable for electronic materials that require extremely high iron content, such as lithium cobaltate, lithium manganate, lithium iron phosphate, lithium iron phosphate, ternary materials, cobalt tetroxide, lithium carbonate, lithium nickel cobaltate and other battery cathode materials.
What are the factors related to the degree of pulverization of the jet mill?
Air jet mill is a kind of fine granularity among dry milling equipment, so it is favored by many industries. So to what extent can the jet mill be crushed? Generally speaking, the crushing range of the jet mill is between 1-74 microns. But it does not mean that it can be as thin as 1 micron, but is affected by many factors. Let's take a look below.
The jet mill uses the kinetic energy of high-speed airflow to make particles collide and rub against each other to crush. It has the characteristics of continuous production process, large production capacity and high degree of automation. It can be used in a variety of fine processing industries, such as electronic materials, chemicals, mining, metal powder, etc.
To what extent can the jet mill crush? It is related to the following factors:
1. For the initial fineness of raw materials, the jet mill generally requires the feed to be below 50 mesh.
2. It is related to the physical properties of the material, the fluidity of the material and the uniformity of the particles are related. Some materials have poor fluidity, many impurities, and high solvent content. There may be material blocking during the production process. At this time, special equipment is needed to do this. Not all materials can be pulverized with standard equipment to achieve pulverization fineness. .
3. It is related to the crushing pressure in the crushing process. The feed pressure of some equipment is greater than the crushing pressure, and the crushing pressure of some equipment is greater than the feed pressure. Specific materials need to be specifically designed.
4. It is related to the feeding speed. Not all materials have good fluidity. Whether it is screw feeding or vibrating feeding, the feeding process is a very important factor. Some very fine materials are difficult to feed. , At this time, it is necessary to use a dedicated personalized configuration to achieve the feeding effect.
5. There is also a relationship with the degree of optimization of the jet mill. There are many manufacturers of jet mills, but the fineness of the same material made by different manufacturers is different, even if it is made by different models of equipment from the same manufacturer. The fineness is also different, but according to experience, the effect of a larger crusher is better than a smaller one.
6. It is related to the operation method of the operator's proficiency. Some equipment requires a small and then large pressure operation to start up, and some are directly operated in one step.
It can be seen from the above that there are many factors that affect the limit particle size of the jet mill, the most important of which is the physical properties of the raw material. The drier and brittler the raw material, the finer the limit particle size that can be reached. For example, raw materials such as carbon powder and graphite have better brittleness. If you use a jet mill, you can easily obtain micron or even sub-micron fine powder.
Air classifier is a favorable equipment to control product particle size
The ultrafine air classifier can be operated in a sterile state. The average particle size of the material after the air classifier is fine, the particle size distribution is narrow, the particle shape is smooth, and it has the characteristics of high purity, high activity, and good dispersion. In addition, no heat is generated during the pulverization process, which is suitable for pulverizing low melting point and heat-sensitive substances. Therefore, the ultrafine airflow crusher is very suitable for the preparation of ultrafine drugs. According to statistics, about 25% of the international ultrafine airflow classifiers are used for Pharmaceutical Industry.
The control of the product particle size by the air classifier mainly depends on the raw material particle size, crushing pressure, feed pressure and feed speed. The logical relationship between the air classifier and these parameters is: the smaller the size of the raw material, the higher the crushing efficiency; the larger the size of the raw material, the lower the crushing efficiency. When the crushing pressure and the feed pressure are constant, reducing the feed speed will make the product finer and thicker. In the case of a certain feed rate, the particle size of the product will be finer, the crushing pressure will be reduced, and the product will become thicker. Therefore, the particle size control depends on the adjustment of the parameters in the ultrafine air classifier process to achieve different grinding fineness. Before smashing, it is necessary to determine the relationship between the feed speed and the pressure and then determine the appropriate smashing parameters to meet the customer's particle size requirements. The particle size of the product needs to be checked by a particle size detector to check the fineness and distribution range. In addition, if the measurement with the electron microscope can be more accurate, of course, it can also be compared with the internationally famous particle size detector.
The air classifier is a relatively precise machine. In the process of daily use and maintenance, some details still need the attention of the operator. In order to improve the classification efficiency of the ultra-fine air classifier, it is necessary to check whether the raw materials meet the requirements before production. Mix foreign matter into the raw material. During the production process, a certain amount of material must be kept in the grinding cavity of the air classifier. Under the condition of constant pulverizing gas flow, there are more materials in the grinding chamber, the current of the classifier is larger, and the materials in the grinding chamber are less, and the current of the classifier is smaller. In addition, the feeding speed must be uniform and stable, not too fast or too slow. If the feeding speed is too fast, the equipment will be overloaded.
The equipment should be maintained regularly, and the air supply pressure should be checked frequently to meet the pressure required for crushing, as well as the classification motor of the airflow classifier. After the equipment runs for 3000 hours, or for long-term shutdown and long-term storage and reuse, please clean the nozzles and grinding chambers. The materials on the inner wall should be cleaned up in time to prevent the classification effect of the air classifier from being affected.
Ultrafine jet mill provides a new way for medical powder
Traditional pulverizers are also very high in particle size and powder extraction rate, and have certain limitations in the powder collection rate and the preservation of effective ingredients, etc., and they need to be adjusted accordingly when used in various industries. The ultra-fine jet mill technology is better when pulverizing, providing a new outlet for ultra-fine Chinese medicine powder.
The working principle of the ultra-fine jet mill is to pass purified and dried compressed air through a special nozzle of a certain shape to form an airflow at a speed of 3,600 kilometers per hour. With its huge kinetic energy, the animal materials collide with each other in the closed pulverizing cavity, making Mohs Materials with a hardness of 1-10 are crushed into superfine powder. The size and output of the required particles can be effectively controlled by adjusting the working parameters of the crushing classifier.
The features of ultra-fine jet mill products are:
- The equipment only needs compressed air to run, and does not require a motor for classification. The equipment itself has an automatic gaseous classification device.
- Low energy consumption, jet pulverization itself is a pulverizing process with higher energy consumption. Our equipment has been optimized so that the pulverizing airflow is greater than the feed airflow without back blowing, thus ensuring lower energy consumption.
- The whole system is made of stainless steel, and the internal mirror surface is 0.2 micron polished, which reduces adhesion and loss.
- The cyclone collection system can effectively reduce the loss of materials and avoid expensive production losses.
- Using twin-screw feeding, it can operate continuously and stably effectively, ensuring stable particle size distribution.
- The equipment is easy to clean and install, and easy to disassemble and assemble.
- The equipment is equipped with casters, which can be easily moved to the cleaning workshop to clean the equipment.
With the continuous advancement of ultrafine jet pulverization technology, the pharmaceutical process is also constantly improving. The jet mill plays a relatively large role in the pharmaceutical crushing process, and has made certain breakthroughs in improving the quality of pharmaceuticals. Improving the efficiency, fineness of pulverization and uniform particle size distribution of the ultrafine jet pulverizer is the direction of enterprise research and development.
Applicable scenarios of laboratory jet mill
The laboratory jet mill is suitable for dry, heat-sensitive materials. The equipment does not heat up during operation, has a simple structure, is easy to use, and has no moving parts. When the chemical raw materials and pharmaceutical materials are stable, the materials can be crushed to the limit of 1-3 microns. After crushing, the materials are pollution-free. The optimized compact appearance is suitable for laboratories with high site requirements. The laboratory jet mill is used in small batch production and experiments, and is suitable for ultrafine pulverization and depolymerization of various dry and brittle raw materials, crystals, etc.
The material of the laboratory jet mill is crushed in a crushing chamber made of high-purity and high-hard materials. Only clean compressed air is in contact with the material, without any other impurities, and no mechanical friction, which greatly guarantees the purity of the product. . The laboratory jet mill is always pulverized at a temperature below normal temperature. Generally, it will not change the chemical properties of materials under room temperature conditions, so it is especially suitable for heat-sensitive raw materials.
The entire system of the laboratory jet mill is sealed and crushed, with less dust, low noise, and the production process is clean and environmentally friendly. The pulverization process of the laboratory jet mill is extremely short, which can be completed in an instant without repeated pulverization, and the efficiency is much higher than other milling equipment. Simple operation, easy disassembly and assembly, and easy cleaning.
The pulverization effect can be achieved by using a laboratory jet mill, all of which require a compressor to provide a compressed air source, but there is a difference between the pulverization process and the process of controlling the particle size.
When choosing a laboratory jet mill, you must understand whether the material you want to process is dangerous. If there is a risk of dust burning or explosion, you have to consider using nitrogen as the pulverizing medium. It must not be used for cost and safety protection. Because the jet mill is ultra-fine pulverization, the finer the raw material particles are processed, the larger the specific surface area. The risk factor is also greater. The other is to consider the safety protection of the equipment itself, whether anti-static filter bags are used, and whether there are measures such as system pressure monitoring.
The laboratory jet mill is an ultrafine pulverizing equipment, not a nanometer pulverizing equipment. This physical method is difficult to reach the nanometer level. The laboratory jet mill is mainly used for a small number of samples, easy to clean is a more important function.
What are the characteristics of jet mill used for silica matting powder
Silica can be used in all coatings. In the processing of silica matting powder, pulverization and classification are indispensable. At this time, a fluidized bed jet mill is needed. The equipment uses high-speed airflow to carry the animal material, so that the particles of the raw material are friction and shear between the particles, and the particles and the inner wall of the equipment collide with each other, so that the raw materials are subjected to double pulverization, and the pulverization efficiency is improved. Therefore, the fluidized bed jet mill is almost instantaneous. The raw materials can be crushed to ultrafine powder state.
The fluidized bed jet mill for silica matting powder has the following characteristics:
The principle and characteristics of the lower crushing area are the same as those of the disc-type supersonic jet mill, so that the powder added to the mill is easily hit by the air flow, and has a higher crushing probability than the fluidized bed collision type model.
The upper classification principle adopts fluidized bed type horizontal turbine forced classification, the cutting point is accurate, the efficiency is high, and any raw material of different hardness can be controlled.
In the crushing process, due to the forced classification of the upper turbine, the coarse material settles on the bottom of the crusher. The powder concentration in the crushing area is much higher than that of the disc jet mill, so this model is more pulverized than the disc jet mill higher efficiency.
The materials of the crushing parts are all made of corundum ceramic materials, including the high-speed classifying impellers are all made of corundum ceramic materials. Ensure that the pulverized material maintains high purity, no contamination by impurities, and the whiteness of the finished product is not affected.
The raw materials can be selected according to the customer's process requirements and performance requirements such as raw material whiteness, transparency, particle hardness, pore volume oil absorption value, etc. The crushing model can process powder products that meet the required particle size.
When processing silica matting powder, its product fineness can be d100<18μm. When it smashes the crushed object, it can adjust the median diameter of the finished product while ensuring the upper limit of the control particle size. The particle size distribution (median diameter) of the required powder product can be controlled manually.
What are the working steps and core technology of the jet mill?
With its unique working principle, the jet mill can process ultrafine powders of various materials in a dry, high-purity, and low-temperature manner. It is widely used in chemicals, mining, abrasives, battery materials, refractory materials, non-metallic minerals, metallurgy, and building materials. , Pharmaceutical, food, pesticide, feed, new materials, environmental protection and other industries and various dry powder materials ultra-fine crushing, breaking and particle shaping.
The jet mill is one of the most important ultra-fine grinding equipment. Among them, the fluidized-bed jet mill has the advantages of low energy consumption, low wear and high classification accuracy, and is the most widely used in the current ultra-fine grinding equipment.
Working principle and characteristics of fluidized bed jet mill:
The fluidized bed jet mill combines the principle of counter-injection or counter-injection with the expanding gas jet flow in the fluidized bed. Its working principle is:
(1) The material is fed into the silo through the star valve, and the screw feeder sends the material into the crushing chamber or directly into the crushing chamber;
(2) The supersonic jet generated by the rapid expansion and acceleration of compressed air through the pulverizing nozzle forms a centripetal reverse jet flow field in the lower part of the pulverizing chamber. Under the action of the pressure difference, the material at the bottom of the mill chamber is fluidized, and the accelerated material The intersections of multiple nozzles converge, causing violent impact, collision, friction and crushing;
(3) The pulverized material moves to a certain height in the upper part of the crushing chamber with the rising air flow. The coarse particles fall back to the lower part of the mill chamber along the wall of the mill under the action of gravity, and the fine powder moves to the upper turbine classifier along with the air flow. machine.
(4) In the flow field generated by the high-speed turbine, the coarse particles are thrown to the vicinity of the cylinder wall under the action of centrifugal force, and fall back to the lower part of the mill chamber together with the stalled coarse powder to be crushed.
(5) The fine powder that meets the fineness requirements is transported to the cyclone separator through the exhaust pipe through the grading sheet flow channel for product collection. A small amount of fine powder is further separated from the gas and solid by the bag trap, and the purified air is discharged by the induced draft fan. outside.
(6) The connecting pipe can keep the pressure of the silo and the crushing chamber consistent.
(7) The upper and lower material levels of the silo are automatically controlled by the precision level sensor to automatically control the star valve feeding, and the material level of the crushing chamber is automatically controlled by the dynamic current transmitter on the classifier to automatically control the feeding speed of the screw feeder, so that the crushing is always at the best status.
The core R&D technologies possessed by the jet mill include: full use of jet energy, high-efficiency classification, strict control over smashing technology, reliable sealing and no leakage technology, large particle control technology, complete, stable and smooth system design technology, constant pulverization cavity Gas-solid concentration ratio technology, ultra-fine powder collection and dust removal and flue gas treatment technology, ultra-fine pulverized particle shape control technology, etc.
Performance characteristics and material selection of multi-stage air classifier
Performance characteristics of multi-stage air classifier:
1. Large output, low energy consumption and high grading efficiency.
2. Concentrated particle size: The machine uses an original vertical impeller for classification. The stable classification technology and special sealing measures effectively prevent the leakage of coarse particles, so that the product has no large particles, the particle size is concentrated, and the classification accuracy is high.
3. Reasonable structure: products with 1-6 granularities can be produced at the same time according to user requirements.
4. Strong applicability: It can be combined with various mills (jet mill, mechanical mill, ball mill, Raymond mill, vibration mill, etc.) to form a closed-circuit or open-circuit combined operation.
5. High degree of automation: all impeller classifiers at all levels adopt electronic frequency modulation and stepless speed regulation, and the automatic circulation type multi-box dust collection process realizes electronic control and automatic dust removal, which improves the stability of the negative pressure of the whole machine.
Maintenance method of multi-stage air classifier:
1. All lubricating points are lubricated with sodium-based grease or calcium-based grease.
2. Check whether the lubricating oil inside the reducer is on the line of the oil needle every shift, and change the oil every 6 months.
3. Frequently check whether the bearing bushes, bearings and sealing rings of the lower support or intermediate frame are worn out, and whether the bearing bushes are damaged in order to replace them in time.
4. For bearing lubrication, a manual dry oil pump must be used to inject high-pressure oil into the bearing every 4 hours to maintain the sealing performance of the bearing.
For the equipment materials of the multi-stage air classifier, there are mainly three types: carbon steel, stainless steel, and carbon steel plus wear protection. Choose the appropriate equipment material according to the characteristics of different materials.
The overall cost of a multi-stage air classifier made of carbon steel is lower than that of stainless steel and carbon steel with wear protection. For materials used in the food and pharmaceutical industries, stainless steel equipment is usually used, so that no pollution will be caused during the classification process. For materials with high hardness such as quartz, carbon steel and internal ceramic wear protection are used to extend the service life of the equipment and reduce the frequency of replacing parts.
Multi-stage air classifiers are widely used in the kaolin industry. Kaolin is a non-metallic mineral with kaolin as the main mineral composition. It is mainly used for household ceramics, building sanitary ceramics and refractory ceramics. It is also used for papermaking and construction. As fillers or white pigments for paints, rubber, plastics, textiles, etc., kaolin has been used in many industries.
At present, kaolin mainly relies on mechanical pulverizers and jet pulverizers for fine and deep processing. The mechanical crusher generally crushes to about 700-1000 mesh, but the use of mechanical crushing will increase the iron content in the final product, which is not suitable for industries that require purity. The jet mill can pulverize to 1000-5000 mesh, and the product produced has a finer particle size and higher purity. For industries with relatively high application purity requirements, multi-stage airflow classifiers should be used.
What are the reasons for the vibration of the jet mill
The jet mill plays a pivotal role in medicine and chemical industry, but it is precisely because of this that the mill equipment has a very important role in actual operation and needs to be extremely valued. Generally speaking, people who only need to have three months of operation will have very easy operation experience. In many cases, we will use the best operator to cooperate. The ceramic-lined pipe is manufactured by the high-tech production process-self-spreading high-temperature clutch synthesis method. The pipe is composed of corundum ceramic, transition layer, and steel from the inside to the outside. The ceramic layer is densely formed at a high temperature above 2200℃. Corundum porcelain (AL2O3) forms a firm bond with the steel pipe through the transition layer.
Air jet pulverizers generally adopt the way that the motor is directly connected to the pulverizing device. This connection is very simple, fast, and easy to maintain. It is the commonly used connection method at present. If the two parts are not well connected during the assembly process, the overall vibration of the jet mill equipment will occur, causing serious damage to the machine body. If we cannot accurately operate the equipment, it will cause damage. There are many reasons for the vibration of the jet mill. We must frequently overhaul the equipment in order to ensure the stable operation of the jet mill during processing.
1. The hammer is installed incorrectly during the maintenance and assembly. In order to prevent the weight of the rotor from losing balance when the hammers are used in reverse, all the hammers in the crusher must be reversed, otherwise strong vibration will occur during operation.
2. Corresponding to the difference between the weight of the two sets of hammers is more than 5 grams. The elimination method is to adjust the weight of the hammer so that the difference between the weight of the corresponding two groups is less than 5 grams.
3. The individual hammer pieces are stuck too tightly and are not thrown off during operation. It can be turned and observed by hand after stopping the machine, and find a way to make the hammer rotate flexibly.
4. The weight of other parts on the rotor is unbalanced. At this time, you need to carefully check and adjust the balance.
5. The main shaft is bent and deformed. The solution is to straighten it or replace it.
6. The bearing clearance exceeds the limit or is damaged. Generally, the problem can be solved by replacing the new bearing.
7. The bottom corner fixing nut is not tightened or loosened during operation. The solution is to tighten it.
The jet mill has a large processing capacity, and the optimized structure of the equipment can increase the throughput of materials by more than 42%, which greatly improves the production capacity. In addition, the discharge port has also been specially modified, which can adjust the discharge particle size in a larger range, which can better meet the needs of customers and the market, and has a stronger market adaptability.