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.
How to ensure the uniform particle size distribution of the product after jet pulverization
Although the application of jet mills is becoming more and more widespread, the emergence of equipment failure problems cannot be avoided. So, what are the faults that often occur in jet milling equipment and how to solve them.
After the jet mill is used for a period of time, the particles may become thicker. How should we deal with this situation? A thicker particle size means that the output may decrease, which may be caused by the wear of blades, bushings and other parts. These commonly used parts require routine maintenance, but also require regular inspections for wear and tear. If it is severely worn, replace it immediately. Otherwise, the grain size will become thicker.
The better the daily maintenance of the jet mill, the longer the service life and the longer the service life, the higher the value created for you.
Installation and debugging of jet mill:
1. After the machine is in place, it should be placed steadily and fixed with foot screws.
2. The inner cavity of the machine should be cleaned before trial operation.
3. During the test, attention should be paid to whether the machine has abnormal noise. If there is noise, it should be stopped in time for inspection.
4. Install the storage bag in the unloading hopper.
5. After turning on the power, pay attention to the rotation direction of the spindle, so that the spindle rotates in the correct direction as shown.
Operation and precautions of jet mill:
1. Before use, check whether all the fasteners of the machine are fastened and the belts are fastened.
2. The running direction of the main shaft must be in accordance with the direction of the arrow shown on the shield, otherwise it will damage the machine and may cause crushing damage to the fuselage.
3. Check whether there are metals and other hard debris in the crushing chamber of the machine, otherwise it will damage the jet mill and affect the operation of the machine.
4. The oil cup on the machine should be filled with lubricating oil continuously to ensure the normal operation of the machine.
5. Regularly check whether the grinder screen is abnormal, if it is damaged, it should be replaced immediately.
6. Check whether the electrical appliances are complete.
7. The purity of the materials must be checked before crushing, and metal debris must not be mixed in, so as to avoid damage to the jet mill or cause combustion and other accidents.
8. Stop feeding before shutting down. If you do not continue to use it, take out the leftover material from the machine.
Advantages of jet mill in the process of disintegrating and disaggregating agglomerated powder
During the crushing process, the mineral material absorbs a large amount of mechanical energy or thermal energy, so that the surface of the new ultrafine particles has a relatively high surface energy, and the particles are in an extremely unstable state. In order to reduce the surface energy of particles, they tend to reach a stable state by gathering close together, and it is also easy to cause particle agglomeration. Therefore, in the processing of ultra-fine powder, dispersing and disaggregating is also an important link, and there are many equipment used to disperse ultra-fine powder, and jet mill is one of them. Jet mill is often used for dry dispersion of agglomerated powder. Its advantages are high particle size reduction rate, no damage to the original morphology of particles, and strict control of large particles.
There are many types of jet mills, and they are also widely used for ultrafine grinding of materials below medium hardness. Its biggest feature is large output, narrow particle size distribution, and low product contamination. In the process of disaggregation and disaggregation of jet mill, agglomerated or agglomerated materials are fed into the dispersing cavity through the screw feeder, and the materials are impacted and sheared by the high-speed rotating rotor to crush and restore the materials. The scattered materials are transported to the material collection area by the ascending airflow, and are collected by the cyclone collector and the pulse dust collector, and the purified air is discharged by the induced draft fan.
Jet mill has the following advantages in the preparation of ultrafine powder by dispersing and disaggregating:
- Adopting innovative dispersing structure, compared with traditional dispersing machine, the unit energy consumption is reduced by 30%.
- The crushing and dispersing parts are made of highly wear-resistant materials, with low wear and long service life.
- The original particle size of the material can be restored after disaggregation and disintegration, and the particle size recovery rate can reach 100%.
- It can be equipped with an air flow classification device to classify materials with different finenesses during the break-up operation.
- The crushing rotor is balanced at high speed, and the machine base adopts anti-vibration design, stable operation and minimal vibration.
- Wide application range: hot air can be introduced to disperse and dry high-humidity materials; inert gas can be input to disperse flammable and explosive materials; cooling system can be added to heat sensitive materials or those with extremely low melting point The materials are broken up.
- The system adopts negative pressure production, and there is no dust pollution on the production site.
- Intelligent feedback control, simple operation and stable operation.
Jet mill can be used for calcining agglomerates, viscous, strong agglomeration powders, such as various metal powders, alloy powders, ultra-fine calcined kaolin, water-washed kaolin, nano-calcium carbonate, flame retardants, strontium carbonate, nano-active calcium, pyrophyllite, Precipitating barium sulfate, aluminum oxide, aluminum hydroxide, chemical raw materials, dyes, etc.
The influence of pressure and temperature on inert gas jet mill
The main factors affecting the crushing effect of the jet mill:
- Pressure
The pressure of the working fluid is the main parameter that produces the jet flow velocity, and it is also the main parameter that affects the pulverization fineness. The kinetic energy of the working fluid jet is proportional to the first power of its mass and the square of its speed. Therefore, the higher the pressure and the faster the speed, the greater the kinetic energy. When the steam pressure increases to a certain value, although the flow rate of the airflow through the nozzle no longer increases, but the pressure increases, the density of the airflow increases, and the kinetic energy increases accordingly. As for how high the pressure to choose when crushing depends on the crushability and fineness requirements of the material, when superheated steam is used to crush the titanium dioxide, the steam pressure is generally 0.8～1.7MPa, and the crushed and calcined materials are generally higher. The material can be lower.
- Temperature
Because of the increase in temperature, the flow rate of the gas can be increased. Take air as an example: the critical velocity at room temperature is 320m/s. When the temperature rises to 480℃, the critical velocity can be increased to 500m/s, that is, the kinetic energy increases by 150%. Increasing the temperature of the working fluid is beneficial to the crushing effect. When pulverizing titanium dioxide, the temperature of superheated steam is generally about 300-400℃. Usually, the temperature is higher when pulverizing the calcined material, and the temperature is lower when pulverizing the surface-treated material. Because some surface treatment agents, especially organic surface treatment agents, are not resistant to high temperatures, sometimes it is only necessary to overheat 100°C on the basis of the original steam temperature.
Note on jet mill:
(1) When the unloading equipment is in operation, the unloading outlet cannot be reached to avoid accidents.
(2) The speed of the impeller cannot exceed the specified speed, otherwise the temperature will be too high and the impeller and motor will be damaged.
(3) The safety valve should be checked regularly to ensure safety.
The jet mill is completely enclosed during the crushing process, and has a professional dust collection device, which will not cause dust leakage. This is a good equipment for many workshops that need to undergo environmental assessment transformation. This jet mill is widely used in chemical, mining, abrasives, refractory materials, battery materials, metallurgy, building materials, pharmaceuticals, ceramics, feed, new materials, environmental protection and other industries, as well as ultra-fine grinding and dispersing of various dry powder materials. And the performance of shaping particles is very good, which can fully meet the mesh size of ultra-fine crushing of various materials.
What factors depend on the particle size of the ultra-fine jet mill
There are two basic methods for obtaining ultra-fine powders, one is physical method, the other is chemical synthesis, and the other is a hybrid method based on these two methods. And nanomaterials are generally prepared by a hybrid method. The main equipment for preparing ultra-fine powder by physical method is grinder, classifier and collection equipment of various principles. The ultra-fine jet mill is an important way to obtain ultra-fine powder by dry processing.
The ultra-fine jet mill is the shearing of the material by the high-pressure airflow, the impact between the particles of the material itself, the impact and friction between the material and other parts of the equipment, and the material is smashed. The ultra-fine jet mill can be operated in an aseptic state. The average particle size of the material after airflow pulverization is fine, the particle size distribution is narrow, the particle shape is regular, the surface is smooth, and it has the characteristics of high purity, high activity, and good dispersibility. Moreover, it does not generate heat during pulverization, and is suitable for pulverizing low-melting and heat-sensitive substances. Therefore, the ultra-fine jet mill is very suitable for the ultra-fine preparation of drugs. According to statistics, about 25% of ultrafine jet mills in the world are used in the pharmaceutical industry.
The control of the particle size of the product by the ultra-fine jet mill mainly depends on the size of the raw material, the crushing pressure, the feeding pressure, and the feeding speed. The specific logical relationship between the ultra-fine jet mill and these parameters is: the smaller the particle size of the raw material, the higher the crushing efficiency; on the contrary, the larger the particle size of the raw material, the relatively low crushing effect. When the crushing pressure and the feed pressure are constant, the product will be finer when the feed rate is reduced, and the product will become coarser when the feed rate is increased. In the case of a certain feed rate, the particle size of the product will be finer when the crushing pressure is increased, and the product will become coarser when the crushing pressure is reduced. Therefore, particle size control is achieved by adjusting the parameters of the ultra-fine jet mill during the crushing process to achieve different crushing fineness. Before crushing, it is necessary to determine the relationship between the feed rate and the pressure and then determine the appropriate crushing parameters to achieve the customer's Granularity requirements. The particle size of the product needs to use a particle size detector to check the fineness and distribution range. In addition, if the electron microscope is used for measurement, it can be more accurate. Of course, you can also compare the detection results with the internationally famous particle size detector.
The ultra-fine jet mill is a relatively precise machine. In the daily use and maintenance process, some details still need to be paid attention to by the operator. In order to improve the crushing efficiency of the ultra-fine jet mill, it is necessary to check whether the raw materials meet the requirements before production. It is strictly forbidden to mix foreign objects in the raw materials. During production, a certain amount of materials must be kept in the grinding cavity of the ultra-fine jet mill. Under the condition of constant pulverizing gas flow, there are more materials in the grinding cavity, and the classifier current is large; there are few materials in the grinding cavity, and the classifier current is small. 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 see if it has reached the pressure required for crushing, as well as the grading motor of the ultra-fine jet mill. After 3000 hours of operation of the equipment, or long-term shutdown and long-term storage before reusing it, please promptly Clean up the materials adhering to the nozzle of the ultra-fine jet mill, the inner wall of the mill cavity and the grading part to prevent the impact of the ultra-fine jet mill's smashing effect.
Significance of ultrafine powder classification
Ultrafine powder is not only the basis for the preparation of structural materials, but also a material with special functions. It is widely used in fine ceramics, electronic components, bioengineering treatments, new printing materials, high-quality refractory materials, and materials related to fine chemicals. And many other fields. With the more and more widespread application of ultrafine powder in modern industry, the status of powder classification technology in powder processing is becoming more and more important.
In the crushing process, only part of the powder meets the particle size requirements. If the products that have reached the requirements are not separated in time, and the products that do not meet the particle size requirements are pulverized together, it will cause energy waste and over-crushing of some products. .
In addition, after the particles are refined to a certain degree, the phenomenon of crushing and agglomeration occurs, and the crushing process is even worse due to the agglomeration of the particles. For this reason, products should be classified during the preparation of ultra-fine powders. On the one hand, the particle size of the product should be controlled within the required distribution range, and on the other hand, the products with the required particle size in the mixture can be separated in time to return the coarse particles. Re-pulverization to improve the pulverization efficiency and reduce energy consumption.
With the increase in the fineness of the powder required and the increase in output, the difficulty of grading technology is getting higher and higher. The problem of powder grading has become the key to restricting the development of powder technology, and it is one of the most important basic technologies in powder technology. one. Therefore, it is necessary to study the technology and equipment of ultrafine powder classification.
Jet mill is more suitable for crushing materials with high added value and good brittleness
The development of ultra-fine pulverization technology is becoming more and more rapid, thanks to the market demand for jet mill equipment. Jet mill, cyclone separator, dust collector, and induced draft fan constitute a complete pulverization system. The pulverization mechanism determines the scope of application of the pulverizer. The characteristics of wide and high fineness of the finished product. Typical applicable materials are: superhard diamond, silicon carbide, metal powder, etc.
The ultrafine pulverizer enters the cylindrical pulverizing chamber through the feed port, and the grinding wheel that moves in a circular motion along the grinding rail performs pulverization and shearing. The crushed materials are brought out of the crushing chamber by the negative pressure airflow generated by the fan and enter the material collection system. After filtering through the filter bag, the air is discharged, the materials and dust are collected, and the crushing is completed. By changing the ordinary air of the gas source into inert gas, such as nitrogen and carbon dioxide, the pulverizer can be used as an inert gas protection device. It broke the bottleneck of the crushing industry and brought the crushing industry to a new level.
The jet mill adopts supersonic jet grinding and cold plasma pulverization, which is completely different from the existing pure mechanical pulverization method. There is no local overheating in the crushing process, even if it is crushed at low temperature, it can be completed immediately, so as to maximize the retention of the biological activity of the powder components, thereby producing the required high-quality products. Due to the supersonic jet grinding, the feed force distribution is relatively uniform, avoiding excessive crushing, and the obtained ultrafine powder has a uniform particle size distribution, which greatly increases the powder's adsorption, solubility, and specific surface area.
The ultra-fine powder jet mill adopts a closed system, which not only avoids polluting the surrounding environment, but also prevents the product from being polluted by dust in the air. It is widely used in the ultra-fine grinding of food and health products. In the crushing process, the microbial content and dust pollution are controlled, and products with ultra-narrow particle size distribution are produced. The collection rate of the conventional jet mill is more than doubled. The automatic control is realized, the operation is simple, the operation is stable, and the equipment is intelligent.
How to deal with the abnormality of the superfine pulverizer to reduce the loss
The superfine pulverizer has powerful functions and is widely used. However, abnormalities will inevitably occur during the use of the equipment, which may affect the production situation, or cause the production line to stop, and the loss is immeasurable. Therefore, when encountering some exceptions, we should master certain handling methods.
The parts of the shredder are damaged or fall off, or if hard objects such as rocks or iron enter the machine, there will be abnormal noises. The inspection should be stopped immediately, and the damaged parts should be replaced or the hard objects should be removed. The main reasons for low production efficiency are insufficient motor power, improper pulley preparation, belt slippage, severe hammer wear, uneven feeding or excessive moisture content of raw materials. If the above situation occurs, you can take corresponding measures to solve the problem, or replace the motor or pulley to increase the speed, but it must not exceed the rated working speed; or adjust the belt tightness, or replace the belt, or replace the hammer. In operation, the feed should be uniformly added in small amounts and quickly to maintain continuous uniformity; over-wet raw materials should be dried and then crushed for processing.
For the operation and use of the ultrafine pulverizer, after unpacking, first carefully check whether the equipment is damaged during transportation, and then put the electrical control devices of the high-speed machine and auxiliary machines in place, and then connect them to the pipelines of the main and auxiliary machines. When the flange of each nozzle is assembled, ensure the sealing of the pipeline. At the same time, a ground connection is adopted between each single unit and the pipe flange to avoid dust explosion caused by static sparks. Before trial operation of each stand-alone machine, check whether there are metal objects in the machine, and remove it if there is any. In addition, check whether the bolts are firm, the tightness of the belt, the reliability of the guard, and so on. The motor starts steadily. After five minutes of no-load operation, the operator should carefully observe the various instruments on the control cabinet and wait for the no-load current to stabilize before feeding.
What should I do if the bearing of the superfine grinder is overheated? When the bearing is poorly lubricated, damaged, or the main shaft is bent, the rotor is severely unbalanced, and the belt is too tight, the bearing will overheat. The bearings can be restored to normal state by adding or replacing lubricating oil, replacing bearings, spindles, balancing rotors, and adjusting belt tightness. The following reasons may cause the crusher to vibrate strongly: the hammers are installed incorrectly, the weight deviation of the corresponding two sets of hammers is too large, the bearing is damaged or the main shaft is bent, and the foot connecting screw is loose. If the hammers are arranged incorrectly, they should be rearranged according to the instructions; if the weight deviation of the corresponding two sets of hammers is too large, the weight should be balanced so that the weight difference does not exceed 5 grams; if the bearing is damaged or the spindle is bent, it should be replaced in time ; If the foot connecting screws are loose, they should be tightened.