Advantages of jet mill
The structure of the jet mill: It is mainly composed of a grinding chamber, a nozzle orifice, a material outlet, an air flow outlet, a compressed air inlet, and a classification zone. The flat jet mill has a wide range of applications due to its simple structure and easy manufacturing.
Working principle: The compressed air or superheated steam is transformed into high-speed air flow through the nozzle. When the material is fed into the crushing chamber through the feeder, it is sheared by the high-speed air flow. The strong impact and intense friction make the material grind into ultra-fine products. The power engine and grinder are smooth and not prominent. Do not change the pulley at will, lest the speed is too high to cause the grinding chamber to burst, or the speed is too low, which will not affect the working efficiency of the grinder. The jet mill should be idling for 2-3 minutes after starting, and there should be no abnormal phenomena before the feeding operation. Pay attention to the working status of the grinder during the operation, feed evenly, prevent clogging, and do not overload the operation for a long time. If there is vibration, noise, bearing and body temperature too high, the appearance of spraying should be stopped immediately, and the operation should be continued after troubleshooting. With the development of society, some devices have made great breakthroughs in order to play a better role. The jet mill has a good effect on the grinding target and occupies a special position. In the process of operation, the use of the jet mill should pay attention to certain operations, which cannot meet the production needs and work overload. Therefore, we should pay attention to the maintenance of the jet mill to ensure its efficiency.
Advantages of jet mill
1. Non-heating, especially suitable for ultra-fine grinding of heat-sensitive materials. In addition, air can be replaced with inert gas, which is suitable for grinding inflammable and explosive materials.
2. The pollution is very small. Since the grinding principle is the collision grinding of the material itself, compared with other grinding forms, the method of blade or ball grinding will be introduced into other grinding media for comparison. The jet mill is a pulverizing process with minimal pollution, especially suitable for industries such as medicine and food.
3. It is easy to clean, and the internal transmission of airflow grinding is smaller than other ultrafine grinding machines. In particular, the spiral airflow grinder is simple in structure, easy to clean, has no dead ends, and can be used as a sterile medicine grinder.
What are the common non-metallic mineral powder fillers
Non-metallic mineral powders are widely used in plastics, rubber, papermaking, coatings, wires and cables, electronic packaging and other products, mainly for filling, reducing production costs, improving product performance, improving production processes, and enhancing the competitiveness of enterprises . Some common powder processing fillers in the market now include calcium carbonate, barium sulfate, talc, silica powder, wollastonite, mica powder, kaolin, bentonite, and so on. At present, as downstream enterprises have higher and higher requirements for powder characteristics, non-metallic mineral powder fillers are developing in the direction of high purity, ultra-fineness and functionalization.
Calcium carbonate: Calcium carbonate is a product with abundant resources and low price among non-metallic mineral powder fillers. Therefore, it has almost become the first choice for non-metallic mineral powder fillers. If calcium carbonate powder can meet the needs of filling and related functions, other more expensive fillers will not be considered.
Talc powder: Talc has excellent properties such as lubricity, acid resistance, insulation, high melting point, good hiding power, good gloss, and strong adsorption. It has a wide range of applications in plastics, rubber, papermaking, paint and other industries. In coatings and other industries, it can replace part of the expensive titanium dioxide.
Barium sulfate: According to different production processes, it can be divided into barite powder and precipitated barium sulfate powder. Barium sulfate powder is mainly used in the paper industry, paint, rubber and plastic industries. Barium sulfate is used in powder coatings. It has the characteristics of high gloss, good leveling, strong weather resistance, and stable chemical properties. It is the main means to increase the powdering rate. Used in rubber products as a filler and a reinforcement, it can enhance the anti-aging performance and weather resistance of the product, the product is not easy to age and become brittle, and can significantly improve the surface finish and reduce the production cost. Good gloss and transparency can be obtained when used in the filling masterbatch.
Silicon powder: In the industry, silicon powder is also called quartz powder. It has the characteristics of excellent dielectric properties, low thermal expansion coefficient and high thermal conductivity. It is widely used in silicone rubber, coatings, adhesives, precision casting, ceramics, epoxy resin potting materials, as well as insulation casting and integration of ordinary electrical appliances and high-voltage components. Circuit molding materials and potting materials, welding rod protective layer and other resin fillers, etc.
Wollastonite and mica powder: Among the non-mineral powder products, wollastonite and mica powder are two types of powder with relatively special particle morphology. The needle-like structure of wollastonite and the aspect ratio of the powder are one of the important indicators for investigation. Mica powder has a flake structure, and the diameter-to-thickness ratio of the powder has an important influence on its application. Wollastonite powder has needle-like, fibrous crystal morphology, high whiteness and unique physical and chemical properties. It is widely used in ceramics, paints, coatings, plastics, rubber, chemicals, papermaking, welding electrodes, metallurgical protective slag and as asbestos Substitutes, etc. Muscovite and phlogopite have good electrical insulation, non-conductivity, acid resistance, alkali resistance and pressure resistance, so they are widely used to make insulating materials in the electronics and electrical industries. Lepidolite is also the main mineral raw material for extracting lithium.
Kaolin, bentonite: Kaolin has become a necessary mineral raw material for dozens of industries such as papermaking, ceramics, rubber, plastics, chemicals, coatings, medicine, and national defense. The ceramic industry is an industry that used kaolin earlier and used a larger amount. Kaolin is used as a material in the rubber industry. Adding it to the latex mixture can improve the properties of rubber, increase the mechanical strength of rubber products, enhance wear resistance and chemical stability, and extend the hardening time of rubber. Kaolin is used as a filler in the plastics industry. Its function is to make the surface smooth, reduce thermal cracking and shrinkage, facilitate polishing, and resist chemical corrosion.
Bentonite: also known as bentonite, bentonite, and the popular name Guanyin clay, known as "a thousand kinds of minerals", it is widely used in metallurgical pellets, casting, drilling mud, textile printing and dyeing, rubber, paper, fertilizer, Pesticides, improved soil, desiccants, cosmetics, toothpaste, cement, ceramic industry, nano materials, inorganic chemicals and other fields.
Brief introduction of cyclone dust collector
The cyclone dust collector is a dust collector that uses the centrifugal force in the high-speed rotating dust-containing airflow to separate dust from the air. Because of its simple structure and easy production, it is widely used. Compared with the gravity sedimentation chamber, the particle size of the dust to be processed is smaller, and the space required to process the same amount of gas is also much smaller. However, the pressure loss of the cyclone dust collector is generally higher than that of the settling chamber, so it consumes more power.
The advantages of cyclone dust collector are:
(1) The equipment has a simple structure and low cost;
(2) The device has no moving parts and is easy to maintain;
(3) It can withstand high temperatures, for example, it can withstand temperatures up to 400°C. If special high-temperature materials are used, it can withstand higher temperatures;
(4) It can withstand high pressure (positive pressure and negative pressure) to collect dust from high-pressure gas;
(5) After the dust collector is covered with a wear-resistant lining, it can be used to purify the flue gas containing high abrasive dust.
The disadvantages of cyclone dust collectors are:
(1) The efficiency of capturing fine dust (less than 5μm) is not high;
(2) Since the dust collection efficiency decreases with the increase of the cylinder diameter, when the processing air volume is large, multiple cyclone dust collectors must be used. If the setting is improper, it will have a greater impact on the dust collection performance.
The housing of the cyclone dust collector is composed of an outer cylinder and a cone. The top of the outer cylinder is closed, and there is an exhaust pipe in the center. The gas inlet pipe is located on the side of the cylinder and is tangent to the outer cylinder. The bottom of the cone is provided with an ash warehouse and a lock air gate. The dust-laden gas enters the device along the tangential direction of the outer cylinder from the air inlet at a higher speed (usually 12-25m/s), and produces a strong rotational movement along the annular space outside the inner cylinder (exhaust pipe). , Divided into two swirling airflows upward and downward. The upward airflow reaches the top cover and then spirals downwards. The downward airflow spirals between the inner and outer cylinders due to the restriction of the inner and outer circle and the upper cover, forming an outer swirling flow. During the rotation, most of the dust particles are thrown to the periphery of the cylinder under the action of inertial centrifugal force, hit the wall of the vessel, lose kinetic energy, slide down the wall, and fall into the ash bin. The dust particles accumulated in the ash bin are automatically discharged through the gate. When the descending outer swirling airflow follows the bottom of the cone, it turns back and rises, forming a bottom-up spiraling inner swirling flow, and is discharged from the top as purified gas through the central exhaust pipe.
Characteristics of Nitrogen Protected Grinding Equipment
Nitrogen protection grinding equipment is suitable for the grinding of explosive and oxidizable substances. The grinding effect of nitrogen protection airflow grinder is good, and the stability and safety are higher than that of general airflow grinder. The nitrogen-protected grinding equipment has a compact structure, polished inner and outer walls, no stock in the grinding box, no dead corners, easy to clean, and meets GMP requirements.
The materials collide and grind, and the materials with Mohs hardness 1-10 can be processed. The products are free of iron pollution and can be mixed and pulverized with several materials; good grinding efficiency and strict particle size distribution can be obtained, and the grinding particle size can be 2 -74μm can be adjusted arbitrarily, up to sub-micron level, and material loss is small; the whole system adopts a touch screen automatic control system, which can realize one-button start and stop, simple and convenient operation, and realize remote control.
Features of Nitrogen Protection Grinding Equipment:
1. Oxygen isolation: Before starting the feed, replace the air in the closed circulation system with nitrogen. At the same time, the closed feeding and unloading system can replace the air in Shaoli during the feeding and unloading process with nitrogen to maintain the oxygen in the system. The content is basically stable. During the grinding process, an oxygen content tester is used to continuously monitor the oxygen content in the airflow, and when it exceeds a certain level, nitrogen is added immediately to keep the oxygen content within the safety production standard.
2. Control the concentration of gas and powder: the feeding system is a fully enclosed, uniform speed device, which is programmed and controlled by the control cabinet. Fully enclosed plays the role of isolating oxygen, while the uniform speed controls the concentration of the materials inside the added equipment, and the feeding speed can be set arbitrarily. If the materials added to the equipment at a constant speed accumulate inside the equipment, there is no guarantee of safety. Therefore, the shape of the equipment, such as the bending angle of the pipe, the shape of each part, etc., are scientifically calculated to eliminate the dead corners inside the equipment. At the same time, the high-speed airflow in the equipment is driven and washed, and the powder will not accumulate in the pipe.
3. Timely release of static electricity and elimination of ignition sources: The special filter material with carbon steel wire used for the pulse blowback collector can eliminate static electricity in time and ensure that the pulse cleaning is clean and thorough. The nitrogen protection grinding equipment is all metal components, all grounded, and try to release the powder static electricity.
4. Circulating air cooling: Because the whole system is a closed circuit system, there are multiple moving parts inside the equipment, which will produce a certain temperature during high-speed movement, and the temperature is very important to the safety of processing. Therefore, the equipment is equipped with a fin-type cooler on the pipeline, which can effectively reduce the safety hazards caused by the equipment working for a long time or working in a high temperature environment.
Basic conditions for choosing an ultra-fine grinder
- Material properties
The nature of the material includes the nature and density of the abrasive material. Under the action of the negative pressure airflow caused by the fan, the material ground by the airflow mill is taken out of the grinding chamber, enters the material collection system, filtered by the filter bag, the air is discharged, the material and dust are collected, and the grinding is completed.
The ultra-micro grinding machine is a device that uses air separation, pressure grinding, and shearing to achieve ultra-micro grinding of dry materials. It is composed of cylindrical grinding chamber, grinding wheel, grinding rail, fan, material collection system and so on. The material of the superfine pulverizer enters the cylindrical grinding chamber through the feeding port, and is crushed and sheared by the grinding wheel that moves in a circular motion along the grinding rail to realize grinding.
- Material status
The material status mainly refers to the humidity and temperature of the material. Unlike wet grinding, in dry grinding, the water content of the material cannot exceed 3%, otherwise the processing capacity of the grinder will drop sharply, especially the dry ball mill is more important.
- Material size
Unlike the crusher, the feed size has a great influence on the output of the crusher, and is one of the main factors affecting the processing capacity of the grinder. Therefore, the energy consumption in the crushing and grinding stages is different, and the energy consumption in the crushing stage is much less. It is very important to apply the principle of more crushing and less grinding in the crushing operation. Therefore, in the crushing stage with less energy consumption, the material should be crushed to a finer particle size as much as possible to reduce the energy consumption in the grinding operation.
- Grinding ability
Even if the product needs to be grinded according to the requirements, the crusher can be selected to obtain the same size of material particles, and then the appropriate grinder can be selected according to the type and size.
- Grinding method
Grinding methods are divided into wet and dry methods. Wet grinders: limited to rotary grinders and tower grinders that use steel balls or other media, and there are also many dry grinders. Which type of grinding machine is used is affected by the operation before and after grinding, the number of grinding sections, and the choice of grinding process.
The composition & function of the air classifier system
Some application fields of ultrafine powder have certain requirements on the particle size distribution or gradation of ultrafine powder. Only fine classification of ultrafine powder products can meet the requirements, such as microelectronics, advanced ceramics, advanced abrasives, paper fillers and Coatings, plastics and rubber fillers, paint pigments or fillers, toners and other industries. Airflow classifier is a professional equipment for fine classification of ultra-fine powder, and it has been widely used in various fields.
The air flow classifier is mainly composed of a feeding control system, a classifier host (1-4 units), a high-efficiency cyclone collector, a pulse bag filter, a high-pressure induced draft fan and an electrical control system.
(1) Feeding control system: The feeding control system is composed of a star feeder or a vibrating feeder combined with a frequency conversion control instrument, a feeding bin, etc., and a continuous uniform speed control of the feeding is achieved by adjusting the output frequency/current level of the feeder.
(2) Classifier host: The classifier host is mainly composed of a motor, a grading wheel, a cylinder, etc., which can effectively classify materials by adjusting the speed of the grading wheel and cooperating with the secondary air.
(3) The impeller of the classifier is adjusted by the frequency converter, and protection measures such as loss of voltage protection, over current protection, material level control, operation status monitoring and alarm system are designed.
(4) Cyclone collector: This equipment is a first-level collection system in classified products. After the dust-laden airflow enters the cyclone collector, due to the centrifugal force, the powder will slide down the wall of the cylinder and be separated and purified at the end of the inner cone. The purified gas and a small amount of fine powder are discharged through the cyclone center tube.
(5) Pulse bag filter: This equipment consists of a bag collection device, a pulse cleaning device and a pneumatic control device.
Performance characteristics of air classifier
Air classifiers are often used in series with grinding equipment because it can precisely control the particle size of the finished product. For example, the airflow grinding equipment with a classification system is screened by the classification system after grinding, and the particles of qualified particle size are passed through the classification wheel with the airflow to the next process, and the coarse particles that do not meet the particle size are returned to the grinding chamber to continue grinding. Because of the precise screening function of the air classifier, it can be used not only alone, but also in series with most grinding equipment.
The principle of the air current classifier is that the material is quantitatively raised to the classification area through the feeder under the action of negative pressure air, and under the action of the strong centrifugal force generated by the high-speed rotating classification turbine, the coarse and fine materials are separated, and the fine particles meeting the particle size requirements pass through The gap between the grading wheel blades enters the cyclone separator or the dust collector to collect, the coarse particles entrained by the part of the fine particles hit the wall and the speed disappears, and descends along the cylinder wall to the secondary air outlet. After the strong elutriation of the secondary air, the coarse and fine particles are separated. The fine particles rise to the classification zone for secondary classification, and the separated coarse particles are discharged through the unloader.
Performance characteristics of air classifier
- It is suitable for fine grading of powder, the particle size of the grading product can reach D50:1~45μm, the product size can be adjusted, and the variety change is extremely convenient.
- High classification efficiency (extraction rate) 60% to 90%.
- The classification accuracy is high, the particle size distribution is narrow, and oversized particles and sieve residues in the product are completely eliminated.
- Low rotation speed and long service life: The rotation speed of the classification wheel is 50% lower than other horizontal and vertical classifiers for the same classification particle size. When producing powder with Mohs hardness <5, the grading wheel has no abrasion; when producing powder with Mohs hardness ≥ 7, the service life of the grading wheel is 5-8 times longer than that of other horizontal and vertical types.
- The vertical grading turbine device is adopted, which has low speed, wear resistance and low system power configuration.
- Multi-stage classifiers can be used in series to produce products with multiple particle sizes at the same time.
- It can be used in series with jet mill, impact mill, ball mill, vibration mill, Raymond mill and other grinding equipment to form a closed loop.
- The system is produced under negative pressure, no dust pollution, excellent environment, high degree of automation, strong stability, and easy operation.
Factors of gear wear of ball mill
According to the investigation, when the ball mill is in operation, most of the components are running very well, except that the large and small gears of the ball mill are frequently worn out, and the scrap rate is very high, which increases the production cost. So what causes the gear wear of the ball mill?
1. Poor lubrication conditions: In actual operation of the ball mill, the lubrication effect of the gear lubrication points is not ideal, because as the gear rotates or the speed increases, most of the grease does not enter the gear surface under the action of centrifugal force. It was thrown to the gear cover, and dropped onto the surface of the gear in the vibration of the gear cover, and was still directed to the gear cover, and finally fell to the bottom of the gear cover. As a result, the gear meshing parts have poor lubrication conditions, and dry friction or boundary friction will occur at the local meshing points of the tooth surface, causing serious wear and failure of the gear surface.
2. Frequent slurry leakage of the equipment: During the operation of the ball mill, due to improper operation or improper maintenance, there is a slurry leakage in the ball mill, and the slurry enters the gear without being cleared in time, causing the gear to wear; or the threaded hole at the hole cover of the ball mill is leaking. Pulp, causing gear wear.
3. Poor sealing performance: If the performance of the sealing element of the ball mill is too poor, a large amount of debris will enter the grease during operation, such as excessive mineral pulp, powder particles and other impurities. As a result, the gear lubrication conditions are worse, aggravate the wear of the gear, shorten the operating life of the gear, and increase the user's production cost.
4. The installation accuracy cannot be achieved: Although the ball mill has a simple structure and high manufacturing and installation accuracy requirements, when installing the gear of the ball mill, the manufacturing process and installation methods must be emphasized. If the lubricating oil is not added in time during installation to relieve the friction of the installation, the wear will be increased and the service life of the ball mill gear will be short.
Types of dust collector
Dust collector is a dust removal equipment that separates dust from flue gas. The performance of the dust collector is expressed by the amount of gas that can be processed, the resistance loss when the gas passes through the dust collector, and the dust removal efficiency. At the same time, the price of the dust collector, operation and maintenance costs, the length of the service life and the difficulty of operation and management are also important factors to consider its performance.
Dust collectors are divided into the following categories according to their principle of action:
- Filter type dust collector, including bag filter and particle layer dust collector, etc.
- Electrostatic precipitators.
- Magnetic dust collector.
Dust collectors are divided into:
- Dry dust collector;
- Semi-dry dust collector;
- Wet dust collector.
The working principle of the dust collector:
After the dust-containing gas enters from the upper air inlet of the ash hopper, under the action of the wind baffle, the air flow flows upward, the flow rate is reduced, and some large particles of dust are separated and fall into the ash hopper due to inertial force. The dust-containing gas enters the middle box and is filtered and purified by the filter bag, and the dust is trapped on the outer surface of the filter bag. The purified gas enters the upper box through the filter bag mouth and is discharged from the air outlet. The most commonly used in modern industry are: electric bag compound dust collector and bag dust collector.
The electric bag compound dust collector is installed in a box, with a short electric field installed at the front end and a filter bag field installed at the back end. The smoke and dust are introduced from the left end and pass through the electric field area first. The dust particles in the electric field area are 80%-90% charged. Dust is collected (use the advantages of electric dust removal to reduce the load on the filter bag field). The flue gas passing through the electric field enters the filter bag area for secondary filtration, and enters the inner cavity of the filter bag through the outer surface of the filter bag. The dust is trapped on the outer surface of the filter bag, and the pure gas is discharged from the inner cavity into the flue. Exhaust from the flue.
The electric bag compound dust collector combines the advantages of the electric dust collector and the pure bag dust collector, and is a new generation of dust removal technology.
Precautions for the use of dust collector:
During use, prevent the gas from cooling below the dew point temperature in the bag chamber, especially when using the bag filter under negative pressure. Because the shell often has air leakage, the air temperature in the bag room is lower than the dew point temperature, and the filter bag will be damp. As a result, the dust is not loosely attached to the filter bag, but sticky to the filter bag, resulting in a paste. The bag cannot remove dust, and the holes of the filter bag are blocked, causing the cleaning failure, and the pressure drop of the dust collector is too large, and the operation of the dust collector cannot be continued.
Reasons for the lower and lower output of ball mills
- "Saturated grinding" is the main reason that affects the output of ball mills
When the output of the ball mill is getting lower and lower, the first thing to consider is whether there is a phenomenon of "saturated grinding". The causes of "saturated grinding" are: too much feed; the hardness and particle size of the grinding material become larger; The material has too much moisture; the steel ball grading is unreasonable; the compartment board or the grate is blocked by debris. The solution to the "full grinding" problem: reduce the amount of feed; when the size or hardness of the grinding material changes, make corresponding adjustments in time; adjust the water content of the grinding material; reasonably configure the large, medium, and small steel balls Than; clean up the blockage of the compartment board or grate seam; increase the ventilation of the ball mill cylinder.
- The working time of the ball mill is too long
The length of the milling time directly affects the product composition and purity, and the impact of the milling time on the particle size is also obvious. In the initial stage, with the extension of time, the particle size decreases faster, but after the ball milling for a certain period of time, even if the ball milling time continues to be extended, the particle size value of the product does not decrease too much. Different materials have different optimal ball milling times. On the other hand, the longer the milling time, the more serious the pollution caused, which affects the purity of the product.
- Failure to add steel balls in time
The grinding effect of the ball mill and the output are restricted by the steel balls of the ball mill. With the grinding and impact of the steel balls in the cylinder, the steel balls will wear out. Therefore, the steel balls must be added in time to ensure the output of the ball mill consistency.
- The temperature in the cylinder rises
The temperature of the ball mill increases during operation, the effective strain of the ball mill to form nanomaterials is reduced, and the crystal grain size increases, which significantly affects the mechanical properties of the powder made into bulk materials. Moreover, whether the final product of ball milling is solid solution, intermetallic compound, nanocrystal, or amorphous phase, diffusion is involved, and diffusion is affected by the grinding temperature, so temperature is also an important factor affecting the output of the ball mill.
- The material moisture content is too high
Due to the large moisture content of the material, the uniformity of the feeding is affected and the feeding time is prolonged. Secondly, because the wet material is fed too much, it may cause the phenomenon of paste ball and paste liner in the mill, and even "full grinding" will be forced to stop the grinding process. Generally speaking, for every 1% increase in the comprehensive moisture of the material entering the mill, the output of the ball mill will decrease by 8%-10%; when the moisture is greater than 5%, the ball mill basically cannot perform grinding operations.
- Addition ratio of grinding aid
Grinding aids are allowed to be added in the cement production process, but the addition amount should not exceed 1%. Adding more than this standard is unreasonable. In addition, most of the grinding aids are substances with strong surface activity, which are not suitable for all materials. They should be added reasonably according to the nature of the materials.
To sum up, if the output of your ball mill is getting lower and lower, first check whether the "full grinding" phenomenon occurs. If not, then perform investigations based on other reasons to find the crux of the problem, and then you can fundamentally solve the problem of low output. The problem caused the ball mill to resume production as soon as possible, bringing greater economic benefits.