Spare Parts

The vertical mill classifier mainly uses centrifugal force, gravity and airflow to classify the ground materials. Its working principle is as follows:

1. Material dispersion: After the material enters the classifier from the feed port, it falls on the spreading plate. The spreading plate rotates at high speed, generating centrifugal force, and evenly sprinkles the material around, so that the material is fully dispersed in the classifier, ready for the subsequent classification process.

2. Airflow action: The fan introduces external air into the classifier to form an upward airflow. The airflow flows from bottom to top in the classifier and interacts with the dispersed material particles. Since the airflow forces on material particles of different particle sizes are different, fine particles are more easily driven up by the airflow, while coarse particles are relatively difficult to be lifted by the airflow.

3. Centrifugal classification: Inside the classifier, a rotor is usually provided. Blades are installed on the rotor. When the rotor rotates, the blades drive the surrounding air to rotate together, forming a strong centrifugal field. The material particles entering this centrifugal field will be affected by both centrifugal force and centripetal force of the airflow. The centrifugal force on the coarse particles is greater than the centripetal force of the airflow, and they will be thrown to the inner wall of the powder selector, then fall along the inner wall, and return to the mill through the coarse powder outlet for further grinding; while the centripetal force on the fine particles is greater than the centrifugal force, and they will continue to rise with the airflow.

4. Fine powder collection: After centrifugal classification, the fine particles rising with the airflow enter the collection device. The collection device usually uses equipment such as cyclone separators or bag dust collectors. The cyclone separator uses centrifugal force to separate the fine powder in the airflow and collect it in the ash hopper at the bottom; the bag dust collector intercepts the fine powder through the filter bag, and the purified gas is discharged from the powder selector, and the collected fine powder is the finished product that meets the particle size requirements.

1. Feeding device: includes feeding port and spreading plate. The feeding port is used to connect the mill so that the material can enter the powder classifier smoothly. The spreading plate is located below the feeding port, and the material is evenly scattered around by high-speed rotation, so that the material is fully dispersed in the powder classifier.

2. Rotor (classifying wheel): As the rotating part of the separator, it is driven by the motor through the drive system to rotate at high speed. During operation, it generates a strong centrifugal force, which helps to accurately classify fine particles and coarse particles according to particle size during the joint movement of the material and the airflow. The coarse particles are thrown around by the centrifugal force, while the fine particles continue to move forward under the action of the airflow.
Guide vane (static blade or shutter ring): It is a fixed blade installed in a specific position. Its function is to guide the direction of the airflow, so that the airflow is more reasonably distributed in the powder classifier, so that the material and the airflow are fully in contact, thereby improving the particle separation efficiency and assisting in the fine classification of the material.

3. Collection device: used to collect qualified fine powder after classification, common ones are cyclone separators and bag dust collectors. The cyclone separator uses centrifugal force to separate the fine powder in the air flow and collect it in the ash hopper at the bottom. The bag dust collector intercepts the fine powder through the filter bag, and the purified gas is discharged, so as to efficiently collect the fine powder and ensure that the discharged gas meets environmental protection requirements.

4. Transmission: that is, the drive system, which consists of a motor and a gearbox. The motor provides the initial power, and the gearbox adjusts the speed according to the actual production needs, accurately provides power to the rotor, and can flexibly adjust the rotor speed to optimize the separation performance of the material and adapt to the requirements of different materials and product particle sizes.

5. Sealed air system: Surrounding the key parts of the powder selector, by delivering sealed air to specific areas, it effectively prevents fine particles from escaping the separator, avoids dust from polluting the environment, and maintains the pressure balance in the machine to ensure the stable operation of the powder selector.

6. Coarse powder return system: works in conjunction with the discharge chute. When the coarse particles are separated during the classification process, the oversized particles are recycled back to the grinding table through the discharge chute, which is the outlet, for further processing, so as to achieve the recycling grinding of the material and improve the qualified rate of the finished product.
Fine powder outlet: It is the part where fine powder of appropriate size leaves the separator for collection. Qualified fine powder after being processed by the classification and collection device is finally output through the fine powder outlet and enters the subsequent collection, packaging and other processes.

7. Air inlet (air flow control system): It bears the key responsibility of controlling the amount and speed of air entering the separator. By regulating the airflow, it affects the movement state of the material in the powder classifier, greatly affects the classification efficiency, and ensures that the powder selection process is efficient and stable.

8. Shell: As the outer shell of the powder classifier, it plays the role of protecting the internal components and sealing the working environment, so that the material and airflow flow in the powder classifier according to the established path, reducing dust leakage and interference from external factors.

9. Bearing and support structure: Provide mechanical stability and support for rotating rotors and static guide vanes and other components. Ensure that each component maintains the correct position and posture during operation, reduce vibration and wear, and extend the service life of the equipment.8.

1. Material characteristics
Particle size distribution: When the feed particle size range is wide and the content of large particles is high, the classification difficulty of the powder classifier will increase and the work efficiency will be reduced; if the material particle size is relatively uniform, the powder classifier can classify more efficiently.

Humidity: High humidity of the material is easy to cause particle agglomeration, affecting the dispersion effect of the material in the powder classifier, so that the fine powder cannot be taken away by the airflow in time, thereby reducing the powder selection efficiency, and in severe cases, it may also cause equipment blockage.

Easy to grind: Materials with good grindability are more likely to produce fine powder during the grinding process, and the amount of fine powder that the powder classifier needs to handle increases. If the capacity of the powder classifier is insufficient, it will affect the work efficiency.

2. Equipment parameters
Rotor speed: The rotor speed determines the size of the centrifugal force. As the speed increases, the centrifugal force increases, which can make the coarse particles more effectively separated, but too high a speed will increase the content of coarse particles in the fine powder; too low a speed will increase the content of fine powder in the coarse powder, which will affect the powder selection efficiency.

Guide vane angle: The guide vane angle affects the direction and speed distribution of the airflow. Reasonable angle adjustment can make the airflow fully contact with the material and evenly distribute it, improving the classification effect; inappropriate angle will cause airflow turbulence and affect the separation of particles.

Ventilation volume of powder selector: ventilation volume directly affects the carrying capacity of airflow for materials. Insufficient ventilation volume cannot bring out enough fine powder, which will cause fine powder to circulate in the powder selector and reduce the powder selection efficiency; excessive ventilation volume will cause too much coarse particles to be brought into the fine powder, affecting product quality and powder selection efficiency.

3. Operation parameters
Feeding volume: If the feeding volume is too large and exceeds the processing capacity of the powder selector, the material cannot be fully dispersed and classified in the powder selector, resulting in an increase in the fine powder content in the coarse powder, a decrease in the quality of the fine powder, and a decrease in the powder selection efficiency; if the feeding volume is too small, the equipment cannot give full play to its production capacity, which also affects the efficiency.

System pressure: The stability of the system pressure of the powder selector is crucial to the powder selection efficiency. Pressure fluctuations will cause changes in airflow speed and direction, affecting the classification effect of the material. Too high or too low pressure will lead to uneven airflow distribution and reduce the working efficiency of the powder selector.

4. Equipment maintenance
Parts wear: The rotor, guide vanes, spreading disc and other parts of the powder classifier will wear out during long-term operation. The worn parts will change the airflow field and the working characteristics of the equipment, affect the dispersion and classification of materials, and reduce the powder selection efficiency.

Sealing performance: If the sealed air system is not sealed tightly, it will cause outside air to enter or internal dust-containing airflow to leak, affecting the airflow field and pressure balance in the powder classifier, and thus affecting the powder selection efficiency.

1. Analysis of the structural disadvantages of traditional vertical mill powder selectors
Uneven distribution of airflow in the classification area: Inside the traditional powder selector, especially between the feed port and the classification rotor, the airflow is prone to form a turbulent area. For example, in a cement plant application, the airflow velocity near the material inlet fluctuates by up to 30%, which makes the material and the airflow inadequately contact, and some coarse particles are mixed into the fine powder, reducing the classification accuracy and affecting the uniformity of product quality.

Defects in rotor structure design: Common rotor blades are of a single form. When running at high speed, materials are easy to accumulate on the edge of the blades, interfering with the airflow and making the centrifugal field unstable. According to tests, when the rotor speed reaches 800r/min, the thickness of the material accumulation on the edge of the traditional blade can reach 5mm, which reduces the effective separation effect of the centrifugal force on the particles and leads to a decrease in the classification efficiency.

Imperfect coarse and fine powder separation and collection system: As the main collection device, the cyclone collector has an unreasonable inlet structure and internal flow field design, which leads to secondary entrainment of fine powder during the collection process, and some separated fine powder is re-mixed into the airflow, reducing the collection efficiency. In actual production, the secondary entrainment rate of the cyclone collector can be as high as 15%, resulting in material waste and subsequent processing burden.

2. Structural optimization strategy
Optimization of airflow uniform distribution structure: Add a guide plate at the feed inlet to evenly guide the material into the classification area, optimize the shape of the air inlet, and adopt a gradual expansion structure to allow the airflow to enter the powder classifier smoothly. The simulation results show that the deviation of the airflow velocity in the classification area can be controlled within 5% after optimization, and the uniformity of contact between the material and the airflow is significantly improved, effectively reducing the probability of coarse particles mixing into fine powder.

Rotor structure innovation: Design a new variable-section rotor blade with a thick root and a thin end to increase the surface roughness of the blade and promote material dispersion. Experiments show that the rotor with this blade basically eliminates the material accumulation phenomenon at a speed of 1000r/min, the centrifugal field is stable, and the classification efficiency is increased by 10% - 15% compared with the traditional rotor.

Improvement of coarse and fine powder collection system: A pre-separation device is set at the entrance of the cyclone collector to separate some coarse particles in advance and reduce the load of the cyclone collector; the internal flow guide structure of the cyclone collector is optimized to reduce secondary entrainment. In actual application, the secondary entrainment rate of the improved cyclone collector is reduced to less than 5%, and the fine powder collection efficiency is increased by 8% - 10%.

3. Optimization effect evaluation
Improvement of classification efficiency: The optimized vertical mill classifier is applied in a cement production enterprise, and the classification efficiency is increased from 65% to 80%, the coarse particle content in the finished fine powder is significantly reduced, the standard deviation of cement product strength is reduced, and the quality stability is enhanced.

Reduction of energy consumption: Due to the improvement of classification efficiency, the material circulation volume is reduced, and the energy consumption of the mill is reduced. According to statistics, the power consumption per ton of cement powder grinding is reduced by 5-8kWh, and the energy saving effect is significant.

Enhanced operation stability: The optimized structure reduces component wear and reduces the frequency of equipment failures. Taking a mining enterprise as an example, the maintenance cycle of the classifier is extended from 2 months to 4 months, which improves production continuity and reduces maintenance costs.

1. Limestone
Performance: Limestone has relatively low hardness and good grindability. It can be easily ground into fine powder in the vertical mill. However, due to its wide particle size distribution, if the parameters of the powder selector are not set properly during the powder selection process, more fine powder may be entrained in the coarse powder, affecting the powder selection efficiency and product quality.

Adjustment strategy: Appropriately increase the rotor speed of the powder selector to enhance the centrifugal force so that the coarse particles can be separated more effectively. At the same time, the ventilation volume can be adjusted according to the humidity of the limestone. If the humidity is high, increase the ventilation volume to facilitate the drying and dispersion of the material and improve the powder selection effect.

2. Baryte
Performance: Barite has a high density and a high hardness. When grinding in the vertical mill, a large grinding pressure and energy input are required. Due to its high density, during the powder selection process, barite particles of the same particle size are subjected to greater gravity than other materials and are more easily separated into coarse powder. However, if the classification accuracy of the powder selector is not high enough, it may cause too many coarse particles to be mixed in the fine powder, affecting the fineness requirements of the product.

Adjustment strategy: According to the characteristics of barite, the guide vane angle of the powder selector should be optimized to make the airflow more evenly distributed in the classification area and improve the separation efficiency of particles. At the same time, the feed amount of the powder selector can be appropriately reduced to allow the material to have more time to be classified in the powder selector to avoid insufficient classification due to too fast feeding.

3. Kaolin
Performance: Kaolin has the characteristics of fine particle size, high humidity and strong viscosity. When processed in the vertical mill powder selector, the material is prone to agglomeration, which affects the classification effect of the powder selector. In addition, kaolin has high requirements for the fineness and purity of the product, and the operating parameters of the powder selector need to be strictly controlled to obtain products that meet the requirements.

Adjustment strategy: In order to reduce the agglomeration of kaolin, a disintegration device can be set at the feed inlet of the powder selector to disperse the agglomerated materials. At the same time, strengthen the role of the sealed air system to prevent outside air from entering the powder selector and maintain the stability of the internal airflow. In terms of operating parameters, the ventilation volume and wind speed should be appropriately increased so that the fine powder can be carried away by the airflow in time, thereby improving the powder selection efficiency and product fineness.

1. Internal structure optimization
Improvement of rotor structure: Change the traditional straight plate rotor blades to twisted or variable cross-section blades. Twisted blades can make the airflow flow more evenly in the rotor, reduce airflow turbulence, and improve classification accuracy; variable cross-section blades can optimize the blade shape according to the changes in the centrifugal force and airflow force on the particles at different positions in the rotor, and enhance the separation ability of particles of different particle sizes. For example, in some cement plant renovation cases, the classification efficiency of the classifier increased by 10% - 15% after the use of variable cross-section rotor blades.

Guide vane optimization: adjust the angle and shape of the guide vane. The appropriate guide vane angle can make the airflow enter the classification area at a more reasonable angle, increase the contact time and effect of particles and airflow, and improve the separation efficiency. Designing the guide vane into a curved shape or using an adjustable guide vane structure can further optimize the airflow distribution. For example, a power plant modified the guide vanes of the vertical mill classifier in the boiler pulverizing system. After using adjustable guide vanes, the guide vane angle can be flexibly adjusted according to different operating conditions, so that the particle size of the coal powder is more uniform and the combustion efficiency is improved.

Add a dispersing device: Add a dispersing device, such as a dispersing disc or a dispersing rod, near the feed port of the powder selector. For materials that are easy to agglomerate, such as clay with high humidity or ultrafine powder materials, the dispersing device can disperse the agglomerated particles so that they can better participate in classification and avoid problems such as inaccurate classification and fine inclusions in coarse powder caused by agglomeration.

2. Improvement of the control system
Use an advanced speed control system: transform the traditional fixed speed drive system into a variable frequency speed control system. The speed of the powder selector rotor is accurately controlled by the frequency converter, and the rotor speed is flexibly adjusted according to the nature of the material, the output requirements and the product fineness index to achieve the best classification effect. For example, when producing cement, for different clinker formulas and admixture dosages, the speed of the powder selector rotor can be quickly adjusted through the variable frequency speed control system, so that the specific surface area and particle grading of the cement product meet different quality requirements, while reducing energy consumption.

Optimize the air volume control system: Install air volume sensors and intelligent regulating valves to monitor and control the air volume in the powder selector in real time. According to the characteristics of the material and the classification requirements, the air volume at the air inlet and outlet is automatically adjusted to maintain the stability of the airflow and the appropriate wind speed in the classification area. For materials with good grindability and high output, the air volume is appropriately increased to improve the collection efficiency of fine powder; for materials that are difficult to grind or have high requirements for fineness, the air volume is reasonably controlled to avoid excessive removal of coarse particles.

Establish an automated monitoring system: Use sensors to monitor the operating parameters of the powder selector in real time, such as rotor speed, air volume, air pressure, material temperature, etc., and transmit the data to the central control system. The data is analyzed and processed by the monitoring software. When the parameters deviate from the set value, the system automatically sends an alarm signal and prompts the operator to make corresponding adjustments, or automatically makes fine adjustments to ensure that the powder selector is always in the best operating state.

1. Operation status monitoring
Vibration monitoring: Use a vibration tester to regularly detect the vibration of the powder selector. Generally, the vibration amplitude is required to be no more than 5-10mm/s. If the vibration value exceeds this range, it may be due to rotor imbalance, bearing damage or loose foundation, and it is necessary to stop the machine for inspection in time.

Temperature monitoring: Use temperature sensors to monitor the temperature of key parts such as bearings and motors. During normal operation, the bearing temperature should be kept below 60-70℃, and the motor temperature should not exceed 80℃. If the temperature is too high, it may be caused by problems such as poor lubrication, poor heat dissipation or equipment overload. The cause needs to be promptly investigated and handled.

2. Lubrication system maintenance
Oil quality inspection: Carry out oil quality inspection at least once a week, and use an oil quality analyzer to detect the viscosity, moisture, acid value and other indicators of the lubricating oil. The viscosity of the lubricating oil should meet the equipment requirements, and the general deviation should not exceed ±10%; the moisture content should be less than 0.1%; the acid value should be within the specified range, usually not exceeding 0.5mgKOH/g. If the oil quality does not meet the requirements, the lubricating oil should be replaced in time.
Oil level check: Check the oil level of the lubricating oil every day to ensure that the oil level is between 1/2 - 2/3 of the oil scale. Too low oil level will lead to poor lubrication and accelerate equipment wear; too high oil level may cause problems such as increased oil temperature and oil leakage.

3. Regular maintenance
Parts wear inspection
Rotor blade wear inspection: Every 2 - 3 months, use a caliper or thickness gauge to measure the thickness of the rotor blades. Generally speaking, when the blade wear exceeds 20% - 30% of the original thickness, it is necessary to consider replacing the blade to ensure the classification efficiency and accuracy of the powder classifier.

Guide vane wear inspection: Also check the guide vane wear every 2 - 3 months, focusing on the edge and surface of the guide vane. When the guide vane wear causes its surface roughness Ra to exceed 12.5μm, or the angle deviation of the guide vane exceeds ±5°, it will affect the airflow distribution and need to be repaired or replaced.

4. Airflow system maintenance
Air volume measurement and adjustment: Use an air volume meter to measure the air volume of the powder selector every month, and control the air volume within an appropriate range according to the material characteristics and product fineness requirements. For example, for cement raw material selection, the air volume is generally controlled at 2000-3000m³/h; for cement finished product selection, the air volume is usually 1500-2500m³/h. If the air volume deviates from the set value, it can be adjusted by adjusting the fan valve or inverter.

Air duct inspection: Perform a comprehensive inspection of the air duct every six months to check whether the air duct has wear, air leakage, etc. The wear of the air duct should not exceed 1/3 of the wall thickness. If there is air leakage, it should be sealed in time, and the air leakage can be repaired by using sealant or welding.

5. Long-term maintenance
Reduce machine maintenance
Regular oil change: The reducer should be changed for the first time after the first 200-300 hours of operation, and the lubricating oil should be changed every 2000-3000 hours or once a year. When replacing the lubricating oil, you should use the same high-quality lubricating oil as the original model, and thoroughly clean the inside of the reducer to avoid impurities.

Gear inspection: Check the gears of the reducer once a year, and use the gear tester to detect the wear, tooth surface bonding, tooth profile error, etc. of the gears. The wear of the gears should not exceed 10% - 15% of the tooth thickness, the tooth surface bonding area should not exceed 10% of the total tooth surface area, and the tooth profile error should be controlled within ±0.05mm. If the gear is found to be seriously damaged, the gear should be replaced in time to ensure the transmission efficiency and stability of the reducer.

6. Motor maintenance
Insulation detection: Use an insulation resistance tester to detect the insulation resistance of the motor every six months, and the insulation resistance of the motor winding should not be less than 0.5MΩ. If the insulation resistance is too low, it may cause safety accidents such as motor short circuit and leakage. The motor needs to be dried or the cause of insulation damage needs to be found and repaired.

Bearing inspection and replacement: The motor bearings are inspected every 1-2 years. If the bearings are found to be obviously worn, the clearance is increased, or the rotation is not flexible, the bearings should be replaced in time. At the same time, when replacing the bearing, pay attention to selecting the appropriate bearing model and accuracy grade to ensure that it matches the motor.6.