In the fine grinding process for lithium battery cathode materials, jet mills and mechanical mills are commonly used equipment. They differ significantly in grinding principles and effectiveness. Selecting the appropriate grinding equipment and optimizing process parameters based on material characteristics is crucial to meet product specifications, quality requirements, and energy consumption targets.
This article, titled “Equipment Focus: Performance Comparison of Jet Değirmeni vs. Mechanical Mill for Fine Grinding”, covers the following sections:
1. Jet Mill
The jet mill discussed here is a fluidized bed jet mill. The system equipment flow is shown in Figure 1.
1 – Air Compressor, 2 – Air Tank, 3 – Cooling and Purification System, 4 – Feeding System, 5 – Grinding Mechanism, 6 – Horizontal Sınıflandırma Mechanism, 7 – Cyclone Classification System, 8 – Filter System, 9 – Suction Fan
Figure 1: Jet Mill System Equipment Flow Diagram
Compressed air, after being refrigerated, filtered, and dried, is injected into the grinding chamber through several nozzles arranged two- or three-dimensionally, forming supersonic airflow. The kinetic energy of this jet fluidizes the material. The accelerated particles converge at the intersection point of the nozzle jets, undergoing intense collision, friction, and shear forces to achieve ultra-fine grinding. The ground material is then conveyed by the rising airflow to the classification zone. Under the centrifugal force of the sınıflandırıcı wheel and the suction force of the fan, coarse and fine particles are separated. Coarse particles fall back into the grinding chamber due to gravity for further grinding. Qualified fine particles meeting the size requirement enter the cyclone separator with the airflow for further separation and collection, while the fines in the material proceed to the dust collection system.
From the jet mill process, key equipment parameters include nozzle diameter, feed rate, grinding pressure, classifier wheel linear speed, and air suction volume. These jointly influence product specifications, quality, and output.
(1) Nozzle
The nozzle used in jet mills was invented by Swedish engineer Gustaf de Laval and is therefore called a “Laval nozzle”. Its front section converges from large to a narrow throat, and then diverges from small to large. This structure causes the airflow velocity (v) to change with the nozzle cross-sectional area, accelerating the airflow from subsonic to sonic, and finally to supersonic speeds.
Figure 2: Schematic Diagram of a Laval Nozzle
After passing through the nozzle, the compressed air becomes supersonic and enters the grinding chamber. Given the impact from airflow and material, the nozzle requires high mechanical strength and wear resistance. As shown in Figure 3a, a stainless steel nozzle exhibits severe wear after one month of use. This wear disrupts the airflow field, affecting particle size and specific surface area of the ground product, and also introduces metal contamination, impacting product quality. To avoid these issues, ceramic nozzles are now commonly used, as shown in Figure 3b.
Figure 3. a Stainless steel nozzle b Ceramic nozzle
(2) Classifier Wheel
The classifier wheel consists of a front flange, a rear flange, multiple blades, and an air-sealing disc. Gaps between adjacent blades serve as feed channels, and the inner sides of the blades form a cavity. Higher classifier wheel linear speed results in smaller product particle size. Linear speed is positively correlated with both the classifier wheel diameter and its rotational speed. The material load in the grinding chamber can be monitored via the classifier wheel motor current; higher current indicates more material in the chamber.
Material collides with and impacts the classifier wheel. Stainless steel classifier wheels show wear after prolonged use, as seen in Figures 4a/b. To prevent this, ceramic classifier wheels are now widely adopted, as shown in Figure 4c.
a. Stainless Steel Material (Worn), b. Stainless Steel Material (Normal), c. Ceramic Material
Figure 4. Classifier Wheel
(3) Product Specifications
The relationship between jet mill parameters and product particle size/output is as follows:
- “—” indicates no direct correlation between nozzle diameter and particle size.
- “↗” indicates the product specification increases as the parameter increases.
- “↘” indicates the product specification decreases as the parameter increases.
Note: The influence weight of each parameter varies.
| Indicator/ Parameter | Nozzle diameter | Feed Rate | Grinding Disc Linear Speed | Classifier Wheel Linear Speed | Suction Draft Level |
| Particle Size | — | ↘ | ↘ | ↘ | ↗ |
| Production Capacity | ↗ | ↗ | ↗ | ↘ | ↗ |
Parameter Adjustment Process:
- Pre-select nozzle size based on equipment model and estimated capacity.
- Determine the appropriate linear speed range (classifier wheel RPM) based on the target particle size of the material.
- Establish a suitable grinding pressure range based on material characteristics (e.g., single-crystal, polycrystalline, hard-agglomerated, soft-agglomerated). Excessive pressure generates excessive fines that are difficult to remove.
- Optimize feed rate and air suction volume based on capacity requirements.
- Re-evaluate whether to optimize nozzle diameter based on final capacity and energy consumption.
2. Mechanical Mill
The mechanical mill discussed here is a mechanical impact mill. The system equipment flow is shown in Figure 5.
1- Electrical Control Cabinet, 2- Feeding System, 3- Grinding Mechanism,
4- Classification Mechanism, 5- Cyclone Separation System, 6- Filter System
Figure 5. Mechanical Mill System Equipment Flow Diagram
Material is evenly fed into the grinding chamber by a feeding system, where it is subjected to strong impact from a high-speed rotating grinding disc. Simultaneously, centrifugal force causes the material to collide with the grinding ring, undergoing combined forces of shear, friction, and impact for size reduction. The ground material is carried by airflow to the classification zone for separation of coarse and fine particles. Coarse particles return to the grinding chamber for further grinding. Qualified fine particles enter the cyclone separator with the airflow for further separation and collection, while fines proceed to the dust collection system.
Key equipment parameters for the mechanical mill include feed rate, grinding disc linear speed, classifier wheel linear speed, and air suction volume, which jointly affect product specifications, quality, and output.
(1) Grinding Disc
The grinding disc is equipped with grinding pins. Material in the chamber is impacted by these high-speed rotating pins. Figure 6a shows a metal grinding disc, which is prone to wear during long-term operation, introducing metal contamination. Ceramic grinding discs are now commonly used. While harder and more wear-resistant, their brittle nature typically requires a lower operational linear speed compared to metal discs, reducing some impact force. Higher grinding disc linear speed results in smaller product particle size. Linear speed is positively correlated with both the disc diameter and its rotational speed.
Figure 6. a. Metal Grinding Disc b. Ceramic Grinding Disc
(2) Product Specifications
The relationship between mechanical mill parameters and product particle size/output is as follows:
- “—” indicates no direct correlation between feed rate and particle size.
- “↗” indicates the product specification increases as the parameter increases.
- “↘” indicates the product specification decreases as the parameter increases.
Note: The influence weight of each parameter varies.
| Indicator/ Parameter | Feed Rate | Grinding disc linear speed | Classifier Wheel Linear Speed | Suction Draft Level |
| Particle Size | — | ↘ | ↘ | ↗ |
| Production Capacity | ↗ | ↗ | ↘ | ↗ |
The adjustment process for the classifier wheel and other parameters in a mechanical mill is similar to that of a jet mill.
(3) Performance Comparison
The differing grinding principles of jet mills and mechanical mills dictate their respective applicability, output, and energy consumption. Fundamentally:
- Jet Mills use supersonic airflow to cause inter-particle collisions for size reduction.
- Mechanical Mills use a rotating disc to hurl material against stationary pins and the chamber wall for size reduction, as illustrated in Figure 7.
Figure 7: Schematic Diagram of Particle Size Reduction in Jet Mill / Mechanical Mill Chambers
| Jet Değirmeni | Mechanical Mill | |
| Principle | Supersonic speed causes collisions between materials | Shear and Collision between Material and Equipment |
| Grinding Intensity | Large：Supersonic speed | Small: Grinding disc linear speed is limited |
| Energy Consumption | High: Compressed air required | Low: Uses circulating water for cooling |
| Cost | High | Low |
| Equipment Footprint | Large | Small |
A comprehensive performance comparison is summarized in the table above. Mechanical mills are more suitable for grinding soft-agglomerated particles (e.g., polycrystalline materials). For some hard-agglomerated single-crystal small particles, even at the maximum disc speed, effective grinding may not be achieved. Jet mills can grind both soft-agglomerated and hard-agglomerated particles (e.g., single-crystal materials), but have disadvantages in energy consumption and cost. For some polycrystalline materials with loose structures, jet milling may cause excessive particle breakdown.
Figure 8 Jet Mill Grinding and Mechanical Mill Grinding
Figure 8 shows SEM images of single-crystal NCM ternary material ground by a jet mill and a mechanical mill, respectively. The jet mill demonstrates significantly superior grinding force, effectively breaking apart hard agglomerates between particles.
Destansı Toz
Destansı Toz is specialized in fine powder processing technology for mineral industry, chemical industry, yiyecek industry, pharama industry, etc. Our team has more than 20 years experience in Various powders processing and had ever designed and installed the biggest Jet Mill Production Line for ultra-fine barite powder production line in China.
We are a professional supplier of powder processing projects, especially powder milling, powder classifying, powder dispersing, powder classifying, powder surface treatment and waste recycling. We supply consultancy, testing, project design, machines, commissioning and training.
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