Raw material grinding is an important link in the preparation process of cement raw materials. After the cement raw materials are crushed, they are sent to the raw material mill for further grinding until they reach a certain fineness, and then enter the clinker calcination process. From the production experience of many cement plants, the selection of cement equipment, especially the raw material mill, will directly affect the project investment, production progress and economic benefits. At present, in order to adapt to the process characteristics of the new dry process cement production line and make full use of the waste heat of the waste gas from the preheating decomposition system at the end of the kiln, we usually use a grinding system that combines drying and crushing into one. Cement raw materials include limestone, gypsum, silica, clay, fly ash and other components. Since these materials are mixed together and have special properties, they have high requirements for the material applicability of the grinding equipment. In the cement production process, the raw material mill of the cement plant grinds the cement raw materials into raw materials, and the raw materials are sent to the cement kiln to make cement clinker. The clinker and other admixtures are ground into cement products by cement mills.
The essential difference between raw material mill and cement mill
In the manufacturing process of the cement industry, two important components stand out: the raw material mill and the cement mill. Although they may seem similar in design and function, there are distinct differences between the two that play a vital role in producing high-quality cement.
1.Raw material mill
Process uncalcined natural raw materials (such as limestone, clay), crush, dry and grind them to produce raw material powder that meets the fineness requirements, and directly send them to the kiln for high-temperature calcination.
2.Cement mill
The calcined clinker is mixed with auxiliary materials such as gypsum and ground to produce finished cement.
3.Key differences
- Raw material characteristics: Raw material mills process materials with higher hardness and moisture, and need to take into account drying functions.
- Equipment design: Raw material mills often use vertical roller mills (VRMs) or air-swept ball mills to cope with high humidity and large particles; cement mills rely more on the fine grinding capabilities of ball mills.
- Energy consumption: Raw material mills usually consume 10%-30% more energy than cement mills due to the need for drying and coarse grinding.
4.Technology Comparison
| Parameter | Raw Material Mill | Cement Mill |
| Material Characteristics | High hardness, high moisture, large particle size | Clinker particles, low moisture, fine particle size |
| Equipment Type | Vertical Roller Mill (VRM), Air-swept Ball Mill | Ball Mill, Roller Press |
| Energy Consumption | 10-30 kWh/t (higher) | 8-20 kWh/t |
| Core Challenges | Drying capacity, material flowability | Particle size uniformity, mixing efficiency |
Two major grinding method of raw material mills: vertical roller mill vs ball mill
1.Vertical roller mill
How it works
- When the vertical raw mill of the cement plant starts to operate, the material enters the mill through the feed port at the top of the mill and then falls on the center of the grinding stone.
- The transmission drives the grinding stone to rotate, and the grinding roller rotates around the grinding roller axis under the friction of the grinding stone. Due to centrifugal force, the material moves from the center of the grinding stone to the edge, and when it passes through the grinding roller track, it is brought between the grinding roller and the crushed grinding stone.
- The vertical raw mill in the cement industry is equipped with a hydraulic tensioning device, which mainly controls the relative pressure of the grinding roller on the grinding stone. The crushing pressure can be adjusted according to the hardness of the abrasive.
- The ground material continues to move to the edge of the grinding stone. There is a jet device on the edge of the grinding stone, and the outflowing hot air flows upward, driving the ground material to rise.
- The large pieces of material will fall back on the grinding stone first due to their own weight, and the small pieces of material will enter the powder selection system under the action of the hot air flow. The fine powder that meets the fineness requirements is collected and stored in the dust collector, while the coarse powder that does not meet the fineness requirements is returned to the grinding stone for grinding.
parameter
| Type | Model | Grinding Disc Diameter (mm) | Roller Diameter (mm) | Feed Particle Size (mm) | Capacity (t/h) | Main Motor Power (kW) | Disc Speed (r/min) | Weight (t) |
| LM Mill | LM0806 | 800 | 600 | ≤30 | 3-5 | 75 | 62 | 13.8 |
| LM1311 Series | 1300 | 1100 | ≤40 | 9-15 | 200 | 43 | 46.5 | |
| LM1512 | 1500 | 1250 | ≤40 | 10-19 | 280 | 43 | 65 | |
| LM1714 | 1700 | 1400 | ≤42 | 13-32 | 400 | 40 | 90 | |
| LM2215 Series | 2250 | 1560 | ≤50 | 25-45 | 800 | 32 | 120 | |
| LM2820 Series | 2800 | 2000 | ≤65 | 35-80 | 960 | 32 | 200 | |
| LM3424 Series | 3450 | 2400 | ≤70 | 60-100 | 1350 | 30 | 300 | |
| LM4831 Series | 4800 | 3150 | ≤115 | 92-200 | 3150 | 26 | 760 | |
| HRM Mill | HRM1411 | 1400 | 1185 | ≤35 | 10-15 | 225 | 37.96 | 49 |
| HRM1612 | 1600 | 1200 | ≤40 | 12-20 | 280 | 36.16 | 65 | |
| HRM1813 | 1800 | 1300 | ≤45 | 16-28 | 350 | 34 | 78 | |
| HRM2115 | 2100 | 1500 | ≤50 | 20-35 | 400 | 31.6 | 87 | |
| HRM2215 | 2250 | 1570 | ≤60 | 25-35 | 500 | 31 | 92 | |
| HRM2417 | 2450 | 1750 | ≤70 | 28-40 | 630 | 29.5 | 114 | |
| HRM2619 | 2650 | 1900 | ≤75 | 35-55 | 710 | 28.1 | 132 | |
| HRM3123 | 3150 | 2300 | ≤80 | 40-80 | 1120 | 25 | 210 | |
| HRM3424 | 3450 | 2430 | ≤80 | 52-85 | 1300 | 24.5 | 310 | |
| HRM3626 | 3600 | 2650 | ≤80 | 60-100 | 1950 | 24 | 450 | |
| HRM4028 | 4000 | 2850 | ≤90 | 70-115 | 3100 | 22.9 | 600 | |
| HRM4230 | 4250 | 3050 | ≤100 | 85-160 | 3400 | 22.18 | 680 | |
| HRM4531 | 4500 | 3150 | ≤110 | 95-200 | 3600 | 21.5 | 750 |
Technical advantages
- High grinding efficiency. The energy consumption of cement vertical mill grinding system is relatively low, 10%-30% lower than that of cement ball mill grinding system. And the reduced value will increase with the increase of raw material moisture.
- Large drying capacity. The cement vertical grinding system can make full use of the low-temperature exhaust gas of the preheater, and its wind speed can reach 60-80m/s, so the drying efficiency is high. If we use a hot air furnace, this grinding system can dry materials with a moisture content of 15%-20%.
- Large feed particle size. The feed particle size of this grinding system is between 50-150 mm. The maximum feed particle size can be calculated as 5% of the roller diameter.
- Small space occupation and low noise. The manufactured cement vertical mill occupies a small area and has low noise. Because it has less equipment, high operation rate and small footprint, it can be set up in the open air without a workshop. Moreover, the unit power consumption and production cost of its products are quite low, so the market share of vertical mills is rising rapidly.
Components
- Base support: The base of the vertical raw mill is a set of steel welded parts buried in concrete. The drive unit of the vertical raw mill and the fixed seat of the tensioning hydraulic cylinder are installed on the base support.
- Grinding table: The grinding table (grinding stone) is installed on the output flange of the reducer with a diameter of 5m.
- Grinding table lining: The wear-resistant lining is fixed on the grinding table, and the grinding roller rotates on the wear-resistant lining. The raw material is ground between the grinding table and the grinding roller.
- Dynamic separator: The cement separator is external type, with a rotor diameter of 6190 mm and a shell outer diameter of 8000 mm.
- Grinding roller: There are four grinding rollers distributed on the grinding table. The diameter of the grinding roller is 2240m. When the grinding table lining and roller skin reach a certain wear limit, they should be replaced.
- Hydraulic tensioning system: The hydraulic cylinder generates the pressure required for tightening the grinding roller, and the pull rod transmits the pulling force of the hydraulic cylinder. The hydraulic cylinder is equipped with a nitrogen airbag to absorb the vibration of the raw mill during operation.
- Nozzle ring: located between the grinding table and the vertical mill housing, the overflowed material is sent to the cement separator through the external circulation system.
- Mill drive: the motor-driven reducer transmits the torque to the grinding table, and the reducer is equipped with a lubricating oil pump station.
- Auxiliary drive: the main drive unit is equipped with an auxiliary drive unit, which enables the vertical mill to start smoothly. The auxiliary drive is also used for the accurate position required for grinding table inspection and roller maintenance.
2.Ball mill
Working Principle
The material is impacted and ground by steel balls inside a low-speed rotating cylinder. It is classified through diaphragm plates and gradually refined to the target particle size.
A typical ball mill is a horizontal cylindrical structure driven by gears at both ends. When the motor starts, the cylinder rotates, and raw materials are fed uniformly through the inlet into the first chamber. The inner wall of this chamber is equipped with stepped or corrugated liners and steel balls of varying sizes as grinding media. As the cylinder rotates, the steel balls and material are lifted to a certain height and then fall, repeatedly impacting and grinding the material. The first chamber performs coarse grinding, after which the material passes through a single-layer diaphragm plate into the second chamber for finer grinding. The second chamber has flat liners and smaller steel balls for more thorough grinding. Ground material exits through the discharge port, where qualified fine particles are separated by classifiers, while unqualified particles are returned to the mill for regrinding.
Technical Parameters
| Specification (m) | Speed (r/min) | Feed Particle Size (mm) | Capacity (t/h) | Grinding Media Load (t) | Main Motor | Main Reducer | Weight (Excl. Motor & Reducer) (t) | |||
| Model | Power (kW) | Speed (r/min) | Model | Speed Ratio | ||||||
| Φ2.2×7 | 21.4 | ≤25 | 20~25 | 31 | YR148-8 | 380 | 740 | ZD70-9 | 5 | 41 |
| Φ2.2×13 | 21.6 | ≤25 | 33-37 | 58-60 | YR630-8/1180 | 630 | 740 | Zhaoteng 630 | 5.6 | 95 |
| Φ2.4×8 | 20.91 | ≤25 | 25-28 | 39-42 | JR1512-8 | 570 | 740 | ZD80-9 | 5 | 76.4 |
| Φ2.4×10 | 20 | ≤25 | 38-40 | 50 | YR710-8/1180 | 710 | 740 | JDX630 Series | 5.6 | 92.4 |
| Φ2.6×10 | 20.6 | ≤25 | 40-42 | 62-65 | YR800-8/1180 | 800 | 740 | JDX710 | 6.3 | 133 |
| Φ3×9 | 19.13 | ≤25 | 50-55 | 76-80 | YR1000-8/1180 | 1000 | 740 | JDX800 | 6.3 | 137 |
| Φ3.2×9 | 18.3 | ≤25 | 60-70 | 90 | YR1250-8/1430 | 1250 | 740 | JDX900 Series | 7.1 | 157 |
| Φ3.5×10 | 17.3 | ≤25 | 75-80 | 87 | YR1250-8/430 | 1600 | 740 | JDSX1000 | 6.3 | 210 |
| Φ3.8×7.5 | 16.7 | ≤20 | 85 | 85 | YR710-8 | 1600 | 740 | JDX900 Series | 5.6 | 218 |
| Φ4.6×10 (Central Drive) | 15.1 | ≤25 | 195 | 190 | YRK1000-8 | 3350 | 740 | JS150-B | – | 315 |
Cement ball mills can simultaneously dry and grind materials. Raw materials entering the mill directly contact high-temperature gases, enabling rapid heat exchange and moisture evaporation. Grinding systems are categorized into two types:
1. Intermediate-Discharge Circulating Grinding System
This system combines features of air-swept mills and end-discharge mills. It functions as a two-stage closed-circuit grinding system. After classification by the separator, most raw material returns to the fine-grinding chamber, while a small portion is sent back to the coarse-grinding chamber.
Advantages:
- Feed Flexibility: Accepts feed sizes up to 25 mm, reduces over-grinding, and improves efficiency.
- Low Resistance: Ventilation resistance at the intermediate discharge diaphragm is lower than in end-discharge mills. Hot air enters from both ends, enabling high airflow and strong drying capacity.
- Heat Distribution: 80–90% of hot air enters from the head, while a small portion enters from the tail to remove residual moisture and prevent condensation.
- Airflow Optimization: High airflow in the coarse-grinding chamber and lower airflow in the fine-grinding chamber match material size distribution.
- Drying Capacity: Can dry raw materials with 6–7% moisture using 320°C kiln exhaust gas. With auxiliary hot air, moisture handling increases to 14%.
2. End-Discharge Circulating Grinding System
This system differs from air-swept mills by including a drying chamber before the grinding chamber. Material is mechanically discharged, and hot air flows from the head to the tail before being filtered and released.
Limitations:
- Low Airflow: Mechanical discharge limits airflow through the mill.
- High Resistance: Discharge grates increase ventilation resistance, restricting airflow to 3–4 m/s.
- Drying Capacity: Can only dry materials with <5% moisture using kiln exhaust. With auxiliary heat, moisture handling reaches 8%.
Comparison of two raw material mills
| Vertical Raw Mill | Ball mill |
| Low investment: The vertical raw material mill integrates crushing, drying, grinding, and grading and conveying. The system is simple, compact, and takes up little space. It can also be arranged outdoors, saving a lot of investment costs. | High output: large crushing ratio, strong production capacity, effectively improve grinding fineness, and increase processing capacity by about 15%. |
| Low operating cost: low energy consumption, less damage, and reduced operating costs. | Safe and reliable system: the maintenance of reducers and gears is more convenient, firm and wear-resistant, and it also reduces downtime, maintenance time and labor intensity of operators. |
| Environmentally friendly and clean: low vibration, low noise, good sealing, the system works under negative pressure, and there is no dust overflow. | Good wear resistance and long life: cement ball mills are made of high-quality wear-resistant materials, and the lining is removable, so the service life of equipment or wearing parts is longer. |
| Stable raw material quality: Since the material stays in the raw material mill for a short time, it is easy to detect and control the product particle size and chemical composition, reduce repeated grinding, and stabilize product quality. |
Selection Guide: How to Choose the Best Raw Material Mill?
Core parameter considerations
The selection of raw material mills should be based on three core dimensions: raw material characteristics, production capacity requirements, and environmental protection and energy consumption. The following is a specific analysis:
(1) Raw material characteristics
Hardness (Bond work index):
High-hardness raw materials (such as quartz, iron ore): Vertical roller mills are preferred, and their rolling crushing efficiency is 30%-50% higher than that of ball mills. For example, the HRM4531 vertical mill adopts a conical grinding roller design and can process hard materials with a Bond work index of >15 kWh/t.
Moisture content:
High moisture (>8%): Vertical roller mills are the only choice. Their integrated hot air drying system can handle raw materials with a moisture content of up to 18%. For example, the MLS3424 vertical mill is equipped with a hot air furnace with a drying capacity of 15%-20%, which is suitable for humid climate areas.
Low moisture (<6%): ball mill (such as air-swept Φ2.4×10 type) is more economical, with an energy consumption of about 20-25kWh/t.
Feed particle size:
Large particles (≤110mm): vertical mill (such as HRM4028) can be directly processed without pre-crushing, saving equipment investment.
Small particles (≤25mm): ball mill (such as Φ2.2×7 type) is suitable for refined production through multi-bin classification grinding.
(2) Capacity requirements
Small production line (<2500t/d):
Ball mill: such as Φ2.4×8 type (processing capacity 25-28t/h, power 570kW), suitable for projects with limited funds and dry raw materials.
Compact vertical mill: such as HRM1612 (processing capacity 12-20t/h, power 280kW), small footprint and support future capacity upgrades.
Large projects (>5000t/d):
High-power vertical mill: such as HRM4531 (processing capacity 95-200t/h, power 3600kW), suitable for 8000t/d ultra-large-scale production lines, a single machine can meet high production capacity requirements.
Raw material vertical mill structure characteristics
Grinding disc design
The largest component of a vertical raw material mill is the grinding disc, which plays an important role in the overall performance of the vertical mill. The design of the grinding disc revolves around grinding capacity, grinding speed and space settings. The grinding capacity of a vertical mill is directly related to the working diameter of the grinding disc. The rotation speed of the grinding disc determines the output speed, but it needs to be adjusted according to the speed requirements of different materials. The grinding speed depends largely on the pressure, number and size of the rollers, as well as the grinding disc diameter, rotation speed, material thickness, etc.
Grinding roller design
Grinding roller is mainly composed of roller shaft, bearing, wheel hub, roller sleeve, etc. The lubrication system of grinding roller lubricates and cools the bearing. Grinding roller squeezes and crushes materials on the grinding table. Under constant pressure, the shape and size of grinding roller have a direct impact on the grinding efficiency of materials.
Rocker arm design
The rocker arm is the component that connects the grinding roller and the tensioning device. The tension generated by the hydraulic cylinder is transmitted to the grinding roller through the rocker arm. Therefore, the rocker arm is the main force-bearing component in the entire clamping system. Therefore, its design is directly related to the output and stability of the vertical mill.
Powder Classifier Design
TONGLI uses the most advanced vortex plane separation method to design the powder classifier, which has high powder selection efficiency; the rotor adopts a low-resistance structure design to reduce the running resistance of the vertical mill and save energy; the rotor adopts an air-sealed design, which is height-adjustable and easy to install and adjust.
Rotary feeder design
The feeding device of the vertical milling machine adopts a rotary feeder, which has a simple structure, stable operation and continuous feeding. The wear-resistant lining of the casing is made of metal with high precision; the gap between the scraper and the wear-resistant scraper is adjustable, both of which are wearing parts and can be replaced. Hot air can enter from both sides of the casing to prevent the feed valve from being blocked.
Finite element analysis of key components
The rocker arm is a component that connects the grinding roller and the tensioning device. The tension generated by the hydraulic cylinder is transmitted to the grinding roller through the rocker arm. Therefore, the rocker arm is the main force-bearing component in the entire clamping system, so its design is directly related to the output and stability of the vertical mill.
Overall structural features
- The roller can be automatically raised and lowered
- The grinding part adopts a horizontal grinding table and a conical grinding roller design, which runs smoothly, has little wear and low energy consumption.
- The wear of the bushing and the grinding disc liner has little effect on the later output, and the reduction in output is within 5%, and the bushing and bushing are easy to repair or replace at any time.
- The vertical mill has a strong drying capacity and can use the waste heat at the end of the kiln to dry raw materials with a moisture content of more than 8%.
- The wind ring area, wind ring angle, and dam ring height can be adjusted according to the working conditions.
- Mechanical, electrical limit and material layer detection devices are equipped to improve safety.
- The large-caliber cartridge valve is used to ensure that the oil pump has a large flow rate and the oil pressure acts quickly. For ultra-fine materials with a large flow rate, the water spray volume can be reduced and the heat consumption can be reduced.
- The grinding roller adopts dustproof felt oil seal, which can effectively prevent dust from entering the bearing.
- Both the roller sleeve and the grinding table lining can be re-welded on the production line and reused, reducing the cost of replacing wearing parts.
- The vertical mill is equipped with a rotating device, which can turn the grinding roller from the outside of the machine for easy maintenance.
Author: Chu Min
Date: 2025/2/19
