The basic guiding principle of this mill design is to increase the grinding action of the grinding media and materials. Since there are various mechanisms for increasing the grinding action, there are many types of structural ploughs for the centrifugal mill. In general, according to the characteristics of the mill barrel installation, it can be divided into two categories: vertical and horizontal; both can be dry or wet.
Figure 1 shows the structure and working principle of a vertical multi-chamber centrifugal mill. The barrel of the machine is installed vertically.
Figure 1 Single tube vertical centrifugal mill
1. Feeding; 2. Pulley; 3. Disc; 4. Steel ball; 5. Mill barrel;
6. Lower end cover; 7. Upper end cover; 8, 9. Main bearing; 10. Spindle
The cylinder body is provided with a rotatable vertical shaft; the shaft is provided with a bladed disc (rotor) which divides the mill cylinder into a plurality of grinding chambers. Each room is filled with a certain amount of grinding mineral medium (grinding ball, steel segment and ore itself, etc.). The Φ530 × 400 mm ring mill developed in China belongs to the basic type of rotor or centrifugal mill. Its main features are: low power consumption per unit, 20% of conventional ball mills when dry grinding limestone ; unit steel consumption is very low, grinding ball consumption is only 40 g / ton, while conventional ball mill ball consumption is up to 1.5 ~2.0 kg / ton; unit production capacity is very high, when grinding limestone, a Φ530 × 400 mm ring mill can reach the capacity of 4 Φ1500 × 1500 mm conventional ball mill, but this mill is used in the beneficiation industry Because of the serious wear of bearings and rotating blades, and the need to regularly check and repair moving parts in order to maintain dynamic balance, the workload is large, so there are not many applications.
China's Hunan Xinsheng Cement Plant and Huxiang Cement Plant used Φ700 and Φ200 mm centrifugal ball mills respectively.
FIG 2 is a development of the former Soviet Union horizontal centrifugal mill, which is structured as follows: 1 is the stationary cylinder, its inner surface shaped manganese steel backing is laid as a truncated cone composed of two pulley 2.3 of the rotor wings . The rotor 3 is fixed to the rotating shaft 4 via the wheel housing 5. A hole 6 is provided in the wheel housing 5 for the circulation of the grinding medium and the slurry 7. The rotary rotor is mounted in the bearing 8. The amount of feed is adjusted by the size of the gap 9 between the rotor 3 and the liner. The ground product is discharged through the discharge pipe 10. When the rotor 3 with the wheel fins rotates, centrifugal force is generated, and the slurry fed to the mill is also rotated by the centrifugal force, thereby generating a large slurry pressure. The material is comminuted under impact and abrasion. The speed of the rotor is up to 12 meters per second, which ensures that the material to be ground can be graded very well, thus greatly reducing the formation of slime. The centrifugal mill was industrially tested at the Barahash concentrator. The technical characteristics and results of the test mill are as follows: cylinder inner diameter 750 mm, length 1000 mm, effective volume 0.35 m 2 , rotor inner diameter 700 mm, length 800 mm, peripheral speed 12 m / s, motor power 75 kW, grinding medium ( The diameter is 6 mm and the loading is 150~250 kg. The machine works in parallel with another ordinary ball mill for comparative tests. The regrind material is the grit of the heavy sand concentrate classified by a hydrocyclone. The test result is: when the feedstock sinking degree is 55~60%, the maximum output according to the original ore meter can reach 25 tons/hour, the average is 11.3 tons/hour, and the electric energy consumption and grinding operation are based on -0.074 mm. The condition is about 11~26 kWh/ton. Tests have shown that the centrifugal mill replaces the ball mill with a volume of 20 m 3 for fine grinding. [next]
Figure 2 Horizontal centrifugal mill
1. cylinder; 2. lining; 3. rotor; 4. shaft; 5. hub; 6. hole; 7. bearing; 8. clearance;
The grinding principle of a centrifugal mill is based on the centrifugal acceleration (rather than the acceleration of gravity), which is typically 10 to 12 times the acceleration of gravity to increase the grinding force. The experimental research shows that the grinding efficiency of the mill is higher when the ratio of the radius of gyration G of the centrifugal mill to the diameter D of the mill is 0.4 to 0.6.
Such ultrafine grinding mills used for wet aspect ore, mineral raw materials, metallurgical and chemical products have many desirable benefits: a large processing capacity, although much reduced in size than the conventional size ball, still be able to achieve the same grinding Mine capacity; unit energy consumption is basically equal to that of conventional ball mills, but in the case of improved fineness of grinding products, power consumption can be saved by 30%. In many cases, investment costs are saved by 25~30%; equipment footprint and occupation The space is small, and it can be combined with the mobile crusher to form a new type of crushing production process. The main problem is that the mill barrel liner wears faster.
German Lurgi mines in South Africa, made a detailed economic comparison of the centrifugal mill equipment and the performance of conventional ball mill, the results were as follows: iron ore mine ground to a fineness of grinding product, each mill output It is 20 million tons per year, the ore particle size is 6 mm, the specific surface area of ​​the fineness of the grinding product is 1700~1800 cm 2 /g, and the same conditions such as wet closed-circuit grinding using a hydrocyclone are used, and one Φ4 is selected. The 2 × 8.5 m conventional tube mill and the Φ1.0 × 1.2 m centrifugal mill were tested and compared. The comparison results are shown in Table 1. As can be seen from the table, the total cost of the centrifugal grinding unit is 74% of the ball mill unit.
Comparison project | Ordinary ball mill | Centrifugal mill |
Total installed power, kW Mill input power, kW Mill weight, t Mill specifications, m Floor area, % Space occupied, % Mill foundation, % Steel structural parts, % total cost,% | 5000 2 × 2000 2 × 220 Φ4.2 × 8.5 100 100 100 100 100 | 4200 2 × 1600 2 × 85 Φ1.0 × 1.2 55 40 52 65 74 |
The results shown in Table 1 show that the particle size composition and specific surface area of ​​the ground product and the wear of the working surface of the grinding media are approximately the same under the conditions that the two mills have substantially the same energy consumption. It can be seen that the use of a centrifugal mill instead of a conventional ball mill has no effect on the process system of the sorting operation.
The comparison of the particle size and metal distribution characteristics of the grinding products of the two mills is shown in Table 2. It can be seen from the table that although the centrifugal mill has a high production capacity, the particle size of the ore-mining product having a particle size of less than 5 μm is almost the same as that of the conventional ball mill. [next]
Mill | Product granularity Mm | Yield % | content,% | Metal distribution, % | ||||
copper | iron | sulfur | copper | iron | sulfur | |||
mill machine give material | -74 -74+44 -44+20 -20+10 -10+5 -5 | 39.8 30.6 15.3 8.7 1.2 4.4 | 4.4 4.8 5.5 10.2 9.0 10.2 | 28.8 39.4 42.4 31.6 27.2 22.1 | 34.1 44.8 48.7 35.8 29.8 22.2 | 31.8 25.5 15.5 16.1 2.0 3.1 | 33.6 35.2 19.3 8.1 0.9 2.9 | 34.6 34.7 19.3 7.9 0.9 2.6 |
total | 100.0 | 5.5 | 34.1 | 39.2 | 100.0 | 100.0 | 100.0 | |
from heart mill machine row material | +74 -74+44 -44+20 -20+10 -10+5 -5 | 21.8 32.4 19.5 15.8 2.6 7.9 | 3.2 4.3 6.0 8.5 9.2 9.2 | 28.9 39.0 42.8 32.1 30.4 22.6 | 33.4 44.0 59.3 36.3 34.3 23.8 | 12.5 25.0 21.0 24.1 4.3 13.1 | 18.0 36.2 23.9 14.5 2.3 5.1 | 18.4 35.9 24.2 14.5 2.2 4.8 |
total | 100.0 | 5.6 | 34.9 | 39.7 | 100.0 | 100.0 | 100.0 | |
often regulation ball mill machine row material | +74 -74+44 -44+20 -20+10 -10+5 -5 | 24.5 31.9 19.2 13.8 2.6 8.0 | 4.5 4.7 6.0 9.3 9.5 9.3 | 29.4 38.0 42.5 31.0 29.3 24.1 | 33.5 43.9 48.6 35.2 33.3 25.5 | 18.1 24.9 19.1 21.3 4.1 12.5 | 20.9 35.2 23.7 12.4 2.2 5.6 | 20.9 35.6 23.7 12.4 2.2 5.2 |
total | 100.0 | 6.0 | 34.5 | 39.3 | 100.0 | 100.0 | 100.0 | |
Tests have shown that the horizontal centrifugal mill has high grinding efficiency when the material is finely ground and superfinely ground. According to the original Soviet test, a centrifugal mill with a volume of 2 m 3 can replace a ball mill with a volume of 20 m 3 . Replacing a billiard mill with a centrifugal mill saves 40,000 rubles in terms of reducing metal consumption. In recent years, the Soviet Union used a Φ800 × 1000 mm centrifugal mill to replace the concentrating plant Φ2700 × 3600 mm ball mill for re-grinding of the middle ore and concentrate. Industrial tests have shown that this can obtain better economic benefits. The large centrifugal mill of Φ1.0 × 1.2 m and 1400 kW developed by Lurgi and South Africa was put into operation in South Africa in 1979.
The centrifugal mill can be used both for wet open processes and for closed loops with hydrocyclones. Grinding results of centrifugal mills (Φ250 × 300 mm) and cyclone closed-circuit grinding and conventional mills are listed in Table 3.
project | Conventional mill 1 | Centrifugal mill 2 |
Grinding medium filling rate, % Grinding ball size, mm Specific surface area of ​​feedstock, cm 2 /g Feeding particle size, D 80 , mm Product size, D 80 ,mm Separation particle size, D 50 , mm Specific surface area of ​​the product, cm 2 /g Energy consumption per unit of product, kW.h/t Grinding medium consumption, kg/t | Rod mill, 25 ball mill, 30 8 0.033 0.015 4000 15~16 0.8 | Steel ball, 60 10 230 2.3 0.033 0.012 3900 15.8 0.72 |
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