(6) Centrifugal mill The basic guiding principle of this mill design is to increase the grinding effect of the grinding media and materials. Since there are various mechanisms for increasing the grinding action, there are many types of centrifugal mills. In general, according to the characteristics of the mill barrel installation, it can be divided into two categories: vertical and horizontal; both can be used in thousand or wet operation. Figure 41 shows the structure and working principle of a vertical multi-chamber centrifugal mill. The barrel of the machine is installed vertically, and 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 φ 530 × 400 mm ring mill can reach the capacity of four φ1500 × 1500 mm conventional ball mill. However, this kind of grinding machine is used in the mineral processing industry. Due to 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 φ1200 mm centrifugal ring mills respectively. 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 of the grinding media. 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. The circumferential speed of the plate, m / s 10 30 40 (8) 0 jet mill Jet mill is also known as jet mill. The mill is characterized in that the material is injected into the mill through a nozzle or other means by using a gas (compressed air or heated vapor); after the gas is injected, the material is produced at a high speed due to depressurization or other reasons (in many cases) Exceeding the speed of sound). In this high-speed motion system, the material is shredded by itself or by collision with other instruments. This method of grinding not only produces very fine particles, but also avoids contamination of the material being ground. Bracket & Roller Frame Series,Cement Plant Belt,Cement Plant Belt Ep900,Cement Plant Belt Ep500 HEBEI GLOBAL TECHNOLOGY CO., LTD , https://www.hebeiglobalbelt.com
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FIG 42 is a development of the former Soviet Union horizontal centrifugal mill, which structure is as follows: 1 is a simplified stationary, its inner surface shaped like a laid manganese steel backing composed of two truncated conical 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 m3 , 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 feed concentration is 55~60%, the maximum output of the original mill can reach 25 tons/hour, the average is 11.3 tons/hour, and the electric energy consumption and grinding operation conditions are based on -0.074 mm. Relevant, about 11~26 kWh/t. Tests have shown that the centrifugal mill is not only much more efficient than the ball mill, but also has less noise. The plant plans to use a centrifugal mill with a volume of 2 m 3 instead of a ball mill with a volume of 20 m 3 for fine grinding. [next]
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 increased 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 a hydrocyclone is used for wet closed-circuit grinding and the like, and a φ4 is selected. 2×8.5 m conventional tube grinding and φ1.0×1.2 m centrifugal grinding machine were tested and compared. The total cost of the centrifugal grinding unit is 74% of the ball mill unit.
The two mills have substantially the same particle size composition and specific surface area of ​​the grinding product and the wear of the working surface of the grinding medium under the condition that the unit energy consumption is substantially the same. 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.
Comparing the particle size and metal distribution characteristics of the grinding products of the two mills, it can be seen 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.
Tests have shown that the horizontal centrifugal mill has high grinding efficiency when the material is finely ground and superfinely ground. The tests showed that the former Soviet Union, a volume of 2 m 3 of a centrifugal mill, a ball mill can be replaced by a volume of 2 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 φ2700×3600 mm ball mill of the concentrator, and carried out re-grinding of the mine 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. Milling machine (φ250×300 mm) and cyclone closed-circuit grinding and grinding results of conventional mills.
(7) Colloid mill [next]
The colloid mill consists of a high speed (about 3000~15000 rpm) rotating disc and a fixed disc. According to the placement position of the colloid mill, it is divided into vertical and horizontal. According to the structure of the colloid mill, it is divided into disc type, hammer type, turbine type and orifice type. Figure 43 is a schematic view of the operation of the colloid mill; the gap between the rotating disc and the fixed disc is 0.005 to 1.0 mm. The shape of the plate can be flat, trough or tapered. The feed size is less than 0.2 mm and is fed between the discs in the form of a slurry. The slurry in the middle of the two plates is pulverized by the shearing, grinding and impact of the high-speed rotating disk; the product size can be less than 1 micron. Tests have shown that the higher the circumferential speed of the plate, the finer the particle size of the product, and the general relationship between them is:
Average particle size of the product, micron 1 0.1 0.01
The technical characteristics of colloid mills produced by Wenzhou Marine Machinery Plant and Shenyang Xinguang Power Machinery Co., Ltd., China. Figure 44 shows the structure of a horizontal and vertical colloid mill produced by Wenzhou Marine Machinery Factory. Colloid mill is suitable for homogenization of various emulsions and ultra-fine grinding of food, chemical raw materials, daily necessities, medicines, ceramics and other materials. In order to meet the production needs of large oil , mining and metallurgical enterprises, the plant produced D-100 colloid mill, which is a hard alloy grinding disc with a production capacity of 30 tons per hour. [next] [next]
Jet mills first appeared in the 1940s and have grown into many types. They have the following four categories: (1) swirl-jet (Mineronizer); (2) elliptical tube jet (Jet-O-Mizer) (3) convection jet type; (4) impact plate jet type.
The main differences are: (1) the first three are air jets separately, the latter one is air solid particles mixed injection; (2) the first two nozzles are sprayed with high-speed airflow to drive high-speed movement of solid particles. The third type is that the gas is injected inward to cause the solid particles to be violently impacted and pulverized; the fourth type is to install an impact plate, which is impacted by the solid particles driven by the high-speed airflow, and superimposed and pulverized on the impact plate.
In addition, in the same type of jet mill due to material feeding mode (pipe, high-speed flow thin layer or fluidized bed), material acceleration mode (free spray or pipe flow), spray mode (baffle, single point free jet or The multi-point free jet) and the hierarchical structure are divided into many models.
The jet mill exit speed is related to the injection pressure, such as the mouth gas pressure, kilopascal (no air pressure) 784.5 (8) 98.1 (10) 1470 (15)
Export speed, m / s 500 600 1100
At present, China's research and development of jet mills include Jiangsu Chemical Machinery Research Institute, Shanghai Chemical Machinery No. 3 Plant, Jiangsu Yixing Non-metal Chemical Machinery Plant, Sichuan Mianzhu Chemical Plant, China Aerodynamics Research Institute and Chengdu Powder Research Institute. These units have produced jet mills of different types and sizes.
The advantages of jet mills are as follows:
(1) The pulverization process is carried out instantaneously at a temperature lower than normal temperature, and does not change the chemical properties of the material, and is particularly suitable for pulverization of brittleness, low melting point, and heat sensitive substances.
(2) The pulverization particle size range is wide, and the product particle size can generally reach 10 microns or less.
(3) The product has a uniform particle size and is lightly pulverized.
(4) It is especially suitable for materials with “three harms†by using dry, degreasing, dust removal and fully closed airflow pulverization without polluting the environment.
(5) Unit energy consumption decreases as processing capacity increases. [next]
The disadvantages of jet mills are:
(1) The particle volume concentration in the pulverizer is adjusted by a classifier. If the concentration is too high, the grading effect is deteriorated, the number of collisions is too low, and the pulverization ability is decreased. Therefore, the matching use of the classifier is important.
(2) The supporting system of compressed air is more complicated than other crushing methods.
(3) There are many capital construction investments, strict operational and management requirements, large maintenance workload and high energy consumption.
A Swirling Jet Mill Figure 45 Swirling Jet Mill. The jet nozzle of the mill protrudes into the machine at an angle of 45°~75 from the circumferential tangential direction; the jet generates a rotary motion in the machine. Due to the different flow rates of the jets of the various layers, the particle group is caused to collide and grind to achieve pulverization. The fine-grained product is discharged downward from the middle of the disc, and the coarser fraction is discharged from above. This type of mill can be made of stainless steel or rubber lining due to the low temperature rise of the ground product. The feed size is generally less than 0.15 mm and is commonly used for fine grinding talc , sulfur, barite , mica , graphite , cryolite, cotton and soft manganese ore. However, the grinding of other fibers (except cotton) and waxy materials cannot be used.