This form of smashing was originally a sniper type, and it is a typical pulverizer with a long history. However, in recent years, many new models have been developed due to research from different angles. Especially for the emergence of new materials, many crushers with higher performance and higher efficiency have been developed. For example, as a toner for electrostatic copying, in order to achieve such a fine pulverization of the grading, most of the air pulverizers have been used in the past, but a mechanical high-speed rotary pulverizer with a new structure has recently been developed. Low-cost, high-efficiency micro-grinding treatment.
1 Classification, characteristics and application technology of high-speed rotary pulverizer
There are many methods for pulverizing high-speed rotary pulverizers. According to the shape and structure, it can be divided into hammer type, rotary type, axial flow type and ring form. In addition, according to the pulverization principle, it can be divided into two categories: impact pulverization and friction (compression, shear).
1.1 hammer type
Hammering is the installation of fixed or rocking hammers or blades on a rotating rotor. As the classification mechanism, a sieve is often used for pulverization of coarser particles which are broken up to 100 μm.
On his rotor, a horse-like rocking cymbal is usually installed, which is suitable for high-speed rotation with a peripheral speed of up to 100 m/s, so it also has a high crushing capacity.
1.2 turntable
Rotary type such as pin grinder or turbine mill. An impact element such as a pin or a blade is fixed to the turntable, which is a device having a larger diameter direction than the axial direction. This type of shredder generally has a greater peripheral speed than the hammer type. Therefore, it is possible to carry out finer crushing. As a classifier, in addition to the use of a screen, a wind classifier with a smaller cut-off point is also used. Further, in order to make the relative speed at the time of impact larger, a micronized structure in which two rotating disks are reversely rotated has been designed.
AM is a general-purpose model of such a micro-grinder. It is mainly composed of two parts: the crushing chamber during impact and the air classification chamber. The pulverization chamber is composed of a pulverizing rotor and a stator with a circular arc. The rotor disc is equipped with hammerheads of varying numbers, with a peripheral speed of up to 100 m/s or even higher. The classification chamber consists of a splitter ring and a staged impeller. The pulverization and grading are respectively driven by the respective motors, and because of the built-in adjustable air classifier, it is possible to obtain a desired product having a uniform particle size distribution. The graded coarse powder is returned to the crushing and is the chamber crushing. The AM pulverizer is characterized by a large air intake and can suppress temperature rise. It is very suitable for crushing various powder coatings, resin raw materials and heat-weak materials. Its application range is also extensive.
Recently, this machine has been newly developed. By improving the impact element on the rotor, the probability of collision during the material pulverization process is increased, thereby increasing the pulverization processing capacity by more than one time. In addition, in order to meet the needs of users for easy cleaning, the machine also adopts an open structure to make a model that is easy to clean.
1.3 axial flow
The axial flow pulverizer material is rotated while being pulverized while being axially moved. In order to control the particle size of the product, improvements are made in the impact element and the hierarchical structure to achieve adjustment of the rotational speed and the air volume.
A different ring is installed in the outlet of the two pulverization chambers for particle size control. Further, in the present apparatus, the residue which has not been pulverized to a certain size is discharged through the spiral nozzle.
After the raw material enters the conical hopper, it is pulverized by a small impact element installed between the pulverization chamber and the bushing, and the most minute pulverization of several m is achieved by an effective crushing shearing effect. In addition, a pulverizer with an eccentric rotation of the rotor shaft and a higher compression effect has been developed.
JM vertical high-speed rotary pulverizer is another high-performance axial flow micro-grinder. The feeder is quantitatively fed and enters the material in the machine together with the air from the lower suction port, and the high-speed rotating rotor dragged by the belt is evenly dispersed in the circumferential direction to reach the crushing zone formed between the rotor and the stator bushing. The surface portions of the rotor and the stator sleeve are respectively formed into a plurality of grooves of a special shape, and the friction is mainly caused by friction on the wall surface of the stator bushing. This mechanism of pulverization is very different from the impact force that usually depends on the edge of the rotor blade. The basic product size range of the machine is d50=5-20μm, the distribution is uniform, and there is spheroidization effect, and the power consumption is saved.
1.4 ring form
The ring crusher is one of the axial flow mills. The rotor and bushings leave a small gap with a number of grooves on both surfaces. The formation of strong eddy currents during the pulverization process is closely related to this effective comminution. It produces a uniform shear velocity field better than other shredders. Therefore, it is possible to ensure a fine powder product having a very uniform particle size.
The fluid distribution around the multi-blade and the bushing at high speed can be seen by the fluid simulation of the pulverizing belt. A small eddy current is emitted in the gap portion of the blade to promote frequent impact and pulverization of the particles.
This pulverization principle is different from the conventional high-speed rotary pulverizer and is also different from the jet mill. The pulverizing treatment capacity and the average particle size of the pulverizer are compared with the conventional high-speed rotary pulverizer. For example, for cellulose, it is necessary to pulverize the fiber to 30 μm or less, which is difficult to achieve in the past high-speed rotary pulverizer.
Since the machine can individually set the pulverizing and grading part of the rotation speed, the average particle size of the product can be controlled to be varied within a wide range of 5-10 μm.
The ring mill can also be used for spheroidization of particles. For the coloring paint for electrostatic lighting, not only the particle size but also the shape and surface characteristics are required, because these characteristics have a great influence on the chargeability, fluidity, and cleaning type of the coating particles. These requirements can be met by adjusting the residence time or processing temperature of the raw materials in the machine.
1.5 blade
The blade mill uses an air vortex between the sharp blade and the fixed bushing that rotates at a high speed to cause collision and shearing between the pulverized materials to achieve pulverization.
This machine is particularly effective for crushing difficult-to-crush raw materials (cellulosic, elastic). In order to clean the residue in the machine, the door cover method is adopted, the door cover is opened, the smashing rotor is exposed, which is convenient for cleaning, and is particularly suitable for small batches of various varieties in the food industry.
The average particle size of the machine can reach 10μm, the particle size distribution range is narrow, and its energy consumption is only half of that of the airflow mill.
2 smashing limit of high speed rotary pulverizer
The high-speed rotary pulverizer can be divided into various forms as described above, and the principle of different pulverizers such as impact, shear, and friction is compounded even in a pulverizer. Therefore, it should be regarded as a composite effect, but in the impact mill, the impact velocity of the particles and the impact element is the decisive factor.
In addition, the pulverization effect is not only related to the mechanical conditions of the pulverizer but also to the physical properties of the material. The raw material is a brittle material, and the maximum impact force Pmax[N] of the impact is given to the particle. The approximate value can be calculated according to the Hertz contact stress theory. Then, according to the impact force, the tensile force S[pa] generated inside the particle is calculated by the flat looseness method. Therefore, at the time of impact, the destructive force Sf[pa] acting on the particles can be calculated by the following equation: Sf = 0.34 (On the other hand, the breaking strength Ss of the particle (volume Vp) and the distribution probability of the crack of the particle Related, so can be expressed in Weibull: through experiments, can be summarized into the following formula: &n bsp; St = aVp-6 (a, b: constant)
Therefore, when the skin receives the skin damage force Sf to avoid the breaking strength Ss, the particles are broken, whereby the limit diameter dpb(m) of the pulverized particles caused by the impact can be obtained. Taking limestone as an example, the physical properties and experimental constants of the impact component are steel parts. By synthesizing the above two types of pulverization, the corresponding pulverization limit particle diameter of the limestone at the impact velocity of V can be obtained.
3 crushing effect of different types of crushers
(1) Screen grading impact pulverizer
Since the mesh of the screen is larger than the limit particle diameter of the pulverized particles, the particles which have not been sufficiently pulverized are also sent out of the system, and the pulverization effect is not good.
(2) The impact pulverizer using the airflow classification has repeated particles circulating in the mill with the diameter of the particles, resulting in finer pulverization, which is better than the screen.
(3) Airflow classification impact grinder pulverizer, this type of machine combines the functions of shearing, friction, etc., and can obtain 5-10μm micropowder, which is more effective than impact pulverization fineness.
However, since the actual pulverization processing capacity is often inversely proportional to the product size, it is necessary to balance the selection of the model according to objective requirements.
4 model selection and operation
4.1 granularity
The high-speed rotary pulverizer is a broad-spectrum pulverizer including hammer type, compression, shearing and abrasive type, and is also a closed pulverizer with a wide range of pulverization size. When the pulverization ratio is large, depending on the pulverization performance of the raw material, the particle size of the raw material and the product, a combination of a general pulverizer and a Tesu pulverizer can be selected to constitute a high-efficiency multi-stage pulverization. From the above description, it is known that the pulverization particle size is gradually tapered from the hammer type, the rotary type to the axial flow type, and the ring form. On the other hand, the ground type is more capable of obtaining fine products than the impact type. If a fine product is obtained directly from the pulverizer, it is effective to use a gas flow classifying mechanism without a screen.
4.2 shape control
In the impact pulverizer, the shape of the particles is different depending on the characteristics of the raw material (such as crystallization) and the mechanical properties (such as the hardness and speed of the impact member). By repeated pulverization, the fine pulverization of the compression shear effect is smaller than the general impact pulverizer, so that the spheroidized particles are more likely to be formed.
4.3 weakly hot substances
Although most of these raw materials are pulverized by airflow, in recent years, the use of impact pulverizers has increased. Because of the large air volume of the AM machine, the cooling and fineness are good, it is very suitable for such pulverization; on the other hand, it can be cooled by cold air or even liquid nitrogen. grinder.
4.4 other
Some raw materials are demanding in the atmosphere, and high-speed impact pulverizers are used to crush air in a vacuum. In order to prevent oxidation, cause deterioration of materials, and prevent dangers such as combustion and explosion, it is possible to pulverize in an atmosphere of an inert gas such as nitrogen.
5 Conclusion
The recent trend of the high-speed rotary pulverizer is to increase the speed of the high-speed rotary pulverizer, so as to avoid the simplification of the decomposition, and to improve the wear resistance and the like. How to make full use of energy in the pulverization process to avoid uselessness is a problem. In addition, a mechanism other than the impact is more effective in smashing.
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