Do you know the principle and performance of the powder separator? Hear what the powder sorting machine manufacturers say!
First, the working principle of the powder separator The function of the powder separator is to separate and collect the qualified and unqualified coarse powder from the coarse and fine powder mixture discharged from the mill according to the requirements of the product fineness or specific surface area. The unqualified coarse powder is returned to the ball mill for re-milling. The general working principle is to use air-powder mixing to form a gas-solid two-phase flow, which causes the dust-containing air flow to rotate, and the coarse powder particles obtain a larger inertial centrifugal force, and also generate a larger radial radial velocity of separation. The coarse and fine powders are separated, and the coarse and fine powders are collected separately by corresponding methods. The above working principle is mainly realized through three functions, which are: spreading, grading and collection of finished products. But the working process of different types of powder sorters to realize these three functions is not exactly the same. The first type of centrifugal powder separator uses the lower part to spread material, and air and powder are circulated in the machine to achieve the separation and collection of coarse and fine powder. Its characteristics are: Because air and powder are circulated inside the body, this type of powder separator is called internal circulation work. The second type of cyclone powder separator also uses the lower part to spread the material, but the air entering is to take the lower tangential inlet air. During the process of air entering and rising, it passes through the spreading material curtain, and then passes through the rotating blades or cones. The cage realizes classification. The classified airflow takes the finished fine powder out of the powder selection chamber, and the dust-containing airflow discharged from the powder selection chamber is sent to the cyclone to separate the air and powder to achieve the collection of the finished product. Its characteristics are: Because the clean airflow from the cyclone enters the fan to circulate, this type of powder separator is called external circulation work. The third type of powder separator, represented by O-Sepa, adopts the upper part of the material distribution. This type of material distribution does not rely on the material distribution disc to make the powder produce inertial centrifugal force to form a material curtain. Free fall is used to form the material curtain, and the plane enters the tangential air, and the cylindrical vortex is used to form the cylindrical vortex to achieve classification. The fine powder of the finished product is discharged from the powder selection chamber into the dust collector to achieve fine powder collection. Its characteristics are: Because this type of powder separator uses a cylindrical rotating cage, it can form a relatively uniform eddy current field, so it has a better classification effect and better powder selection efficiency. At the same time, the airflow from the dust collector directly passes through the fan exhaust. Empty, no loop work.
Second, the working principle and analysis of the spreading mechanism
The dusting of the powder separator is the first step in the main working process of the powder separator. Its function is to spread the mixed material so that it can fully interact with the air flow, so that the powder that meets the requirements can be carried by the air flow. To make it enter the next step of the grading process in the powder selection process. However, the feeding mechanism and principle of different types of powder separators are different. In terms of the positional relationship between spreading and grading, it can be roughly divided into two categories, one is spreading the material down and grading up; the other is spreading the material up and grading down. The structure and performance analysis of these two types of spreading mechanisms are as follows:
(1) The principle and performance analysis of the lower part of the spreader The design of the spreading mechanism of the centrifugal powder separator, cyclone powder separator, combined powder separator and improved powder separator is arranged in the lower part of the classification mechanism. Because this structure generally adopts the lower air inlet, the airflow passes through the spreading material curtain and carries a part of the dust to form a dust-containing airflow. The dust-containing airflow then enters the classification zone or classification mechanism to achieve the classification of the powder. The spreading quality can be measured by the effect of dust carried by the airflow through the material curtain. Under the same airflow condition, the spreading effect can be measured by the following two indicators, one is the carrying rate of qualified fine powder; the other is the carrying of coarse powder of unqualified products. The rates are represented by CX and CC, and their expressions are: Among them: Fxs: is the qualified fine powder amount in the powder as the air flow rises,
Fxz: is the total amount of qualified fine powder in the coarse and fine mixed powder,
Fxc: the amount of unqualified coarse powder in the rising powder,
Fs: In order to increase the total amount of powder, there are currently several types of spreading pans in the market:
1. Flat Spreader
It is the powder falling from the top onto the spreading plate through the rotation of the spreading plate, and at the same time, the material generates radial inertia centrifugal force and radial movement, so that the material has a scattering movement in the radial and tangential directions, so that the material is dispersed. A layer of material curtain is formed on the cross section of the powder separator, and the airflow from the lower part of the machine passes through the material curtain to bring qualified fine powder and a part of coarse powder into the classification zone. It can be seen that the more uniform the material curtain is and the more loose the material curtain is, the more likely it is that qualified products will be taken away under appropriate airflow conditions. In addition to the above-mentioned spreading mechanism, the spreading tray also has the following two functions:
(1) The pre-classification is achieved by the self-weight of the coarse powder. The mechanism is to bring the fine powder into the classification zone from bottom to top using an airflow with a certain speed. Or equal to the weight of the fine powder, the fine powder will rise with the airflow, because the viscosity of the airflow to the fine powder is the surface force, and the gravity of the material is the volume force, so the larger particle size cannot be easily lifted. In order to achieve the material pre-classification function. The higher the air velocity, the larger the particle size of the material that can be taken away by the air stream.
(2) The pre-classification is achieved by using the inertia centrifugal force generated by the material. The material is scattered by relying on the spreading disc to make the material rotate, and at the same time the material obtains the inertia centrifugal force to generate radial movement. Therefore, large materials can also obtain larger inertial centrifugal force and relatively small viscous damping force. Thicker materials produce higher speeds of movement, and coarse powder will be in front and fine powder will be behind. At a certain rotation speed, the coarse powder hits the surrounding shells, so that the purpose of pre-grading can also be achieved. However, this method of spreading also has the following shortcomings:
(1) Rotating speed problem In the centrifugal powder separator, the spreading disc adopts the structure of coaxially collecting and classifying small wind blades and fine powder collection. The rotor is coaxial. Because of the coaxial structure, only one speed can be used in the work. However, whether it is a centrifugal large or small blade or a cyclone-type grading mechanism, it is related to the different speed requirements of the spreading disc. In general, the speed of the powder separator is mainly to obtain qualified products, so the speed of the powder separator is adjusted based on the speed requirements of the grading rotor, and the actual spreading situation of the spreading tray will not be considered, although in the product design Will consider the unity between the spreading tray and the classification system, but each user will take different speeds according to different product fineness requirements and actual operating conditions, that is to say the same structure, different occasions have different speeds, Therefore, in general, it is difficult to have a suitable rotation speed for the spreading tray. This is the most important defect of flat plate spreading. Nor can it be overcome by changing the structure of the spreading pan and other operating parameters.
There are two kinds of phenomena:
A. One is the insufficient rotation speed, which makes the material unable to be fully scattered, on the one hand, there are more dense material groups, on the other hand, the material curtain cannot cover the entire cross section to form a gap, which will affect the carrying effect of fine powder.
B. Another situation is that the rotation speed is too high. If the rotation speed is too high, the powder will be over-spattered, which will cause the powder to impact the cylinder wall, which will also form a dense material group and a large gap.
(2) Feeding problem The lower spreading mechanism adopts the upper single-point feeding method. Because it is a single-point entering powder, it will fall on the corresponding position of the spreading disc, which will cause the rotor of the spreading disc to be biased. The load is even more serious because the single-point blanking prevents the spreading disc from being evenly spread on the entire circumference.That is to say, on the circular section of the cloth that can be distributed, a fan-shaped cavity will appear, and the airflow flows through it. , No material curtain filtration, causing waste. Due to the above-mentioned speed factor and single-point feeding reasons, in fact, using this method of spreading, there are voids on the fabric section, large or small.
2. Spiral Spreading
This type of spreading device uses a number of inclined blades to replace the disc-type flat surface spreading device in structure. The powder to be sprayed is dropped onto these inclined blades, and a plurality of sheet curtains are formed by rotating the sprayed powder on the body. The distribution is staggered inside to form a layer, forming a three-dimensional dispersed material curtain. The powder is loosely distributed in the spraying space, which is conducive to taking away the fine powder when the airflow passes through. Obviously, this type of spreading effect is better than the flat spreading device. The defects of the feeding device still exist on the propeller spreader.
1. Non-spreading tray device There is a combined powder classifier on the market now that adopts the structure of the lower cloth without the spreading device. The structure adopts the lower air intake, the middle feed and cloth, and the upper grade. Its spreading process is to fall on a cone through the middle feed. The powder slides to the lower edge of the cone under its own weight. After falling, it forms a circular material curtain. The air inlet is below the cone. Carry the fine powder through the material curtain and enter the classification zone. This structure adopts a small-diameter cylinder and high-speed air flow to achieve the lifting of the material without a spreading disc, and the structure is simple. The main problems with this structure are:
1. The size of the guide cone structure is limited. From the perspective of the cloth, it is desirable to have a larger bottom diameter, so that a thin material curtain can be formed. When the air flow passes through the material curtain, more fine powder can be taken away, and a higher Cx can be obtained. However, a larger bottom diameter will decrease the airflow penetration speed on the one hand, and increase the speed difference after passing through the cone. Both factors will affect the fine powder carrying rate; the diameter of the bottom of the cone is too small The thickness of the material curtain is greatly increased, and air holes are easily formed when the high-speed airflow passes through, which will also reduce the fine powder carrying rate and increase the coarse powder carrying capacity.
2. Due to the use of conical guides, there is a phenomenon of uneven distribution of powder along the circumference, which results in uneven thickness of the material curtain distributed along the circumference, and even voids. The effect of such voids on the fine powder carrying rate is greater. . Such a mechanism generally adopts high wind speed to carry material, and then utilizes the characteristics of air flow deceleration and coarse powder self-heavy to achieve pre-classification during the dust-containing air flow rising process. The distance between the inlet of the lower airflow and the cone has a greater impact on the powder carrying effect. The principle and analysis of the upper part of the material spreading The third type of powder sorting machine, represented by the O-Sepa powder sorting machine, is above the classification zone, and the air inlet and the classification zone are at the same height. Due to the different structural arrangements, the spreading mechanism and effect are very different. The spreading process and the spreading mechanism of the structure are realized as follows: the powder to be selected enters from the top of the shell of the classification zone, and falls on the spreading disc on the upper part of the classification cage, which is also synchronized with the classification cage. Rotate to make the falling powder produce inertial centrifugal force, and generate radial and tangential movements, throw the powder onto the fixed buffer baffle, and then fall down freely along the buffer baffle to form a vertical material distributed along the circumference. The powder of this structure is not ended here. During the vertical falling of the material curtain, the material dispersion operation must be completed before the powder classification. In the free falling process of the vertical material curtain, due to the classification, The rotation of the rotating cage produces a high tangential velocity, and there is a large speed gradient between the rotating cage and the guide blades. Due to these two factors, the vertically falling material curtain is stripped layer by layer, so that the powder and air flow Fully mix to form a gas-solid two-phase flow. Only after the air and powder are fully mixed can the subsequent good classification effect be obtained. The spreading effect of this spreading mechanism depends on the spreading disc, which is different from the case of lower spreading. The spreading device only needs to distribute the powder falling on the spreading disc evenly along the circumference. The size and the degree of dispersion of the material curtain are irrelevant. Compared with the effect of the lower material, the effect of this material is not sensitive to the speed requirements, although the material distribution disc is also coaxial with the classifying cage. Without much influence, the distribution of the powder along the circumference can be controlled not only by speed adjustment, but also by other methods.
At present, this type of spreading device is mainly deficient in two aspects. On the one hand, the powder is unevenly distributed in the circumferential direction of the spreading disc, especially the structure of the upper air makes the annular area of the spreading disc smaller, that is, the powder. The runnable radial distance is too small to achieve uniform distribution in the circumferential direction, although some manufacturers currently add radial partitions on the spreading disc to enable the powder to run a longer distance along the circumference to achieve uniform distribution. Function, but this method can only improve the spreading situation in a limited range, and this method will also bring side effects. The powder is concentrated at the radial partition, which will also cause the uneven thickness of the material curtain. On the other hand, how to disperse the vertically falling material curtain as soon as possible and rotate synchronously with the airflow. If the material curtain is too thick, or the powder falls into a ball, it even falls below the classification zone. After passing through the classification zone, there is actually no classification treatment process. The longer the dispersion process of the same material screen, the shorter the powder participation time for classification, and the worse the classification effect.
2. Improvement measures of the spreading mechanism According to the spreading principle and performance analysis of the aforementioned spreading mechanism, the following improvement measures are proposed:
1. For the traditional situation of uneven feeding due to single-point unloading, a feeding mechanism can be used to change one-point feeding to two-point feeding or multi-point feeding. Allow the spreading mechanism to have a symmetrical load. Under the same rotation speed condition, the original one-point blanking 360 ° spreads the material into two-point blanking, each point 180 ° or 90 ° spreads the material, thereby improving the uniformity of the spreading. Sex. This structure is relatively simple and easy to implement.
2. Double-spreading is adopted for the double-spreading tray. This structure is above the original spreading tray, and a spreading tray is set in the falling pipe. The working process of the double feed tray is as follows: the powder coming from the upper part first falls on the upper feed tray, and the upper feed tray throws the powder and hits the inner wall of the lower pipe, and then falls from the inner wall of the lower pipe to the lower layer On the spreading disc, the lower level spreading disc is thrown to form a material curtain. In this way, a uniform material curtain can be obtained throughout the cross section of the ring.
3. The upwardly curved spreading plate is used to form a parabolic trajectory of upward spreading. This structure is not very sensitive to the speed of the spreading effect of the spreading plate. When the speed is high or low, it can only reflect the height of the parabola. , Will not be formed because the speed is too high or too low.
4. Adopting independent driving structure for spreading, the most suitable spreading speed can be obtained. However, this structure is relatively complicated and the power consumption is high.
5. The upper sprinkler can also be combined with a material-gas mixing device to make the material-gas mix in advance so that it can enter the classification state as soon as possible.