1.1 Material properties The nature of the material is an important factor affecting the screening effect. In the production process, the vibrating screen tends to be enriched, that is, the screen is piled up, the effective screening area is reduced, and the process efficiency is reduced. This is mainly related to the material composition type, material bulk density, material size and the like.
1) The material type and the type of the granular material are different, and the physical properties are also different. The types of materials can be divided into two categories: brittleness and viscosity. In the process of vibrating screening, viscous materials are easy to form dense adhesion of materials, block the screen, and reduce the permeability, while brittle materials are not, the process efficiency can be guaranteed. . The particle shape of the material will affect the permeability of the material. The shape of the cube and the material of the sphere are easy to pass through, while the sheet material is easy to get stuck in the sieve hole, which affects the process efficiency.
2) Material loose density The material particles are basically layered and sieved according to the volume of the particles, that is, the loose density of the material directly affects the processing capacity of the vibrating screen. The loose bulk material is easy to pass through the sieve and the screening efficiency is also high; on the contrary, the loose bulk material and the powdery material are not easily permeable, and the screening efficiency is low.
3) Material moisture The moisture content of the material is too high, and it is easy to form adhesion. During the vibration process, the blocks are squeezed each other, and the adhesion is more encrypted, thereby increasing the resistance of the material movement, so that the material particles are difficult to stratify and sieve; Adhesion of the material also reduces the size of the mesh, clogging the mesh, reducing the effective screening area, and sometimes the material with too high water content cannot be sieved. Therefore, when the moisture content of the material is too high, the screening process should consider some remedies, such as taking measures to dry the material.
4) Material granularity composition The screening probability of the material in the screening process is affected by many factors, and the direct and important factor of the Zui is the relative size of the material size and the mesh size. The ratio of material size to mesh size is referred to as relative particle size. The smaller the relative particle size, the higher the permeability probability. When the relative particle size is close to 1, the permeability probability approaches zero. Therefore, the material with the relative particle size equal to 0.7-1 is usually called the difficult sieve material or the critical material. The greater the content of the difficult-to-screen material in the material, the smaller the permeability probability and the lower the screening efficiency; otherwise, the higher the screening efficiency. In order to obtain higher screening efficiency, the content of difficult-to-screen materials in the aggregate should be minimized. In addition, the difference in particle size index also has a certain influence on the screening efficiency. The difference in particle size index is too large. The dumb will cause a large production cycle, which restricts the quality and processing ability of the product. Therefore, the grading of the aggregate should be strictly controlled.
1.2 Screen surface structure parameters 1) Screen length and width It is generally believed that the screen width directly affects productivity, while the screen surface length directly affects the screening efficiency. The screen surface is wide, the effective area is increased, and the productivity is improved. The sieve surface is long, the material stays on the sieve surface for a long time, and the sieve has many opportunities, so the screening efficiency is high, but the longer the better, because the relationship between the screening efficiency and the time the material travels on the entire sieve surface It is complicated. At the beginning, due to the large number of fine-grained materials on the sieve surface, the probability of permeation per unit time is large, and the permeation rate is high. After a certain period of time, the particle size of the material remaining on the sieve surface is mostly difficult to sieve material close to the size of the sieve hole, even if the material stays on the sieve surface for a long time (that is, the length of the sieve surface is large), it is difficult to increase The permeable rate of the material leads to a decrease in work efficiency.
Therefore, the selection of a suitable screen length can effectively improve the screening efficiency. In fact, the screen width is different for the screening efficiency, and the screen length has different degrees of shadow orientation. The matching of the two is also very important. Generally, the width to length ratio is 1:2~1:3. .
2) Mesh shape Although the shape of the mesh mainly depends on the size of the sieved product and the requirements for the use of the product under the sieve, it also has a certain influence on the screening efficiency. Compared with other shapes of sieve holes, the circular sieve holes have smaller particle size through the circular sieve holes under the same nominal size. For example, the average size of the sieve through the circular sieve particles is only transparent. 80%~95% of the square mesh particles of the same size and the effective area of â€‹â€‹the sieve of the rectangular sieve L is large, the quality of the sieve surface is light, the production capacity is large, and the material size of the sieve through the sieve is larger than the nominal size through the sieve. The particle size of the circular and square mesh openings. Therefore, in order to achieve higher screening efficiency, different mesh shapes must be selected for different screening materials.
3) Screen size and opening ratio of the screen surface In the case of a certain amount of screening material, the size of the screen has a great influence on the screening efficiency. The larger the size of the mesh, the stronger the permeability of the material particles, and the greater the processing capacity of the vibrating screen. Of course, the mesh size is mainly determined by the process requirements of the material to be screened. The opening ratio of the sieve surface refers to the ratio of the opening area of â€‹â€‹the sieve surface to the area of â€‹â€‹the screen surface (effective area factor). The high opening ratio increases the probability of the material particles being permeable, and the processing capacity of the vibrating screen is high. On the contrary, the processing capacity of the vibrating screen is low. Therefore, in order to improve the screening efficiency, a screen surface with a large effective area factor should be selected.
4) The material of the screen surface is non-metallic screen surface, such as rubber graded screen surface, polyurethane braided graded screen surface, polyurethane strip screen surface, nylon screen surface, etc., due to the characteristics of these non-metallic materials, the screening process The secondary high-frequency vibration is generated, which makes the plugging phenomenon difficult to occur, which is beneficial to the screening of the material, and the processing efficiency of the vibrating screen of the metal mesh surface is improved.
1.3 Vibration characteristics Parameters Vibration characteristics parameters include vibration frequency, amplitude, vibration direction angle and screen inclination angle.
1) Screen inclination angle Î±
The angle between the screen surface and the horizontal plane is called the screen inclination angle. The size of the dip is closely related to the throughput of the screening equipment and the screening efficiency. When the inclination angle is increased, the throwing strength of the material on the sieve will be increased, so that the forward movement speed of the material on the sieve surface is accelerated, so that the treatment amount of the vibrating screen is increased, but the residence time of the material on the sieve surface is shortened, and the opportunity for screening the sieve is reduced. , thereby reducing the screening efficiency. On the contrary, the throughput is reduced and the screening efficiency is improved. In order to control the screening efficiency of the vibrating screen to a relatively ideal range, the screen inclination angle of the circular vibrating screen is generally between 15-25Â°, and the screen inclination angle of the linear vibrating screen is between 0-8Â°.
2) Vibration direction angle Î²
The angle between the vibration direction line and the upper screen surface is called the vibration direction angle. The larger the value of the vibration direction angle is, the shorter the distance moved by the material is, and the slower the movement speed of the material on the screen surface, the material can be fully sieved, thereby obtaining a larger screening efficiency. The smaller the value of the vibration direction angle is, the farther the material throws and advances each time. The faster the material passes through the screen surface, the higher the processing capacity, but the material cannot be fully sieved. Therefore, the vibration direction angle should be reasonably selected. For difficult-to-screen materials, the vibration direction angle should be taken as a large value. For easy-screen materials, the vibration direction angle should be small; in general, the vibration direction angle of the circular vibrating screen is 90Â°. The vibrating direction angle of the linear vibrating screen ranges from 30 to 60Â°, often 45Â°. This value not only has good performance for various screening, but also can achieve good moving speed and high productivity.
3) Amplitude A
As the amplitude increases, the clogging of the sieve å‘L will be greatly reduced, and it will also facilitate the stratification of the material.
However, too large amplitude is also destructive to the device. The choice of amplitude is based on the particle size and nature of the material being screened. In general, the larger the vibrating screen size, the larger the selected amplitude. n When the linear vibrating screen is used for classification, the amplitude is slightly larger; when used for dehydration and desilting, the amplitude should be smaller. When the particle size of the treated material is large, the amplitude should be correspondingly increased; when the particle size of the treated material is small, the amplitude should be smaller. Usually, the amplitude of the linear vibrating screen is A=3.5~6mm.
4) Vibration frequency Ï‰
The increase of the vibration frequency can increase the number of beats of the material on the screen surface, which increases the permeability of the material. This is helpful for speeding up the screening speed and improving the screening efficiency, but too high will reduce the service life of the equipment. .
For larger particle sizes, use larger amplitudes and lower frequencies; for finer particles, use smaller amplitudes and higher frequencies.
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