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Summary of factors in the screening process of vibrating screen

Release time: 2019/8/26 Click times: 3221

Influence of the properties of raw materials into the sieve (1) Water content
The moisture content of a material is also called humidity or moisture. The external moisture attached to the surface of the material has a great impact on the screening of the material; the moisture in the cracks of the material and the moisture combined with the material have no effect on the screening process. For example, the external moisture of the coal is the main factor affecting the screening. Generally, the external moisture is below 6%, which can be used for dry screening. If the external moisture exceeds 6%, the screening is difficult because of the coal's The moisture is basically covered on the surface; however, although the moisture content of the lignite with many pores has reached 45%, the sieving process can still proceed normally.
The effect of moisture is particularly prominent when the materials are sieved on a fine-mesh screen. Due to the large specific surface area of fine-grained materials, the external moisture content is also high. The external moisture of the material can make the fine particles adhere to each other and cling to the large pieces. This sticky material can block the screen holes. In addition, the moisture attached to the screen wire may form a water film under the effect of surface tension, covering the screen holes. All of these conditions prevent the material from being layered on the sieve surface according to the size, making it difficult for fine particles to pass through the sieve holes and remain in the product on the sieve.

(2) Mud content
If the material contains mixtures that are prone to agglomeration (such as clay, etc.), sieving may occur even when the moisture content is small. Because the clay material will stick into agglomerates during sieving, so that the fine mud is mixed into the product on the sieve; in addition, the clay can easily block the sieve holes. Clay materials and viscous materials can only be sieved with a sieve with a larger sieve in certain special cases. Special measures must be adopted when sieving viscous ore, including: wet sieving Spray water on the moving material); remove the mud before screening; dry the screening materials. Screening wet and sticky ore with electric heating screen can get good results.

(3) Granularity characteristics
The particle size characteristics that affect the sieving process mainly refer to the content of the raw materials containing various grades of material that are of particular significance to the sieving process. The raw material contains more difficult-to-sieve granules and hindering granules compared to other grades, which is disadvantageous to the sieving process; while the easy-to-sieve granules and non-inhibiting granules contain more than other grades, it is beneficial to the screening process.

The particle size characteristics that affect the sieving process also include the shape of the particles. For particles that are close in three dimensions, such as spheres, cubes, polyhedra, etc., it is easier to sieve. For particles that have large differences in three dimensions, such as flakes, strips, weird bodies, etc., the other conditions are the same. Screening is more difficult under these circumstances.
(4) Density characteristics
When all particles in the material are of the same density, it generally has no effect on screening. But when there is a density difference between coarse and fine particles in the material, the situation is very different. If the coarse grain density is small and the fine grain density is large, it is easy to sieving, for example, the fine sand mixed in from the rice is screened out. This is because the barrier effect of the coarse-grained layer is relatively small, while the fine-grained layer has a larger penetrating and sieving effect. On the contrary, if the density of coarse particles is large and the density of fine particles is small, such as coal containing more coarse-grained vermiculite, the screening will be relatively difficult.

Influence of sieve performance (1) shape of sieve plate and sieve hole
The sieving particle size is more than 25 mm. Punching or drilling sieve plates are generally used. Most of the holes are round holes and diamonds. Braided screens can be used below 25 mm, and the screens are made into square holes. For the 25 mm sieve, you can use a punching sieve plate or a woven sieve. The woven sieve should prevent the sieve bar from sliding and the sieve hole deformed. For sieving below 1 mm (including desliming, dewatering, dislodging), a slotted sieve plate below 0.5 mm can be used with a slotted sieve plate (through a screw rod through the ring or welded on the sieve rod) or nylon screen. Whether it is a screen or screen, it must be tightened and fastened to the screen box. This is the most important. It can prolong the life of the sieve plate, screen, and screen box, improve the screening efficiency, and reduce the noise.
For screens larger than 50 mm, they are often made of steel or light rail. Especially the use of old rails for fixed screens is more suitable. The rod-shaped sieve bars are made wedge-shaped, with the upper width and the narrow width, to facilitate the passage of materials.
The circular sieve, the diameter of the sieve is used to indicate the size of the sieve, which can ensure that the particle size passed is smaller than the size of the sieve. The under-screen product basically does not contain a size larger than the sieve. The side length is 1.414 times. Some data suggest that the largest particle passing through a square hole is equivalent to 1.23 times the largest particle size passing through a circular hole. The rectangular sieve takes the short side of the rectangle as the nominal size of the sieve. In this case, the particle size exceeding the sieve size, especially the flat particles, will pass through the sieve long side. There are also irregularly shaped screen holes, such as some woven screens. The sieve openings of probability sieves are often larger than the separation size and are calculated using the projection of the sieve openings. In any case, the particle size of a sieved product is a measure of particle size.

(2) Length and width of screen
The width of the screen surface determines the processing capacity of the screening machine. If the width of the screen surface is large, the throughput of the material is large; the length of the screen surface determines the screening efficiency of the screening machine. The longer the screen surface, the longer the material passes through the screening, and the more thorough the screening. However, the excessively long sieve face does not improve the screening efficiency significantly, but merely lengthens the size of the sieving machine unnecessarily.
Existing sieving machines in our country have sieve surface length, coarse-grained sieving of 3.5 to 4 m, medium-fine-grained sieving of 5.5 to 5.6 m, and dehydration and deintercalation of 6.5 m.
(3) Angle of screen
The inclination of the screen surface affects the moving speed of the material on the screen. Large inclination angle, fast material movement and high processing capacity. The inclination of the screen surface and the structure of the screen are related to the quality requirements of the screened product. Generally, the sieve holes are above 50 mm. For pre-screening, circular motion sieving machines are used, such as inertial vibrating screens and self-centering vibrating screens. The inclination angle is 15 ~ 20 . The linear motion screening machine is generally installed horizontally, its inclination angle is zero degrees, and the material moves on the screen surface. Depending on the projecting force of the screen facing the material, this screen machine is generally used for coal dewatering, desliming, and dislodging.
(4) Amplitude and frequency
Amplitude refers to half the stroke of the screen box, and frequency refers to the number of reciprocating vibrations of the screen box. In addition to the inclination of the screen surface, the screen box must have a sufficient speed to make the material on the screen surface advance. The experimental research shows that the acceleration of the vibrating screen box for coal does not exceed 70 ~ 80 m / s2, the amplitude is approximately 2 ~ 5 mm, and the rotation speed is 800 ~ 1500 r / min.
In order to measure the amplitude of a linear motion sieving machine, a triangle for measuring amplitude is usually drawn on the linear vibrating screen, and a set of parallel lines parallel to the baseline is drawn on the measuring triangle. The scale is marked above it to indicate the corresponding cutting width of the triangle . When the screen box vibrates and people are visually stranded, they will see the two triangles, and the intersection width of the intersection of the hypotenuse is the stroke of the screening machine (double the amplitude).
(5) Projection angle
The projection angle is the angle formed by the moving direction of the screen box and the screen surface. If the projecting angle is large, it is beneficial for the material to pass through the screen, but the processing capacity is small. The linear motion sieve mainly pushes the material forward by the projectile effect and makes the fine particles pass through the sieve. The projection angle of a linear motion sieve is generally between 30 and 55 . In China, 45 is adopted. The circular motion sieving machine contact number: 18637368911. Manager Liu also has a projection effect, but its projection angle is not fixed and it is related to the frequency and Amplitude related.
(6) Processing capacity
Increasing the processing capacity (processing capacity per unit area or unit width) too much will seriously affect the screening efficiency and increase the number of particles on the sieve that are smaller than the sieve size.

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